Genomic architecture of autism from comprehensive whole-genome sequence annotation.

Fully understanding autism spectrum disorder (ASD) genetics requires whole-genome sequencing (WGS). We present the latest release of the Autism Speaks MSSNG resource, which includes WGS data from 5,100 individuals with ASD and 6,212 non-ASD parents and siblings (total n = 11,312). Examining a wide variety of genetic variants in MSSNG and the Simons Simplex Collection (SSC; n = 9,205), we identified ASD-associated rare variants in 718/5,100 individuals with ASD from MSSNG (14.1%) and 350/2,419 from SSC (14.5%). Considering genomic architecture, 52% were nuclear sequence-level variants, 46% were nuclear structural variants (including copy-number variants, inversions, large insertions, uniparental isodisomies, and tandem repeat expansions), and 2% were mitochondrial variants. Our study provides a guidebook for exploring genotype-phenotype correlations in families who carry ASD-associated rare variants and serves as an entry point to the expanded studies required to dissect the etiology in the ∼85% of the ASD population that remain idiopathic.

A framework for an evidence-based gene list relevant to autism spectrum disorder.

Autism spectrum disorder (ASD) is often grouped with other brain-related phenotypes into a broader category of neurodevelopmental disorders (NDDs). In clinical practice, providers need to decide which genes to test in individuals with ASD phenotypes, which requires an understanding of the level of evidence for individual NDD genes that supports an association with ASD. Consensus is currently lacking about which NDD genes have sufficient evidence to support a relationship to ASD. Estimates of the number of genes relevant to ASD differ greatly among research groups and clinical sequencing panels, varying from a few to several hundred. This Roadmap discusses important considerations necessary to provide an evidence-based framework for the curation of NDD genes based on the level of information supporting a clinically relevant relationship between a given gene and ASD.

Genome-wide detection of tandem DNA repeats that are expanded in autism.

Tandem DNA repeats vary in the size and sequence of each unit (motif). When expanded, these tandem DNA repeats have been associated with more than 40 monogenic disorders1. Their involvement in disorders with complex genetics is largely unknown, as is the extent of their heterogeneity. Here we investigated the genome-wide characteristics of tandem repeats that had motifs with a length of 2-20 base pairs in 17,231 genomes of families containing individuals with autism spectrum disorder (ASD)2,3 and population control individuals4. We found extensive polymorphism in the size and sequence of motifs. Many of the tandem repeat loci that we detected correlated with cytogenetic fragile sites. At 2,588 loci, gene-associated expansions of tandem repeats that were rare among population control individuals were significantly more prevalent among individuals with ASD than their siblings without ASD, particularly in exons and near splice junctions, and in genes related to the development of the nervous system and cardiovascular system or muscle. Rare tandem repeat expansions had a prevalence of 23.3% in children with ASD compared with 20.7% in children without ASD, which suggests that tandem repeat expansions make a collective contribution to the risk of ASD of 2.6%. These rare tandem repeat expansions included previously undescribed ASD-linked expansions in DMPK and FXN, which are associated with neuromuscular conditions, and in previously unknown loci such as FGF14 and CACNB1. Rare tandem repeat expansions were associated with lower IQ and adaptive ability. Our results show that tandem DNA repeat expansions contribute strongly to the genetic aetiology and phenotypic complexity of ASD.

Truncating SRCAP variants outside the Floating-Harbor syndrome locus cause a distinct neurodevelopmental disorder with a specific DNA methylation signature.

Truncating variants in exons 33 and 34 of the SNF2-related CREBBP activator protein (SRCAP) gene cause the neurodevelopmental disorder (NDD) Floating-Harbor syndrome (FLHS), characterized by short stature, speech delay, and facial dysmorphism. Here, we present a cohort of 33 individuals with clinical features distinct from FLHS and truncating (mostly de novo) SRCAP variants either proximal (n = 28) or distal (n = 5) to the FLHS locus. Detailed clinical characterization of the proximal SRCAP individuals identified shared characteristics: developmental delay with or without intellectual disability, behavioral and psychiatric problems, non-specific facial features, musculoskeletal issues, and hypotonia. Because FLHS is known to be associated with a unique set of DNA methylation (DNAm) changes in blood, a DNAm signature, we investigated whether there was a distinct signature associated with our affected individuals. A machine-learning model, based on the FLHS DNAm signature, negatively classified all our tested subjects. Comparing proximal variants with typically developing controls, we identified a DNAm signature distinct from the FLHS signature. Based on the DNAm and clinical data, we refer to the condition as "non-FLHS SRCAP-related NDD." All five distal variants classified negatively using the FLHS DNAm model while two classified positively using the proximal model. This suggests divergent pathogenicity of these variants, though clinically the distal group presented with NDD, similar to the proximal SRCAP group. In summary, for SRCAP, there is a clear relationship between variant location, DNAm profile, and clinical phenotype. These results highlight the power of combined epigenetic, molecular, and clinical studies to identify and characterize genotype-epigenotype-phenotype correlations.

