Updates in the care of youths with intellectual disability and autism spectrum disorder

Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5]. Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes. The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20]. The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43]. Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation. Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20]. In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25]. Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15]. This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology. Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40]. Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements. In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23]. Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43]. Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation. Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20]. In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25]. Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15]. This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology. Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40]. Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements. In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23]. Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43]. Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation. Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20]. In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25]. Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15]. This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology. Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40]. Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements. In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23]. Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43]. Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation. Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20]. In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25]. Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15]. This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology. Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40]. Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements. In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23]. Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43]. Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation. Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20]. In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25]. Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15]. This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology. Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40]. Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements. In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23]. Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43]. Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation. Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20]. In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25]. Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15]. This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology. Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40]. Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements. In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23]. Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43]. Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation. Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20]. In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25]. Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15]. This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology. Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40]. Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements. In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23]. Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43]. Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation. Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20]. In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25]. Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15]. This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology. Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40]. Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements. In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23]. Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43]. Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation. Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20]. In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25]. Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15]. This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology. Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40]. Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements. In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23]. Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43]. Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation. Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20]. In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25]. Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15]. This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology. Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40]. Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements. In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23]. Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43]. Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation. Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20]. In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25]. Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15]. This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology. Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40]. Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements. In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23]. Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43]. Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation. Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20]. In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25]. Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements.In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15]. This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology. Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23].Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40]. Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43].Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.Purpose of reviewSince the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions, the high health vulnerability, especially mental vulnerability, and the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care. The present review addresses the main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood.Despite the existence of specific recommendations, persons with IDD/ASD lack access to quality mental healthcare within communities, receive inadequate diagnosis and intervention, including medication overuse as well as ineffective residential, educational, employment, financial, and social support services. The lack of a unified care system that provides services across all domains and life ages may be the cause of users' perceptions and experiences of inefficiencies.The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation. Quality of life appears to be an ideal conceptual reference for care planning and outcome evaluation.Papers of particular interest, published within the annual period of review, have been highlighted as:Since the turn of the new millennium, care for people with intellectual disability/intellectual developmental disorders (IDD) and/or autism spectrum disorder (ASD) has drawn increasing attention because of the continuous prevalence increase of these two conditions and the high mental and physical vulnerability as well as the crucial role of care provision in the setting of continued deinstitutionalization and the shift to community care.Despite the increasing rate of prenatal screening-related abortions, IDD prevalence has grown by around 25% in the last decades [1] and is currently reported to have a world mean of around 1.5% [2]. Last ASD prevalence is reported to be one in 36 [3].Due to their social-communication deficits, rigidity, behavioural issues (including self-injurious and aggressive behaviours), high prevalence of complicated medical and psychiatric comorbidities, children and adolescents with IDD and/or ASD have high care need but frequently have difficulty receiving high-quality physical and mental health treatment [4]. Children with ASD have been found to be major healthcare users, with visit times and general health expenditure being two and seven time higher, respectively than children without ASD [5]. The biggest cost factors were psychiatric inpatient treatment (19.8%), medication (11.1%), and occupational therapy (11.1%). In a regression model, greater expenses were linked to female sex (cost ratio: 1.65), lower IQ (1.90), and Asperger syndrome (1.54) [5].IDD, ASD, and other neurodevelopmental disorders (NDD) frequently co-occur and those who are afflicted by this co-occurrence may have additional impairments that make it even more necessary to get healthcare.Considerable writing and discussion have occurred across time about care and models of care, but no agreed-upon definition has been offered yet. According to the WHO, quality of care is the degree to which health services increase the likelihood of desired health outcomes and are effective (evidence-based); safe (avoid harm); and person-centred (respond to individual preferences, needs and values). To realize the benefits of quality healthcare, health services must be timely, equitable, integrated, and efficient [6]. A model of care is a comprehensive plan for delivering a particular type of healthcare service that is shaped by a conceptual basis and specific requirements. In reference to mental healthcare for people with IDD and/or ASD, the international evolution of comparable models is dependent on the sharing of knowledge, training, and technology. In spite of progress and scandals that have made providers and commissioners reflect on what makes up suitable services, the main challenges seem to be long standing and include access to both mainstream and specialist services, clear interfaces with other agencies to provide collaborative working, proactive commissioning strategies, development of academic centres and further research into service models that deliver improved outcomes.The present article reviews the recent literature covering these and the other main issues related to mental healthcare in youth with IDD and/or ASD with a specific focus on adolescence and transition to adulthood. no caption availablePsychopathological co-occurrences are common in IDD and ASD. Reported point prevalence rates in children and adolescents with IDD range from 30 to 50%, with about half of them presenting two or more comorbid psychiatric disorders [7]. For ASD, prevalence of psychopathology increases up to 70% and about 40% of persons with ASD may have two or more comorbidities [8-10]. For instance, the most recent studies reported that in persons with ASD, the prevalence rates of depression range from 11 to 23%, those of anxiety disorders from 17 to 27%, and those of obsessive-compulsive disorders from 9 to 22% [11].The risk for persons with NDD to develop adjunctive mental health issues increases with the complexity of the NDD itself (i.e. co-occurrence of IDD and ASD) and age, with the transition from late childhood to adolescence and early adulthood being a particularly critical period [12]. Many researchers agree on the fundamental role played by psychiatric co-occurrence on the increase of the severity of functioning impairment and the onset or accentuation of problem behaviours, such as impulsivity, irritability, aggressiveness, or self-injury, although these behaviours involve a multitude of factors at the interface between the person and her/his environment [13].Compared with persons with high-functioning ASD, persons with IDD or more severe NDD are more likely to have unmet healthcare needs and receive lower quality care, especially for mental health [14,15].This high vulnerability would benefit from higher primary and secondary prevention, starting from primary schools and general paediatrics, and including early and accurate diagnosis as well as multidimensional interventions to promote short-term and long-term outcomes, including academic achievement, peer integration, and community inclusion [16]. For instance, school-aged children with IDD and/or ASD frequently begin social contacts or express displeasure in ways that can be viewed as socially undesirable, such as