Background: There is a paucity of valid instruments to assess behaviours directly related with greenhouse gas reduction. In this study, the Climate Mitigation Behaviour Scale (CLIMBS) was developed, adapted from the General Ecological Behaviour framework to capture everyday climate-relevant behaviours across key domains. Methods: An initial 30-item pool including mobility, food, consumption, and engagement themes was refined through expert review and administered to adults participating in an intervention study in Sweden (N = 694). Items used five-point response formats aligned to behavioural frequency. Dimensionality was tested using bifactor item factor analysis (graded response model). Reliability was evaluated via ordinal α and McDonald’s ω. Associations with related constructs, including sustainability interest, knowledge, lifestyle, climate importance, and worry, assessed external validity. Results: A bifactor model with one general factor and four orthogonal domains showed the best fit (RMSEA = .045, CFI = .92, TLI = .91). After removing seven weak items, the final 23-item scale showed a strong general dimension (ω_total = .83, Ω_H = .69). Subscale reliability was acceptable (α = .68–.85). The general factor showed moderate to strong associations with related constructs (r = .39–.55, all p < .001), with negligible age and gender effects. A reduction of the full scale resulted into an 8-item short form (CLIMBS-8), which correlated highly with the general factor (r = .91). Conclusions: CLIMBS is a psychometrically supported measure of climate change mitigation behaviour with a dominant general factor and interpretable domains. The CLIMBS-8 provides a brief alternative with minimal loss of information.

The global rise in youth mental ill-health is exacerbated by a shortage of clinicians trained in evidence-based care, making it difficult to translate research into effective practice – especially for body dysmorphic disorder (BDD), an adolescent-onset condition that often goes undetected and untreated. This study aimed to explore clinicians’ experiences of participation in an online educational programme focused on the assessment and treatment of BDD in youth. We also aimed to investigate their use of newly learned skills after completing the programme. Semi-structured interviews were conducted with 12 clinicians who had completed the online education. Conventional content analysis was used, identifying three main categories. The online format – personal and flexible included reports on building personal connection within online education, flexibility allowing for individualised and integrated learning, and on-demand online supervision facilitating participation. Educational content – motivated learning and facilitated application concerned diverse perceptions of test value, challenge and impact, varying content presentation making the education effective and credible, interactive and practical content for real-world application, and personalised and supportive learning through detailed feedback. Learning outcomes – increased knowledge and changed working practices included descriptions of enhanced proficiency in assessment and treatment of BDD, transdiagnostic value and use, and spreading knowledge and improving clinical routines. Participants reported generally positive experiences of the training and changes in working practices following training. Limitations were also noted, such as insufficient applied skills training and peer support. Future improvements should focus on enhancing practical skills training and providing additional implementation support at both clinician and organisational level.

The causal link between potentially traumatic events and obsessive-compulsive disorder (OCD) remains unclear due to reliance on retrospective self-reports and limited control for familial factors. Here, in this Swedish population-based cohort study, we identified 3,340,945 individuals born between 1975 and 2008 and prospectively examined the associations of objectively recorded assault/victimization and transport accidents with subsequent OCD diagnoses. Individuals exposed to assault/victimization, but not transport accidents, had an increased OCD risk (hazard ratio (HR) 1.73, 95% confidence interval (CI) 1.63-1.83), especially within the first year (HR 2.31, 95% CI 1.98-2.70), decreasing thereafter (HR 1.67, 95% CI 1.57-1.77). The association persisted in discordant full sibling comparisons (HR 1.37, 95% CI 1.23-1.54). Quantitative genetic modeling indicated that the phenotypic correlation (r = 0.12) was primarily due to additive genetic (69%) and unique environmental factors (31%). These findings highlight a complex relationship between assault/victimization and OCD, involving both genetic vulnerability and individual environmental exposure.