The Phenotypic variability of 16p11.2 distal BP2-BP3 deletion in a transgenerational family and in neurodevelopmentally ascertained samples.

BACKGROUND: We present genomic and phenotypic findings of a transgenerational family consisting of three male offspring, each with a maternally inherited distal 220 kb deletion at locus 16p11.2 (BP2-BP3). Genomic analysis of all family members was prompted by a diagnosis of autism spectrum disorder (ASD) in the eldest child, who also presented with a low body mass index. METHODS: All male offspring underwent extensive neuropsychiatric evaluation. Both parents were also assessed for social functioning and cognition. The family underwent whole-genome sequencing. Further data curation was undertaken from samples ascertained for neurodevelopmental disorders and congenital abnormalities. RESULTS: On medical examination, both the second and third-born male offspring presented with obesity. The second-born male offspring met research diagnostic criteria for ASD at 8 years of age and presented with mild attention deficits. The third-born male offspring was only noted as having motor deficits and received a diagnosis of developmental coordination disorder. Other than the 16p11.2 distal deletion, no additional contributing variants of clinical significance were observed. The mother was clinically evaluated and noted as having a broader autism phenotype. CONCLUSION: In this family, the phenotypes observed are most likely caused by the 16p11.2 distal deletion. The lack of other overt pathogenic mutations identified by genomic sequencing reinforces the variable expressivity that should be heeded in a clinical setting. Importantly, distal 16p11.2 deletions can present with a highly variable phenotype even within a single family. Our additional data curation provides further evidence on the variable clinical presentation among those with pathogenetic 16p11.2 (BP2-BP3) mutations.

Autistic traits in youth with familial adenomatous polyposis: A Dutch-Canadian case-control study.

This study investigated the neurodevelopmental impact of pathogenic adenomatous polyposis coli (APC) gene variants in patients with familial adenomatous polyposis (FAP), a cancer predisposition syndrome. We hypothesized that certain pathogenic APC variants result in behavioral-cognitive challenges. We compared 66 FAP patients (cases) and 34 unaffected siblings (controls) to explore associations between APC variants and behavioral and cognitive challenges. Our findings indicate that FAP patients exhibited higher Social Responsiveness Scale (SRS) scores, suggesting a greater prevalence of autistic traits when compared to unaffected siblings (mean 53.8 vs. 47.4, Wilcoxon p = 0.018). The distribution of SRS scores in cases suggested a bimodal pattern, potentially linked to the location of the APC variant, with scores increasing from the 5' to 3' end of the gene (Pearson's r = 0.33, p = 0.022). While we observed a trend toward lower educational attainment in cases, this difference was not statistically significant. This study is the first to explore the connection between APC variant location and neurodevelopmental traits in FAP, expanding our understanding of the genotype-phenotype correlation. Our results emphasize the importance of clinical assessment for autistic traits in FAP patients, shedding light on the potential role of APC gene variants in these behavioral and cognitive challenges.

Support to caregivers who have received genetic information about neurodevelopmental and psychiatric vulnerability in their young children: A narrative review.

Diagnosis of pathogenic genetic variants associated with neurodevelopmental and psychiatric disorders (NPDs) is increasingly made early in life. This narrative review focuses on the need for, and provision of, psychological supports following genetic diagnosis. We conducted a literature search of publications on how caregivers are informed about the NPD vulnerability associated with genetic variants, challenges and unmet needs when receiving this information, and whether psychological supports are provided. Given its early recognition, the 22q11.2 deletion has been studied thoroughly for two decades, providing generalizable insights. This literature indicates the complex caregivers' needs related to learning about potential NPD vulnerabilities associated with a genetic variant, include how to communicate the diagnosis, how to identify early signs of NPDs, how to deal with stigma and a lack of medical expertise outside of specialized genetics clinics. With one exception, no publications describe psychotherapeutic support provided to parents. In the absence of support, caregivers struggle with several unmet needs regarding potential longer-term NPD implications of a genetic diagnosis. The field needs to go beyond explaining genetic diagnoses and associated vulnerabilities, and develop approaches to support caregivers with communicating and managing NPD implications across the child's lifespan.

