ABSTRACT Targeted precision therapies are increasingly used in the treatment of individuals with vascular anomalies (VAs). This increases the need for rapid, accurate and inexpensive genetic diagnosis. Droplet digital polymerase chain reaction (ddPCR) is an alternative to next-generation sequencing (NGS), permitting rapid, highly sensitive interrogation of recurrent pathogenic mosaic variants. We examined the feasibility of ddPCR as a primary diagnostic tool in a large cohort of individuals with VAs. Lesional tissue was collected for ddPCR of up to 46 recurrent pathogenic variants across 16 genes associated with VAs. Specimens were assessed on a subset of assays for each individual based on clinical phenotype. Most individuals who had negative ddPCR results went on to high-depth gene panel or deep exome NGS, or Sanger sequencing. Here we report the phenotypic and molecular findings for 78 newly recruited and tested individuals in addition to the 60 individuals already reported from our cohort. The overall diagnostic yield for our cohort when combined with individuals previously reported was 104/138 (75%). Of 138 individuals tested, recurrent pathogenic variants were detected in 71 (51%) on ddPCR. Variants were most frequently identified in PIK3CA (n=28), TEK (n=18), GNAQ (n=12), or MAP2K1 (n=7). In a further 33 individuals, pathogenic variants were identified on NGS or Sanger sequencing. Our findings indicate that ddPCR is an efficient method achieving a high diagnostic yield in our cohort when used prior to sequencing.

Chronic pain is a critical health problem with a need for new effective treatments. Nocifensive behaviour testing is used to evaluate animal responses to noxious or painful stimuli and is important in basic pain research for understanding pain mechanisms and developing new treatments. A major problem with this technique, however, is that there can be large differences in baseline measurements even when the same sex and strain of rodent is used. We posit that these differences may be due to variation between testers. This project explored factors that contribute to potential inter-rater variability observed in nocifensive behaviour. Adult Sprague Dawley rats underwent evoked somatosensory testing using von Frey filaments and the simplified up-down (SUDO) approach with two different testers, while other environmental conditions such as location, testing time, and acclimation periods were carefully controlled for. The paw withdrawal threshold between testers was different with baseline scores ranging from 3 g to 18.5 g for individual rats. These results suggest that most observed variation in behavioural outcomes is due to tester differences relative to any other factors. Tester differences that could contribute to this variation include sex, genetics, or odour. These results highlight the importance of maintaining one tester for a series of experiments. We conclude that inter-rater variability is an important factor that must be considered when conducting von Frey nocifensive behaviour testing.

Variants in spliceosomal small nuclear RNA (snRNA) genes RNU4-2 (ReNU syndrome), RNU5B-1, and RNU2-2 have recently been linked to dominant neurodevelopmental disorders (NDDs), revealing a major, previously overlooked role for noncoding snRNAs in human disease. Here, we systematically analysed 200 potentially functional snRNA genes in a French cohort comprising 26,911 individuals with rare disorders and through international collaborations. We identify de novo and biallelic variants in RNU2-2 associated with both dominant and recessive NDDs in 126 individuals from 108 unrelated families. Recessive RNU2-2 NDD is at least twice as frequent as the dominant NDD caused by n.4G>A and n.35A>G, and often arises from a de novo variant in trans with an inherited allele, reflecting the high mutability of snRNA genes. Dominant and recessive RNU2-2-NDDs share overlapping clinical features with frequent epilepsy. Blood transcriptomics and DNA methylation analyses revealed subtle, variant-specific effects on splicing and episignatures. Our findings support a gradient-of-impact model and a continuum between dominant and recessive inheritance, establishing RNU2-2 variants as a frequent cause of NDDs, nearly as prevalent as ReNU syndrome.