Recent announcements by the US Government linking paracetamol use during pregnancy to autism in offspring highlight the risks of misinterpreting observational research to inform policy; this is a clear example of the principle that association does not equal causation. Unmeasured familial confounding is a common bias in epidemiological studies, whereby shared genetic or environmental factors within families produce spurious associations between risk factors and outcomes. In this Viewpoint, aimed at clinicians from a range of disciplines working with children and young people with neurodevelopmental and mental health conditions, we discuss the concept of familial confounding and why it matters for causal inference. We illustrate the concept through several examples and outline study designs that can be used to minimise bias due to familial confounding, along with their strengths and limitations. We also highlight the potential consequences of ignoring familial confounding, both for causal inference and for policy making. Finally, we emphasise triangulation across complementary study designs as a key strategy for strengthening causal inference and informing policy decisions based on observational evidence.

In epidemiological studies, obsessive-compulsive disorder (OCD) is robustly associated with increased risk of cardiometabolic disorders, including cardiovascular diseases, type 2 diabetes, and obesity. However, the mechanisms behind these associations are unclear. We conducted genetic correlation analyses to explore shared genetic etiology and bi-directional summary-level Mendelian randomization (MR) to explore potential causal effects between genetic liability to OCD and 14 cardiometabolic phenotypes (e.g., coronary artery disease, blood pressure, body mass index [BMI]). If causal effects were observed, we planned to conduct multivariable MR to explore indirect effects via health behaviors. We found no evidence for genetic correlations between OCD and any of the cardiometabolic phenotypes under study, except for a negative correlation with BMI (rG = -0.123, SE = 0.029, p < 0.001). Summary-level MR showed no evidence for causal effects. Therefore, multivariable MR was not conducted. We found limited evidence for shared genetic etiology or causal effects using the largest OCD GWAS to date. However, we were predominantly only powered to detect medium to large effects in the direction of OCD to cardiometabolic traits, leaving the possibility of smaller causal effects existing. Future studies with larger, more representative samples will help to further interpret findings.

Body dysmorphic disorder (BDD) is a prevalent and impairing mental disorder that typically onsets in adolescence. Cognitive-behavior therapy (CBT) may be effective for adolescent BDD, although the supporting evidence is currently limited. CBT for BDD is a highly specialized treatment, creating a considerable gap in access to care for young people. Therapist-guided Internet-delivered CBT (ICBT) may help bridge this gap. The primary aim of this study is to determine the efficacy of a therapist-guided ICBT program for children and adolescents with BDD versus an active comparator. Secondary aims are to examine the 6-month durability of the treatment effects and to evaluate its relative cost-effectiveness from multiple perspectives. This is a 3-site superiority randomized controlled trial including 154 young people (12–17 years) with BDD recruited throughout Sweden. Participants are randomized 1:1 to 12 weekly modules of either therapist-supported ICBT primarily based on exposure with response prevention or an active comparator consisting of therapist-supported Internet-delivered relaxation training. Data will be collected at baseline, mid-treatment, post-treatment, and 1 month (primary endpoint), 3 months, and 6 months post-treatment. The primary outcome is BDD symptom severity measured with the Yale-Brown Obsessive-Compulsive Scale Modified for Body Dysmorphic Disorder, Adolescent version. All study personnel who can be blinded to study aims/hypotheses and group allocation will be blinded. Assessors conducting post-treatment and follow-up assessments will be external to the research team and blinded to study aims/hypotheses and group allocation at all assessment points. Analyses will be conducted according to the intention-to-treat principle and will follow a pre-specified statistical and health economic analysis plan. Participant recruitment started on 22 February 2024 and is currently ongoing. Data analysis for the primary aim will commence after the last participant reaches the primary endpoint. ClinicalTrials.gov NCT06262412. Registered on 16 February 2024, https://clinicaltrials.gov/study/NCT06262412 .

