Histone Lysine Methylases and Demethylases in the Landscape of Human Developmental Disorders

Chromatin modification abnormalities by CHD7 and KMT2C loss promote medulloblastoma progression

Medulloblastoma (MB), a common malignant pediatric brain tumor arising in the cerebellum, is characterized by mutations in chromatin modifiers, highlighting the significance of chromatin modification abnormalities in its progression. While animal models have effectively demonstrated this, a comprehensive evaluation of the oncogenic potential of these mutations remains incomplete. In this study, we use CRISPR-mediated gene editing to knock out chromatin modifier genes mutated in human SHH MB, along with the Ptch1 gene, in cerebellar granule neuron progenitors of neonatal mice. This reveals that depletion of Chd7 and Kmt2c accelerates tumor growth. Multi-layered omics analysis uncovers that inhibition of the neuronal differentiation program by chromatin dysregulation is a key signaling pathway in tumor progression. Additionally, forced expression of Neurod1, a common target of these chromatin modifiers, inhibits proliferation and promotes differentiation. These findings highlight converging chromatin modification abnormalities from distinct mutations in Sonic Hedgehog MB and suggest that epigenetic drugs activating neuronal genes have significant potential as novel treatments.

Long term follow-up of multiorgan disease in Kleefstra syndrome 2 in an adult - case report

OBJECTIVES

The Kleefstra syndrome spectrum (KSS) is a group of neurodevelopmental disorders characterized by intellectual disability, behavioral disorders, growth and neurodevelopmental delay, facial dysmorphism and neurological deficits. Kleefstra syndrome 2 (KLEFS2) is a part of KSS and is due to heterozygous loss-of-function variants in the KMT2 C gene. We report the long-term clinical course and multi-organ manifestations of a patient with KLEFS2 caused by a novel heterozygous pathogenic variant in KMT2 C.

METHODS

A patient with KSS phenotype developed proteinuria with progressive kidney dysfunction secondary to focal segmental glomerular sclerosis. She subsequently developed recurrent episodes that mimicked mitochondrial stroke-like episodes. The phenotype included encephalopathy, stroke-like episodes with focal status epilepticus with impaired consciousness associated with cortical and subcortical T2/FLAIR signal hyperintensities that partially responded to intravenous arginine infusions.

RESULTS

Exome sequencing revealed a heterozygous pathogenic nonsense variant in KMT2 C (NM_170606.3) c.3940C > T (p.Gln1314Ter). Nuclear and mitochondrial DNA variants associated with mitochondrial disorders have been excluded.

DISCUSSION

This is a case of KLEFS2 with longitudinal 10 year follow up and its previously unreported multi-organ clinical manifestations including stroke-like episodes and nephrotic disease. Our report further expands the phenotypic spectrum of KLEFS2. Further reports of patients with KLEFS2 with multi-organ involvement should be sought to confirm our findings.

DOT1L in neural development and neurological and psychotic disorders

Disruptor of Telomeric Silencing 1-Like (DOT1L) is the sole methyltransferase in mammals responsible for catalyzing the mono-, di-, and trimethylation of histone H3 at lysine 79 (H3K79), a modification crucial for various cellular processes, including gene transcription, cell cycle regulation, DNA repair, and development. Recent studies have increasingly linked DOT1L to the nervous system, where it plays a vital role in neurodevelopment and neuronal function. It has been shown to regulate the proliferation and differentiation of neural progenitor cells, promote neuronal maturation, and influence synaptic function, all of which are essential for proper neural circuit formation and brain function. Moreover, dysregulation of DOT1L has been associated with several neurological disorders, highlighting its potential role in disease pathology. Abnormal expression or activity of DOT1L has been implicated in cognitive deficits and neurodegenerative diseases, underscoring the enzyme's significance in both the development and maintenance of the nervous system. This review synthesizes recent findings on DOT1L's role in the nervous system, emphasizing its importance in neurodevelopment and exploring its potential as a therapeutic target for treating neurological disorders.

FBXO22 deficiency defines a pleiotropic syndrome of growth restriction and multi-system anomalies associated with a unique epigenetic signature

FBXO22 encodes an F-box protein, which acts as a substrate-recognition component of the SKP1-CUL1-F-box (SCF) E3 ubiquitin ligase complex. Despite its known roles in the post-translational ubiquitination and degradation of specific substrates, including histone demethylases, the impact of FBXO22 on human development remains unknown. Here, we characterize a pleiotropic syndrome with prominent prenatal onset growth restriction and notable neurodevelopmental delay across 16 cases from 14 families. Through exome and genome sequencing, we identify four distinct homozygous FBXO22 variants with loss-of-function effects segregating with the disease: three predicted to lead to premature translation termination due to frameshift effects and a single-amino-acid-deletion variant, which, we show, impacts protein stability in vitro. We confirm that affected primary fibroblasts with a frameshift mutation are bereft of endogenous FBXO22 and show increased levels of the known substrate histone H3K9 demethylase KDM4B. Accordingly, we delineate a unique epigenetic signature for this disease in peripheral blood via long-read sequencing. Altogether, we identify and demonstrate that FBXO22 deficiency leads to a pleiotropic syndrome in humans, encompassing growth restriction and neurodevelopmental delay, the pathogenesis of which may be explained by broad chromatin alterations.

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.

Variable expressivity of KMT2B variants at codon 2565 in patients with dystonia and developmental disorders

INTRODUCTION

Variable expressivity is an emerging characteristic of KMT2B-related dystonia. However, it remains poorly understood whether variants reoccurring at specific sites of lysine-specific methlytransferase-2B (KMT2B) can drive intra- and interfamilial clinical heterogeneity. Our goal was to ascertain independent families with variants affecting residue Arg2565 of KMT2B.

METHODS

Whole-exome/genome sequencing, multi-site recruitment, genotype-phenotype correlations, and DNA methylation episignature analysis were performed.

RESULTS

We report four individuals from two families harboring the variant c.7693C > G, p.Arg2565Gly. In an additional patient, a de-novo c.7693C > T, p.Arg2565Cys variant was identified. The observed phenotypic spectrum ranged from childhood-onset dystonia (N = 2) over unspecific intellectual disability syndromes (N = 2) to undiagnosed behavioral symptoms in adulthood (N = 1). Samples bearing p.Arg2565Gly had a KMT2B-typical episignature, although the effect on methylation was less pronounced than in carriers of loss-of-function KMT2B variants.

