Case report: severe hypertrophic cardiomyopathy in a female neonate caused by de novo variant in NDUFB11.

Background: Hypertrophic cardiomyopathy in the neonate has a diverse genetic background, and non-sarcomeric variants may not be identified on commercial genetic testing panels. NDUFB11 is an X-linked mitochondrial Complex I protein and is known to cause histiocytoid cardiomyopathy but has not been described in female infants with hypertrophic cardiomyopathy. We present this first reported case of obstructive hypertrophic cardiomyopathy in a female neonate secondary to a pathogenic variant in NDUFB11. Case summary: A term female neonate presented following a prenatal diagnosis of biventricular hypertrophy and growth restriction. She developed lactic acidosis after birth and whole-genome sequencing identified a de novo variant in the mitochondrial Complex I gene, NDUFB11 (c.391G>A, p.Glu131Lys). There was progression of left ventricular hypertrophy and obstruction, with rapid development of heart failure symptoms. She was unresponsive to beta-blocker medical therapy and was not suitable for advanced mechanical support. There was subsequent clinical deterioration resulting in death by 3 months of age. Discussion: Hemizygous variants in NDUFB11 have been associated with hypertrophic cardiomyopathy in male infants previously, and skewed X-linked inactivation likely resulted in the presentation described here in a female infant. This variant was not identifiable by commercial cardiomyopathy panels. We highlight the importance of rapid whole-genome sequencing in cases of infantile hypertrophic cardiomyopathy and the importance of genetic diagnosis in guiding prognosis and care for these individuals.

Exploring the neurological features of individuals with germline PTEN variants: A multicenter study.

OBJECTIVE: PTEN, a known tumor suppressor gene, is a mediator of neurodevelopment. Individuals with germline pathogenic variants in the PTEN gene, molecularly defined as PTEN hamartoma tumor syndrome (PHTS), experience a variety of neurological and neuropsychiatric challenges during childhood, including autism spectrum disorder (ASD). However, the frequency and nature of seizures and the utilization of allied health services have not been described. METHODS: Young patients with PHTS and sibling controls were recruited across five centers in the United States and followed every 6-12 months for a mean of 2.1 years. In addition to the history obtained from caregivers, neurodevelopmental evaluations and structured dysmorphology examinations were conducted, and brain MRI findings, received therapies, and epilepsy characteristics were reported. RESULTS: One hundred and seven patients with PHTS (median age 8.7 years; range 3-21 years) and 38 controls were enrolled. ASD and epilepsy were frequent among patients with PHTS (51% and 15%, respectively), with generalized epilepsy strongly associated with ASD. Patients with epilepsy often required two antiseizure medications. Neuroimaging revealed prominent perivascular spaces and decreased peritrigonal myelination in individuals with PHTS-ASD. Allied therapy use was frequent and involved physical, occupational, speech, and social skills therapies, with 89% of all patients with PHTS, regardless of ASD diagnosis, utilizing at least one service. INTERPRETATION: This prospective, longitudinal study highlights the wide neurological spectrum seen in young individuals with PHTS. ASD is common in PHTS, comorbid with epilepsy, and allied health services are used universally. Our findings inform care discussions with families about neurological outcomes in PHTS.

Registry-derived stage (RD-Stage) for capturing stage at diagnosis for pancreatic carcinoma in Australia.