Background Hypochondriasis, or health anxiety disorder, is associated with increased mortality, mainly from potentially preventable causes. Substance misuse is a well-known contributor to premature death, yet its relationship with hypochondriasis remains unclear. We assessed the risk of broadly defined substance-related problems in individuals diagnosed with hypochondriasis.Methods This Swedish register-based matched cohort study included 4,129 individuals diagnosed with hypochondriasis in specialist services between 1997 and 2020 and 41,290 demographically matched unexposed individuals. Stratified Cox proportional hazards models were fitted to estimate hazard ratios (HRs) for the association between hypochondriasis and substance-related problems - defined as alcohol and drug use disorders, dispensed medications for alcohol dependence and opioid use disorders, and alcohol- and drug-related accidental poisonings, deaths, and suspected criminal offenses. Models were adjusted for sociodemographic variables, parental substance-related problems, and personal psychiatric history.Results Substance-related problems were identified in 504 (12.2%) individuals with hypochondriasis and 1,924 (4.7%) matched unexposed individuals. After adjustment for sociodemographic and parental covariates, hypochondriasis was significantly associated with an increased risk of substance-related problems (HR, 2.55; 95% confidence interval [CI], 2.30-2.84). Similar results were observed in individuals without preexisting substance-related problems (HR, 2.85; 95% CI, 2.48-3.27). Further adjustment for psychiatric comorbidity, particularly anxiety and depression, reduced the risk estimates, but the associations remained statistically significant. In an additional analysis including primary care diagnoses of hypochondriasis (presumably reflecting less complex cases), the risk of substance-related problems remained elevated (HR, 1.61; 95% CI, 1.39-1.86).Conclusion Improved recognition of, and clinical awareness of substance misuse may help reduce long-term adverse outcomes in individuals with hypochondriasis.

To evaluate the feasibility, acceptability, safety, preliminary efficacy, and preliminary maintenance of TICNET, an online therapist-guided exposure and response prevention (ERP) for adults with Tourette syndrome or chronic tic disorder (TS/CTD). Single-group, unmasked feasibility trial. A psychiatric outpatient clinic specialized in obsessive-compulsive and related disorders in Stockholm, Sweden. Adult participants with TS/CTD were recruited nationwide by means of self- and clinical referrals. The 10-week online, ERP-based, therapist-supported programme TICNET consisted of eight chapters provided on a secure platform. The RE-AIM framework (Reach, Efficacy, Adoption, Implementation, and Maintenance) was used to assess feasibility and acceptability. Safety was measured with an adverse events questionnaire. Preliminary intervention effects on tic severity were measured with the Yale Global Tic Severity Scale – Total Tic Severity subscale. Outcome measures were collected at pre- and post-treatment, as well as at the 3-, 6- and 12-month follow-up. Out of 73 screened participants, 31 met inclusion criteria, with the most common reason for exclusion being not fulfilling the diagnostic criteria for TS/CTD. The participants completed an average of 6.5 out of 8 treatment chapters and 90

IntroductionThe latest climate reports underscore the importance of climate change mitigation behaviours in reducing greenhouse gas emissions and achieving the climate goals. There is a growing demand among the general population for guidance on sustainable behaviour change. Previous research has indicated that behavioural interventions could play a significant role in facilitating this type of behaviour change. However, the effectiveness of such approaches has yet to be rigorously tested under scientific conditions. This project aims to assess whether a novel, intervention "Sustainable Choices" effectively promotes climate change mitigation behaviours when compared to a control condition.MethodsVoluntary participants will be recruited from the general population in Sweden and randomized to either "Sustainable Choices", an online, behavioural intervention targeted at Climate Change Mitigation Behaviours (CCMBs), or a waitlist, both 5 weeks of duration. The target sample size is N = 680. The primary outcome of the study will be pre- to post-intervention difference in climate change mitigation behaviours, measured with the Climate Mitigation Behaviour Scale (CLIMBS). Secondary outcomes will include acceptability measures and effects on psychological well-being. Naturalistic follow-up assessments will be administered at 1-, 3- and 6-months after the post-measurement.DiscussionThe increasing awareness of the link between climate change and individual sustainable lifestyle choices has generated a significant interest in this field. Our aim is to evaluate a scalable intervention targeted at CCMBs, while also promoting psychological well-being associated with sustainable lifestyles.