Neurodevelopmental functioning in probands and non-proband carriers of 22q11.2 microduplication.

Microduplication of the LCR22-A to LCR22-D region on chromosome 22q11.2 is a recurrent copy number variant found in clinical populations undergoing chromosomal microarray, and at lower frequency in controls. Often inherited, there is limited data on intellectual (IQ) and psychological functioning, particularly in those individuals ascertained through a family member rather than because of neurodevelopmental disorders. To investigate the range of cognitive-behavioral phenotypes associated with 22q11.2 duplication, we studied both probands and their non-proband carrier relatives. Twenty-two individuals with 22q11.2 duplication (10 probands, 12 non-proband carriers) were prospectively assessed with a battery of neuropsychological tests, physical examination, and medical record review. Assessment measures with standardized norms included IQ, academic, adaptive, psychiatric, behavioral, and social functioning. IQ and academic skills were within the average range, with a trend toward lower scores in probands versus non-probands. Adaptive skills were within age expectations. Prevalence of attention deficits (probands only) and anxiety (both groups) was high compared with norms. The prevalence of autism spectrum disorder was relatively low (5% of total sample). Assessment of both probands and non-probands with 22q11.2 duplication suggests that the phenotypic spectrum with respect to neurodevelopment overlaps significantly with the general population. IQ and academic abilities are in the average range for most of the individuals with 22q11.2 duplication in our study, regardless of ascertainment as a proband or non-proband relative. Symptoms of attention deficit and anxiety were identified, which require further study. Results of this study further clarify the phenotype of individuals with 22q11.2 duplication, and provides important information for genetic counseling regarding this recurrent copy number variant.

Sleep phenotype of individuals with autism spectrum disorder bearing mutations in the PER2 circadian rhythm gene.

The Per family of genes functions as a primary circadian rhythm maintenance in the brain. Mutations in PER2 are associated with familial advanced sleep-phase syndrome 1 (FASPS1), and recently suggested in delayed sleep phase syndrome and idiopathic hypersomnia. The detection of PER2 variants in individuals with autism spectrum disorder (ASD) and without reported sleep disorders, has suggested a role of circadian-relevant genes in the pathophysiology of ASD. It remains unclear whether these individuals may have, in addition to ASD, an undiagnosed circadian rhythm sleep disorder. The MSSNG database was used to screen whole genome sequencing data of 5,102 individuals with ASD for putative mutations in PER2. Families identified were invited to complete sleep phenotyping consisting of a structured interview and two standardized sleep questionnaires: the Pittsburgh Sleep Quality Index and the Morningness-Eveningness Questionnaire. From 5,102 individuals with ASD, two nonsense, one frameshift, and one de novo missense PER2 variants were identified (0.08%). Of these four, none had a diagnosed sleep disorder. Three reported either a history of, or ongoing sleep disturbances, and one had symptoms highly suggestive of FASPS1 (as did a mutation carrier father without ASD). The individual with the missense variant did not report sleep concerns. The ASD and cognitive profiles of these individuals varied in severity and symptoms. The results support a possible role of PER2-related circadian rhythm disturbances in the dysregulation of sleep overall and sometimes FASPS1. The relationship between dysregulated sleep and the pathophysiology of ASD require further exploration.

Correction: Meta-analysis and multidisciplinary consensus statement: exome sequencing is a first-tier clinical diagnostic test for individuals with neurodevelopmental disorders.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Meta-analysis and multidisciplinary consensus statement: exome sequencing is a first-tier clinical diagnostic test for individuals with neurodevelopmental disorders.

