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There is evidence that transcription factor (TF) encoding genes, which temporally control development in multiple cell types, can have tens of enhancers that regulate their expression. The NR2F1 TF developmentally promotes caudal and ventral cortical regional fates. Here, we epigenomically compared the activity of Nr2f1's enhancers during mouse cortical development with their activity in a transgenic assay. We identified at least six that are likely to be important in prenatal cortical development, with three harboring de novo mutants identified in ASD individuals. We chose to study the function of two of the most robust enhancers by deleting them singly or together. We found that they have distinct and overlapping functions in driving Nr2f1's regional and laminar expression in the developing cortex. Thus, these two enhancers, probably in combination with the others that we defined epigenetically, precisely tune Nr2f1's regional, cell type, and temporal expression during corticogenesis. [ABSTRACT FROM AUTHOR]

Recent advances in gene therapy, particularly for single‐gene disorders (SGDs), have led to significant progress in developing innovative precision medicine approaches that hold promise for treating conditions such as primary hydrocephalus (CH), which is characterized by increased cerebrospinal fluid (CSF) volumes and cerebral ventricular dilation as a result of impaired brain development, often due to genetic causes. CH is a significant contributor to childhood morbidity and mortality and a driver of healthcare costs. In many cases, prenatal ultrasound can readily identify ventriculomegaly as early as 14–20 weeks of gestation, with severe cases showing poor neurodevelopmental outcomes. Postnatal surgical approaches, such as ventriculoperitoneal shunts, do not address the underlying genetic causes, have high complication rates, and result in a marginal improvement of neurocognitive deficits. Prenatal somatic cell gene therapy (PSCGT) promises a novel approach to conditions such as CH by targeting genetic mutations in utero, potentially improving long‐term outcomes. To better understand the pathophysiology, genetic basis, and molecular pathomechanisms of CH, we conducted a scoping review of the literature that identified over 160 published genes linked to CH. Mutations in L1CAM, TRIM71, MPDZ, and CCDC88C play a critical role in neural stem cell development, subventricular zone architecture, and the maintenance of the neural stem cell niche, driving the development of CH. Early prenatal interventions targeting these genes could curb the development of the expected CH phenotype, improve neurodevelopmental outcomes, and possibly limit the need for surgical approaches. However, further research is needed to establish robust genotype‐phenotype correlations and develop safe and effective PSCGT strategies for CH. [ABSTRACT FROM AUTHOR]

CRISPR-based gene activation (CRISPRa) is a strategy for upregulating gene expression by targeting promoters or enhancers in a tissue/cell-type specific manner. Here, we describe an experimental framework that combines highly multiplexed perturbations with single-cell RNA sequencing (sc-RNA-seq) to identify cell-type-specific, CRISPRa-responsive cis-regulatory elements and the gene(s) they regulate. Random combinations of many gRNAs are introduced to each of many cells, which are then profiled and partitioned into test and control groups to test for effect(s) of CRISPRa perturbations of both enhancers and promoters on the expression of neighboring genes. Applying this method to a library of 493 gRNAs targeting candidate cis-regulatory elements in both K562 cells and iPSC-derived excitatory neurons, we identify gRNAs capable of specifically upregulating intended target genes and no other neighboring genes within 1 Mb, including gRNAs yielding upregulation of six autism spectrum disorder (ASD) and neurodevelopmental disorder (NDD) risk genes in neurons. A consistent pattern is that the responsiveness of individual enhancers to CRISPRa is restricted by cell type, implying a dependency on either chromatin landscape and/or additional trans-acting factors for successful gene activation. The approach outlined here may facilitate large-scale screens for gRNAs that activate genes in a cell type-specific manner. Scalable CRISPRa screening of cis-regulatory elements in non-cancer cell lines has proved challenging. Here, the authors describe a scalable, CRISPR activation screening framework to identify regulatory element-gene pairs in diverse cell types including cancer cells and neurons. [ABSTRACT FROM AUTHOR]

This cohort study analyzes sex-specific differences in heritability of autism spectrum disorder among individuals in Sweden. Key Points: Question: What are the sex-specific etiological origins of autism spectrum disorder? Findings: In this cohort study including 1 047 649 Swedish children, 12 226 (1.17%) received a diagnosis of autism spectrum disorder; heritability was estimated at 87.0% for males and 75.7% for females, a statistically significant difference. Meaning: These findings suggest that variation in the occurrence of autism spectrum disorder in the population differs between males and females, indicating that some of the underlying causes and prevalence of the condition may differ between the 2 sexes. Importance: Autism spectrum disorder (ASD) is a neurodevelopmental disorder more prevalent in males than in females. The cause of ASD is largely genetic, but the association of genetics with the skewed sex ratio is not yet understood. To our knowledge, no large population-based study has provided estimates of heritability by sex. Objective: To estimate the sex-specific heritability of ASD. Design, Setting, and Participants: This was a population-based, retrospective analysis using national health registers of nontwin siblings and cousins from Sweden born between January 1, 1985, and December 31, 1998, with follow-up to 19 years of age. Data analysis occurred from August 2022 to November 2023. Main Outcomes and Measures: Models were fitted to estimate the relative variance in risk for ASD occurrence owing to sex-specific additive genetics, shared environmental effects, and a common residual term. The residual term conceptually captured other factors that promote individual behavioral variation (eg, maternal effects, de novo variants, rare genetic variants not additively inherited, or gene-environment interactions). Estimates were adjusted for differences in prevalence due to birth year and maternal and paternal age by sex. Results: The sample included 1 047 649 individuals in 456 832 families (538 283 males [51.38%]; 509 366 females [48.62%]). Within the entire sample, 12 226 (1.17%) received a diagnosis of ASD, comprising 8128 (1.51%) males and 4098 (0.80%) females. ASD heritability was estimated at 87.0% (95% CI, 81.4%-92.6%) for males and 75.7% (95% CI, 68.4%-83.1%) for females with a difference in heritability estimated at 11.3% (95% CI, 1.0%-21.6%). There was no support for shared environmental contributions. Conclusions and Relevance: These findings suggest that the degree of phenotypic variation attributable to genetic differences (heritability) differs between males and females, indicating that some of the underlying causes of the condition may differ between the 2 sexes. The skewed sex ratio in ASD may be partly explained by differences in genetic variance between the sexes. [ABSTRACT FROM AUTHOR]