INTRODUCTION: Stage of pancreatic carcinoma at diagnosis is a strong prognostic indicator of morbidity and mortality, yet is poorly notified to population-based cancer registries ("cancer registries"). Registry-derived stage (RD-Stage) provides a method for cancer registries to use available data sources to compile and record stage in a consistent way. This project describes the development and validation of rules to capture RD-Stage (pancreatic carcinoma) and applies the rules to data currently captured in each Australian cancer registry. MATERIALS AND METHODS: Rules for deriving RD-stage (pancreatic carcinoma) were developed using the American Joint Commission on Cancer (AJCC) Staging Manual 8th edition and endorsed by an Expert Working Group comprising specialists responsible for delivering care to patients diagnosed with pancreatic carcinoma, cancer registry epidemiologists and medical coders. Completeness of data fields required to calculate RD-Stage (pancreatic carcinoma) and an overall proportion of cases for whom RD stage could be assigned was assessed using data collected by each Australian cancer registry, for period 2018-2019. A validation study compared RD-Stage (pancreatic carcinoma) calculated by the Victorian Cancer Registry with clinical stage captured by the Upper Gastro-intestinal Cancer Registry (UGICR). RESULTS: RD-Stage (pancreatic carcinoma) could not be calculated in 4/8 (50%) of cancer registries; one did not collect the required data elements while three used a staging system not compatible with RD-Stage requirements. Of the four cancer registries able to calculate RD-Stage, baseline completeness ranged from 9% to 76%. Validation of RD-Stage (pancreatic carcinoma) with UGICR data indicated that there was insufficient data available in VCR to stage 174/457 (38%) cases and that stage was unknown in 189/457 (41%) cases in the UGICR. Yet, where it could be derived, there was very good concordance at stage level (I, II, III, IV) between the two datasets. (95.2% concordance], Kendall's coefficient = 0.92). CONCLUSION: There is a lack of standardisation of data elements and data sources available to cancer registries at a national level, resulting in poor capacity to currently capture RD-Stage (pancreatic carcinoma). RD-Stage provides an excellent tool to cancer registries to capture stage when data elements required to calculate it are available to cancer registries.

Understanding the impact of pediatric single large-scale mtDNA deletion syndromes on caregivers: Burdens and challenges.

Single large-scale mitochondrial deletion syndromes (SLSMDS) are ultra-rare, progressive multi-system diseases that make children largely dependent on their caregivers for both medical and non-medical needs. Yet, few studies have examined the burden felt among caregivers. As part of a larger research study, 42 caregivers of children with SLSMDS completed two surveys to assess caregiver burden. The Mitochondrial Care Network Patient Needs Survey (MCN-PNS) is a novel assessment that examines the logistical, time, and financial costs experienced by caregivers of children with SLSMDS. The Zarit Burden Interview (ZBI-22) is a validated assessment that examines caregivers' psychological health. Results demonstrate the unique burden experienced by caregivers of children with SLSMDS. One notable finding was the high psychological burden. Nearly 90% of caregivers experience psychological burden, with 20% of caregivers at risk for anxiety and depression. Caregivers were primarily concerned about what the future held for their child. Additional burdens included the time required to coordinate the child's healthcare visits and financial strains. Caregivers reported minimal delays in establishing care with a mitochondrial care specialist and felt confident in their understanding of their child's disease and treatment(s). Overall, there is a need for expanded logistical, financial, and psychological support from mitochondrial disease centers and advocacy groups for caregivers of children with SLSMDS.

Evaluation of treatment and outcome for patients with haemophilia A and haemophilia B on extended half-life (EHL) factor products: A 12-month data analysis.

INTRODUCTION: Extended half-life (EHL) factor VIII and IX concentrates as prophylaxis against bleeds have been available to selected persons with haemophilia (PWH) in Australia since March 2018. Preliminary analysis of switching to EHL demonstrated increased treatment adherence, fewer injections and improved bleeding outcomes. AIMS: To characterise clinical practices regarding the use of EHL in Australia, to further evaluate treatment regimens and bleeding outcomes, and to analyse the influence of EHL product pharmacokinetics on clinical decision-making. METHODS: A national, retrospective study was conducted using the Australian Bleeding Disorders Registry (ABDR). Patients on EHL products during the entire 2019 calendar year were included for analysis. RESULTS: A complete and validated dataset of 174 PWH was analysed, 115 Haemophilia A (HA) and 59 Haemophilia B (HB). Adherence to EHL therapy was 85.7% in HA and 87.2% in HB. About 63.5% of HA and 64.4% of HB PWH reported zero spontaneous bleeds over 12months. Ankles were the most frequent spontaneous bleed site. Approximately one-third patients underwent dose adjustments, with most frequent reasons being pharmacokinetics, body weight change and breakthrough bleeds. About 19.5% of PWH had target joint history, with spontaneous bleeds reported in 58% of that cohort on EHL. Multivariate regression showed significant impact of non-adherence, target joint history and short half-life on spontaneous bleeds in the HA cohort; however only short half-life had significant impact in the HB cohort. CONCLUSION: EHL usage in Australia shows excellent treatment adherence and bleeding outcomes. This study affirms the use and value of widely available population-based pharmacokinetics as a clinical tool.