PURPOSE: For neurodevelopmental disorders (NDDs), etiological evaluation can be a diagnostic odyssey involving numerous genetic tests, underscoring the need to develop a streamlined algorithm maximizing molecular diagnostic yield for this clinical indication. Our objective was to compare the yield of exome sequencing (ES) with that of chromosomal microarray (CMA), the current first-tier test for NDDs. METHODS: We performed a PubMed scoping review and meta-analysis investigating the diagnostic yield of ES for NDDs as the basis of a consensus development conference. We defined NDD as global developmental delay, intellectual disability, and/or autism spectrum disorder. The consensus development conference included input from genetics professionals, pediatric neurologists, and developmental behavioral pediatricians. RESULTS: After applying strict inclusion/exclusion criteria, we identified 30 articles with data on molecular diagnostic yield in individuals with isolated NDD, or NDD plus associated conditions (such as Rett-like features). Yield of ES was 36% overall, 31% for isolated NDD, and 53% for the NDD plus associated conditions. ES yield for NDDs is markedly greater than previous studies of CMA (15-20%). CONCLUSION: Our review demonstrates that ES consistently outperforms CMA for evaluation of unexplained NDDs. We propose a diagnostic algorithm placing ES at the beginning of the evaluation of unexplained NDDs.

Global developmental delay and a de novo deletion of the 16p13.13 region.

Many rare genetic variants are associated with the risk of atypical neurodevelopmental trajectories. In this study, we report a patient with developmental delay, autistic traits and multiple congenital anomalies, including congenital heart anomalies and orofacial cleft, with a 0.832 Mb de novo deletion of the 16p13.13 region classified as a variant of uncertain significance. Comparison of similar sized deletions and duplications overlapping the same genes in the DECIPHER database, revealed seven reports of copy number variants (CNVs), four duplications and three deletions. A neurodevelopmental phenotype including learning disability and intellectual disability was noted in some of the DECIPHER entries where phenotype was provided. Although the association between a deletion in this region and an atypical neurodevelopmental trajectory remains to be elucidated, the overlapping CNVs with neurodevelopmental phenotypes suggests possible candidate genes within the 16p13.13 region.

An integrated clinical approach to children at genetic risk for neurodevelopmental and psychiatric conditions: interdisciplinary collaboration and research infrastructure.

BACKGROUND: A sizeable proportion of pathogenic genetic variants identified in young children tested for congenital differences are associated with neurodevelopmental psychiatric disorders (NPD). In this growing group, a genetic diagnosis often precedes the emergence of diagnosable developmental concerns. Here, we describe DAGSY (Developmental Assessment of Genetically Susceptible Youth), a novel interdisciplinary 'genetic-diagnosis-first' clinic integrating psychiatric, psychological and genetic expertise, and report our first observations and feedback from families and referring clinicians. METHODS: We retrieved data on referral sources and indications, genetic and NPD diagnoses and recommendations for children seen at DAGSY between 2018 and 2022. Through a survey, we obtained feedback from twenty families and eleven referring clinicians. RESULTS: 159 children (mean age 10.2 years, 57.2% males) completed an interdisciplinary (psychiatry, psychology, genetic counselling) DAGSY assessment during this period. Of these, 69.8% had a pathogenic microdeletion or microduplication, 21.5% a sequence-level variant, 4.4% a chromosomal disorder, and 4.4% a variant of unknown significance with emerging evidence of pathogenicity. One in four children did not have a prior NPD diagnosis, and referral to DAGSY was motivated by their genetic vulnerability alone. Following assessment, 76.7% received at least one new NPD diagnosis, most frequently intellectual disability (24.5%), anxiety (20.7%), autism spectrum (18.9%) and specific learning (16.4%) disorder. Both families and clinicians responding to our survey expressed satisfaction, but also highlighted some areas for potential improvement. CONCLUSIONS: DAGSY addresses an unmet clinical need for children identified with genetic variants that confer increased vulnerability for NPD and provides a crucial platform for research in this area. DAGSY can serve as a model for interdisciplinary clinics integrating child psychiatry, psychology and genetics, addressing both clinical and research needs for this emerging population.

Developmental implications of genetic testing for physical indications.