Variants in cis -regulatory elements link the noncoding genome to human pathology; however, detailed analytic tools for understanding the association between cell-level brain pathology and noncoding variants are lacking. CWAS-Plus, adapted from a Python package for category-wide association testing (CWAS), enhances noncoding variant analysis by integrating both whole-genome sequencing (WGS) and user-provided functional data. With simplified parameter settings and an efficient multiple testing correction method, CWAS-Plus conducts the CWAS workflow 50 times faster than CWAS, making it more accessible and user-friendly for researchers. Here, we used a single-nuclei assay for transposase-accessible chromatin with sequencing to facilitate CWAS-guided noncoding variant analysis at cell-type-specific enhancers and promoters. Examining autism spectrum disorder WGS data (n  = 7280), CWAS-Plus identified noncoding de novo variant associations in transcription factor binding sites within conserved loci. Independently, in Alzheimer's disease WGS data (n  = 1087), CWAS-Plus detected rare noncoding variant associations in microglia-specific regulatory elements. These findings highlight CWAS-Plus's utility in genomic disorders and scalability for processing large-scale WGS data and in multiple-testing corrections. CWAS-Plus and its user manual are available at https://github.com/joonan-lab/cwas/ and https://cwas-plus.readthedocs.io/en/latest/ , respectively. [ABSTRACT FROM AUTHOR]

Motivation Pediatric kidney disease is a widespread, progressive condition that severely impacts growth and development of children. Chronic kidney disease is often more insidious in children than in adults, usually requiring a renal biopsy for diagnosis. Biopsy evaluation requires copious examination by trained pathologists, which can be tedious and prone to human error. In this study, we propose an artificial intelligence (AI) method to assist pathologists in accurate segmentation and classification of pediatric kidney structures, named as AI-based Pediatric Kidney Diagnosis (APKD). Results We collected 2935 pediatric patients diagnosed with kidney disease for the development of APKD. The dataset comprised 93 932 histological structures annotated manually by three skilled nephropathologists. APKD scored an average accuracy of 94% for each kidney structure category, including 99% in the glomerulus. We found strong correlation between the model and manual detection in detected glomeruli (Spearman correlation coefficient r  = 0.98, P  < .001; intraclass correlation coefficient ICC = 0.98, 95% CI = 0.96–0.98). Compared to manual detection, APKD was approximately 5.5 times faster in segmenting glomeruli. Finally, we show how the pathological features extracted by APKD can identify focal abnormalities of the glomerular capillary wall to aid in the early diagnosis of pediatric kidney disease. Availability and implementation https://github.com/ChunyueFeng/Kidney-DataSet. [ABSTRACT FROM AUTHOR]

The function of regulatory elements is highly dependent on the cellular context, and thus for understanding the function of elements associated with psychiatric diseases these would ideally be studied in neurons in a living brain. Massively Parallel Reporter Assays (MPRAs) are molecular genetic tools that enable functional screening of hundreds of predefined sequences in a single experiment. These assays have not yet been adapted to query specific cell types in vivo in a complex tissue like the mouse brain. Here, using a test-case 3′UTR MPRA library with genomic elements containing variants from autism patients, we developed a method to achieve reproducible measurements of element effects in vivo in a cell type-specific manner, using excitatory cortical neurons and striatal medium spiny neurons as test cases. This targeted technique should enable robust, functional annotation of genetic elements in the cellular contexts most relevant to psychiatric disease. A Cre-dependent massively parallel reporter assay allows for cell-type specific assessment of the functional effects of non-coding elements in vivo, using excitatory cortical neurons and striatal medium spiny neurons as test cases. [ABSTRACT FROM AUTHOR]

Objective: Pathogenic variants in KCNT2 are rare causes of developmental epileptic encephalopathy (DEE). We herein describe the phenotypic and genetic features of patients with KCNT2‐related DEE, and the in vitro functional and pharmacological properties of KCNT2 channels carrying 14 novel or previously untested variants. Methods: Twenty‐five patients harboring KCNT2 variants were investigated: 12 were identified through an international collaborative network, 13 were retrieved from the literature. Clinical data were collected and included in a standardized phenotyping sheet. Novel variants were detected using exome sequencing and classified using ACMG criteria. Functional and pharmacological studies were performed by whole‐cell electrophysiology in HEK‐293 and SH‐SY5Y cells. Results: The phenotypic spectrum encompassed: (a) intellectual disability/developmental delay (21/22 individuals with available information), ranging from mild to severe/profound; (b) epilepsy (15/25); (c) neurological impairment, with altered muscle tone (14/22); (d) dysmorphisms (13/20). Nineteen pathogenic KCNT2 variants were found (9 new, 10 reported previously): 16 missense, 1 in‐frame deletion of a single amino acid, 1 nonsense, and 1 frameshift. Among tested variants, 8 showed gain‐of‐function (GoF), and 6 loss‐of‐function (LoF) features when expressed heterologously in vitro. Quinidine and fluoxetine blocked all GoF variants, whereas loxapine and riluzole activated some LoF variants while blocking others. Interpretation: We expanded the phenotypic and genotypic spectrum of KCNT2‐related disorders, highlighting novel genotype–phenotype associations. Pathogenic KCNT2 variants cause GoF or LoF in vitro phenotypes, and each shows a unique pharmacological profile, suggesting the need for in vitro functional and pharmacological investigation to enable targeted therapies based on the molecular phenotype. ANN NEUROL 2023;94:332–349 [ABSTRACT FROM AUTHOR]

Autism spectrum disorder (ASD) is a common, complex, and highly heritable condition with contributions from both common and rare genetic variations. While disruptive, rare variants in protein-coding regions clearly contribute to symptoms, the role of rare non-coding remains unclear. Variants in these regions, including promoters, can alter downstream RNA and protein quantity; however, the functional impacts of specific variants observed in ASD cohorts remain largely uncharacterized. Here, we analyzed 3600 de novo mutations in promoter regions previously identified by whole-genome sequencing of autistic probands and neurotypical siblings to test the hypothesis that mutations in cases have a greater functional impact than those in controls. We leveraged massively parallel reporter assays (MPRAs) to detect transcriptional consequences of these variants in neural progenitor cells and identified 165 functionally high confidence de novo variants (HcDNVs). While these HcDNVs are enriched for markers of active transcription, disruption to transcription factor binding sites, and open chromatin, we did not identify differences in functional impact based on ASD diagnostic status. [ABSTRACT FROM AUTHOR]