bullying behaviours and other behavioural issues, impulsivity, and self-injury. On the other hand, because of their relational and behavioural issue, children with IDD and/or ASD are often object of abuse and maltreatment by their peers [12], which has been reported to increase the risk of developing adjunctive mental health issues during the transition to adulthood [17,18]. Depression and anxiety are particularly common and addressing early indicators of these disorders is crucial.The lack of accessibility and availability of high-quality care within communities is more severe and has greater detrimental effects on adolescence and the transition to adulthood. In fact, this time period is crucial for changing in abilities over the lifespan and inadequate care planning and guidance can have a substantial impact on continued achievement and healthy development. Service transitions occur when people change status from being ineligible to being eligible or from one healthcare system to another. Furthermore, transition is already difficult for persons with NDD and their families as they must consider higher education options, safe housing options, and community engagement services [19]. The difficulties experienced can only be made worse by the complexity of the healthcare industry, which includes poor training for health-care transitions, fragmentation of healthcare services, and specialized knowledge gaps for professionals caring for young adults with special needs. Poor long-term health outcomes for young individuals with NDD are threatened by primary care providers' ignorance of their health needs, particularly in rural or low-resource settings [20].In addition to limited general practitioner education or experience, Shea and colleagues identified communication difficulties and inadequate continuity of care as the other most frequently reported issues to impact access to general practice. Less frequently reported factors were the health literacy levels, promotion of general practice services, and availability of complete medical records [21]. In the Netherlands, around 80% of persons with mild IDD have been found to be not registered by their general practitioner with the ICPC code 'mental retardation', although general practitioners provide more care to people with mild IDD and mental health problems than people without IDD but with mental health problems regarding consultations and medication [22].When getting into transition, persons with NDD have to be multidimensionally reassessed to define a new plan of interventions and a project for life. Community programming, academic performance, and life skill development are necessary as well as assistance to succeed in higher studies or careers as long as they move to adulthood [20].One potential way to improve community-based healthcare across the lifetime is using remote technology.Although it did not alter provider behaviour, the Extension for Community Healthcare Outcomes (ECHO) model adaptation allowed information transfer from centres of excellence to primary care clinicians concerning the care of transition-aged NDD patients. ECHO has also been used to link autism specialists with primary care doctors in far-flung regions of the world, thereby promoting optimum primary care practice [20].Most levels of care, including those in government and policy creation, have very little knowledge and comprehension of IDD/ASD. One of the primary issues highlighted is that the government and care systems do not recognize ASD as a distinct condition that calls for assistance that are both targeted and specialized in addition to those for all children with developmental difficulties. Additionally, care and resources in communities may be so limited or ambiguous that it may be challenging to locate current care systems where early detection and early intervention for ASD might be included [20]. This lack of adequate outpatient care through community-based regular care leads to an excessive recourse to emergency health services and high risk of hospitalization after emergency visits [23]. Furthermore, it is unclear how existing care systems may be integrated into continuing detection and intervention for new physical and mental health issues affecting people with ASD as early as mid-childhood [20]. Given the unwillingness of many sectors (such as health, education, and social care) to assume main responsibility for ASD, establishing and implementing intersectoral autism policies is important [20].The difficulties that persons with NDD have accessing mental healthcare seem to be attributable to three main groups of factors: a dearth of professionals who are familiar with NDD; the use of treatments that may not be tailored to meet specific requirements; and difficulty navigating the complicated healthcare system [24]. More specifically, families of children with ASD are dissatisfied with the timeliness of care, insurance coverage, and the overall impact of healthcare on the family's finances than families of children with IDD or attention-deficit/hyperactivity disorder, despite higher costs and longer visits. Families of children with ASD report difficulty receiving family-centered, thorough, and coordinated treatment, and care is frequently more fragmented [5]. Children with ASD were 24% less likely to have care coordination and 23% less likely to have a medical home compared with kids with non-ASD emotional and behavioural disorders. Patients with IDD report negative experiences with mental health services, including poor accessibility and information provision [25], extensive use of pharmacotherapy, often without an appropriate psychiatric assessment and diagnosis [26].Many of the current issues of healthcare provision to persons with IDD and/or ASD seem to be associated with years of stigma and ignorance regarding NDD among caregivers, doctors, and policymakers. In some contexts, this has arrived to cause neglect and maltreatment [27,28].The primary symptoms and deficits connected to IDD and/or ASD can be correlated onto many of the patient variables that hinder care delivery. Social communication issues can make it difficult for patients to communicate their symptoms and requirements to the care team, patients may misinterpret nonverbal cues meant to reassure them, and increase anxiety when dealing with new healthcare professionals and environments. These communication issues are reported to be one of the root reasons of challenging behaviour [29].Healthcare