Missense and truncating variants in CHD5 in a dominant neurodevelopmental disorder with intellectual disability, behavioral disturbances, and epilepsy

Molecular and clinical aspects of histone-related disorders

Epigenetics is the coordination of gene expression without alterations in the DNA sequence. Epigenetic gene expression is regulated by an intricate system that revolves around the interaction of histone proteins and DNA within the chromatin structure. Histones remain at the core of the epigenetic gene transcription regulation where histone proteins, along with the histone modification enzymes, and the subunits of chromatin remodelers and epigenetic readers play essential roles in regulating gene expression. Histone-related disorders encompass the syndromes induced by pathogenic variants in genes encoding histones, genes encoding histone modification enzymes, and genes encoding subunits of chromatin remodeler and epigenetic reader complexes. Defects in genes encoding histones lead to the expression of abnormal histone proteins. Abnormalities in genes encoding histone modification enzymes result in aberrant histone modifications. Defects in genes encoding subunits of the chromatin remodeler complexes result in defective chromatin remodeling. Defects in genes that code for the epigenetic readers (bromodomain proteins) will hinder their ability to regulate gene transcription. These disorders typically present manifestations that impact the nervous system which is particularly sensitive due to its need for specific patterns of gene expression for neural cell function and differentiation. To date, 72 histone-related disorders have been described including 7 syndromes due to defects in histone genes, 35 syndromes due to histone modifications defects, 26 syndromes due to defects in chromatin remodeling, and 4 due to defects in epigenetic readers. In this review article, the molecular basis of histone structure and function is first explained, followed by a summary of the histone-related syndromes.

Two distinct phenotypes in Snijders Blok-Campeau syndrome and characterization of the behavioral phenotype in a zebrafish model

Chromatin remodeling is an important system controlling gene expression. CHD3, which is a causative gene of Snijders Blok-Campeau syndrome (SNIBCPS), is a member of the chromodomain helicase DNA-binding (CHD) family related to chromatin remodeling. SNIBCPS is characterized by developmental delay (DD), intellectual disability (ID), macrocephaly, and facial features including a prominent forehead and hypertelorism. Hypersociability/overfriendliness is a notable behavioral feature in patients. Here, we describe five SNIBCPS patients with CHD3 variants from four families, including a sibling pair caused by parental gonosomal mosaicism. We observed two distinct phenotypes in our patients in accordance with previous observations. Phenotype 1: macrocephaly, hypertelorism, overgrowth, DD, and ID; and Phenotype 2: microcephaly, growth retardation, DD, and ID. Phenotype 1 was consistent with the typical SNIBCPS phenotype, while Phenotype 2 was distinct. To understand further the features of the patients with SNIBCPS, we generated chd3-knockout (KO) zebrafish using CRISPR-Cas9 genome editing. No morphological changes were observed in chd3-KO zebrafish. However, behavioral tests showed that chd3-KO zebrafish had strong and sustained interest in others, and were less aggressive toward others, suggesting a recapitulation of the hypersociability/overfriendliness phenotype in patients with SNIBCPS. Metabolomic analysis using whole brains showed changes in metabolites processed by specific mitochondrial enzymes in chd3-KO zebrafish. The administration of metformin, which reportedly ameliorates mitochondrial dysfunction and behavioral abnormalities, attenuated the abnormal behavior of chd3-KO zebrafish. Our study helps delineate the phenotypes of patients with SNIBCPS, provides insights into a characteristic behavior of the disease, and suggests a potential treatment to improve the behavioral symptoms of patients.