The aim of this study was to catalog and evaluate response biomarkers correlated with autism spectrum disorder (ASD) symptoms to improve clinical trials. A systematic review of MEDLINE, Embase, and Scopus was conducted in April 2020. Seven criteria were applied to focus on original research that includes quantifiable response biomarkers measured alongside ASD symptoms. Interventional studies or human studies that assessed the correlation between biomarkers and ASD-related behavioral measures were included. A total of 5,799 independent records yielded 280 articles for review that reported on 940 biomarkers, 755 of which were unique to a single publication. Molecular biomarkers were the most frequently assayed, including cytokines, growth factors, measures of oxidative stress, neurotransmitters, and hormones, followed by neurophysiology (e.g., EEG and eye tracking), neuroimaging (e.g., functional MRI), and other physiological measures. Studies were highly heterogeneous, including in phenotypes, demographic characteristics, tissues assayed, and methods for biomarker detection. With a median total sample size of 64, almost all of the reviewed studies were only powered to identify biomarkers with large effect sizes. Reporting of individual-level values and summary statistics was inconsistent, hampering mega- and meta-analysis. Biomarkers assayed in multiple studies yielded mostly inconsistent results, revealing a "replication crisis." There is currently no response biomarker with sufficient evidence to inform ASD clinical trials. This review highlights methodological imperatives for ASD biomarker research necessary to make definitive progress: consistent experimental design, correction for multiple comparisons, formal replication, sharing of sample-level data, and preregistration of study designs. Systematic "big data" analyses of multiple potential biomarkers could accelerate discovery. [ABSTRACT FROM AUTHOR]

We are living in a golden age of medicine in which the availability of prenatal diagnosis, fetal therapy, and gene therapy/editing make it theoretically possible to repair almost any defect in the genetic code. Furthermore, the ability to diagnose genetic disorders before birth and the presence of established surgical techniques enable these therapies to be delivered safely to the fetus. Prenatal therapies are generally used in the second or early third trimester for severe, life‐threatening disorders for which there is a clear rationale for intervening before birth. While there has been promising work for prenatal gene therapy in preclinical models, the path to a clinical prenatal gene therapy approach is complex. We recently held a conference with the University of California, San Francisco–Stanford Center of Excellence in Regulatory Science and Innovation, researchers, patient advocates, regulatory (members of the Food and Drug Administration), and other stakeholders to review the scientific background and rationale for prenatal somatic cell gene therapy for severe monogenic diseases and initiate a dialogue toward a safe regulatory path for phase 1 clinical trials. This review represents a summary of the considerations and discussions from these conversations. [ABSTRACT FROM AUTHOR]

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Many autism spectrum disorder (ASD)-associated genes act as transcriptional regulators (TRs). Chromatin immunoprecipitation sequencing (ChIP-seq) was used to identify the regulatory targets of ARID1B, BCL11A, FOXP1, TBR1, and TCF7L2, ASD-associated TRs in the developing human and mouse cortex. These TRs shared substantial overlap in the binding sites, especially within open chromatin. The overlap within a promoter region, 1–2,000 bp upstream of the transcription start site, was highly predictive of brain-expressed genes. This signature was observed in 96 out of 102 ASD-associated genes. In vitro CRISPRi against ARID1B and TBR1 delineated downstream convergent biology in mouse cortical cultures. After 8 days, NeuN+ and CALB+ cells were decreased, GFAP+ cells were increased, and transcriptomic signatures correlated with the postmortem brain samples from individuals with ASD. We suggest that functional convergence across five ASD-associated TRs leads to shared neurodevelopmental outcomes of haploinsufficient disruption. [Display omitted] • ASD-associated TRs share substantial genomic binding sites in developing human and mouse cortex • The overlap within a promoter region was highly predictive of brain-expressed genes • Functional convergence of ASD-associated TRs leads to shared neurodevelopmental disorders Using NGS approaches, Fazel Darbandi et al. demonstrate that ASD-associated TRs in the developing cortex share substantial overlap in their binding sites. In vitro CRISPRi delineated downstream convergent biology that correlates with the postmortem brain samples from individuals with ASD. We suggest that functional convergence of ASD-associated TRs leads to shared neurodevelopmental disorders. [ABSTRACT FROM AUTHOR]

Knowledge representation and reasoning (KR&R) has been successfully implemented in many fields to enable computers to solve complex problems with AI methods. However, its application to biomedicine has been lagging in part due to the daunting complexity of molecular and cellular pathways that govern human physiology and pathology. In this article, we describe concrete uses of Scalable PrecisiOn Medicine Knowledge Engine (SPOKE), an open knowledge network that connects curated information from thirty‐seven specialized and human‐curated databases into a single property graph, with 3 million nodes and 15 million edges to date. Applications discussed in this article include drug discovery, COVID‐19 research and chronic disease diagnosis, and management. [ABSTRACT FROM AUTHOR]

Knowledge representation and reasoning (KR&R) has been successfully implemented in many fields to enable computers to solve complex problems with AI methods. However, its application to biomedicine has been lagging in part due to the daunting complexity of molecular and cellular pathways that govern human physiology and pathology. In this article, we describe concrete uses of Scalable PrecisiOn Medicine Knowledge Engine (SPOKE), an open knowledge network that connects curated information from thirty-seven specialized and humancurated databases into a single property graph, with 3 million nodes and 15 million edges to date. Applications discussed in this article include drug discovery, COVID-19 research and chronic disease diagnosis, and management. [ABSTRACT FROM AUTHOR]

Neurodevelopmental neuropsychiatric disorders, such as autism spectrum disorder and schizophrenia, have strong genetic risk components, but the underlying mechanisms have proven difficult to decipher. Rare, high‐risk variants may offer an opportunity to delineate the biological mechanisms responsible more clearly for more common idiopathic diseases. Indeed, different rare variants can cause the same behavioral phenotype, demonstrating genetic heterogeneity, while the same rare variant can cause different behavioral phenotypes, demonstrating variable expressivity. These observations suggest convergent underlying biological and neurological mechanisms; identification of these mechanisms may ultimately reveal new therapeutic targets. At the 2021 Keystone eSymposium "Neuropsychiatric and Neurodevelopmental Disorders: Harnessing Rare Variants" a panel of experts in the field described significant progress in genomic discovery and human phenotyping and raised several consistent issues, including the need for detailed natural history studies of rare disorders, the challenges in cohort recruitment, and the importance of viewing phenotypes as quantitative traits that are impacted by rare variants. [ABSTRACT FROM AUTHOR]