Cerebral cavernous malformations (CCMs) are intracranial vascular lesions associated with risk of haemorrhages and seizures. While the majority are sporadic and often associated with somatic variants in PIK3CA and MAP3K3, around 20% are familial with germline variants in one of three CCM genes-KRIT1/CCM1, CCM2 and PDCD10/CCM3. We performed comprehensive phenotyping and genetic analysis of nine multiplex families and ten sporadic individuals with CCM. In the familial cases, initial standard analyses had a low yield, we therefore searched for small copy number changes and deep intronic variants. Subsequently, pathogenic germline variants in KRIT1/CCM1 or CCM2 were identified in all 9 multiplex families. Single or multiple exon deletions or splice site variants in KRIT1/CCM1 were found in 3/9 families. Where cavernous malformation tissue was available, second hit somatic PIK3CA variants were identified in 4/7 individuals. These 4 individuals were from separate families with germline KRIT1/CCM1 variants. In 8/10 sporadic cases, we detected recurrent pathogenic somatic PIK3CA, MAP3K3 or CCM2 variants. All familial cases had multiple CCMs, whereas the sporadic cases had a single lesion only, which was in the temporal lobe in 9/10 individuals. Our comprehensive approach interrogating deep intronic variants combined with detection of small copy number variants warrants implementation in standard clinical genetic testing pipelines to increase diagnostic yield. We also build on the established second hit germline and somatic variant mechanism in some CCM lesions. Genetic diagnosis has clinical implications such as reproductive counselling and provides potential eligibility for precision medicine therapies to treat rapidly growing CCMs.

Neural tube closure defect pathomechanisms in human embryonic development are poorly understood. Here we identified spina bifida patients expressing novel variants of the TOGARAM gene family. TOGARAM1 has been associated with the ciliopathy Joubert syndrome, but its connection to spina bifida and role in neural development is unknown. We show that Togaram1 is expressed in the neural tube and Togaram1 knockout mice have abnormal cilia, reduced sonic hedgehog (Shh) signaling, abnormal neural tube patterning, and display neural tube closure defects. Neural stem cells from Togaram1 knockout embryos showed reduced cilia and defects in Shh signaling. Overexpression in IMCD3 and HEK293 cells of TOGARAM1 carrying the variant found in the spina bifida patient resulted in cilia defect along with reduced pericentriolar material one (PCM1), a critical constituent of centriolar satellites involved in transporting proteins toward the centrosome and primary cilia. Our results demonstrate the role of TOGARAM1 in regulating Shh signaling during early neural development that is critical for neural tube closure and elucidates potential mechanisms whereby the ciliopathy-associated gene TOGARAM1 gives rise to spina bifida aperta in humans.

Polypyrimidine tract-binding protein 1 (PTBP1) is a heterogeneous nuclear ribonucleoprotein primarily known for its alternative splicing activity. It shuttles between the nucleus and cytoplasm via partially overlapping N-terminal nuclear localization (NLS) and export (NES) signals. Despite its fundamental role in cell growth and differentiation, its involvement in human disease remains poorly understood. We identified 27 individuals from 25 families harboring de novo or inherited pathogenic variants - predominantly start-loss (89%) and, to a lesser extent, missense (11%) - affecting NES/NLS motifs. Affected individuals presented with a syndromic neurodevelopmental disorder and variable skeletal dysplasia with disproportionate short stature with short limbs. Intellectual functioning ranged from normal to moderately delayed. Start-loss variants led to translation initiation from an alternative downstream in-frame methionine, resulting in loss of the NES and the first half of the bipartite NLS, and increased cytoplasmic stability. Start-loss and missense variants shared a DNA methylation episignature in peripheral blood and altered nucleocytoplasmic distribution in vitro and in vivo with preferential accumulation in processing bodies, causing aberrant gene expression but normal RNA splicing. Transcriptomic analysis of patient-derived fibroblasts revealed dysregulated pathways involved in osteochondrogenesis and neurodevelopment. Overall, our findings highlight a cytoplasmic role for PTBP1 in RNA stability and disease pathogenesis.