CONCLUSIONS

We established the existence of a KMT2B missense-mutation hotspot associated with varying degrees of disease severity and expression, providing information for patient counseling and elucidation of pathomechanisms.

De novo variants in KDM2A cause a syndromic neurodevelopmental disorder

Germline variants that disrupt components of the epigenetic machinery cause syndromic neurodevelopmental disorders. Using exome and genome sequencing, we identified de novo variants in KDM2A, a lysine demethylase crucial for embryonic development, in 18 individuals with developmental delays and/or intellectual disabilities. The severity ranged from learning disabilities to severe intellectual disability. Other core symptoms included feeding difficulties, growth issues such as intrauterine growth restriction, short stature and microcephaly as well as recurrent facial features like epicanthic folds, upslanted palpebral fissures, thin lips, and low-set ears. Expression of human disease-causing KDM2A variants in a Drosophila melanogaster model led to neural degeneration, motor defects, and reduced lifespan. Interestingly, pathogenic variants in KDM2A affected physiological attributes including subcellular distribution, expression and stability in human cells. Genetic epistasis experiments indicated that KDM2A variants likely exert their effects through a potential gain-of-function mechanism, as eliminating endogenous KDM2A in Drosophila did not produce noticeable neurodevelopmental phenotypes. Data from Enzymatic-Methylation sequencing supports the suggested gene-disease association by showing an aberrant methylome profiles in affected individuals' peripheral blood. Combining our genetic, phenotypic and functional findings, we establish de novo variants in KDM2A as causative for a syndromic neurodevelopmental disorder.

Gonadal Mosaicism for an ASH1L Intragenic Deletion Makes a Bridge Between MRD52 and 1q22 Microdeletion

ASH1L gene encodes a histone lysine methyltransferase, highly expressed in both embryonic and adult human brain. De novo loss-of-function variants in ASH1L are described in an ultrarare monogenic neurodevelopmental disorder, previously called mental retardation type 52 (MRD52). At the same time, a few cases are reported in the literature and DECIPHER with 1q22 microdeletions spanning ASH1L. We report three siblings presenting non-syndromic intellectual disability (ID) and an ASH1L intragenic deletion extending from exons 2 to 12 detected at SNP-array. Both parents resulted noncarrier suggesting gonadal/gonosomal mosaicism in one of the parents. This observation restricted the smallest region of overlap of the 1q22 microdeletion to ASH1L, and allowed to consider MRD52 and 1q22 microdeletion the same ASH1L-related neurodevelopmental disorder. We also reported the first example of gonadal/gonosomal mosaicism for an ASH1L deleterious variant, a fact that should generate the suspicion of recurrence also in sporadic cases of ASH1L-related neurodevelopmental disorder.

Insights on the Shared Genetic Landscape of Neurodevelopmental and Movement Disorders

PURPOSE OF REVIEW

Large-scale studies using hypothesis-free exome sequencing have revealed the strong heritability of neurodevelopmental disorders (NDDs) and their molecular overlap with later-onset, progressive, movement disorders phenotypes. In this review, we focus on the shared genetic landscape of NDDs and movement disorders.

RECENT FINDINGS

Cumulative research has shown that up to 30% of cases labelled as "cerebral palsy" have a monogenic etiology. Causal pathogenic variants are particularly enriched in genes previously associated with adult-onset progressive movement disorders, such as spastic paraplegias, dystonias, and cerebellar ataxias. Biological pathways that have emerged as common culprits are transcriptional regulation, neuritogenesis, and synaptic function. Defects in the same genes can cause neurological dysfunction both during early development and later in life. We highlight the implications of the increasing number of NDD gene etiologies for genetic testing in movement disorders. Finally, we discuss gaps and opportunities in the translation of this knowledge to the bedside.

Sequencing in over 50,000 cases identifies coding and structural variation underlying atrial fibrillation risk

Atrial fibrillation (AF) is a prevalent and morbid abnormality of the heart rhythm with a strong genetic component. Here, we meta-analyzed genome and exome sequencing data from 36 studies that included 52,416 AF cases and 277,762 controls. In burden tests of rare coding variation, we identified novel associations between AF and the genes MYBPC3, LMNA, PKP2, FAM189A2 and KDM5B. We further identified associations between AF and rare structural variants owing to deletions in CTNNA3 and duplications of GATA4. We broadly replicated our findings in independent samples from MyCode, deCODE and UK Biobank. Finally, we found that CRISPR knockout of KDM5B in stem-cell-derived atrial cardiomyocytes led to a shortening of the action potential duration and widespread transcriptomic dysregulation of genes relevant to atrial homeostasis and conduction. Our results highlight the contribution of rare coding and structural variants to AF, including genetic links between AF and cardiomyopathies, and expand our understanding of the rare variant architecture for this common arrhythmia.

Pathogenic variants in chromatin-related genes: Linking immune dysregulation to neuroregression and acute neuropsychiatric disorders

We report eight children with de novo pathogenic DNA variants in chromatin-related genes: MORC2, CHD7, KANSL1, KMT2D, ZMYND11, HIST1HIE, EP300, and KMT2B. All children experienced infection or vaccine-provoked neuroregression or abrupt-onset neuropsychiatric syndromes. Most had delayed development (n = 6) before the first regression, and four had immune deficiency or autoimmunity (n = 4). At a mean age of 4 years 2 months (range 1-8 years), symptoms included infection-provoked autistic/language regression (n = 6), cognitive decline (n = 3), gait deterioration (n = 3), or abrupt-onset anxiety, obsessive-compulsive disorder, and/or tics (n = 5). Three children had ongoing infection-provoked deteriorations. Six children benefited from intravenous immunoglobulin (n = 3) or antibiotics (n = 4). Ribonucleic acid expression of the eight chromatin genes was similar in neuronal, glial, and peripheral leukocytes, unlike non-chromatin neurodevelopmental genes, which have predominantly neuronal expression. These cases demonstrate the role of chromatin dysregulation in autistic regression and abrupt-onset neuropsychiatric syndromes, potentially related to brain and immune gene dysregulation.