Background: Recent large‐scale initiatives have led to systematically collected phenotypic data for several rare genetic conditions implicated in autism spectrum disorder (ASD). The onset of developmentally expected skills (e.g. walking, talking) serve as readily quantifiable aspects of the behavioral phenotype. This study's aims were: (a) describe the distribution of ages of attainment of gross motor and expressive language milestones in several rare genetic conditions, and (b) characterize the likelihood of delays in these conditions compared with idiopathic ASD. Methods: Participants aged 3 years and older were drawn from two Simons Foundation Autism Research Initiative registries that employed consistent phenotyping protocols. Inclusion criteria were a confirmed genetic diagnosis of one of 16 genetic conditions (Simons Searchlight) or absence of known pathogenic genetic findings in individuals with ASD (SPARK). Parent‐reported age of acquisition of three gross motor and two expressive language milestones was described and categorized as on‐time or delayed, relative to normative expectations. Results: Developmental milestone profiles of probands with genetic conditions were marked by extensive delays (including nonattainment), with highest severity in single gene conditions and more delays than idiopathic ASD in motor skills. Compared with idiopathic ASD, the median odds of delay among the genetic groups were higher by 8.3 times (IQR 5.8–16.3) for sitting, 12.4 times (IQR 5.3–19.5) for crawling, 26.8 times (IQR 7.7–41.1) for walking, 2.7 times (IQR 1.7–5.5) for single words, and 5.7 times (IQR 2.7–18.3) for combined words. Conclusions: Delays in developmental milestones, particularly in gross motor skills, are frequent and may be among the earliest indicators of differentially affected developmental processes in specific genetically defined conditions associated with ASD, as compared with those with clinical diagnoses of idiopathic ASD. The possibility of different developmental pathways leading to ASD‐associated phenotypes should be considered when deciding how to employ specific genetic conditions as models for ASD. [ABSTRACT FROM AUTHOR]

Genetics, environment, and their interactions impact autism spectrum disorder etiology. Smoking is a suspected autism spectrum disorder risk factor due to biological plausibility and high prevalence. Using two large epidemiological samples, we examined whether autism spectrum disorder was associated with prenatal paternal smoking in a Discovery sample (N = 10,245) and an independent Replication sample (N = 29,773). Paternal smoking was retrospectively assessed with questionnaires. Likelihood of having autism spectrum disorder was estimated with the Autism Spectrum Screening Questionnaire at three levels: low (<10), intermediate (10–14), and high (⩾15). Ordinal regression was used to examine the relationship between prenatal paternal smoking and likelihood of having autism spectrum disorder, adjusting for confounders. A total of 36.5% of Discovery sample fathers and 63.3% of Replication sample fathers smoked during the pregnancy period; 7% of the Replication sample smoker fathers smoked during the pre-conception period but quit during pregnancy period. Discovery sample prenatal paternal smoking significantly increased the likelihood of having autism spectrum disorder in their offspring (adjusted odds ratio=1.27). This was confirmed in the Replication sample with adjusted odds ratio of 1.15 among smoking pre-conception period + pregnancy period fathers; 14.4% and 11.1% increased high likelihood of autism spectrum disorder was attributable to prenatal paternal smoking in Discovery sample and Replication sample, respectively. Smoking prevention, especially in pregnancy planning, may decrease autism spectrum disorder risk in offspring. What is Already Known about This Subject: Genetics, (including de novo mutations), environmental factors (including toxic exposures), and their interactions impact autism spectrum disorder etiology. Paternal smoking is a candidate risk for autism spectrum disorder due to biological plausibility, high prevalence, and potential intervention. What This Study Adds: This original study and its replication confirms that paternal factors can substantially contribute to autism spectrum disorder risk for their offspring. It specifically indicates that paternal smoking both before and during pregnancy contributes significantly to autism spectrum disorder risk. Implications for practice, research, or policy: Smoking prevention, especially in pregnancy planning, may decrease autism spectrum disorder risk in offspring. [ABSTRACT FROM AUTHOR]

Background: Genetic variants in the voltage-gated sodium channels SCN1A, SCN2A, SCN3A, and SCN8A are leading causes of epilepsy, developmental delay, and autism spectrum disorder. The mRNA splicing patterns of all four genes vary across development in the rodent brain, including mutually exclusive copies of the fifth protein-coding exon detected in the neonate (5N) and adult (5A). A second pair of mutually exclusive exons is reported in SCN8A only (18N and 18A). We aimed to quantify the expression of individual exons in the developing human brain. Methods: RNA-seq data from 783 human brain samples across development were analyzed to estimate exon-level expression. Developmental changes in exon utilization were validated by assessing intron splicing. Exon expression was also estimated in RNA-seq data from 58 developing mouse neocortical samples. Results: In the mature human neocortex, exon 5A is consistently expressed at least 4-fold higher than exon 5N in all four genes. For SCN2A, SCN3A, and SCN8A, a brain-wide synchronized 5N to 5A transition occurs between 24 post-conceptual weeks (2nd trimester) and 6 years of age. In mice, the equivalent 5N to 5A transition begins at or before embryonic day 15.5. In SCN8A, over 90% of transcripts in the mature human cortex include exon 18A. Early in fetal development, most transcripts include 18N or skip both 18N and 18A, with a transition to 18A inclusion occurring from 13 post-conceptual weeks to 6 months of age. No other protein-coding exons showed comparably dynamic developmental trajectories. Conclusions: Exon usage in SCN1A, SCN2A, SCN3A, and SCN8A changes dramatically during human brain development. These splice isoforms, which alter the biophysical properties of the encoded channels, may account for some of the observed phenotypic differences across development and between specific variants. Manipulation of the proportion of splicing isoforms at appropriate stages of development may act as a therapeutic strategy for specific mutations or even epilepsy in general. [ABSTRACT FROM AUTHOR]