CLN2 and CLN3 diseases, the most common types of Batten disease (also known as neuronal ceroid lipofuscinosis), are childhood dementias associated with progressive loss of speech, language and feeding skills. Here we delineate speech, language, non-verbal communication and feeding phenotypes in 33 individuals (19 females) with a median age of 9.5 years (range 3-28 years); 16 had CLN2 and 17 CLN3 disease; 8/15 (53%) participants with CLN2 and 8/17 (47%) participants with CLN3 disease had speech and language impairments prior to genetic diagnosis. At the time of study all participants, bar one, had language impairments. The remaining participant with typical language was tested at age 3 years, following pre-symptomatic enzyme replacement therapy (ERT) from age 9 months. CLN2 and CLN3 disease had different profiles. For CLN2 disease, all affected individuals showed language impairment with dysarthria; older individuals with classical disease progressively became non-verbal. For CLN3 disease, the presentation was more heterogeneous. Speech impairment was evident early in the disease course, with dysarthria (13/15, 87%), often manifesting as neurogenic stuttering (5/15, 33%). Participants with CLN2 disease had comparable expressive and receptive language skills (p > 0.99), yet participants with CLN3 disease had stronger expressive language than receptive language skills (p = 0.004). Speech, cognitive and language impairment and adaptive behaviour showed progressive decline in both diseases. Individuals with pre-symptomatic ERT or atypical CLN2 disease were less impaired. Challenging behaviours were common in CLN3 (11/17, 65%), but less frequent in CLN2 (4/16, 25%) disease. Individuals with Batten disease require tailored speech therapy incorporating communication partner training utilising environment adaptations and informal communication behaviours.

Loss of GABAergic and glycinergic inhibitory efficacy in the spinal dorsal horn is associated with neuropathic pain and opioid-induced hyperalgesia in rodent models. Downregulation of the KCC2 chloride extrusion transporter is a key mechanism underlying this decreased inhibitory efficacy, but to-date there is no evidence supporting or opposing this hypothesis in humans. Here, we demonstrate that KCC2 expression is decreased in superficial dorsal horn neurons of organ donors who died with a documented history of pain, or of long-term opioid use. We show profoundly decreased KCC2 dorsal horn membrane expression in a primary cohort associated with either chronic pain or opioid use, and in a replication cohort of mixed chronic pain and opioid use history. These results show that decreased dorsal horn inhibitory efficacy likely promotes chronic pain in humans and support the development of therapeutics augmenting KCC2 function as a treatment for chronic pain and opioid use disorders.

The Ca V 3.2 isoform of T-type voltage-gated calcium channels plays a crucial role in regulating the excitability of nociceptive neurons; the endogenous molecules that modulate its activity, however, remain poorly understood. Here, we used serum proteomics and patch-clamp physiology to discover a novel peptide albumin (1-26) that facilitates channel gating by chelating trace metals that tonically inhibit Ca V 3.2 via H191 residue. Importantly, serum also potently modulated T-currents in human and rodent dorsal root ganglion (DRG) neurons. In vivo pain studies revealed that injections of serum and albumin (1-26) peptide resulted in robust mechanical and heat hypersensitivity. This hypersensitivity was abolished with a T-channel inhibitor, in Ca V 3.2 null mice and in Ca V 3.2 H191Q knock-in mice. The discovery of endogenous chelators of trace metals in the serum deepens our understanding of the role of Ca V 3.2 channels in neuronal hyperexcitability and may facilitate the design of novel analgesics with unique mechanisms of action.