KMT2B-related disorders: expansion of the phenotypic spectrum and long-term efficacy of deep brain stimulation

Heterozygous mutations in KMT2B are associated with an early-onset, progressive and often complex dystonia (DYT28). Key characteristics of typical disease include focal motor features at disease presentation, evolving through a caudocranial pattern into generalized dystonia, with prominent oromandibular, laryngeal and cervical involvement. Although KMT2B-related disease is emerging as one of the most common causes of early-onset genetic dystonia, much remains to be understood about the full spectrum of the disease. We describe a cohort of 53 patients with KMT2B mutations, with detailed delineation of their clinical phenotype and molecular genetic features. We report new disease presentations, including atypical patterns of dystonia evolution and a subgroup of patients with a non-dystonic neurodevelopmental phenotype. In addition to the previously reported systemic features, our study has identified co-morbidities, including the risk of status dystonicus, intrauterine growth retardation, and endocrinopathies. Analysis of this study cohort (n = 53) in tandem with published cases (n = 80) revealed that patients with chromosomal deletions and protein truncating variants had a significantly higher burden of systemic disease (with earlier onset of dystonia) than those with missense variants. Eighteen individuals had detailed longitudinal data available after insertion of deep brain stimulation for medically refractory dystonia. Median age at deep brain stimulation was 11.5 years (range: 4.5-37.0 years). Follow-up after deep brain stimulation ranged from 0.25 to 22 years. Significant improvement of motor function and disability (as assessed by the Burke Fahn Marsden's Dystonia Rating Scales, BFMDRS-M and BFMDRS-D) was evident at ł months, 1 year and last follow-up (motor, P = 0.001, P = 0.004, and P = 0.012; disability, P = 0.009, P = 0.002 and P = 0.012). At 1 year post-deep brain stimulation, >50% of subjects showed BFMDRS-M and BFMDRS-D improvements of >30%. In the long-term deep brain stimulation cohort (deep brain stimulation inserted for >5 years, n = 8), improvement of >30% was maintained in 5/8 and 3/8 subjects for the BFMDRS-M and BFMDRS-D, respectively. The greatest BFMDRS-M improvements were observed for trunk (53.2%) and cervical (50.5%) dystonia, with less clinical impact on laryngeal dystonia. Improvements in gait dystonia decreased from 20.9% at 1 year to 1ł.2% at last assessment; no patient maintained a fully independent gait. Reduction of BFMDRS-D was maintained for swallowing (52.9%). Five patients developed mild parkinsonism following deep brain stimulation. KMT2B-related disease comprises an expanding continuum from infancy to adulthood, with early evidence of genotype-phenotype correlations. Except for laryngeal dysphonia, deep brain stimulation provides a significant improvement in quality of life and function with sustained clinical benefit depending on symptoms distribution.

2-Oxoglutarate-dependent dioxygenases as oxygen sensors: their importance in health and disease

Since low oxygen conditions below physiological levels, hypoxia, are associated with various diseases, it is crucial to understand the molecular basis behind cellular response to hypoxia. Hypoxia-inducible factors (HIFs) have been revealed to primarily orchestrate the hypoxic response at the transcription level and have continuously attracted great attention over the past three decades. In addition to these hypoxia-responsive effector proteins, 2-oxoglutarate-dependent dioxygenase (2-OGDD) superfamily including prolyl-4-hydroxylase domain-containing proteins (PHDs) and factor inhibiting HIF-1 (FIH-1) has attracted even greater attention in recent years as factors that act as direct oxygen sensors due to their necessity of oxygen for the regulation of the expression and activity of the regulatory subunit of HIFs. Herein, we present a detailed classification of 2-OGDD superfamily proteins, such as Jumonji C-domain-containing histone demethylases, ten-eleven translocation enzymes, AlkB family of DNA/RNA demethylases and lysyl hydroxylases, and discuss their specific functions and associations with various diseases. By introducing the multifaceted roles of 2-OGDD superfamily proteins in the hypoxic response, this review aims to summarize the accumulated knowledge about the complex mechanisms governing cellular adaptation to hypoxia in various physiological and pathophysiological contexts.

Meta-analysis reveals transcription factors and DNA binding domain variants associated with congenital heart defect and orofacial cleft

Many structural birth defect patients lack genetic diagnoses because there are many disease genes as yet to be discovered. We applied a gene burden test incorporating de novo predicted-loss-of-function (pLoF) and likely damaging missense variants together with inherited pLoF variants to a collection of congenital heart defect (CHD) and orofacial cleft (OC) parent-offspring trio cohorts (n = 3,835 and 1,844, respectively). We identified 17 novel candidate CHD genes and 10 novel candidate OC genes, of which many were known developmental disorder genes. Shorter genes were more powered in a "de novo only" analysis as compared to analysis including inherited pLoF variants. TFs were enriched among the significant genes; 14 and 8 transcription factor (TF) genes showed significant variant burden for CHD and OC, respectively. In total, 30 affected children had a de novo missense variant in a DNA binding domain of a known CHD, OC, and other developmental disorder TF genes. Our results suggest candidate pathogenic variants in CHD and OC and their potentially pleiotropic effects in other developmental disorders.

Polycomb-associated and Trithorax-associated developmental conditions-phenotypic convergence and heterogeneity

Polycomb group (PcG) and Trithorax group (TrxG) complexes represent two major components of the epigenetic machinery. This study aimed to delineate phenotypic similarities and differences across developmental conditions arising from rare variants in PcG and TrxG genes, using data-driven approaches. 462 patients with a PcG or TrxG-associated condition were identified in the DECIPHER dataset. We analysed Human Phenotype Ontology (HPO) data to identify phenotypes enriched in this group, in comparison to other monogenic conditions within DECIPHER. We then assessed phenotypic relationships between single gene diagnoses within the PcG and TrxG group, by applying semantic similarity analysis and hierarchical clustering. Finally, we analysed patient-level phenotypic heterogeneity in this group, irrespective of specific genetic diagnosis, by applying the same clustering approach. Collectively, PcG/TrxG diagnoses were associated with increased reporting of HPO terms relating to integument, growth, head and neck, limb and digestive abnormalities. Gene group analysis identified three multi-gene clusters differentiated by microcephaly, limb/digit dysmorphologies, growth abnormalities and atypical behavioural phenotypes. Patient-level analysis identified two large clusters differentiated by neurodevelopmental abnormalities and facial dysmorphologies respectively, as well as smaller clusters associated with more specific phenotypes including behavioural characteristics, eye abnormalities, growth abnormalities and skull dysmorphologies. Importantly, patient-level phenotypic clusters did not align with genetic diagnoses. Data-driven approaches can highlight pathway-level and gene-level phenotypic convergences, and individual-level phenotypic heterogeneities. Future studies are needed to understand the multi-level mechanisms contributing to both convergence and variability within this population, and to extend data collection and analyses to later-emerging health characteristics.