Aire-expressing cells defend the fetus: The normal maternal immune system adapts to pregnancy by learning to tolerate both allogeneic paternal and pregnancy-associated antigens expressed by the fetus and placenta. Gillis-Buck et al. investigated the contribution of cells expressing the autoimmune regulator (Aire) gene to maintaining fetal health using a mouse model in which Aire-expressing cells were deleted during early pregnancy. Ablation of Aire-expressing cells did not impair fetal implantation but resulted in intrauterine fetal growth restriction during both allogeneic and syngeneic pregnancies associated with increased activation of effector T cells. Selective deletion of extrathymic Aire-expressing cells (eTACs) while preserving Aire-expressing thymic epithelial cells revealed that eTACs are required for maintaining tolerance and fetal health. These findings demonstrate an unanticipated role for eTACs as guardians of fetal health during pregnancy. Healthy pregnancy requires tolerance to fetal alloantigens as well as syngeneic embryonic and placental antigens. Given the importance of the autoimmune regulator (Aire) gene in self-tolerance, we investigated the role of Aire-expressing cells in maternal-fetal tolerance. We report that maternal ablation of Aire-expressing (Aire+) cells during early mouse pregnancy caused intrauterine growth restriction (IUGR) in both allogeneic and syngeneic pregnancies. This phenotype is immune mediated, as IUGR was rescued in Rag1-deficient mice, and involved a memory response, demonstrated by recurrence of severe IUGR in second pregnancies. Single-cell RNA sequencing demonstrated that Aire+ cell depletion in pregnancy results in expansion of activated T cells, particularly T follicular helper cells. Unexpectedly, selective ablation of either Aire-expressing medullary thymic epithelial cells or extrathymic Aire-expressing cells (eTACs) mapped the IUGR phenotype exclusively to eTACs. Thus, we report a previously undescribed mechanism for the maintenance of maternal-fetal immune homeostasis and demonstrate that eTACs protect the conceptus from immune-mediated IUGR. [ABSTRACT FROM AUTHOR]

Interactions between genetic variants--epistasis--is pervasive in model systems and can profoundly impact evolutionary adaption, population disease dynamics, genetic mapping, and precision medicine efforts. In this work, we develop a model for structured polygenic epistasis, called coordinated epistasis (CE), and prove that several recent theories of genetic architecture fall under the formal umbrella of CE. Unlike standard epistasis models that assume epistasis and main effects are independent, CE captures systematic correlations between epistasis and main effects that result from pathway-level epistasis, on balance skewing the penetrance of genetic effects. To test for the existence of CE, we propose the even-odd (EO) test and prove it is calibrated in a range of realistic biological models. Applying the EO test in the UK Biobank, we find evidence of CE in 18 of 26 traits spanning disease, anthropometric, and blood categories. Finally, we extend the EO test to tissue-specific enrichment and identify several plausible tissue-trait pairs. Overall, CE is a dimension of genetic architecture that can capture structured, systemic forms of epistasis in complex human traits. [ABSTRACT FROM AUTHOR]

Clinical exome sequencing is frequently used to identify gene-disrupting variants in individuals with neurodevelopmental disorders. While splice-disrupting variants are known to contribute to these disorders, clinical interpretation of cryptic splice variants outside of the canonical splice site has been challenging. Here, we discuss papers that improve such detection. [ABSTRACT FROM AUTHOR]

Literature indicates that some children with ASD may show behavioral improvements during fever; however, little is known about the behavioral profiles of these children. This study aims to (a) investigate the subset of children who show parent‐reported behavioral improvements associated with fever and (b) compare the demographic, behavioral, and genetic characteristics of this subset of children to children whose parents report no change during fever. Parents of 2,152 children from the Simons Simplex Collection provided information about whether and in which areas their child improved during fever. Children were randomly assigned into discovery or replication samples. In discovery analyses, children who reportedly improved with fever (Improve Group) were compared to those who reportedly did not improve (No Improve Group) on demographics, medical history, ASD symptoms, adaptive skills, and presence of de novo ASD‐associated mutations. Significant and marginal results from discovery analyses were tested in the replication sample. Parent reports of 17% of children indicated improvements during fever across a range of domains. Discovery and replication analyses revealed that the Improve Group had significantly lower non‐verbal cognitive skills (NVIQ) and language levels and more repetitive behaviors. Groups did not differ on demographic variables, parent‐report of current ASD symptoms or the presence of de novo mutations. Understanding the profiles of children who improve during episodes of fever may provide insights into innovative treatments for ASD. Autism Res2018, 11: 175–184. © 2017 International Society for Autism Research, Wiley Periodicals, Inc. Lay Summary: This study explored characteristics of children with ASD who are reported to improve during fever. Parents of 17% of children with ASD report improvements across a range of domains during fever including cognition, communication, repetitive behaviors, social interaction, and behavior. Children who are reported to improve during fever have significantly lower non‐verbal cognitive skills and language levels and more repetitive behaviors. Understanding the profiles of children who improve during episodes of fever may provide insights into new treatments for ASD. [ABSTRACT FROM AUTHOR]

Objective: Aside from features associated with risk of neurogenetic syndromes in general (e.g., cognitive impairment), limited progress has been made in identifying phenotype-genotype relationships in autism spectrum disorder (ASD). The objective of this study was to extend work in the Simons Simplex Collection by comparing the phenotypic profiles of ASD probands with or without identified de novo loss of function mutations or copy number variants in high-confidence ASD-associated genes or loci.Method: Analyses preemptively accounted for documented differences in sex and IQ in affected individuals with de novo mutations by matching probands with and without these genetic events on sex, IQ, and age before comparing them on multiple behavioral domains.Results: Children with de novo mutations (N=112) had a greater likelihood of motor delay during early development (later age at walking), but they were less impaired on certain measures of ASD core symptoms (parent-rated social communication abnormalities and clinician-rated diagnostic certainty about ASD) in later childhood. These children also showed relative strengths in verbal and language abilities, including a smaller discrepancy between nonverbal and verbal IQ and a greater likelihood of having achieved fluent language (i.e., regular use of complex sentences).Conclusions: Children with ASD with de novo mutations may exhibit a "muted" symptom profile with respect to social communication and language deficits relative to those with ASD with no identified genetic abnormalities. Such findings suggest that examining early milestone differences and standardized testing results may be helpful in etiologic efforts, and potentially in clinical differentiation of various subtypes of ASD, but only if developmental and demographic variables are properly accounted for first. [ABSTRACT FROM AUTHOR]