Hypothalamic Hamartoma (HH) Syndrome is a rare condition in which benign subcortical lesion attached to the hypothalamus results in a multitude of symptoms including refractory epilepsy, endocrine dysfunction, developmental delay and psychiatric comorbidities. Gelastic "laughing" seizures are the identifying symptom of HH syndrome, but often remain unidentified until other seizure types occur. In this review we summarize typical presentations that lead to diagnosis. The literature suggests that early MRI imaging, detailed assessment of endocrine function and formal neuropsychological testing are most important after diagnosis. EEG tests are usually less valuable than in other epilepsies and gelastic seizures may occur without ictal EEG changes. Experts agree that most patients with seizures are refractory to antiseizure medications. Therefore, early surgical intervention is recommended. Three main minimally invasive techniques are currently used: Laserinterstitial thermal therapy, radiosurgery and radiofrequency thermocoagulation. Three large meta-analysis collecting data from more than 500 patients treated with these techniques have been published. Safety profiles of all three methods are good and superior to micro-surgical approaches used previously. Most common complications are hypothalamic-endocrine dysfunction and mild neurological symptoms. 70-90% of patients are seizure free after the interventions, around 20-30% requiring multiple treatment to archive this outcome. Overall, minimally invasive approaches have revolutionized long-term outcomes in HH. Meanwhile, new genetic methods are being developed to better understand mechanisms that cause HH. Most importantly knowledge is still lacking about how these localized lesions can cause substantial developmental delay and psychiatric comorbidity that persist even after successful surgical removal.

Protein-activated kinases mediate spine morphogenesis and synaptic plasticity. PAK3 is part of the p21-activated kinases (PAKs) family of Ras-signaling serine/threonine kinases. Pathogenic variants in the X-linked gene PAK3 have been described in patients with neurodevelopmental syndromes. We analyzed an Italian family with sleep-related hypermotor epilepsy, intellectual disability, psychiatric and behavioral problems, and dysmorphic facial features. A novel PAK3 c.342_344del (p.Lys114del) inframe deletion was detected in the family. Protein structure analysis supported deleterious impact of p.Lys114 deletion through loss or partial loss of autoinhibition of PAK3 protein kinase activity. The male proband had drug-resistant hypermotor seizures and moderate intellectual disability. His brother had drug-responsive hypermotor seizures and mild intellectual disability. Both brothers were hemizygous and had psychiatric and behavioral problems as well as dysmorphic facial features. Their mother had never had seizures but was shown to be mosaic for the PAK3 pathogenic variant. She had normal intellect but did have short stature and dysmorphic facial features similar to her sons. This is the first reported association of a PAK3 pathogenic variant with sleep-related hypermotor epilepsy. PAK3 testing should be considered in families with suspected X-linked sleep-related hypermotor epilepsy and intellectual disability, including for mosaicism in mildly affected females. PLAIN LANGUAGE SUMMARY: We studied an Italian family with sleep-related hypermotor epilepsy, intellectual disability, psychiatric and behavioral problems, and dysmorphic facial features. A novel PAK3 c.342_344del (p.Lys114del) inframe deletion was detected in the family. Protein structure analysis supported deleterious impact of p.Lys114 deletion through loss or partial loss of autoinhibition of PAK3 protein kinase activity. This is the first reported association of a PAK3 pathogenic variant with sleep-related hypermotor epilepsy. PAK3 testing should be considered in families with suspected X-linked sleep-related hypermotor epilepsy and intellectual disability, including for mosaicism in mildly affected females.

Different types of germline de novo SETBP1 variants cause clinically distinct and heterogeneous neurodevelopmental disorders: Schinzel-Giedion syndrome (SGS, via missense variants at a critical degron region) and SETBP1-haploinsufficiency disorder. However, due to the lack of systematic investigation of genotype-phenotype associations of different types of SETBP1 variants, and limited understanding of its roles in neurodevelopment, the extent of clinical heterogeneity and how this relates to underlying pathophysiological mechanisms remains elusive. This imposes challenges for diagnosis. Here, we present a comprehensive investigation of the largest cohort to date of individuals carrying SETBP1 missense variants outside the degron region (n = 18). We performed thorough clinical and speech phenotyping with functional follow-up using cellular assays and transcriptomics. Our findings suggest that such variants cause a clinically and functionally variable developmental syndrome, showing only partial overlaps with classical SGS and SETBP1-haploinsufficiency disorder. We provide evidence of loss-of-function pathophysiological mechanisms impairing ubiquitination, DNA-binding, transcription, and neuronal differentiation capacity and morphologies. In contrast to SGS and SETBP1 haploinsufficiency, these effects are independent of protein abundance. Overall, our study provides important novel insights into diagnosis, patient care, and aetiology of SETBP1-related disorders.