ChromBPNet: bias factorized, base-resolution deep learning models of chromatin accessibility reveal cis-regulatory sequence syntax, transcription factor footprints and regulatory variants

Despite extensive mapping of cis-regulatory elements (cREs) across cellular contexts with chromatin accessibility assays, the sequence syntax and genetic variants that regulate transcription factor (TF) binding and chromatin accessibility at context-specific cREs remain elusive. We introduce ChromBPNet, a deep learning DNA sequence model of base-resolution accessibility profiles that detects, learns and deconvolves assay-specific enzyme biases from regulatory sequence determinants of accessibility, enabling robust discovery of compact TF motif lexicons, cooperative motif syntax and precision footprints across assays and sequencing depths. Extensive benchmarks show that ChromBPNet, despite its lightweight design, is competitive with much larger contemporary models at predicting variant effects on chromatin accessibility, pioneer TF binding and reporter activity across assays, cell contexts and ancestry, while providing interpretation of disrupted regulatory syntax. ChromBPNet also helps prioritize and interpret regulatory variants that influence complex traits and rare diseases, thereby providing a powerful lens to decode regulatory DNA and genetic variation.

Clinical characteristics and genetic analysis of four pediatric patients with Kleefstra syndrome

BACKGROUND

Kleefstra syndrome spectrum (KLEFS) is an autosomal dominant disorder that can lead to intellectual disability and autism spectrum disorders. KLEFS encompasses Kleefstra syndrome-1 (KLEFS1) and Kleefstra syndrome-2 (KLEFS2), with KLEFS1 accounting for more than 75%. However, limited information is available regarding KLEFS2. KLEFS1 is caused by a subtelomeric chromosomal abnormality resulting in either deletion at the end of the long arm of chromosome 9, which contains the EHMT1 gene, or by variants in the EHMT1 gene and the KMT2C gene that cause KLEFS2.

METHODS

This study was a retrospective analysis of clinical data from four patients with KLEFS. Exome sequencing (ES) and Sanger sequencing techniques were used to identify and validate the candidate variants, facilitating the analysis of genotype‒phenotype correlations of the EHMT1 and KMT2C genes. Protein structure modeling was performed to evaluate the effects of the variants on the protein's three-dimensional structure. In addition, real-time quantitative reverse transcription‒polymerase chain reaction (RT‒qPCR) and western blotting were used to examine the protein and mRNA levels of the KMT2C gene.

RESULTS

Two patients with KLEFS1 were identified: one with a novel variant (c.2382 + 1G > T) and the other with a previously reported variant (c.2426 C > T, p.Pro809Leu) in the EHMT1 gene. A De novo deletion at the end of the long arm of chromosome 9 was also reported. Furthermore, a patient with KLEFS2 was identified with a novel variant in the KMT2C gene (c.568 C > T, p.Arg190Ter). The RT‒qPCR and western blot results revealed that the expression of the KMT2C gene was downregulated in the KLEFS2 sample.

CONCLUSION

This study contributes to the understanding of both KLEFS1 and KLEFS2 by identifying novel variants in EHMT1 and KMT2C genes, thereby expanding the variant spectrum. Additionally, we provide the first evidence of how a KMT2C variant leads to decreased gene and protein expression, enhancing our understanding of the molecular mechanisms underlying KLEFS2. Based on these findings, children exhibiting developmental delay, hypotonia, distinctive facial features, and other neurodevelopmental abnormalities should be considered for ES to ensure early intervention and treatment.

Chemogenetic Inhibition of Prefrontal Cortex Ameliorates Autism-Like Social Deficits and Absence-Like Seizures in a Gene-Trap Ash1l Haploinsufficiency Mouse Model

BACKGROUND

ASH1L (absent, small, or homeotic-like 1), a histone methyltransferase, has been identified as a high-risk gene for autism spectrum disorder (ASD). We previously showed that postnatal Ash1l severe deficiency in the prefrontal cortex (PFC) of male and female mice caused seizures. However, the synaptic mechanisms underlying autism-like social deficits and seizures need to be elucidated.

OBJECTIVE

The goal of this study is to characterize the behavioral deficits and reveal the synaptic mechanisms in an Ash1l haploinsufficiency mouse model using a targeted gene-trap knockout (gtKO) strategy.

METHOD

A series of behavioral tests were used to examine behavioral deficits. Electrophysiological and chemogenetic approaches were used to examine and manipulate the excitability of pyramidal neurons in the PFC of Ash1l+/GT mice.

RESULTS

Ash1l+/GT mice displayed social deficits, increased self-grooming, and cognitive impairments. Epileptiform discharges were found on electroencephalograms (EEGs) of Ash1l+/GT mice, indicating absence-like seizures. Ash1l haploinsufficiency increased the susceptibility for convulsive seizures when Ash1l+/GT mice were challenged by pentylenetetrazole (PTZ, a competitive GABAA receptor antagonist). Whole-cell patch-clamp recordings showed that Ash1l haploinsufficiency increased the excitability of pyramidal neurons in the PFC by altering intrinsic neuronal properties, enhancing glutamatergic synaptic transmission, and diminishing GABAergic synaptic inhibition. Chemogenetic inhibition of pyramidal neurons in the PFC of Ash1l+/GT mice ameliorated autism-like social deficits and abolished absence-like seizures.

CONCLUSIONS

We demonstrated that increased neural activity in the PFC contributed to the autism-like social deficits and absence-like seizures in Ash1l+/GT mice, which provides novel insights into the therapeutic strategies for patients with ASH1L-associated ASD and epilepsy.

The histone demethylase KDM5 has insulator activity in the brain

KDM5 family proteins are best known for their demethylation of the promoter proximal chromatin mark H3K4me3. KDM5-regulated transcription is critical in the brain, with variants in the X-linked paralog KDM5C causing the intellectual disability (ID) disorder Claes-Jensen syndrome. Although the demethylase activity of KDM5C is known to be important for neuronal function, the contribution of non-enzymatic activities remain less characterized. We therefore used Drosophila to model the ID variant Kdm5 L854F , which disrupts a C5HC2 zinc finger adjacent to the enzymatic JmjC domain. Kdm5 L854F causes similar transcriptional changes in the brain to a demethylase dead strain, Kdm5 J1310C * , despite having little effect on enzymatic activity. KDM5 L854F is also distinct from KDM5 J1310C * in its reduced interactions with insulator proteins and enhancement of position effect variegation. Instead, the common transcriptional deficits likely result from both the JmjC and C5HC2 domains driving proper genomic organization through their activity in promoting proper loop architecture.