Navigating Life With Primary Mitochondrial Myopathies: The Importance of the Patient Voice and Implications for Clinical Practice.

Primary mitochondrial myopathies (PMM) are rare disorders with diverse and progressive symptom presentations that cause a substantial, detrimental impact on the quality of life of patients and their caregivers. The burden of symptoms is compounded by their visibility and their unpredictable, progressive nature, leading to a sense of social stigmatization, limited autonomy, social isolation, and grief. There is also a lack of awareness and expertise in the medical community, which presents huge obstacles to diagnosis and provision of coordinated multidisciplinary care for these patients, along with a lack of disease-modifying treatments. The present commentary serves to raise awareness of the challenges faced by patients with PMM and their caregivers in their own words, including diagnostic delays, the burden of disease, and the need for further trials to develop disease-modifying treatments and improved understanding of the disease course. We also provide commentary on considerations for clinical practice, including the need for holistic care and multidisciplinary care teams, details of common 'red flag' symptoms, proposed diagnostic approaches, and suggested descriptions of multisystemic symptoms for physician-patient dialogue. In addition, we highlight the role patient advocacy and support groups play in supporting patients and providing access to reliable, up-to-date information and educational resources on these rare diseases.

Single-cell multi-omics of mitochondrial DNA disorders reveals dynamics of purifying selection across human immune cells.

Pathogenic mutations in mitochondrial DNA (mtDNA) compromise cellular metabolism, contributing to cellular heterogeneity and disease. Diverse mutations are associated with diverse clinical phenotypes, suggesting distinct organ- and cell-type-specific metabolic vulnerabilities. Here we establish a multi-omics approach to quantify deletions in mtDNA alongside cell state features in single cells derived from six patients across the phenotypic spectrum of single large-scale mtDNA deletions (SLSMDs). By profiling 206,663 cells, we reveal the dynamics of pathogenic mtDNA deletion heteroplasmy consistent with purifying selection and distinct metabolic vulnerabilities across T-cell states in vivo and validate these observations in vitro. By extending analyses to hematopoietic and erythroid progenitors, we reveal mtDNA dynamics and cell-type-specific gene regulatory adaptations, demonstrating the context-dependence of perturbing mitochondrial genomic integrity. Collectively, we report pathogenic mtDNA heteroplasmy dynamics of individual blood and immune cells across lineages, demonstrating the power of single-cell multi-omics for revealing fundamental properties of mitochondrial genetics.

Epilepsy with eyelid myoclonia in the setting of de novo pathogenic variant in ATP1A3.

Mutations in the ATP1A3 gene have been associated with several syndromes, including rapid-onset dystonia-parkinsonism, alternating hemiplegia of childhood, and cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss. In this clinical commentary, we report a 2-year-old female patient with de novo pathogenic variant in the ATP1A3 gene associated with an early-onset form of epilepsy with eyelid myoclonia. The patient had frequent eyelid myoclonia occurring 20-30 times per day, without loss of awareness or other motor manifestations. EEG showed generalized polyspikes and spike-and-wave complexes maximal in the bifrontal regions, with prominent eye closure sensitivity. A sequencing-based epilepsy gene panel revealed a de novo pathogenic heterozygous variant in ATP1A3. The patient showed some response to flunarizine and clonazepam. This case highlights the importance of considering ATP1A3 mutations in the differential diagnosis of early-onset epilepsy with eyelid myoclonia and the potential benefit of flunarizine in improving language and coordination development in patients with ATP1A3-related disorders.

Haemophilia joint health score (HJHS) usage, patterns and outcome data in patients with haemophilia A and haemophilia B in Australia: A descriptive study using the Australian Bleeding Disorders Registry (ABDR).