It Takes a Village of Chromatin Remodelers to Regulate rDNA Expression

Ribosome biogenesis is one of the most fundamental and energetically demanding cellular processes. In humans, the ribosomal DNA (rDNA) repeats span a large region of DNA and comprise 200 to 600 copies of a ~43 kb unit spread over five different chromosomes. Control over ribosome biogenesis is closely tied to the regulation of the chromatin environment of this large genomic region. The proportion of rDNA loci which are active or silent is altered depending on the proliferative or metabolic state of the cell. Repeat silencing is driven by epigenetic changes culminating in a repressive heterochromatin environment. One group of proteins facilitating these epigenetic changes in response to growth or metabolic demands are ATP-dependent chromatin remodeling protein complexes that use ATP hydrolysis to reposition nucleosomes. Indeed, some chromatin remodelers are known to have indispensable roles in regulating the chromatin environment of rDNA. In this review, we highlight these proteins and their complexes and describe their mechanistic roles at rDNA. We also introduce the developmental disorders arising from the dysfunction of these proteins and discuss how the consequent dysregulation of rDNA loci may be reflected in the phenotypes observed.

Discovery of a DNA methylation profile in individuals with Sifrim-Hitz-Weiss syndrome

Pathogenic heterozygous variants in CHD4 cause Sifrim-Hitz-Weiss syndrome, a neurodevelopmental disorder associated with brain anomalies, heart defects, macrocephaly, hypogonadism, and additional features with variable expressivity. Most individuals have non-recurrent missense variants, complicating variant interpretation. A few were reported with truncating variants, and their role in disease is unclear. DNA methylation episignatures have emerged as highly accurate diagnostic biomarkers in a growing number of rare diseases. We aimed to study evidence for the existence of a CHD4-related DNA methylation episignature. We collected blood DNA samples and/or clinical information from 39 individuals with CHD4 variants, including missense and truncating variants. Genomic DNA methylation analysis was performed on 28 samples. We identified a sensitive and specific DNA methylation episignature in samples with pathogenic missense variants within the ATPase/helicase domain. The same episignature was observed in a family with variable expressivity, a de novo variant near the PHD domain, variants of uncertain significance within the ATPase/helicase domain, and a sample with compound heterozygous variants. DNA methylation data revealed higher percentages of shared probes with BAFopathies, CHD8, and the terminal ADNP variants encoding a protein known to form the ChAHP complex with CHD4. Truncating variants, as well as a sample with a recurrent pathogenic missense variant, exhibited DNA methylation profiles distinct from the ATPase/helicase domain episignature. These DNA methylation differences, together with the distinct clinical features observed in those individuals, provide preliminary evidence for clinical and molecular sub-types in the CHD4-related disorder.

EEG Abnormalities and Phenotypic Correlates in Preschoolers with Autism Spectrum Disorder: A Single-Center Study

Background: The literature suggests the existence of an association between autism spectrum disorders (ASDs) and subclinical electroencephalographic abnormalities (SEAs), which show a heterogeneous prevalence rate (12.5-60.7%) within the pediatric ASD population. The aim of this study was to investigate the EEG findings in a cohort of ASD preschoolers and their correlation with the phenotypic characteristics. Methods: We retrospectively reviewed data on 141 ASD preschoolers evaluated in a tertiary care university hospital over the period 2008-2018. All participants underwent at least one standard polygraphic electroencephalogram (EEG) and a clinical multidisciplinary assessment with standardized instruments. Results: 77 patients (55%) showed SEAs, which were mainly represented by epileptiform discharges (p < 0.00001), especially focal and multifocal (p = 0.010). Abnormal EEG (p = 0.035) and epileptiform discharges (p = 0.014) were associated with seizure onset and were predominant in sleep (p < 0.00001). Patients with abnormal tracing (p = 0.031) and slow abnormalities (p < 0.001) were significantly younger. ASD severity was not found to be correlated with EEG results, which showed a potential, albeit non-significant, association with some psychometric parameters. Very similar results were found when patients were divided according to sex. Conclusions: EEG abnormalities appear to correlate more with ASD internalizing, externalizing and emotional comorbidities, rather than with ASD core symptoms; larger samples are needed to further investigate this association.