Dynamic Regulation OF The Chromatin Environment By Ash1L Modulates Human Neuronal Structure And Function

Precise regulation of the chromatin environment through post-translational histone modification modulates transcription and controls brain development. Not surprisingly, mutations in a large number of histone-modifying enzymes underlie complex brain disorders. In particular, the histone methyltransferase ASH1L modifies histone marks linked to transcriptional activation and has been implicated in multiple neuropsychiatric disorders. However, the mechanisms underlying the pathobiology of ASH1L-asociated disease remain underexplored. We generated human isogenic stem cells with a mutation in ASH1L's catalytic domain. We find that ASH1L dysfunction results in reduced neurite outgrowth, which correlates with alterations in the chromatin profile of activating and repressive histone marks, as well as the dysregulation of gene programs important for neuronal structure and function implicated in neuropsychiatric disease. We also identified a novel regulatory node implicating both the SP and Krüppel -like families of transcription factors and ASH1L relevant to human neuronal development. Finally, we rescue cellular defects linked to ASH1L dysfunction by leveraging two independent epigenetic mechanisms that promote transcriptional activation. In summary, we identified an ASH1L-driven epigenetic and transcriptional axis essential for human brain development and complex brain disorders that provide insights into future therapeutic strategies for ASH1L-related disorders.

The clinical spectrum and pathogenesis associated with KMT2B variants in Chinese pediatric patients

OBJECTIVE

To evaluate the clinical spectrum and pathogenesis associated with KMT2B variants in Chinese children with dystonia or developmental delay.

METHODS

We reported twenty-seven (fourteen males and thirteen females) pediatric patients with KMT2B variants identified via next-generation sequencing from a single Chinese center. Moreover, transcriptomics and proteomics assays were performed on fibroblasts from patients with different genotypes to investigate the pathogenic mechanisms involved.

RESULTS

Twenty-six patients had dystonia including generalized dystonia (n = 19), multifocal dystonia (n = 6), and segmental dystonia (n = 1), and one patient had nondystonic severe-developmental delay (DD). All the twenty-six patients had complex dystonia compounded with other manifestations of movement disorders (tremor (n = 6), myoclonus (n = 5), status dystonicus (n = 2), and tic (n = 1)) or dysmorphic features and developmental delay. The onset of dystonia was between 1 month and 13 years 8 months (median 4 years 4 months). Dystonia was aggravated by fever (n = 11), and diurnal and climate fluctuations (n = 4). Eleven patients underwent deep brain stimulation and experienced significant improvements in motor function and disability. We identified twenty-six intragenic heterozygous KMT2B pathogenic variants and one Chr:19q13.12 contiguous gene deletion. Sixteen variants were novel. Differentially expressed genes induced by KMT2B variants were significantly enriched for mitochondria-related biological processes in patient fibroblasts. As a result, mitochondrial morphology of mitochondria was altered, and aerobic respiration was impaired.

CONCLUSION

Our study reports the pediatric cases of KMT2B-related disorder from a single center in China. Additionally, our study highlights the role of KMT2B variants in mitochondrial dysfunction.

Prenatal Perfluoroalkyl Substance Exposure in Association with Global Histone Post-Translational Methylation in 2-Year-Old Children

Perfluoroalkyl substances (PFASs) have elimination half-lives in years in humans and are persistent in the environment. PFASs can cross the placenta and impact fetal development. Exposure to PFASs may lead to adverse effects through epigenetic mechanisms. This study aimed to investigate whether prenatal exposure to perfluorooctyl sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluoroundecanoic acid (PFUA) was associated with global histone methylation level changes among the 130 2-year-old children followed-up in a birth cohort study in Taiwan. PFOS, PFOA, PFNA, and PFUA were measured by UHPLC/MS/MS in cord blood. Global histone methylation levels were measured from the blood leukocytes of 2-year-old children by Western blotting. Multivariable regression analyses were applied to adjust for potential confounding effects. Among the 2-year-old children, an IQR increase in the natural log-transformed PFUA exposure was associated with an increased H3K4me3 level by 2.76-fold (95%CI = (0.79, 4.73), p = 0.007). PFOA and PFNA exposures was associated with a decreased H3K27me3 level by 2.35-fold (95%CI = (-4.29, -0.41), p = 0.01) and 2.01-fold (95%CI = (-4.00, -0.03), p = 0.04), respectively. Our findings suggest that prenatal PFAS exposure affected histone post-translational modifications.

Clinical and Genetic Characterization of Adolescent-Onset Epilepsy: A Single-Center Experience in Republic of Korea

OBJECTIVES

This study investigated the characteristics of adolescent-onset epilepsy (AOE) and conducted genetic tests on a cohort of 76 Korean patients to identify variants and expand the spectrum of mutations associated with AOE.

METHODS

Clinical exome sequencing after routine karyotyping and chromosomal microarray was performed to identify causative variants and expand the spectrum of mutations associated with AOE.

RESULTS

In cases of AOE without neurodevelopmental delay (NDD), this study identified four likely pathogenic variants (LPVs) or variants of uncertain significance (VUS) and two copy number variations (CNVs). To explore the unique features of AOE; clinical manifestations were compared between patients with and without NDD. The analysis revealed statistically significant differences in the prevalence of males and the yield of genetic testing results. AOE without NDD had a lower prevalence in males (49%) compared to AOE with NDD (60%) (p = 0.007). Genetic alterations: AOE with NDD exhibited a higher frequency of genetic alterations (35%) compared to AOE without NDD (12%) (p = 0.011). Thorough evaluation of AOE can be particularly challenging in adolescent patients. Some individuals may display genetic variations due to a phenomenon known as locus heterogeneity, where different genetic causes lead to similar clinical presentations.

CONCLUSIONS

Implementing a robust genetic workflow is crucial for accurately diagnosing AOE, even in cases with complex genetic underpinnings. This study underscores the importance of genetic testing as an essential diagnostic tool for AOE. Identifying genetic variants and understanding their clinical correlations can aid in improving diagnostic accuracy and optimizing treatment approaches for adolescent patients with epilepsy.