INTRODUCTION: Assessment of joint health is an essential component of haemophilia management. A variety of clinical tools have been developed to standardise this assessment process. One such tool, the Haemophilia Joint Health Score (HJHS), is embedded for use within the Australian Bleeding Disorders Registry (ABDR). This provides a unique opportunity to analyse patterns of tool usage as well as associations between scores, demographics and clinical outcome factors. AIMS: To characterise clinician practices regarding use of HJHS in routine clinical assessment of persons with haemophilia (PWH), to examine relationships between HJHS, and age, inhibitor status and body mass index (BMI), and to identify potential barriers to HJHS tool usage. METHODS: A national, retrospective study was conducted using data extracted from the ABDR between 2014 and 2020, complemented by a qualitative questionnaire exploring haemophilia treatment centre (HTC) structure, resourcing and clinician perspectives about HJHS. RESULTS: 28.1% (622/2220) of PWH had at least one HJHS recorded in the ABDR during the defined study period (546 haemophilia A, 76 haemophilia B). HJHS were recorded more in children than adults and performed more in severe than non-severe haemophilia. Multivariate analysis demonstrated significant association of age, severity and inhibitor status with HJHS. No association was identified between BMI and HJHS. Qualitative surveys revealed significant variation in physiotherapy funding, availability and methods of tool use between HTCs. CONCLUSION: This study provides valuable insights into joint health assessment in Australia. It improved our understanding of factors influencing long-term joint outcomes. Practical limitations of HJHS tool were also discussed.

Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial.

BACKGROUND AND OBJECTIVES: Primary mitochondrial myopathies (PMMs) encompass a group of genetic disorders that impair mitochondrial oxidative phosphorylation, adversely affecting physical function, exercise capacity, and quality of life (QoL). Current PMM standards of care address symptoms, with limited clinical impact, constituting a significant therapeutic unmet need. We present data from MMPOWER-3, a pivotal, phase-3, randomized, double-blind, placebo-controlled clinical trial that evaluated the efficacy and safety of elamipretide in participants with genetically confirmed PMM. METHODS: After screening, eligible participants were randomized 1:1 to receive either 24 weeks of elamipretide at a dose of 40 mg/d or placebo subcutaneously. Primary efficacy endpoints included change from baseline to week 24 on the distance walked on the 6-minute walk test (6MWT) and total fatigue on the Primary Mitochondrial Myopathy Symptom Assessment (PMMSA). Secondary endpoints included most bothersome symptom score on the PMMSA, NeuroQoL Fatigue Short-Form scores, and the patient global impression and clinician global impression of PMM symptoms. RESULTS: Participants (N = 218) were randomized (n = 109 elamipretide; n = 109 placebo). The m0ean age was 45.6 years (64% women; 94% White). Most of the participants (n = 162 [74%]) had mitochondrial DNA (mtDNA) alteration, with the remainder having nuclear DNA (nDNA) defects. At screening, the most frequent bothersome PMM symptom on the PMMSA was tiredness during activities (28.9%). At baseline, the mean distance walked on the 6MWT was 336.7 ± 81.2 meters, the mean score for total fatigue on the PMMSA was 10.6 ± 2.5, and the mean T score for the Neuro-QoL Fatigue Short-Form was 54.7 ± 7.5. The study did not meet its primary endpoints assessing changes in the 6MWT and PMMSA total fatigue score (TFS). Between the participants receiving elamipretide and those receiving placebo, the difference in the least squares mean (SE) from baseline to week 24 on distance walked on the 6MWT was -3.2 (95% CI -18.7 to 12.3; p = 0.69) meters, and on the PMMSA, the total fatigue score was -0.07 (95% CI -0.10 to 0.26; p = 0.37). Elamipretide treatment was well-tolerated with most adverse events being mild to moderate in severity. DISCUSSION: Subcutaneous elamipretide treatment did not improve outcomes in the 6MWT and PMMSA TFS in patients with PMM. However, this phase-3 study demonstrated that subcutaneous elamipretide is well-tolerated. TRIAL REGISTRATION INFORMATION: Trial registered with clinicaltrials.gov, Clinical Trials Identifier: NCT03323749; submitted on October 12, 2017; first patient enrolled October 9, 2017. CLINICALTRIALS: gov/ct2/show/NCT03323749?term = elamipretide&draw = 2&rank = 9. CLASSIFICATION OF EVIDENCE: This study provides Class I evidence that elamipretide does not improve the 6MWT or fatigue at 24 weeks compared with placebo in patients with primary mitochondrial myopathy.

Currently available therapies in mitochondrial disease.