Gatad2b, associated with the neurodevelopmental syndrome GAND, plays a critical role in neurodevelopment and cortical patterning

GATAD2B (GATA zinc finger domain containing 2B) variants are associated with the neurodevelopmental syndrome GAND, characterized by intellectual disability (ID), infantile hypotonia, apraxia of speech, epilepsy, macrocephaly and distinct facial features. GATAD2B encodes for a subunit of the Nucleosome Remodeling and Histone Deacetylase (NuRD) complex. NuRD controls transcriptional programs critical for proper neurodevelopment by coupling histone deacetylase with ATP-dependent chromatin remodeling activity. To study mechanisms of pathogenesis for GAND, we characterized a mouse model harboring an inactivating mutation in Gatad2b. Homozygous Gatad2b mutants die perinatally, while haploinsufficient Gatad2b mice exhibit behavioral abnormalities resembling the clinical features of GAND patients. We also observed abnormal cortical patterning, and cellular proportions and cell-specific alterations in the developmental transcriptome in these mice. scRNAseq of embryonic cortex indicated misexpression of genes key for corticogenesis and associated with neurodevelopmental syndromes such as Bcl11b, Nfia and H3f3b and Sox5. These data suggest a crucial role for Gatad2b in brain development.

Children with Autism Spectrum Disorder and Abnormalities of Clinical EEG: A Qualitative Review

Over the last decade, the comorbidity between Autism Spectrum Disorder (ASD) and epilepsy has been widely demonstrated, and many hypotheses regarding the common neurobiological bases of these disorders have been put forward. A variable, but significant, prevalence of abnormalities on electroencephalogram (EEG) has been documented in non-epileptic children with ASD; therefore, several scientific studies have recently tried to demonstrate the role of these abnormalities as a possible biomarker of altered neural connectivity in ASD individuals. This narrative review intends to summarize the main findings of the recent scientific literature regarding abnormalities detected with standard EEG in children/adolescents with idiopathic ASD. Research using three different databases (PubMed, Scopus and Google Scholar) was conducted, resulting in the selection of 10 original articles. Despite an important lack of studies on preschoolers and a deep heterogeneity in results, some authors speculated on a possible association between EEG abnormalities and ASD characteristics, in particular, the severity of symptoms. Although this correlation needs to be more strongly elucidated, these findings may encourage future studies aimed at demonstrating the role of electrical brain abnormalities as an early biomarker of neural circuit alterations in ASD, highlighting the potential diagnostic, prognostic and therapeutic value of EEG in this field.

Divergent phenotypes in constitutive versus conditional mutant mouse models of Sifrim-Hitz-Weiss syndrome

Chromatin remodellers are among the most important risk genes associated with neurodevelopmental disorders (NDDs), however, their functions during brain development are not fully understood. Here, we focused on Sifrim-Hitz-Weiss Syndrome (SIHIWES)-an intellectual disability disorder caused by mutations in the CHD4 chromodomain helicase gene. We utilized mouse genetics to excise the Chd4 ATPase/helicase domain-either constitutively, or conditionally in the developing telencephalon. Conditional heterozygotes exhibited no change in cortical size and cellular composition, and had only subtle behavioral phenotypes. Telencephalon-specific conditional knockouts had marked reductions in cortical growth, reduced numbers of upper-layer neurons, and exhibited alterations in anxiety and repetitive behaviors. Despite the fact that whole-body heterozygotes exhibited comparable growth defects, they were unaffected in these behaviors, but instead exhibited female-specific alterations in learning and memory. These data reveal unexpected phenotypic divergence arising from differences in the spatiotemporal deployment of loss-of-function manipulations, underscoring the importance of context in chromatin remodeller function during neurodevelopment.

Chromatin gatekeeper and modifier CHD proteins in development, and in autism and other neurological disorders