Posttranscriptional RNA modifications by adenosine-to-inosine (A-to-I) editing are abundant in the brain, yet elucidating functional sites remains challenging. To bridge this gap, we investigate spatiotemporal and genetically regulated A-to-I editing sites across prenatal and postnatal stages of human brain development. More than 10,000 spatiotemporally regulated A-to-I sites were identified that occur predominately in 3′ UTRs and introns, as well as 37 sites that recode amino acids in protein coding regions with precise changes in editing levels across development. Hyper-edited transcripts are also enriched in the aging brain and stabilize RNA secondary structures. These features are conserved in murine and non-human primate models of neurodevelopment. Finally, thousands of cis -editing quantitative trait loci (edQTLs) were identified with unique regulatory effects during prenatal and postnatal development. Collectively, this work offers a resolved atlas linking spatiotemporal variation in editing levels to genetic regulatory effects throughout distinct stages of brain maturation. [Display omitted] • Alu editing activity is tightly regulated and increases across neurodevelopment • Spatiotemporally regulated sites in 3′ UTRs and coding regions offer functional insights • Hyper-edited RNA is enriched in the aging brain and stabilizes RNA secondary structures • cis -editing quantitative trait loci have unique regulatory effects in development This resource article illuminates precise regulation of A-to-I editing throughout human brain development. These findings provide an atlas of spatiotemporally and genetically regulated A-to-I sites and their putative functional effects during prenatal and postnatal periods. Additional avenues to dissect the role of RNA editing in neurodevelopment are provided. [ABSTRACT FROM AUTHOR]

One of the most consistent findings in autism spectrum disorder (ASD) research is a higher rate of ASD diagnosis in males than females. Despite this, remarkably little research has focused on the reasons for this disparity. Better understanding of this sex difference could lead to major advancements in the prevention or treatment of ASD in both males and females. In October of 2014, Autism Speaks and the Autism Science Foundation co-organized a meeting that brought together almost 60 clinicians, researchers, parents, and self-identified autistic individuals. Discussion at the meeting is summarized here with recommendations on directions of future research endeavors. [ABSTRACT FROM AUTHOR]

Background: A 4:1 male to female sex bias has consistently been observed in autism spectrum disorder (ASD). Epidemiological and genetic studies suggest a female protective effect (FPE) may account for part of this bias; however, the mechanism of such protection is unknown. Quantitative assessment of ASD symptoms using the Social Responsiveness Scale (SRS) shows a bimodal distribution unique to females in multiplex families. This leads to the hypothesis that a single, common genetic locus on chromosome X might mediate the FPE and produce the ASD sex bias. Such a locus would represent a major therapeutic target and is likely to have been missed by conventional genome-wide association study (GWAS) analysis. Methods: To explore this possibility, we performed an association study in affected versus unaffected females, considering three tiers of single nucleotide polymorphisms (SNPs) as follows: 1) regions of chromosome X that escape X-inactivation, 2) all of chromosome X, and 3) genome-wide. Results: No evidence of a SNP meeting the criteria for a single FPE locus was observed, despite the analysis being well powered to detect this effect. Conclusions: The results do not support the hypothesis that the FPE is mediated by a single genetic locus; however, this does not exclude the possibility of multiple genetic loci playing a role in the FPE. [ABSTRACT FROM AUTHOR]

Autism is a multifactorial neurodevelopmental disorder affecting more males than females; consequently, under a multifactorial genetic hypothesis, females are affected only when they cross a higher biological threshold. We hypothesize that deleterious variants at conserved residues are enriched in severely affected patients arising from female-enriched multiplex families with severe disease, enhancing the detection of key autism genes in modest numbers of cases. Here we show the use of this strategy by identifying missense and dosage sequence variants in the gene encoding the adhesive junction-associated δ-catenin protein (CTNND2) in female-enriched multiplex families and demonstrating their loss-of-function effect by functional analyses in zebrafish embryos and cultured hippocampal neurons from wild-type and Ctnnd2 null mouse embryos. Finally, through gene expression and network analyses, we highlight a critical role for CTNND2 in neuronal development and an intimate connection to chromatin biology. Our data contribute to the understanding of the genetic architecture of autism and suggest that genetic analyses of phenotypic extremes, such as female-enriched multiplex families, are of innate value in multifactorial disorders. [ABSTRACT FROM AUTHOR]

The combination of family-based linkage analysis with high-throughput sequencing is a powerful approach to identifying rare genetic variants that contribute to genetically heterogeneous syndromes. Using parametric multipoint linkage analysis and whole exome sequencing, we have identified a gene responsible for microcephaly (MCP), severe visual impairment, intellectual disability, and short stature through the mapping of a homozygous nonsense alteration in a multiply-affected consanguineous family. This gene, DIAPH1, encodes the mammalian Diaphanous-related formin (mDia1), a member of the diaphanous-related formin family of Rho effector proteins. Upon the activation of GTP-bound Rho, mDia1 generates linear actin filaments in the maintenance of polarity during adhesion, migration, and division in immune cells and neuroepithelial cells, and in driving tangential migration of cortical interneurons in the rodent. Here, we show that patients with a homozygous nonsense DIAPH1 alteration (p.Gln778*) have MCP as well as reduced height and weight. diap1 (mDia1 knockout (KO))-deficient mice have grossly normal body and brain size. However, our histological analysis of diap1 KO mouse coronal brain sections at early and postnatal stages shows unilateral ventricular enlargement, indicating that this mutant mouse shows both important similarities as well as differences with human pathology. We also found that mDia1 protein is expressed in human neuronal precursor cells during mitotic cell division and has a major impact in the regulation of spindle formation and cell division. [ABSTRACT FROM AUTHOR]

Autism spectrum disorders (ASDs) are characterized by phenotypic and genetic heterogeneity. Our analysis of functional networks perturbed in ASD suggests that both truncating and nontruncating de novo mutations contribute to autism, with a bias against truncating mutations in early embryonic development. We find that functional mutations are preferentially observed in genes likely to be haploinsufficient. Multiple cell types and brain areas are affected, but the impact of ASD mutations appears to be strongest in cortical interneurons, pyramidal neurons and the medium spiny neurons of the striatum, implicating cortical and corticostriatal brain circuits. In females, truncating ASD mutations on average affect genes with 50-100% higher brain expression than in males. Our results also suggest that truncating de novo mutations play a smaller role in the etiology of high-functioning ASD cases. Overall, we find that stronger functional insults usually lead to more severe intellectual, social and behavioral ASD phenotypes. [ABSTRACT FROM AUTHOR]

Contactins and Contactin-Associated Proteins, and Contactin-Associated Protein-Like 2 (CNTNAP2) in particular, have been widely cited as autism risk genes based on findings from homozygosity mapping, molecular cytogenetics, copy number variation analyses, and both common and rare single nucleotide association studies. However, data specifically with regard to the contribution of heterozygous single nucleotide variants (SNVs) have been inconsistent. In an effort to clarify the role of rare point mutations in CNTNAP2 and related gene families, we have conducted targeted next-generation sequencing and evaluated existing sequence data in cohorts totaling 2704 cases and 2747 controls. We find no evidence for statistically significant association of rare heterozygous mutations in any of the CNTN or CNTNAP genes, including CNTNAP2, placing marked limits on the scale of their plausible contribution to risk. [ABSTRACT FROM AUTHOR]