setting are often not adequate to the sensory integration issues of persons with NDD, with loud noises, bright lights, strange odours, strange cuisines, and alien tactile inputs, such as peripheral intravenous lines or the hospital identification wristband being the most often reported. Furthermore, common standard settings, do not foresee the availability of activities, toys, or materials to which persons with NDD are more interested in and that could improve involvement in medical care practice [5].Further issues are specifically related to the quality of care for patients with a combination of IDD, including borderline intellectual functioning, and mental health disorders in mental health services. Either the IDD or the mental health disorder may often be missed when symptoms are attributed exclusively to either of these specific disorders despite both states being present, so-called diagnostic overshadowing [25]. For this and other diagnostic issues, a considerable rate of hidden psychopathology is reported in persons with NDD, especially when major cognitive and communication issues are present [13]. In addition to diagnosing co-occurring mental health disorders, identification of the IDD/ASD itself may be a challenge and they are often under-recognized within mental health services. On the contrary, when specifically assessed for research reasons, NDD are reported to be highly prevalent among mental health service users, up to around 43% for borderline intellectual functioning and mild IDD, and 19% for ASD [30,31], although some scholars identified some risks of overestimation for more recent data on ASD [32].These factors contribute to insufficient care and can result in chronic, more difficult-to-treat mental health issues. Research findings show that when compared with the general psychiatric population, people with IDD attending mental health services are younger, more often men, have different diagnostic profiles, receive fewer diagnostic and treatment activities, require more interprofessional consultations outside of the service, require more crisis interventions, and more psychiatric hospital admissions [25].Despite the increasing sociocultural movement towards deinstitutionalization, the healthcare system is unprepared to accommodate the specific needs of persons with IDD and/or ASD since adolescence and transition to adulthood, underscoring the need for targeted change throughout the system. In fact, despite the existence of specific recommendations [33,34], persons with NDD typically lack access to quality healthcare, receive inadequate diagnosis and postdiagnostic support as well as ineffective intervention, residential, educational, employment, financial, and social support services [35,36]. The lack of a unified care system that provides services across all domains may be the cause of users' perceptions and experiences of inefficiencies [37].There is little research on how mental healthcare should be organized and provided to people with IDD and/or ASD. There is no conclusive evidence on better level of services or outcomes being provided either by the general psychiatric services or specialist IDD psychiatric services [38]. This is also because of the difficulty of converging patient, provider, and system-level issues, including the recently increasing call from a portion of the autistic community to consider ASD as one form of variation within a diversity of minds and not as a disorder [39,40].Some evidence was found for intensive case management and assertive outreach for individuals with mild IDD but this was not replicated in further studies. In terms of treatment, there is no high-quality evidence found for pharmacological interventions and some limited evidence around psychological therapy, with specific reference to depression. The scientific community seems to converge on that care should be provided in accordance with principles of interdisciplinarity, life-span view, precision, personalization, and participation [26]. Identifying the key intervention needs requires the adoption of a holistic person-centred and family-centred approach, which considers all major aspects of a person's life and their family interrelated and involves a partnership among healthcare professionals, patients and families for information sharing, decision-making, planning, and delivery of care [41,42].An ideal conceptual reference for care planning and outcome evaluation appears to be quality of life, which should be assessed using instruments that have a good balance between personal and shared quality-of-life components [43]. Communication with the patient and their parents or caregivers as well as professional care providers is key to collect all relevant information about a patient's specific sensitivities, cognitive abilities, modes of communication, motivating factors and interests, health history, and current clinical condition.An example of a multidisciplinary approach using clinical history and biomarkers to personalize medical treatment for children with ASD is provided by Frye [44].Strategies to optimize the care in medical settings, include previsit planning, anticipating, and reducing sources of distress as well as emotional or behavioural challenges, and employing environmental interventions [5]. It is also important to clarify guardianship status with respect to medical decision-making and for adult patients, attention should be given to respect the individual's right to privacy and consent to treatment [5].To promote mental health among individuals with NDD, greater emphasis should be given to early and accurate diagnosis and nonpharmacologic interventions. To meet these and the other above-mentioned mental health needs, specialized training programs and interventions are needed within schools, paediatric care, and psychiatric services as well as general psychiatry residency programs and consultation-liaison psychiatry fellowship training. Web-based training for workplace learning has been shown to be effective in the strengthening of professional care for persons with IDD and challenging behaviour [29]. Workforce development initiatives for mental health professionals would be particularly useful, such as 'direct service professionals' who specialize in providing behavioural, communicational, and functional support across the life-span with special attention to the transition to adulthood [16].We thank Dr Claudia Cardaci for her assistance in revising and checking the references.