Chromatin, a protein-DNA complex, is a dynamic structure that stores genetic information within the nucleus and responds to molecular/cellular changes in its structure, providing conditional access to the genetic machinery. ATP-dependent chromatin modifiers regulate access of transcription factors and RNA polymerases to DNA by either "opening" or "closing" the structure of chromatin, and its aberrant regulation leads to a variety of neurodevelopmental disorders. The chromodomain helicase DNA-binding (CHD) proteins are ATP-dependent chromatin modifiers involved in the organization of chromatin structure, act as gatekeepers of genomic access, and deposit histone variants required for gene regulation. In this review, we first discuss the structural and functional domains of the CHD proteins, and their binding sites, and phosphorylation, acetylation, and methylation sites. The conservation of important amino acids in SWItch/sucrose non-fermenting (SWI/SNF) domains, and their protein and mRNA tissue expression profiles are discussed. Next, we convey the important binding partners of CHD proteins, their protein complexes and activities, and their involvements in epigenetic regulation. We also show the ChIP-seq binding dynamics for CHD1, CHD2, CHD4, and CHD7 proteins at promoter regions of histone genes, as well as several genes that are critical for neurodevelopment. The role of CHD proteins in development is also discussed. Finally, this review provides information about CHD protein mutations reported in autism and neurodevelopmental disorders, and their pathogenicity. Overall, this review provides information on the progress of research into CHD proteins, their structural and functional domains, epigenetics, and their role in stem cell, development, and neurological disorders.

Ophthalmologic diagnoses in youths with autism spectrum disorder: Prevalence and clinical correlates

Autism spectrum disorder (ASD) is associated with a high prevalence of visual dysfunction. This study aimed to investigate the rates of amblyopia, refractive errors, and strabismus, as well as their clinical correlates in ASD. This population-based matched-cohort study used data from the Taiwan National Health Insurance Research Database. A total of 3,551 youths with ASD and 35,510 non-autistic control participants matched by age and sex were included. All the participants were followed-up until they were 18 years old. The prevalence of amblyopia, refractive errors, and strabismus was compared between the ASD and control groups. Effect modifiers, including sex, ASD subgroup, and co-diagnosis of intelligence disability, were examined. Compared to the control group, youths with ASD had a significantly increased risk of amblyopia (adjusted odds ratio [aOR] = 1.75), anisometropia (aOR = 1.66), astigmatism (aOR = 1.51), hypermetropia (aOR = 2.08), exotropia (aOR = 2.86), and esotropia (aOR = 2.63), but a comparable likelihood of myopia according to age. Males with ASD had a significantly lower likelihood of exotropia, but a higher likelihood of myopia than females with ASD. The autism subgroup had a higher OR for hypermetropia, but a lower OR for myopia than the other ASD subgroups. ASD youths with intelligence disabilities demonstrated significantly higher ORs for amblyopia, hypermetropia, and all types of strabismus and lower OR for myopia than those without intelligence disabilities. In conclusion, the rates of amblyopia, refractive errors, and strabismus were higher in youths with ASD. Ocular abnormalities in youths with ASD require a comprehensive assessment and management.

De novo variants in GATAD2A in individuals with a neurodevelopmental disorder: GATAD2A-related neurodevelopmental disorder

GATA zinc finger domain containing 2A (GATAD2A) is a subunit of the nucleosome remodeling and deacetylase (NuRD) complex. NuRD is known to regulate gene expression during neural development and other processes. The NuRD complex modulates chromatin status through histone deacetylation and ATP-dependent chromatin remodeling activities. Several neurodevelopmental disorders (NDDs) have been previously linked to variants in other components of NuRD's chromatin remodeling subcomplex (NuRDopathies). We identified five individuals with features of an NDD that possessed de novo autosomal dominant variants in GATAD2A. Core features in affected individuals include global developmental delay, structural brain defects, and craniofacial dysmorphology. These GATAD2A variants are predicted to affect protein dosage and/or interactions with other NuRD chromatin remodeling subunits. We provide evidence that a GATAD2A missense variant disrupts interactions of GATAD2A with CHD3, CHD4, and CHD5. Our findings expand the list of NuRDopathies and provide evidence that GATAD2A variants are the genetic basis of a previously uncharacterized developmental disorder.