While it is widely accepted that somatic variants that activate the PI3K-mTOR pathway are a major cause of drug-resistant focal epilepsy, typically associated with focal cortical dysplasia (FCD) type 2, understanding the mechanism of epileptogenesis requires identifying genotype-associated changes at the single-cell level, which is technically challenging with existing methods. Here, we performed single-nucleus RNA-sequencing (snRNA-seq) of 18 FCD type 2 samples removed surgically for treatment of drug-resistant epilepsy, and 17 non-FCD control samples, and analyzed additional published data comprising >400,000 single nuclei. We also performed simultaneous single-nucleus genotyping and gene expression analysis using two independent approaches: 1) a method that we called genotyping of transcriptomes enhanced with nanopore sequencing (GO-TEN) that combines targeted cDNA long-read sequencing with snRNA-seq, 2) ResolveOME snRNA-seq and DNA genotyping. snRNA-seq showed similar cell identities and proportions between cases and controls, suggesting that mosaic pathogenic variants in PI3K-mTOR pathway genes in FCD exert their effect by disrupting transcription in conserved cell types. GO-TEN and ResolveOME analyses confirmed that pathogenic variant-carrying cells have well-differentiated neuronal or glial identities, with enrichment of variants in cells of the neuroectodermal lineage, pointing to cortical neural progenitors as possible loci of somatic mutation. Within FCD type 2 lesions, we identified upregulation of PI3K-mTOR signaling and related pathways in variant-carrying neurons, downregulation of these pathways in non-variant-carrying neurons, as well as associated changes in microglial activation, cellular metabolism, synaptic homeostasis, and neuronal connectivity, all potentially contributing to epileptogenesis. These genotype-specific changes in mosaic lesions highlight potential disease mechanisms and therapeutic targets.

OBJECTIVE:To understand the etiological landscape and phenotypic differences between 2 developmental and epileptic encephalopathy (DEE) syndromes: DEE with spike-wave activation in sleep (DEE-SWAS) and epileptic encephalopathy with spike-wave activation in sleep (EE-SWAS). METHODS:All patients fulfilled International League Against Epilepsy (ILAE) DEE-SWAS or EE-SWAS criteria with a Core cohort (n = 91) drawn from our Epilepsy Genetics research program, together with 10 etiologically solved patients referred by collaborators in the Expanded cohort (n = 101). Detailed phenotyping and analysis of molecular genetic results were performed. We compared the phenotypic features of individuals with DEE-SWAS and EE-SWAS. Brain-specific gene co-expression analysis was performed for D/EE-SWAS genes. RESULTS:We identified the etiology in 42/91 (46%) patients in our Core cohort, including 29/44 (66%) with DEE-SWAS and 13/47 (28%) with EE-SWAS. A genetic etiology was identified in 31/91 (34%). D/EE-SWAS genes were highly co-expressed in brain, highlighting the importance of channelopathies and transcriptional regulators. Structural etiologies were found in 12/91 (13%) individuals. We identified 10 novel D/EE-SWAS genes with a range of functions: ATP1A2, CACNA1A, FOXP1, GRIN1, KCNMA1, KCNQ3, PPFIA3, PUF60, SETD1B, and ZBTB18, and 2 novel copy number variants, 17p11.2 duplication and 5q22 deletion. Although developmental regression patterns were similar in both syndromes, DEE-SWAS was associated with a longer duration of epilepsy and poorer intellectual outcome than EE-SWAS. INTERPRETATION:DEE-SWAS and EE-SWAS have highly heterogeneous genetic and structural etiologies. Phenotypic analysis highlights valuable clinical differences between DEE-SWAS and EE-SWAS which inform clinical care and prognostic counseling. Our etiological findings pave the way for the development of precision therapies. ANN NEUROL 2024;96:932-943.