Higher order interaction analysis quantifies coordination in the epigenome revealing novel biological relationships in Kabuki syndrome

Complex direct and indirect relationships between multiple variables, termed higher order interactions (HOIs), are characteristics of all natural systems. Traditional differential and network analyses fail to account for the omic datasets richness and miss HOIs. We investigated peripheral blood DNA methylation data from Kabuki syndrome type 1 (KS1) and control individuals, identified 2,002 differentially methylated points (DMPs), and inferred 17 differentially methylated regions, which represent only 189 DMPs. We applied hypergraph models to measure HOIs on all the CpGs and revealed differences in the coordination of DMPs with lower entropy and higher coordination of the peripheral epigenome in KS1 implying reduced network complexity. Hypergraphs also capture epigenomic trans-relationships, and identify biologically relevant pathways that escape the standard analyses. These findings construct the basis of a suitable model for the analysis of organization in the epigenome in rare diseases, which can be applied to investigate mechanism in big data.

Loss of DOT1L function disrupts neuronal transcription, animal behavior, and leads to a novel neurodevelopmental disorder

Individuals with monoallelic pathogenic variants in the histone lysine methyltransferase DOT1L display global developmental delay and varying congenital anomalies. However, the impact of monoallelic loss of DOT1L remains unclear. Here, we present a largely female cohort of 11 individuals with DOT1L variants with developmental delays and dysmorphic facial features. We found that DOT1L variants include missense variants clustered in the catalytic domain, frameshift, and stop-gain variants. We demonstrate that specific variants cause loss of methyltransferase activity and therefore sought to define the effects of decreased DOT1L function. Using RNA-sequencing of cultured neurons and single nucleus RNA-sequencing of mouse cortical tissue, we found that partial Dot1l depletion causes sex-specific transcriptional responses and disrupts transcription of synaptic genes. Further, Dot1l loss alters neuron branching and expression of synaptic proteins. Lastly using zebrafish and mouse models, we found behavioral disruptions that include sex-specific deficits in mice. Overall, we define how DOT1L loss leads to neurological dysfunction by demonstrating that partial Dot1l loss impacts transcription, neuron morphology, and behavior across multiple models and systems.

Abnormal H3K4 enzyme catalytic activity and neuronal morphology caused by ASH1L mutations in individuals with Tourette syndrome

ASH1L potentially contributes to Tourette syndrome (TS) and other neuropsychiatric disorders, as our previous studies have shown. It regulates essential developmental genes by counteracting polycomb-mediated transcriptional repression, which restricts chromatin accessibility at target genes. ASH1L is highly expressed in the adult brain, playing a crucial role in the early stage. However, it remains unclear how ASH1L mutations carried by patients with TS participate in regulating neuronal growth processes leading to TS traits. Five TS families recruited in our study underwent comprehensive physical examinations and questionnaires to record clinical phenotypes and environmental impact factors. We validated the variants via Sanger sequencing and constructed two mutants near the catalytic domain of ASH1L. We conducted molecular modeling, in vitro assays, and primary neuron cultures to find the role of ASH1L in neuronal development and its correlation with TS. In this study, we validated five pathogenic ASH1L rare variants and observed symptoms in patients with simple tics and behavioral comorbidities. Mutations near the catalytic domain of TS patients cause mental state abnormalities and disrupt ASH1L function by destabilizing its spatial conformation, leading to decreased activity of catalytic H3K4, thereby affecting the neurite growth. We need to conduct larger-scale studies on TS patients and perform additional neurological evaluations on mature neurons. We first reported the effects of ASH1L mutations in TS patients, including phenotypic heterogeneity, protein function, and neurological growth. This information contributes to understanding the neurodevelopmental pathogenesis of TS in patients with ASH1L mutations.

Genome Sequencing Identifies 13 Novel Candidate Risk Genes for Autism Spectrum Disorder in a Qatari Cohort

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by deficits in social communication, restricted interests, and repetitive behaviors. Despite considerable research efforts, the genetic complexity of ASD remains poorly understood, complicating diagnosis and treatment, especially in the Arab population, with its genetic diversity linked to migration, tribal structures, and high consanguinity. To address the scarcity of ASD genetic data in the Middle East, we conducted genome sequencing (GS) on 50 ASD subjects and their unaffected parents. Our analysis revealed 37 single-nucleotide variants from 36 candidate genes and over 200 CGG repeats in the FMR1 gene in one subject. The identified variants were classified as uncertain, likely pathogenic, or pathogenic based on in-silico algorithms and ACMG criteria. Notably, 52% of the identified variants were homozygous, indicating a recessive genetic architecture to ASD in this population. This finding underscores the significant impact of high consanguinity within the Qatari population, which could be utilized in genetic counseling/screening program in Qatar. We also discovered single nucleotide variants in 13 novel genes not previously associated with ASD: ARSF, BAHD1, CHST7, CUL2, FRMPD3, KCNC4, LFNG, RGS4, RNF133, SCRN2, SLC12A8, USP24, and ZNF746. Our investigation categorized the candidate genes into seven groups, highlighting their roles in cognitive development, including the ubiquitin pathway, transcription factors, solute carriers, kinases, glutamate receptors, chromatin remodelers, and ion channels.

Biallelic loss-of-function variants of EZH1 cause a novel developmental disorder with central precocious puberty

Pathogenic variants of polycomb repressive complex-2 (PRC2) subunits are associated with overgrowth syndromes and neurological diseases. EZH2 is a major component of PRC2 and mediates the methylation of H3K27 trimethylation (H3K27me3). Germline variants of EZH2 have been identified as a cause of Weaver syndrome (WS), an overgrowth/intellectual disability (OGID) syndrome characterized by overgrowth, macrocephaly, accelerated bone age, intellectual disability (ID), and characteristic facial features. Germline variants of SUZ12 and EED, other components of PRC2, have also been reported in the WS or Weaver-like syndrome. EZH1 is a homolog of EZH2 that interchangeably associates with SUZ12 and EED. Recently, pathogenic variants of EZH1 have been reported in individuals with dominant and recessive neurodevelopmental disorders. We herein present sisters with biallelic loss-of-function variants of EZH1. They showed developmental delay, ID, and central precocious puberty, but not the features of WS or other OGID syndromes.