Success and Pitfalls of Genetic Testing in Undiagnosed Diseases: Whole Exome Sequencing and Beyond

Novel approaches to uncover the molecular etiology of neurodevelopmental disorders (NDD) are highly needed. Even using a powerful tool such as whole exome sequencing (WES), the diagnostic process may still prove long and arduous due to the high clinical and genetic heterogeneity of these conditions. The main strategies to improve the diagnostic rate are based on family segregation, re-evaluation of the clinical features by reverse-phenotyping, re-analysis of unsolved NGS-based cases and epigenetic functional studies. In this article, we described three selected cases from a cohort of patients with NDD in which trio WES was applied, in order to underline the typical challenges encountered during the diagnostic process: (1) an ultra-rare condition caused by a missense variant in MEIS2, identified through the updated Solve-RD re-analysis; (2) a patient with Noonan-like features in which the NGS analysis revealed a novel variant in NIPBL causing Cornelia de Lange syndrome; and (3) a case with de novo variants in genes involved in the chromatin-remodeling complex, for which the study of the epigenetic signature excluded a pathogenic role. In this perspective, we aimed to (i) provide an example of the relevance of the genetic re-analysis of all unsolved cases through network projects on rare diseases; (ii) point out the role and the uncertainties of the reverse phenotyping in the interpretation of the genetic results; and (iii) describe the use of methylation signatures in neurodevelopmental syndromes for the validation of the variants of uncertain significance.

The NuRD Complex in Neurodevelopment and Disease: A Case of Sliding Doors

The Nucleosome Remodelling and Deacetylase (NuRD) complex represents one of the major chromatin remodelling complexes in mammalian cells, uniquely coupling the ability to "open" the chromatin by inducing nucleosome sliding with histone deacetylase activity. At the core of the NuRD complex are a family of ATPases named CHDs that utilise the energy produced by the hydrolysis of the ATP to induce chromatin structural changes. Recent studies have highlighted the prominent role played by the NuRD in regulating gene expression during brain development and in maintaining neuronal circuitry in the adult cerebellum. Importantly, components of the NuRD complex have been found to carry mutations that profoundly affect neurological and cognitive development in humans. Here, we discuss recent literature concerning the molecular structure of NuRD complexes and how the subunit composition and numerous permutations greatly determine their functions in the nervous system. We will also discuss the role of the CHD family members in an array of neurodevelopmental disorders. Special emphasis will be given to the mechanisms that regulate the NuRD complex composition and assembly in the cortex and how subtle mutations may result in profound defects of brain development and the adult nervous system.

Genome-wide association study for single nucleotide polymorphism associated with mural and cumulus granulosa cells of PCOS (polycystic ovary syndrome) and non-PCOS patients

Background

The genetic make-up of local granulosa cells and their function in the pathophysiology of polycystic ovary syndrome (PCOS) is crucial to a full comprehension of the disorder. The major purpose of this study was to compare the Single Nucleotide Polymorphism (SNP) of cumulus granulosa cells (CGCs) and mural granulosa cells (MGCs) between healthy individuals and women with PCOS using genome-wide association analysis (GWA). A case–control study was conducted in a total of 24 women diagnosed with PCOS and 24 healthy non-PCOS women of reproductive age aggregated into 4 samples of 6 patients each. GWA studies entail several processes, such as cell separation, cellular DNA extraction, library preparation followed by interpretation using bioinformatics databases. SNP locations were identified by reference gene also involves the use of Matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF) mass spectrometry (MS) (MALDI-TOF-MS) for the first sorting. Hybridization with the gene chip was followed by reading the SNP genotypes according to the publications in the literature. TASSEL (Trait Analysis by aSSociation, Evolution and Linkage) program and methods were used for GWA studies.

Results

An aggregate of 21,039 SNP calls were obtained from our samples. Genes of autoimmune illnesses, obesity, inflammatory illnesses, nervous system diseases such as retinitis pigmentosa, autism, neural tube defects, and Alzheimer's disease; and various malignancies such as lung cancer, colorectal cancer, breast cancer were also identified in these cells. Gene ranking score reveals that granulosa cells carry key genes of neurological system and reproductive systems especially in brain and testis, respectively.

Conclusions

Mural and Cumulus Granulosa cells were shown to have the PCOS directly and indirectly related genes MMP9, PRKAA2, COMT and HP. We found that the expression of ARID4B, MUC5AC, NID2, CREBBP, GNB1, KIF2C, COL18A1, and HNRNPC by these cells may contribute to PCOS.