Introduction: Hypochondriasis is a prevalent psychiatric condition associated with substantial individual suffering and healthcare utilization. Despite its clinical importance, little is known about its etiology, and the extent to which familial and genetic factors contribute to its development remains unclear. Methods: In this population-based cohort study, we identified 5,809,325 individuals born in Sweden between 1950 and 2008 with information on both biological parents, excluding those who emigrated or died before age 6 or before 1997. From this cohort, we identified clusters of full siblings, half siblings, and cousins. We compared the risk of hypochondriasis among relatives of individuals diagnosed with hypochondriasis to that of relatives of individuals without hypochondriasis. Previously validated ICD-10 diagnoses of hypochondriasis were identified through the Swedish National Patient Register (NPR). Cox regression models with time-varying exposures and attained age as the underlying time scale were used to estimate hazard ratios (HRs). Results: A total of 3,202 individuals were diagnosed with hypochondriasis (57.1% women; median age at first diagnosis 32.1 years). Relatives of individuals with hypochondriasis had a higher risk of the disorder, compared with relatives of individuals without hypochondriasis, and the risk increased with the degree of genetic relatedness. The strongest association was observed in full siblings (HR, 9.5; 95% CI, 5.1-17.5), followed by half siblings (HR, 5.6; 95% CI, 2.1-14.9) and cousins (HR, 2.6; 95% CI, 1.4-4.9). Conclusion: Hypochondriasis is a familial and likely heritable disorder.

Aims Social anxiety disorder (SAD) is one of the most common anxiety disorders and is associated with significant impairment and societal costs. The association between SAD and mortality remains poorly understood, partly because in epidemiological research it is rarely studied independently from other anxiety disorders. In this population-based matched cohort and sibling control study, we estimated the risk of all-cause and cause-specific mortality in individuals with SAD.Methods From a population of individuals born from 1932 and living in Sweden between 1997 and 2020, we identified all cases of SAD (Swedish ICD-10 code F40.1) in the National Patient Register. Each of these individuals was matched on sex, birth year and county of residence with 10 individuals who had never received a diagnosis. Mortality data were extracted from the Cause of Death Register. Risks were estimated using Cox proportional hazards regression models. Models adjusted for sociodemographic covariates and other lifetime psychiatric disorders. We also identified all clusters of full siblings and conducted within-sibling comparisons to account for unmeasured familial confounding.Results The matched cohort included 57,360 individuals with SAD and 573,600 unexposed individuals. During the follow-up, 2355 deaths were registered within the exposed cohort vs. 7800 deaths in the matched cohort (crude mortality rates, 5.25 and 1.73 per 1000 person-years, respectively). The full cohort was followed up for a mean of 7.87 years (standard deviation 5.23). In models adjusting for sociodemographic variables, individuals with SAD had a 2.24-fold increased hazard of all-cause mortality (95% confidence interval [CI], 2.13-2.35). The increased risk was observed for both natural (adjusted hazard ratio [HR], 1.62; 95% CI 1.52-1.72) and unnatural causes of death (HR, 4.18; 95% CI 3.82-4.58). The results were robust to additional adjustment for psychiatric comorbidities, but the magnitude of the associations was attenuated, particularly when adjusting for substance use disorders. In the sibling cohort, 39,993 individuals with SAD were compared with their 64,640 unaffected siblings. While the estimates were also attenuated, they remained statistically significant (HR for all-cause mortality, 1.40; 95% CI 1.36-1.45).Conclusions Individuals with SAD face an increased risk of mortality, attributable primarily to unnatural causes of death, such as suicide, but also to natural causes, even after adjusting for socioeconomic variables. Psychiatric comorbidities, particularly substance use disorders, and shared familial factors may also contribute to this excess death. Further study of underlying mechanisms may inform prevention and early intervention strategies to reduce mortality in this vulnerable population.