Expanding the molecular landscape of childhood apraxia of speech: evidence from a single-center experience

Background

Childhood apraxia of speech (CAS) is a genetically heterogeneous pediatric motor speech disorder. The advent of whole exome sequencing (WES) and whole genome sequencing techniques has led to increased identification of pathogenic variants in CAS genes. In an as yet uncharacterized Italian cohort, we aimed both to identify new pathogenic gene variants associated with CAS, and to confirm the disease-related role of genes already reported by others. We also set out to refine the clinical and neurodevelopmental characterization of affected children, with the aim of identifying specific, gene-related phenotypes.

Methods

In a single-center study aiming to explore the genetic etiology of CAS in a cohort of 69 Italian children, WES was performed in the families of the 34 children found to have no copy number variants. Each of these families had only one child affected by CAS.

Results

High-confidence (HC) gene variants were identified in 7/34 probands, in two of whom they affected KAT6A and CREBBP, thus confirming the involvement of these genes in speech impairment. The other probands carried variants in low-confidence (LC) genes, and 20 of these variants occurred in genes not previously reported as associated with CAS. UBA6, ZFHX4, and KAT6A genes were found to be more enriched in the CAS cohort compared to control individuals. Our results also showed that most HC genes are involved in epigenetic mechanisms and are expressed in brain regions linked to language acquisition processes.

Conclusion

Our findings confirm a relatively high diagnostic yield in Italian patients.

A Pilot Study Based on the Correlation Between Whole Exome and Transcriptome Reveals Potent Variants in the Indian Population of Cervical Cancer

Cervical malignancy (CC) is the 2nd most prevalent malignancy among females, leading to cancer mortality. Primary detection of CC tumors results in an improved prognosis. CC is a malignant gynecological tumor, with few treatment options. New diagnostic and therapeutic agents are required to expand patient survival and quality of life. If CC tumors can be found at an early stage, the prognosis is much brighter. New diagnostic and therapeutic agents are needed to increase patient survival and quality of life. In this work, we performed whole-exome sequencing utilizing V5 (Illumina platform) 10 samples, 5 control and 5 CC tumour tissue, and we compared the results with transcriptome studies. KMT2C variations were shown to be among the most vicious in this analysis. From an Indian viewpoint, we found a plethora of SNVs and mutations, including those with known, unknown, and possible effects on health. Based on our findings, we know that the KMT2C gene is on chr. Seven and in exon 8, all three recognized variants are missense, synonymous, coding synonymous, non-coding variants, and GnomAD MAF (- 0.05). The variation at position (7:152265091, T > A, SNV 62478356) in KMT2C is unique, potent, and pathogenic. The missense coding transcript CIQTNF maps to chromosome 7 and displays T > C SNV. In addition, we performed single strand conformational polymorphism analysis on 64 samples and further confirmed them using Sanger sequencing to understand and verify the mutations. KMT2C shows a log FC value of - 1.16. Understanding emerging harmful mutations from an Indian viewpoint is facilitated by our bioinformatics-based, extensive correlation studies of WES analysis. Potentially harmful and new mutations were found in our preliminary analysis; among these ten top mutated genes, KMT2C and CIQTNF were altered in ten cases of CC with an Indian phenotype.

Pathogenic variants in KMT2C result in a neurodevelopmental disorder distinct from Kleefstra and Kabuki syndromes

Trithorax-related H3K4 methyltransferases, KMT2C and KMT2D, are critical epigenetic modifiers. Haploinsufficiency of KMT2C was only recently recognized as a cause of neurodevelopmental disorder (NDD), so the clinical and molecular spectrums of the KMT2C-related NDD (now designated as Kleefstra syndrome 2) are largely unknown. We ascertained 98 individuals with rare KMT2C variants, including 75 with protein-truncating variants (PTVs). Notably, ∼15% of KMT2C PTVs were inherited. Although the most highly expressed KMT2C transcript consists of only the last four exons, pathogenic PTVs were found in almost all the exons of this large gene. KMT2C variant interpretation can be challenging due to segmental duplications and clonal hematopoesis-induced artifacts. Using samples from 27 affected individuals, divided into discovery and validation cohorts, we generated a moderate strength disorder-specific KMT2C DNA methylation (DNAm) signature and demonstrate its utility in classifying non-truncating variants. Based on 81 individuals with pathogenic/likely pathogenic variants, we demonstrate that the KMT2C-related NDD is characterized by developmental delay, intellectual disability, behavioral and psychiatric problems, hypotonia, seizures, short stature, and other comorbidities. The facial module of PhenoScore, applied to photographs of 34 affected individuals, reveals that the KMT2C-related facial gestalt is significantly different from the general NDD population. Finally, using PhenoScore and DNAm signatures, we demonstrate that the KMT2C-related NDD is clinically and epigenetically distinct from Kleefstra and Kabuki syndromes. Overall, we define the clinical features, molecular spectrum, and DNAm signature of the KMT2C-related NDD and demonstrate they are distinct from Kleefstra and Kabuki syndromes highlighting the need to rename this condition.

A Genotype/Phenotype Study of KDM5B-Associated Disorders Suggests a Pathogenic Effect of Dominantly Inherited Missense Variants

Bi-allelic disruptive variants (nonsense, frameshift, and splicing variants) in KDM5B have been identified as causative for autosomal recessive intellectual developmental disorder type 65. In contrast, dominant variants, usually disruptive as well, have been more difficult to implicate in a specific phenotype, since some of them have been found in unaffected controls or relatives. Here, we describe individuals with likely pathogenic variants in KDM5B, including eight individuals with dominant missense variants. This study is a retrospective case series of 21 individuals with variants in KDM5B. We performed deep phenotyping and collected the clinical information and molecular data of these individuals' family members. We compared the phenotypes according to variant type and to those previously described in the literature. The most common features were developmental delay, impaired intellectual development, behavioral problems, autistic behaviors, sleep disorders, facial dysmorphism, and overgrowth. DD, ASD behaviors, and sleep disorders were more common in individuals with dominant disruptive KDM5B variants, while individuals with dominant missense variants presented more frequently with renal and skin anomalies. This study extends our understanding of the KDM5B-related neurodevelopmental disorder and suggests the pathogenicity of certain dominant KDM5B missense variants.