Purpose:Drugs that attenuate hyperactivation of the phosphatidylinositol 3-kinase-Akt and Ras-mitogen-activated protein kinase signaling pathways are emerging treatments for children with rare, intractable vascular anomalies or PIK3CA-related overgrowth spectrum (PROS) with an eligible genetic diagnosis. However, access to genetic testing remains a barrier to genetic diagnosis. Here, we implement a targeted molecular diagnostic strategy for vascular anomalies or PROS. Methods:We applied a novel genetic testing strategy to children with vascular anomalies or PROS using a tiered approach of (1) droplet digital PCR, (2) Sanger sequencing, (3) high-depth exome sequencing, and (4) reanalysis of existing clinical exome data. Results:We applied this strategy to 60 individuals detecting pathogenic somatic variants in 33 of 60 (55%). This included 26 individuals with slow-flow lesions with variants in PIK3CA, TEK, GNAQ, GNA11, BRAF, or PIK3R1, 4 individuals with fast-flow lesions with variants in KRAS or MAP2K1, 1 individual with a PIK3CA variant and a mixed phenotype, and 2 individuals with PIK3CA variants and PROS without vascular anomalies. Conclusion:We demonstrate an effective genetic diagnostic strategy for children with vascular anomalies or PROS identifying somatic variants in 55% of individuals. Increasing genetic diagnostic yield extends the clinicogenetic spectrum and may provide access for those with intractable disease to therapeutic drug trials.

Objectives:Purine-rich element-binding protein alpha (PURA) regulates gene expression and is ubiquitously expressed with an enrichment in neural tissues. Pathogenic variants in PURA cause the neurodevelopmental disorder PURA syndrome that has a variable phenotype but typically comprises moderate-to-severe global developmental delay, intellectual disability, early-onset hypotonia and hypothermia, epilepsy, feeding difficulties, movement disorders, and subtle facial dysmorphism. Speech is reportedly absent in most, but the specific linguistic phenotype is not well described. Methods:We used genome sequencing to identify a pathogenic gene variant as part of a study of children ascertained for severe primary speech disorder in the absence of moderate or severe ID. Results:The novel PURA c.296G>T (p.Arg99Leu) pathogenic missense variant segregated in the female proband and her affected mother. The proband had dysarthria; phonological disorder; and severe receptive and expressive language impairment, borderline intellect, attention difficulties, oropharyngeal dysmotility, and dysmorphic facial features. Her mother had dysarthria, moderate receptive language impairment, and borderline intellect. Both the proband and her mother completed mainstream schooling with classroom support. Discussion:This is the first inherited PURA pathogenic germline variant in over 600 unrelated families documented on ClinVar or reported in the literature. PURA testing should be considered in families with primary speech disorder and borderline intellectual disability, given the specific genetic counseling implications.

Most patients with GNB1 encephalopathy have developmental delay and/or intellectual disability, brain anomalies and seizures. Recently, two cases with GNB1 encephalopathy caused by haploinsufficiency have been reported that also show a Prader-Willi-like phenotype of childhood hypotonia and severe obesity. Here we present three new cases from our expert centre for genetic obesity in which GNB1 truncating and splice variants, probably leading to haploinsufficiency, were identified. They all have obesity, hyperphagia and intellectual deficit. The clinical cases and their weight courses are presented, together with a review of all 68 published cases with GNB1 encephalopathy. Information on weight was not mentioned in most of these articles, so we contacted authors for additional clinical information on weight status and hyperphagia. Of the 42 patients whose weight status we could determine, obesity was present in 8 patients (19%). Obesity is significantly over-represented in the group with truncating and splicing variants. In this group, we see an obesity prevalence of 75%. Since GNB1 has been linked to several key genes in the hypothalamic leptin-melanocortin pathway, which regulates satiety and energy expenditure, our data support the potential association between GNB1 haploinsufficiency and genetic obesity. We also suggest GNB1 is a candidate gene for the known obesity phenotype of the 1p36 microdeletion syndrome given this chromosomal region includes the GNB1 gene. Knowledge of an additional obesity phenotype is important for prognosis, early interventions against obesity and awareness when prescribing weight-inducing medication.