Abstract Objectives Although obsessive-compulsive disorder (OCD) is strongly associated with a range of modifiable somatic health problems, little is known about how the disorder influences the adoption and maintenance of healthy lifestyle habits, as well as how it shapes patients' experiences of seeking and receiving general healthcare. Methods Sixteen individuals with OCD and cardiometabolic risk who participated in the piloting of a lifestyle intervention completed a semi-structured interview about the impact of OCD on their lifestyle habits and their experiences with general medical services. The interviews were analysed using reflexive thematic analysis. Results The analysis generated three main themes and one overarching theme. The main themes were: (1) Living with multiple barriers to engage in healthy behaviours; (2) Changes in lifestyle habits – challenging but possible; and (3) OCD is a roadblock in general medical care. The overarching theme was: (4) It is not just OCD. The themes reflected that the participants experienced both disorder-specific and general barriers when trying to implement healthy lifestyle behaviours. Changing lifestyle habits was regarded as difficult, but facilitators of change were also identified. Participants reported that OCD affected seeking and receiving healthcare for their somatic problems. OCD was generally viewed as only one of many elements that affected health and lifestyle. Conclusions Our results indicate the need for tailored support for this at-risk group to change and maintain healthy lifestyles, as well as a need of increasing knowledge of OCD among general medical care practitioners. Trial registration Not applicable. Clinical trial number Not applicable.

Background: Individual climate change mitigation behaviours (CCMBs) can meaningfully reduce greenhouse gas emissions, yet many people report uncertainty about what actions to take and difficulty changing established habits. Scalable, digital behavioural interventions remain largely untested. This randomized controlled trial evaluated the effectiveness and acceptability of Sustainable Choices, a five-week, internet-delivered intervention designed to promote CCMBs and psychological well-being. Methods: Adults in Sweden (N = 694) were randomized 1:1 to Sustainable Choices or a waitlist control. The primary outcome was CCMBs at post-intervention, assessed with the Climate Mitigation Behaviour Scale (CLIMBS) and analysed using item-response-theory–derived latent scores in mixed-effects models under an intention-to-treat framework. Secondary outcomes included well-being (SWEMWBS), climate-related worry (GAD-2), low mood (PHQ-2), and meaning and purpose (PROMIS-6a). Follow-ups were conducted at 1, 3, and 6 months. Complier Average Causal Effect analyses examined dose–response relations, and acceptability was assessed through adherence and satisfaction. Results: Compared with controls, the intervention produced significantly greater increases in CCMBs on the CLIMBS general factor (d = 0.34, p &lt; .001), with improvements in food, consumption, and engagement domains but not mobility. Meaning and purpose increased relative to controls (d = 0.23, p = .004), whereas changes in well-being, worry, and low mood were not significant. Engagement showed robust dose-dependent effects: each completed module increased CCMBs by 0.09 points, and full adherence yielded a 0.45-point gain. Satisfaction was high, with 84% recommending the course. Conclusions: Sustainable Choices achieved small-to-moderate improvements in climate mitigation behaviours and enhanced perceived meaning and purpose. Fully digital behavioural interventions may provide a scalable complement to broader climate strategies, meriting further evaluation in diverse populations and with objective behavioural measures.

BACKGROUND:Body dysmorphic disorder (BDD) is a debilitating and understudied psychiatric condition of largely unknown etiology. Emerging evidence suggests that BDD may be a familial and heritable disorder, but family studies of diagnosed individuals and their biological relatives are yet to be conducted. METHODS:We identified 4,857,049 individuals born in Sweden between 1960 and 2008 with information on both biological parents who were living in Sweden in 1997. From this cohort, we identified clusters of full siblings, half siblings, and cousins and compared the risk of BDD among those with a relative diagnosed with BDD and those without. Previously validated ICD-10 diagnoses of BDD were identified through the Swedish National Patient Register. To estimate hazard ratios (HRs), we fitted a series of Cox regression models with time-varying exposures and attained age as the underlying time scale. Individuals were considered unexposed before their relative's BDD diagnosis and exposed thereafter. RESULTS:Relatives of individuals with BDD had a higher risk of BDD compared with relatives of individuals without BDD, with the highest risk observed in full siblings (HR, 16.2; 95% CI, 9.2-28.7), followed by half-siblings (HR, 7.8; 95% CI, 2.5-23.9) and cousins (HR, 2.8; 95% CI, 1.3-6.2), showing a gradient by degree of genetic relatedness. CONCLUSIONS:Our findings indicate that BDD is a familial disorder and suggest an important role for genetic factors.