Graphical abstract

Chd5 Regulates the Transcription Factor Six3 to Promote Neuronal Differentiation

Chromodomain helicase DNA-binding protein 5 (Chd5) is an ATP-dependent chromatin remodeler that promotes neuronal differentiation. However, the mechanism behind the action of Chd5 during neurogenesis is not clearly understood. Here we use transcriptional profiling of cells obtained from Chd5 deficient mice at early and late stages of neuronal differentiation to show that Chd5 regulates neurogenesis by directing stepwise transcriptional changes. During early stages of neurogenesis, Chd5 promotes expression of the proneural transcription factor Six3 to repress Wnt5a, a non-canonical Wnt ligand essential for the maturation of neurons. This previously unappreciated ability of Chd5 to transcriptionally repress neuronal maturation factors is critical for both lineage specification and maturation. Thus, Chd5 facilitates early transcriptional changes in neural stem cells, thereby initiating transcriptional programs essential for neuronal fate specification.

Prediction of Neurodevelopmental Disorders Based on De Novo Coding Variation

The early detection of neurodevelopmental disorders (NDDs) can significantly improve patient outcomes. The differential burden of non-synonymous de novo mutation among NDD cases and controls indicates that de novo coding variation can be used to identify a subset of samples that will likely display an NDD phenotype. Thus, we have developed an approach for the accurate prediction of NDDs with very low false positive rate (FPR) using de novo coding variation for a small subset of cases. We use a shallow neural network that integrates de novo likely gene-disruptive and missense variants, measures of gene constraint, and conservation information to predict a small subset of NDD cases at very low FPR and prioritizes NDD risk genes for future clinical study.

1p36 deletion syndrome: Review and mapping with further characterization of the phenotype, a new cohort of 86 patients

Chromosome 1p36 deletion syndrome (1p36DS) is one of the most common terminal deletion syndromes (incidence between 1/5000 and 1/10,000 live births in the American population), due to a heterozygous deletion of part of the short arm of chromosome 1. The 1p36DS is characterized by typical craniofacial features, developmental delay/intellectual disability, hypotonia, epilepsy, cardiomyopathy/congenital heart defect, brain abnormalities, hearing loss, eyes/vision problem, and short stature. The aim of our study was to (1) evaluate the incidence of the 1p36DS in the French population compared to 22q11.2 deletion syndrome and trisomy 21; (2) review the postnatal phenotype related to microarray data, compared to previously publish prenatal data. Thanks to a collaboration with the ACLF (Association des Cytogénéticiens de Langue Française), we have collected data of 86 patients constituting, to the best of our knowledge, the second-largest cohort of 1p36DS patients in the literature. We estimated an average of at least 10 cases per year in France. 1p36DS seems to be much less frequent than 22q11.2 deletion syndrome and trisomy 21. Patients presented mainly dysmorphism, microcephaly, developmental delay/intellectual disability, hypotonia, epilepsy, brain malformations, behavioral disorders, cardiomyopathy, or cardiovascular malformations and, pre and/or postnatal growth retardation. Cardiac abnormalities, brain malformations, and epilepsy were more frequent in distal deletions, whereas microcephaly was more common in proximal deletions. Mapping and genotype-phenotype correlation allowed us to identify four critical regions responsible for intellectual disability. This study highlights some phenotypic variability, according to the deletion position, and helps to refine the phenotype of 1p36DS, allowing improved management and follow-up of patients.

Role of ATP-dependent chromatin remodelers in hematopoietic stem and progenitor cell maintenance

PURPOSE OF REVIEW

ATP-dependent chromatin remodeling factors utilize energy from ATP hydrolysis to modulate DNA-histone structures and regulate gene transcription. They are essential during hematopoiesis and for hematopoietic stem and progenitor cell (HSPC) function. This review discusses the recently unveiled roles of these chromatin remodelers in HSPC regulation, with an emphasis on the mechanism of chromodomain helicase DNA-binding (CHD) family members.