Excitatory glutamatergic NMDA receptors (NMDARs) are key regulators of spinal pain processing, and yet the biophysical properties of NMDARs in dorsal horn nociceptive neurons remain poorly understood. Despite the clinical implications, it is unknown whether the molecular and functional properties of NMDAR synaptic responses are conserved between males and females as well as from rodents to humans. To address these translational gaps, we systematically compared individual and averaged excitatory synaptic responses from lamina I pain-processing neurons of adult Sprague Dawley rats and human organ donors, including both sexes. By combining patch-clamp recordings of outward miniature excitatory postsynaptic currents with non-biased data analyses, we uncovered a wide range of decay constants of excitatory synaptic events within individual lamina I neurons. Decay constants of quantal synaptic responses were distributed in a continuum from 1-20 ms to greater than 1000 ms, suggesting that individual lamina I neurons contain AMPA receptor (AMPAR)-only as well as GluN2A-, GluN2B-, and GluN2D-NMDAR-dominated synaptic events. This intraneuronal heterogeneity in AMPAR– and NMDAR-mediated decay kinetics was observed across sex and species. However, we discovered a decreased relative contribution of GluN2B-dominated NMDAR responses as well as larger amplitude GluN2D-like events at human lamina I synapses compared to rodent synapses, suggesting species differences relevant to NMDAR subunit-targeting therapeutic approaches. The conserved heterogeneity in decay rates of excitatory synaptic events within individual lamina I pain-processing neurons may enable synapse-specific forms of plasticity and sensory integration within dorsal horn nociceptive networks.

Severe speech disorders lead to poor literacy, reduced academic attainment and negative psychosocial outcomes. As early as the 1950s, the familial nature of speech disorders was recognized, implying a genetic basis; but the molecular genetic basis remained unknown. In 2001, investigation of a large three generational family with severe speech disorder, known as childhood apraxia of speech (CAS), revealed the first causative gene; FOXP2. A long hiatus then followed for CAS candidate genes, but in the past three years, genetic analysis of cohorts ascertained for CAS have revealed over 30 causative genes. A total of 36 pathogenic variants have been identified from 122 cases across 3 cohorts in this nascent field. All genes identified have been in coding regions to date, with no apparent benefit at this stage for WGS over WES in identifying monogenic conditions associated with CAS. Hence current findings suggest a remarkable one in three children have a genetic variant that explains their CAS, with significant genetic heterogeneity emerging. Around half of the candidate genes identified are currently supported by medium (6 genes) to strong (9 genes) evidence supporting the association between the gene and CAS. Despite genetic heterogeneity; many implicated proteins functionally converge on pathways involved in chromatin modification or transcriptional regulation, opening the door to precision diagnosis and therapies. Most of the new candidate genes for CAS are associated with previously described neurodevelopmental conditions that include intellectual disability, autism and epilepsy; broadening the phenotypic spectrum to a distinctly milder presentation defined by primary speech disorder in the setting of normal intellect. Insights into the genetic bases of CAS, a severe, rare speech disorder, are yet to translate to understanding the heritability of more common, typically milder forms of speech or language impairment such as stuttering or phonological disorder. These disorders likely follow complex inheritance with polygenic contributions in many cases, rather than the monogenic patterns that underly one-third of patients with CAS. Clinical genetic testing for should now be implemented for individuals with CAS, given its high diagnostic rate, which parallels many other neurodevelopmental disorders where this testing is already standard of care. The shared mechanisms implicated by gene discovery for CAS highlight potential new targets for future precision therapies.