Traditional case-control studies show that obsessive-compulsive disorder (OCD) is associated with disturbances in cortico-striatal-thalamo-cortical (CSTC) brain circuits. Whether these findings represent underlying familial vulnerabilities (i.e. shared genetic and environmental factors) or are the result of acquired non-shared environmental influences, such as chronic stress or lifestyle factors, is unknown. Using a unique sample of monozygotic twin pairs discordant for lifetime OCD diagnoses (14 pairs, 28 twins) and resting-state functional MRI, we examined the contribution of non-shared environmental influences to CSTC functional connectivity while strictly controlling for shared genetic and environmental factors. Further, we examined familial vulnerability effects by comparing the unaffected co-twins of OCD-affected twins to a sample of control twins (14 pairs, 28 twins). Non-shared environmental influences were statistically significantly associated with thalamostriatal hypoconnectivity, whereas familial vulnerability was significantly associated with heightened connectivity between the striatum and the medial orbitofrontal cortex. These findings suggest that non-shared environmental and familial factors may differentially relate to distinct CSTC circuit disturbances in OCD.

BACKGROUND:Postinfectious autoimmune processes are hypothesized to be causally implicated in tic disorders, including Tourette syndrome and chronic tic disorder. However, this hypothesis remains controversial. In this nationwide cohort study, we aimed to clarify the mechanisms underlying the association between proneness to infections and tic disorders. METHODS:Using Swedish national registers, we identified 3,886,533 individuals (probands) born between 1970 and 2008 with available data on both biological parents. Probands were linked to six clusters of relatives: parents, full siblings, maternal half-siblings, paternal half-siblings, aunts/uncles, and cousins. Cox proportional hazards regression models were used to estimate the risk of tic disorders in probands exposed to infections and their relatives, compared with unexposed probands and their relatives. We also examined dose-response associations using logistic regression models. RESULTS:Probands exposed to infections had an increased risk of tic disorders (hazard ratio [HR], 1.46; 95% confidence interval [CI], 1.40-1.52), as did their relatives. The observed risks increased with the degree of genetic relatedness, from HR (95% CI) of 1.15 (1.12-1.19) in cousins to 1.31 (1.25-1.37) in first-degree relatives. There was a dose-response association between the number of infections in the probands and the odds for tic disorders in the probands and their relatives. Results remained consistent after adjustment for infections in relatives, tic disorders in probands, and autoimmune diseases in probands and relatives. CONCLUSIONS:Our results suggest an important role of shared genetic factors in the association between infections and tic disorders, potentially pointing to pleiotropic mechanisms.

BACKGROUND:Suicide is more common among males and in older age, but the understanding of sex-specific and age-specific risk indicators is limited. OBJECTIVE:To describe the sex-specific and age-specific prevalence of 25 suicide risk indicators in the year preceding suicide and estimate their associations with suicide. METHODS:Register-based population-nested case-control study in Sweden, 2009-2021, comprising 19 741 suicide cases and 197 296 general population controls matched by sex, age and county of residence. Death by suicide was collected from the cause of death register. 25 suicide risk indicators covering psychiatric history, somatic disorders, bereavement and sociodemographic factors in the previous year were collected from nationwide registers. Sex-specific and age-specific ORs of suicide for the presence/absence of each risk indicator in the prior year were estimated and complemented by risk differences. FINDINGS:Suicide cases were 70% male, 9% were aged 15-24 years, 29% 25-44 years, 36% 45-64 years and 26% 65+ years. In the year preceding suicide, the prevalence of most risk indicators was the lowest among males and people aged 65+ years. Most risk indicators also showed weaker 1-year associations with suicide in these groups. The median OR (IQR) of suicide across the 25 risk indicators was 14.6 (5.2, 29.1) in females versus 10.3 (4.3, 21.3) in males, and 17.4 (6.5, 28.9) in 24-44 year-olds versus 8.0 (3.6, 23.7) in people aged 65+years. Risk differences of suicide were larger in males across nearly all risk indicators. CONCLUSIONS:There was considerable heterogeneity across sex and age groups, both in the prevalence of risk indicators preceding suicide and in their associations with suicide. Risk indicators were generally less common and displayed weaker associations with suicide on the relative risk scale among males and older people. CLINICAL IMPLICATIONS:Suicides in males and older people may be harder to predict, as indicators are rarer. When males present with risk indicators, they generally have a higher absolute risk of suicide, making them important targets for prevention even when risk indicators do not cause suicide. Our findings underscore the importance of considering sex-specific and age-specific risk indicators for individualised suicide prediction and prevention.