RECENT FINDINGS

Recent studies of ATP-dependent chromatin remodelers have revealed that individual CHD family members engage in distinct mechanisms in regulating HSPC cell fate. For example, CHD8 is required for HSPC survival by restricting both P53 transcriptional activity and protein stability in steady state hematopoiesis while the related CHD7 physically interacts with RUNX family transcription factor 1 (RUNX1) and suppresses RUNX1-induced expansion of HSPCs during blood development. Moreover, other CHD subfamily members such as CHD1/CHD2 and CHD3/CHD4, as well as the switch/sucrose non-fermentable, imitation SWI, and SWI2/SNF2 related (SWR) families of chromatin modulators, have also been found important for HSPC maintenance by distinct mechanisms.

SUMMARY

The expanding knowledge of ATP-dependent chromatin remodelers in hematopoiesis illustrates their respective critical roles in HSPC maintenance including the regulation of HSPC differentiation, survival, and self-renewal. Further studies are warranted to elucidate how different chromatin remodeling complexes are integrated in various HSPC cell fate decisions during steady-state and stress hematopoiesis.

Analysis of recent shared ancestry in a familial cohort identifies coding and noncoding autism spectrum disorder variants

Autism spectrum disorder (ASD) is a collection of neurodevelopmental disorders characterized by deficits in social communication and restricted, repetitive patterns of behavior or interests. ASD is highly heritable, but genetically and phenotypically heterogeneous, reducing the power to identify causative genes. We performed whole genome sequencing (WGS) in an ASD cohort of 68 individuals from 22 families enriched for recent shared ancestry. We identified an average of 3.07 million variants per genome, of which an average of 112,512 were rare. We mapped runs of homozygosity (ROHs) in affected individuals and found an average genomic homozygosity of 9.65%, consistent with expectations for multiple generations of consanguineous unions. We identified potentially pathogenic rare exonic or splice site variants in 12 known (including KMT2C, SCN1A, SPTBN1, SYNE1, ZNF292) and 12 candidate (including CHD5, GRB10, PPP1R13B) ASD genes. Furthermore, we annotated noncoding variants in ROHs with brain-specific regulatory elements and identified putative disease-causing variants within brain-specific promoters and enhancers for 5 known ASD and neurodevelopmental disease genes (ACTG1, AUTS2, CTNND2, CNTNAP4, SPTBN4). We also identified copy number variants in two known ASD and neurodevelopmental disease loci in two affected individuals. In total we identified potentially etiological variants in known ASD or neurodevelopmental disease genes for ~61% (14/23) of affected individuals. We combined WGS with homozygosity mapping and regulatory element annotations to identify candidate ASD variants. Our analyses add to the growing number of ASD genes and variants and emphasize the importance of leveraging recent shared ancestry to map disease variants in complex neurodevelopmental disorders.

Sentinels of chromatin: chromodomain helicase DNA-binding proteins in development and disease

Chromatin is highly dynamic, undergoing continuous global changes in its structure and type of histone and DNA modifications governed by processes such as transcription, repair, replication, and recombination. Members of the chromodomain helicase DNA-binding (CHD) family of enzymes are ATP-dependent chromatin remodelers that are intimately involved in the regulation of chromatin dynamics, altering nucleosomal structure and DNA accessibility. Genetic studies in yeast, fruit flies, zebrafish, and mice underscore essential roles of CHD enzymes in regulating cellular fate and identity, as well as proper embryonic development. With the advent of next-generation sequencing, evidence is emerging that these enzymes are subjected to frequent DNA copy number alterations or mutations and show aberrant expression in malignancies and other human diseases. As such, they might prove to be valuable biomarkers or targets for therapeutic intervention.

Advances in Chromodomain Helicase DNA-Binding (CHD) Proteins Regulating Stem Cell Differentiation and Human Diseases

Background: Regulation of gene expression is critical for stem cell differentiation, tissue development, and human health maintenance. Recently, epigenetic modifications of histone and chromatin remodeling have been verified as key controllers of gene expression and human diseases.

Objective: In this study, we review the role of chromodomain helicase DNA-binding (CHD) proteins in stem cell differentiation, cell fate decision, and several known human developmental disorders and cancers.

Conclusion: CHD proteins play a crucial role in stem cell differentiation and human diseases.