Spontaneously arising (de novo) mutations have an important role in medical genetics. For diseases with extensive locus heterogeneity, such as autism spectrum disorders (ASDs), the signal from de novo mutations is distributed across many genes, making it difficult to distinguish disease-relevant mutations from background variation. Here we provide a statistical framework for the analysis of excesses in de novo mutation per gene and gene set by calibrating a model of de novo mutation. We applied this framework to de novo mutations collected from 1,078 ASD family trios, and, whereas we affirmed a significant role for loss-of-function mutations, we found no excess of de novo loss-of-function mutations in cases with IQ above 100, suggesting that the role of de novo mutations in ASDs might reside in fundamental neurodevelopmental processes. We also used our model to identify ∼1,000 genes that are significantly lacking in functional coding variation in non-ASD samples and are enriched for de novo loss-of-function mutations identified in ASD cases. [ABSTRACT FROM AUTHOR]

A key component of genetic architecture is the allelic spectrum influencing trait variability. For autism spectrum disorder (herein termed autism), the nature of the allelic spectrum is uncertain. Individual risk-associated genes have been identified from rare variation, especially de novo mutations. From this evidence, one might conclude that rare variation dominates the allelic spectrum in autism, yet recent studies show that common variation, individually of small effect, has substantial impact en masse. At issue is how much of an impact relative to rare variation this common variation has. Using a unique epidemiological sample from Sweden, new methods that distinguish total narrow-sense heritability from that due to common variation and synthesis of results from other studies, we reach several conclusions about autism's genetic architecture: its narrow-sense heritability is ∼52.4%, with most due to common variation, and rare de novo mutations contribute substantially to individual liability, yet their contribution to variance in liability, 2.6%, is modest compared to that for heritable variation. [ABSTRACT FROM AUTHOR]

The proximal region of chromosome 15 is one of the genomic hotspots for copy number variants ( CNVs). Among the rearrangements observed in this region, CNVs from the interval between the common breakpoints 1 and 2 ( BP1 and BP2) have been reported cosegregating with autism spectrum disorder ( ASD). Although evidence supporting an association between BP1- BP2 CNVs and autism accumulates, the magnitude of the effect of BP1- BP2 CNVs remains elusive, posing a great challenge to recurrence-risk counseling. To gain further insight into their pathogenicity for ASD, we estimated the penetrance of the BP1- BP2 CNVs for ASD as well as their effects on ASD-related phenotypes in a well-characterized ASD sample (n = 2525 families). Transmission disequilibrium test revealed significant preferential transmission only for the duplicated chromosome in probands (20 T:9 NT). The penetrance of the BP1- BP2 CNVs for ASD was low, conferring additional risks of 0.3% (deletion) and 0.8% (duplication). Stepwise regression analyses suggest a greater effect of the CNVs on ASD-related phenotype in males and when maternally inherited. Taken together, the results are consistent with BP1- BP2 CNVs as risk factors for autism. However, their effect is modest, more akin to that seen for common variants. To be consistent with the current American College of Medical Genetics guidelines for interpretation of postnatal CNV, the BP1- BP2 deletion and duplication CNVs would probably best be classified as variants of uncertain significance ( VOUS): they appear to have an impact on risk, but one so modest that these CNVs do not merit pathogenic status. Autism Res 2014, 7: 355-362. © 2014 International Society for Autism Research, Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Background De novo loss-of-function (dnLoF) mutations are found twofold more often in autismspectrumdisorder (ASD) probands than their unaffected siblings. Multiple independent dnLoF mutations in the same gene implicate the gene in risk and hence provide a systematic, albeit arduous, path forward for ASD genetics. It is likely that using additional non-genetic data will enhance the ability to identify ASD genes. Methods To accelerate the search for ASD genes, we developed a novel algorithm, DAWN, to model two kinds of data: rare variations from exome sequencing and gene co-expression in the mid-fetal prefrontal and motor-somatosensory neocortex, a critical nexus for risk. The algorithm casts the ensemble data as a hidden Markov random field in which the graph structure is determined by gene co-expression and it combines these interrelationships with node-specific observations, namely gene identity, expression, genetic data and the estimated effect on risk. Results Using currently available genetic data and a specific developmental time period for gene coexpression, DAWN identified 127 genes that plausibly affect risk, and a set of likely ASD subnetworks. Validation experiments making use of published targeted resequencing results demonstrate its efficacy in reliably predicting ASD genes. DAWN also successfully predicts known ASD genes, not included in the genetic data used to create the model. Conclusions Validation studies demonstrate that DAWN is effective in predicting ASD genes and subnetworks by leveraging genetic and gene expression data. The findings reported here implicate neurite extension and neuronal arborization as risks for ASD. Using DAWN on emerging ASD sequence data and gene expression data from other brain regions and tissues would likely identify novel ASD genes. DAWN can also be used for other complex disorders to identify genes and subnetworks in those disorders. [ABSTRACT FROM AUTHOR]

De novo mutations affect risk for many diseases and disorders, especially those with early-onset. An example is autism spectrum disorders (ASD). Four recent whole-exome sequencing (WES) studies of ASD families revealed a handful of novel risk genes, based on independent de novo loss-of-function (LoF) mutations falling in the same gene, and found that de novo LoF mutations occurred at a twofold higher rate than expected by chance. However successful these studies were, they used only a small fraction of the data, excluding other types of de novo mutations and inherited rare variants. Moreover, such analyses cannot readily incorporate data from case-control studies. An important research challenge in gene discovery, therefore, is to develop statistical methods that accommodate a broader class of rare variation. We develop methods that can incorporate WES data regarding de novo mutations, inherited variants present, and variants identified within cases and controls. TADA, for Transmission And De novo Association, integrates these data by a gene-based likelihood model involving parameters for allele frequencies and gene-specific penetrances. Inference is based on a Hierarchical Bayes strategy that borrows information across all genes to infer parameters that would be difficult to estimate for individual genes. In addition to theoretical development we validated TADA using realistic simulations mimicking rare, large-effect mutations affecting risk for ASD and show it has dramatically better power than other common methods of analysis. Thus TADA's integration of various kinds of WES data can be a highly effective means of identifying novel risk genes. Indeed, application of TADA to WES data from subjects with ASD and their families, as well as from a study of ASD subjects and controls, revealed several novel and promising ASD candidate genes with strong statistical support. [ABSTRACT FROM AUTHOR]