BACKGROUND:Postinfectious autoimmune processes have been proposed as potential causal risk factors for obsessive-compulsive disorder (OCD). In this large population-based study, we aimed to clarify the familial coaggregation pattern between severe infections and OCD across clusters of relatives with varying degrees of relatedness. METHODS:We identified 4,916,898 individuals born in Sweden between 1960 and 2008 and followed them until the end of 2020. Each individual was linked to their first-, second-, and third-degree relatives, including monozygotic and dizygotic twins, mothers, fathers, full siblings, maternal and paternal half siblings, aunts, uncles, and cousins. OCD and infection diagnoses from inpatient and specialized outpatient settings were retrieved from the Swedish National Patient Register. We compared the risk of OCD in relatives of probands with severe infections to those of probands without severe infections. Cox proportional hazard regression models, incorporating time-varying exposures, were used to estimate hazard ratios. Dose-response associations were examined using logistic regression models. RESULTS:Relatives of probands with severe infections had a higher risk of OCD, which increased with genetic relatedness, with hazard ratios (95% CI) ranging from 1.46 (1.07-1.98) in monozygotic twins to 1.10 (1.09-1.11) in cousins. The results remained robust after adjusting for severe infections among relatives, OCD in probands, and comorbid autoimmune disorders in both probands and relatives. A dose-response association was observed between the number of infections in the probands and their odds of OCD, as well as in their relatives. CONCLUSIONS:The results strongly suggest that the association between severe infections and OCD may be largely driven by shared genetic factors.

IntroductionTourette syndrome (TS) and chronic motor or vocal tic disorder (CTD) are neurodevelopmental disorders associated with functional impairment and reduced quality of life. Behavioral therapy (BT) is an effective treatment, but lack of experienced practitioners makes it hard for patients to receive appropriate help. One approach to bridge the gap between demand and availability is to offer the treatment remotely over the internet with minimal support from a therapist.MethodsThis single-blind randomized controlled superiority trial including 110 participants will compare internet-delivered BT (I-BT) primarily consisting of exposure and response prevention (ERP) to a control condition consisting of internet-delivered general psychological support. The primary aim of the trial is to evaluate whether ERP-based I-BT is superior to the control condition in reducing TS/CTD symptoms. The primary outcome measure is the Yale Global Tic Severity Scale - Total Tic Severity score administered by blinded raters at primary endpoint 11 weeks after the treatment start. Secondary endpoints occur at week 23 and 14 months after the treatment start, and the secondary outcomes include tic-related impairment, rates of responders, self-rated tic severity, symptoms of depression, quality of life and cost-effectiveness. Data on dropout rates and adverse events is also collected.DiscussionThis is the first randomized controlled trial to evaluate therapist-guided ERP-based I-BT for adults with TS/CTD. The study has been approved by the Swedish Ethical Review Authority (EPM 2023-06541-01). The hypotheses were pre-registered before the start of the data collection. Results from all analyses will be reported according to the Consolidated Standards of Reporting Trials statement for non-pharmacological trials (CONSORT) and Consolidated Health Economic Evaluation Reporting Standards (CHEERS). The participants in the control condition will have the opportunity to receive I-BT after the data from the first follow-up is collected. The study will be published in open access and the results will be shared with service user organizations. At the moment of submission, the study has recruited 87 out of 110 planned participants and the recruitment is expected to be completed in February 2025.Trial registrationOpen Science Framework: https://osf.io/cq97b/ (uploaded 31/01/2024); Clinicaltrials.gov: NCT06271083 (submitted 14/02/2024).