In children undergoing genetic testing for physical health concerns, we examined how often the results also revealed information about their risk for neurodevelopmental disorders. The study sample consisted of 3056 genetic tests (1686 chromosomal microarrays--CMAs, and 1378 next-generation sequencing--NGS panels) ordered at a tertiary pediatric hospital because of a physical/congenital health problem. Tests ordered to investigate developmental concerns were excluded. Pathogenic, or likely pathogenic variants were manually reviewed for diagnostic likelihood, and for evidence of an association with a neurodevelopmental disorder (e.g., autism or intellectual disability). A total of 169 CMAs (10%) and 232 NGS panels (17%) had likely diagnostic results. More than half (52%) of all diagnostic results had established evidence of a neurodevelopmental disorder association. In summary, there is a high prevalence of neurodevelopmental implications from genetic tests ordered for physical/congenital indications. This broad clinical utility suggests a growing need for genetics-first developmental care pathways.

Expanding the neurodevelopmental phenotypes of individuals with de novo KMT2A variants.

De novo loss-of-function (LoF) variants in the KMT2A gene are associated with Wiedemann-Steiner Syndrome (WSS). Recently, de novo KMT2A variants have been identified in sequencing studies of cohorts of individuals with neurodevelopmental disorders (NDDs). However, most of these studies lack the detailed clinical information required to determine whether those individuals have isolated NDDs or WSS (i.e. syndromic NDDs). We performed thorough clinical and neurodevelopmental phenotyping on six individuals with de novo KMT2A variants. From these data, we found that all six patients met clinical criteria for WSS and we further define the neurodevelopmental phenotypes associated with KMT2A variants and WSS. In particular, we identified a subtype of Autism Spectrum Disorder (ASD) in five individuals, characterized by marked rigid, repetitive and inflexible behaviours, emotional dysregulation, externalizing behaviours, but relative social motivation. To further explore the clinical spectrum associated with KMT2A variants, we also conducted a meta-analysis of individuals with KMT2A variants reported in the published literature. We found that de novo LoF or missense variants in KMT2A were significantly more prevalent than predicted by a previously established statistical model of de novo mutation rate for KMT2A. Our genotype-phenotype findings better define the clinical spectrum associated with KMT2A variants and suggest that individuals with de novo LoF and missense variants likely have a clinically unrecognized diagnosis of WSS, rather than isolated NDD or ASD alone. This highlights the importance of a clinical genetic and neurodevelopmental assessment for individuals with such variants in KMT2A.

A large data resource of genomic copy number variation across neurodevelopmental disorders.

Copy number variations (CNVs) are implicated across many neurodevelopmental disorders (NDDs) and contribute to their shared genetic etiology. Multiple studies have attempted to identify shared etiology among NDDs, but this is the first genome-wide CNV analysis across autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), schizophrenia (SCZ), and obsessive-compulsive disorder (OCD) at once. Using microarray (Affymetrix CytoScan HD), we genotyped 2,691 subjects diagnosed with an NDD (204 SCZ, 1,838 ASD, 427 ADHD and 222 OCD) and 1,769 family members, mainly parents. We identified rare CNVs, defined as those found in <0.1% of 10,851 population control samples. We found clinically relevant CNVs (broadly defined) in 284 (10.5%) of total subjects, including 22 (10.8%) among subjects with SCZ, 209 (11.4%) with ASD, 40 (9.4%) with ADHD, and 13 (5.6%) with OCD. Among all NDD subjects, we identified 17 (0.63%) with aneuploidies and 115 (4.3%) with known genomic disorder variants. We searched further for genes impacted by different CNVs in multiple disorders. Examples of NDD-associated genes linked across more than one disorder (listed in order of occurrence frequency) are NRXN1, SEH1L, LDLRAD4, GNAL, GNG13, MKRN1, DCTN2, KNDC1, PCMTD2, KIF5A, SYNM, and long non-coding RNAs: AK127244 and PTCHD1-AS. We demonstrated that CNVs impacting the same genes could potentially contribute to the etiology of multiple NDDs. The CNVs identified will serve as a useful resource for both research and diagnostic laboratories for prioritization of variants.

Communicating complex genomic information: A counselling approach derived from research experience with Autism Spectrum Disorder.