Background The aim of this prospective observational cohort study was to investigate relationships between acute mountain sickness (AMS) and physical and mental health during a high altitude expedition. Methods Forty-four participants (mean age, 34 ± 13 y; body mass index, 23.6 ± 3.5 kg·m2; 57% male) completed the Dhaulagiri base camp trek in Nepal, a 19-day expedition attaining 5,372 m. Participants self-reported the following daily physical and mental health: AMS (defined by Lake Louise diagnosis and individual and total symptom scores), upper respiratory symptoms, diarrhea, and anxiety, plus physiological and behavioral factors. Results The rate of Lake Louise-defined AMS per 100 person days was 9.2 (95% CI: 7.2-11.7). All investigated illnesses except diarrhea increased with altitude (all p < 0.001 by analysis of variance). Total AMS symptom score was associated with a lower arterial oxygen saturation, higher resting heart rate, more upper respiratory and diarrhea symptoms, greater anxiety, and lower fluid intake (all p < 0.02 by longitudinal multiple regression analyses). However, only upper respiratory symptoms, heart rate, arterial oxygen saturation, and fluid intake predicted future AMS symptoms [eg, an increase in upper respiratory symptoms by 5 units predicted an increase in the following day's AMS total symptom score by 0.72 units (0.54-0.89)]. Conclusions Upper respiratory symptoms and anxiety increasingly contributed to symptom burden as altitude was gained. Data were consistent with increased heart rate, decreased arterial oxygen saturation, reduced fluid intake, and upper respiratory symptoms being causally associated with AMS. Upper respiratory symptoms and fluid intake are the simplest targets for intervention to reduce AMS during high altitude exposure. [ABSTRACT FROM AUTHOR]

Multiple studies have confirmed the contribution of rare de novo copy number variations to the risk for autism spectrum disorders. But whereas de novo single nucleotide variants have been identified in affected individuals, their contribution to risk has yet to be clarified. Specifically, the frequency and distribution of these mutations have not been well characterized in matched unaffected controls, and such data are vital to the interpretation of de novo coding mutations observed in probands. Here we show, using whole-exome sequencing of 928 individuals, including 200 phenotypically discordant sibling pairs, that highly disruptive (nonsense and splice-site) de novo mutations in brain-expressed genes are associated with autism spectrum disorders and carry large effects. On the basis of mutation rates in unaffected individuals, we demonstrate that multiple independent de novo single nucleotide variants in the same gene among unrelated probands reliably identifies risk alleles, providing a clear path forward for gene discovery. Among a total of 279 identified de novo coding mutations, there is a single instance in probands, and none in siblings, in which two independent nonsense variants disrupt the same gene, SCN2A (sodium channel, voltage-gated, type II, ? subunit), a result that is highly unlikely by chance. [ABSTRACT FROM AUTHOR]

Background: Autism spectrum disorders (ASD) are early onset neurodevelopmental syndromes typified by impairments in reciprocal social interaction and communication, accompanied by restricted and repetitive behaviors. While rare and especially de novo genetic variation are known to affect liability, whether common genetic polymorphism plays a substantial role is an open question and the relative contribution of genes and environment is contentious. It is probable that the relative contributions of rare and common variation, as well as environment, differs between ASD families having only a single affected individual (simplex) versus multiplex families who have two or more affected individuals. Methods: By using quantitative genetics techniques and the contrast of ASD subjects to controls, we estimate what portion of liability can be explained by additive genetic effects, known as narrow-sense heritability. We evaluate relatives of ASD subjects using the same methods to evaluate the assumptions of the additive model and partition families by simplex/multiplex status to determine how heritability changes with status. Results: By analyzing common variation throughout the genome, we show that common genetic polymorphism exerts substantial additive genetic effects on ASD liability and that simplex/multiplex family status has an impact on the identified composition of that risk. As a fraction of the total variation in liability, the estimated narrow-sense heritability exceeds 60% for ASD individuals from multiplex families and is approximately 40% for simplex families. By analyzing parents, unaffected siblings and alleles not transmitted from parents to their affected children, we conclude that the data for simplex ASD families follow the expectation for additive models closely. The data from multiplex families deviate somewhat from an additive model, possibly due to parental assortative mating. Conclusions: Our results, when viewed in the context of results from genome-wide association studies, demonstrate that a myriad of common variants of very small effect impacts ASD liability. [ABSTRACT FROM AUTHOR]

Loss-of-function variants in the gene SCN2A , which encodes the sodium channel Na V 1.2, are strongly associated with autism spectrum disorder and intellectual disability. An estimated 20%–30% of children with these variants also suffer from epilepsy, with altered neuronal activity originating in neocortex, a region where Na V 1.2 channels are expressed predominantly in excitatory pyramidal cells. This is paradoxical, as sodium channel loss in excitatory cells would be expected to dampen neocortical activity rather than promote seizure. Here, we examined pyramidal neurons lacking Na V 1.2 channels and found that they were intrinsically hyperexcitable, firing high-frequency bursts of action potentials (APs) despite decrements in AP size and speed. Compartmental modeling and dynamic-clamp recordings revealed that Na V 1.2 loss prevented potassium channels from properly repolarizing neurons between APs, increasing overall excitability by allowing neurons to reach threshold for subsequent APs more rapidly. This cell-intrinsic mechanism may, therefore, account for why SCN2A loss-of-function can paradoxically promote seizure. [Display omitted] • Conditional deletion of Na V 1.2 channels increases action potential (AP) excitability • Na V 1.2 regulates somatodendritc excitability, and Na V 1.6 regulates axonal action potential initiation • Lack of Na V 1.2 channels impairs AP repolarization by reducing K V activation • Reduced K V -mediated AP after hyperpolarization increases AP output Loss of sodium channels in individual neurons is expected to reduce neuronal excitability. Spratt and colleagues show that loss of Scn2a -encoded Na V 1.2 channels in mouse prefrontal pyramidal cells can paradoxically increase excitability due to Na V 1.2's distinct role in regulating somatodendritic excitability, independent of action potential electrogenesis in the axon. [ABSTRACT FROM AUTHOR]