Mitochondrial diseases are a heterogeneous group of multisystem disorders caused by impaired mitochondrial function. These disorders occur at any age and involve any tissue, typically affecting organs highly dependent on aerobic metabolism. Diagnosis and management are extremely difficult due to various underlying genetic defects and a wide range of clinical symptoms. Preventive care and active surveillance are strategies to try to reduce morbidity and mortality by timely treatment of organ-specific complications. More specific interventional therapies are in early phases of development and no effective treatment or cure currently exists. A variety of dietary supplements have been utilized based on biological logic. For several reasons, few randomized controlled trials have been completed to assess the efficacy of these supplements. The majority of the literature on supplement efficacy represents case reports, retrospective analyses and open-label studies. We briefly review selected supplements that have some degree of clinical research support. In mitochondrial diseases, potential triggers of metabolic decompensation or medications that are potentially toxic to mitochondrial function should be avoided. We shortly summarize current recommendations on safe medication in mitochondrial diseases. Finally, we focus on the frequent and debilitating symptoms of exercise intolerance and fatigue and their management including physical training strategies.

Regulation of Liprin-α phase separation by CASK is disrupted by a mutation in its CaM kinase domain.

CASK is a unique membrane-associated guanylate kinase (MAGUK) because of its Ca2+/calmodulin-dependent kinase (CaMK) domain. We describe four male patients with a severe neurodevelopmental disorder with microcephaly carrying missense variants affecting the CaMK domain. One boy who carried the p.E115K variant and died at an early age showed pontocerebellar hypoplasia (PCH) in addition to microcephaly, thus exhibiting the classical MICPCH phenotype observed in individuals with CASK loss-of-function variants. All four variants selectively weaken the interaction of CASK with Liprin-α2, a component of the presynaptic active zone. Liprin-α proteins form spherical phase-separated condensates, which we observe here in Liprin-α2 overexpressing HEK293T cells. Large Liprin-α2 clusters were also observed in transfected primary-cultured neurons. Cluster formation of Liprin-α2 is reversed in the presence of CASK; this is associated with altered phosphorylation of Liprin-α2. The p.E115K variant fails to interfere with condensate formation. As the individual carrying this variant had the severe MICPCH disorder, we suggest that regulation of Liprin-α2-mediated phase condensate formation is a new functional feature of CASK which must be maintained to prevent PCH.

Community Consensus Guidelines to Support FAIR Data Standards in Clinical Research Studies in Primary Mitochondrial Disease.

Primary mitochondrial diseases (PMD) are genetic disorders with extensive clinical and molecular heterogeneity where therapeutic development efforts have faced multiple challenges. Clinical trial design, outcome measure selection, lack of reliable biomarkers, and deficiencies in long-term natural history data sets remain substantial challenges in the increasingly active PMD therapeutic development space. Developing "FAIR" (findable, accessible, interoperable, reusable) data standards to make data sharable and building a more transparent community data sharing paradigm to access clinical research metadata are the first steps to address these challenges. This collaborative community effort describes the current landscape of PMD clinical research data resources available for sharing, obstacles, and opportunities, including ways to incentivize and encourage data sharing among diverse stakeholders. This work highlights the importance of, and challenges to, developing a unified system that enables clinical research structured data sharing and supports harmonized data deposition standards across clinical consortia and research groups. The goal of these efforts is to improve the efficiency and effectiveness of drug development and improve understanding of the natural history of PMD. This initiative aims to maximize the benefit for PMD patients, research, industry, and other stakeholders while acknowledging challenges related to differing needs and international policies on data privacy, security, management, and oversight.

The clinical and molecular spectrum of QRICH1 associated neurodevelopmental disorder.

De novo variants in QRICH1 (Glutamine-rich protein 1) has recently been reported in 11 individuals with intellectual disability (ID). The function of QRICH1 is largely unknown but it is likely to play a key role in the unfolded response of endoplasmic reticulum stress through transcriptional control of proteostasis. In this study, we present 27 additional individuals and delineate the clinical and molecular spectrum of the individuals (n = 38) with QRICH1 variants. The main clinical features were mild to moderate developmental delay/ID (71%), nonspecific facial dysmorphism (92%) and hypotonia (39%). Additional findings included poor weight gain (29%), short stature (29%), autism spectrum disorder (29%), seizures (24%) and scoliosis (18%). Minor structural brain abnormalities were reported in 52% of the individuals with brain imaging. Truncating or splice variants were found in 28 individuals and 10 had missense variants. Four variants were inherited from mildly affected parents. This study confirms that heterozygous QRICH1 variants cause a neurodevelopmental disorder including short stature and expands the phenotypic spectrum to include poor weight gain, scoliosis, hypotonia, minor structural brain anomalies, and seizures. Inherited variants from mildly affected parents are reported for the first time, suggesting variable expressivity.