Individuals with Autism Spectrum Disorder (ASD) share characteristics (impairments in socialization and communication, and repetitive interests and behaviour), but differ in their developmental course, pattern of symptoms, and cognitive and language abilities. The development of standardized phenotyping has revealed ASD to clinically be vastly heterogeneous, ranging from milder presentations to more severe forms associated with profound intellectual disability. Some 100 genes have now been implicated in the etiology of ASD, and advances in genome-wide testing continue to yield new data at an unprecedented rate. As the translation of this data is incorporated into clinical care, genetic professionals/counsellors, as well as other health care providers, will benefit from guidelines and tools to effectively communicate such genomic information. Here, we present a model to facilitate communication regarding the complexities of ASD, where clinical and genetic heterogeneity, as well as overlapping neurological conditions are inherent. We outline an approach for counselling families about their genomic results grounded in our direct experience from counselling families participating in an ASD research study, and supported by rationale from the literature.

Does personal genome testing drive service utilization in an adult preventive medicine clinic?

Personal genome testing (PGT) that assesses risk for common diseases may influence the use of preventive health services, but outcome data are limited. We aimed to assess health service utilization following PGT. We conducted a retrospective matched cohort study at an adult health clinic. Medical records of clients who pursued PGT at their comprehensive health assessment (CHA) over a 1-year period (N = 388) were reviewed and compared to age- and sex-matched clients who underwent CHA but not PGT (N = 388). We measured condition-specific health services used post CHA up to two subsequent visits while accounting for confounding factors (e.g., family history, health status, and age). A relatively equal number of post CHA services were used by clients who pursued PGT and those who did not pursue PGT (52% and 48%, respectively). Overall and across the majority of conditions examined, clients' service utilization was significantly associated with health status, e.g., clients identified as "at risk" on CHA for heart attack used 2.86 times more services than clients not at risk. Pursuing PGT was not significantly associated with increased use of services post CHA overall or for most of the conditions examined. Our data demonstrate that health status rather than pursuing PGT is the strongest driver of service utilization in this population. Overall, pursuit of PGT and PGT results does not appear to significantly drive the utilization of downstream health services.

Variable phenotype expression in a family segregating microdeletions of the NRXN1 and MBD5 autism spectrum disorder susceptibility genes.

Autism Spectrum Disorder (ASD) is a developmental condition of early childhood onset, which impacts socio-communicative functioning and is principally genetic in etiology. Currently, more than 50 genomic loci are deemed to be associated with susceptibility to ASD, showing de novo and inherited unbalanced copy number variants (CNVs) and smaller insertions and deletions (indels), more complex structural variants (SVs), as well as single nucleotide variants (SNVs) deemed of pathological significance. However, the phenotypes associated with many of these genes are variable, and penetrance is largely unelaborated in clinical descriptions. This case report describes a family harboring two CNV microdeletions, which affect regions of NRXN1 and MBD5 - each well-established in association with risk of ASD and other neurodevelopmental disorders. Although each CNV would likely be categorized as pathologically significant, both genomic alterations are transmitted in this family from an unaffected father to the proband, and shared by an unaffected sibling. This family case illustrates the importance of recognizing that phenotype can vary among exon overlapping variants of the same gene, and the need to evaluate penetrance of such variants in order to properly inform on risks.

Mutations in RAB39B in individuals with intellectual disability, autism spectrum disorder, and macrocephaly.

Background: Autism spectrum disorder (ASD), a developmental disorder of early childhood onset, affects males four times more frequently than females, suggesting a role for the sex chromosomes. In this study, we describe a family with ASD in which a predicted pathogenic nonsense mutation in the X-chromosome gene RAB39B segregates with ASD phenotype. Methods: Clinical phenotyping, microarray, and whole genome sequencing (WGS) were performed on the five members of this family. Maternal and female sibling X inactivation ratio was calculated, and phase was investigated. Mutant-induced pluripotent stem cells engineered for an exon 2 nonsense mutation were generated and differentiated into cortical neurons for expression and pathway analyses. Results: Two males with an inherited RAB39B mutation both presented with macrocephaly, intellectual disability (ID), and ASD. Their female sibling with the same mutation presented with ID and a broad autism phenotype. In contrast, their transmitting mother has no neurodevelopmental diagnosis. Our investigation of phase indicated maternal preferential inactivation of the mutated allele, with no such bias observed in the female sibling. We offer the explanation that this bias in X inactivation may explain the absence of a neurocognitive phenotype in the mother. Our cellular knockout model of RAB39B revealed an impact on expression in differentiated neurons for several genes implicated in brain development and function, supported by our pathway enrichment analysis. Conclusions: Penetrance for ASD is high among males but more variable among females with RAB39B mutations. A critical role for this gene in brain development and function is demonstrated.