Semaphorin-Plexin Signaling: From Axonal Guidance to a New X-Linked Intellectual Disability Syndrome.

BACKGROUND: Semaphorins and plexins are ligands and cell surface receptors that regulate multiple neurodevelopmental processes such as axonal growth and guidance. PLXNA3 is a plexin gene located on the X chromosome that encodes the most widely expressed plexin receptor in fetal brain, plexin-A3. Plexin-A3 knockout mice demonstrate its role in semaphorin signaling in vivo. The clinical manifestations of semaphorin/plexin neurodevelopmental disorders have been less widely explored. This study describes the neurological and neurodevelopmental phenotypes of boys with maternally inherited hemizygous PLXNA3 variants. METHODS: Data-sharing through GeneDx and GeneMatcher allowed identification of individuals with autism or intellectual disabilities (autism/ID) and hemizygous PLXNA3 variants in collaboration with their physicians and genetic counselors, who completed questionnaires about their patients. In silico analyses predicted pathogenicity for each PLXNA3 variant. RESULTS: We assessed 14 boys (mean age, 10.7 [range 2 to 25] years) with maternally inherited hemizygous PLXNA3 variants and autism/ID ranging from mild to severe. Other findings included fine motor dyspraxia (92%), attention-deficit/hyperactivity traits, and aggressive behaviors (63%). Six patients (43%) had seizures. Thirteen boys (93%) with PLXNA3 variants showed novel or very low allele frequencies and probable damaging/disease-causing pathogenicity in one or more predictors. We found a genotype-phenotype correlation between PLXNA3 cytoplasmic domain variants (exons 22 to 32) and more severe neurodevelopmental disorder phenotypes (P < 0.05). CONCLUSIONS: We report 14 boys with maternally inherited, hemizygous PLXNA3 variants and a range of neurodevelopmental disorders suggesting a novel X-linked intellectual disability syndrome. Greater understanding of PLXNA3 variant pathogenicity in humans will require additional clinical, computational, and experimental validation.

Pediatric single large-scale mtDNA deletion syndromes: The power of patient reported outcomes.

There is a limited understanding of system-level clinical outcomes and interventions associated with single large-scale mitochondrial DNA deletion syndromes (SLSMDS). Additionally, no research exists that describes patient reported outcomes (PROs) of children with SLSMDS. A global and observational registry was established to understand the multi-systemic course of SLSMDS and track clinical outcomes. The development and design of the registry is described. Demographic characteristics, history and diagnoses, and system level prevalence of problems and interventions are reported for 42 children. System level problems and interventions include information on the following body systems: audiology, cardiac, endocrine, gastrointestinal (including pancreatic and hepatobiliary system), hematological, metabolic, neurological (including autonomic, mobility, & learning), ophthalmic, psychiatric, renal, and respiratory. Results emphasize the need of patient registries and suggest that the diagnostic odyssey and burden of disease for children with SLSMDS is significant. System-level findings may help families and clinical providers with diagnosis, prognostication, and treatment. A multidisciplinary team of clinical experts with a central coordinating specialist for children with SLSMDS is recommended.

Identification of disease-linked hyperactivating mutations in UBE3A through large-scale functional variant analysis.

The mechanisms that underlie the extensive phenotypic diversity in genetic disorders are poorly understood. Here, we develop a large-scale assay to characterize the functional valence (gain or loss-of-function) of missense variants identified in UBE3A, the gene whose loss-of-function causes the neurodevelopmental disorder Angelman syndrome. We identify numerous gain-of-function variants including a hyperactivating Q588E mutation that strikingly increases UBE3A activity above wild-type UBE3A levels. Mice carrying the Q588E mutation exhibit aberrant early-life motor and communication deficits, and individuals possessing hyperactivating UBE3A variants exhibit affected phenotypes that are distinguishable from Angelman syndrome. Additional structure-function analysis reveals that Q588 forms a regulatory site in UBE3A that is conserved among HECT domain ubiquitin ligases and perturbed in various neurodevelopmental disorders. Together, our study indicates that excessive UBE3A activity increases the risk for neurodevelopmental pathology and suggests that functional variant analysis can help delineate mechanistic subtypes in monogenic disorders.