The Role of KDM2A and H3K36me2 Demethylation in Modulating MAPK Signaling During Neurodevelopment

Intellectual disability (ID) is a condition characterized by cognitive impairment and difficulties in adaptive functioning. In our research, we identified two de novo mutations (c.955C>T and c.732C>A) at the KDM2A locus in individuals with varying degrees of ID. In addition, by using the Gene4Denovo database, we discovered five additional cases of de novo mutations in KDM2A. The mutations we identified significantly decreased the expression of the KDM2A protein. To investigate the role of KDM2A in neural development, we used both 2D neural stem cell models and 3D cerebral organoids. Our findings demonstrated that the reduced expression of KDM2A impairs the proliferation of neural progenitor cells (NPCs), increases apoptosis, induces premature neuronal differentiation, and affects synapse maturation. Through ChIP-Seq analysis, we found that KDM2A exhibited binding to the transcription start site regions of genes involved in neurogenesis. In addition, the knockdown of KDM2A hindered H3K36me2 binding to the downstream regulatory elements of genes. By integrating ChIP-Seq and RNA-Seq data, we made a significant discovery of the core genes' remarkable enrichment in the MAPK signaling pathway. Importantly, this enrichment was specifically linked to the p38 MAPK pathway. Furthermore, disease enrichment analysis linked the differentially-expressed genes identified from RNA-Seq of NPCs and cerebral organoids to neurodevelopmental disorders such as ID, autism spectrum disorder, and schizophrenia. Overall, our findings suggest that KDM2A plays a crucial role in regulating the H3K36me2 modification of downstream genes, thereby modulating the MAPK signaling pathway and potentially impacting early brain development.

Rare de novo damaging DNA variants are enriched in attention-deficit/hyperactivity disorder and implicate risk genes

Research demonstrates the important role of genetic factors in attention-deficit/hyperactivity disorder (ADHD). DNA sequencing of families provides a powerful approach for identifying de novo (spontaneous) variants, leading to the discovery of hundreds of clinically informative risk genes for other childhood neurodevelopmental disorders. This approach has yet to be extensively leveraged in ADHD. We conduct whole-exome DNA sequencing in 152 families, comprising a child with ADHD and both biological parents, and demonstrate a significant enrichment of rare and ultra-rare de novo gene-damaging mutations in ADHD cases compared to unaffected controls. Combining these results with a large independent case-control DNA sequencing cohort (3206 ADHD cases and 5002 controls), we identify lysine demethylase 5B (KDM5B) as a high-confidence risk gene for ADHD and estimate that 1057 genes contribute to ADHD risk. Using our list of genes harboring ultra-rare de novo damaging variants, we show that these genes overlap with previously reported risk genes for other neuropsychiatric conditions and are enriched in several canonical biological pathways, suggesting early neurodevelopmental underpinnings of ADHD. This work provides insight into the biology of ADHD and demonstrates the discovery potential of DNA sequencing in larger parent-child trio cohorts.

Penetrance, variable expressivity and monogenic neurodevelopmental disorders

PURPOSE

Incomplete penetrance is observed for most monogenic diseases. However, for neurodevelopmental disorders, the interpretation of single and multi-nucleotide variants (SNV/MNVs) is usually based on the paradigm of complete penetrance.

METHOD

From 2020 to 2022, we proposed a collaboration study with the French molecular diagnosis for intellectual disability network. The aim was to recruit families for whom the index case, diagnosed with a neurodevelopmental disorder, was carrying a pathogenic or likely pathogenic variant for an OMIM morbid gene and inherited from an asymptomatic parent. Grandparents were analyzed when available for segregation study.

RESULTS

We identified 12 patients affected by a monogenic neurodevelopmental disorder caused by likely pathogenic or pathogenic variant (SNV/MNV) inherited from an asymptomatic parent. These genes were usually associated with de novo variants. The patients carried different variants (1 splice-site variant, 4 nonsense and 7 frameshift) in 11 genes: CAMTA1, MBD5, KMT2C, KMT2E, ZMIZ1, MN1, NDUFB11, CUL3, MED13, ARID2 and RERE. Grandparents have been tested in 6 families, and each time the variant was confirmed de novo in the healthy carrier parent.

CONCLUSION

Incomplete penetrance for SNV and MNV in neurodevelopmental disorders might be more frequent than previously thought. This point is crucial to consider for interpretation of variants, family investigation, genetic counseling, and prenatal diagnosis. Molecular mechanisms underlying this incomplete penetrance still need to be identified.

The Intellectual Disability Risk Gene Kdm5b Regulates Long-Term Memory Consolidation in the Hippocampus

The histone lysine demethylase KDM5B is implicated in recessive intellectual disability disorders, and heterozygous, protein-truncating variants in KDM5B are associated with reduced cognitive function in the population. The KDM5 family of lysine demethylases has developmental and homeostatic functions in the brain, some of which appear to be independent of lysine demethylase activity. To determine the functions of KDM5B in hippocampus-dependent learning and memory, we first studied male and female mice homozygous for a Kdm5b Δ ARID allele that lacks demethylase activity. Kdm5b Δ ARID/ Δ ARID mice exhibited hyperactivity and long-term memory deficits in hippocampus-dependent learning tasks. The expression of immediate early, activity-dependent genes was downregulated in these mice and hyperactivated upon a learning stimulus compared with wild-type (WT) mice. A number of other learning-associated genes were also significantly dysregulated in the Kdm5b Δ ARID/ Δ ARID hippocampus. Next, we knocked down Kdm5b specifically in the adult, WT mouse hippocampus with shRNA. Kdm5b knockdown resulted in spontaneous seizures, hyperactivity, and hippocampus-dependent long-term memory and long-term potentiation deficits. These findings identify KDM5B as a critical regulator of gene expression and synaptic plasticity in the adult hippocampus and suggest that at least some of the cognitive phenotypes associated with KDM5B gene variants are caused by direct effects on memory consolidation mechanisms.

Novel KMT5B variant associated with neurodevelopmental disorder in a Chinese family: A case report

Background

We report here the clinical and genetic features of KMT5B-related neurodevelopmental disorder caused by a novel heterozygous frameshift variant in KMT5B in a Chinese family.

Case presentation

A 7-year-old Chinese boy with mild-to-moderate intellectual disability, significant language impairment, motor disability, and coordination difficulties presented to our hospital because he "could not speak and did not look at others." He was diagnosed with autism spectrum disorder previously owing to developmental delays in cognition, language expression, and understanding. The child also had variable nonspecific features including macrocephaly, wide button-hole space and nasal bridge, low ear, social behavior disorder, and foot deformities. Exome sequencing (ES) revealed that both the proband and his younger brother had inherited a novel heterozygous frameshift variant c.438_439ins[ASD; KT192064.1:1_310] of the KMT5B gene from their father. Bioinformatics analysis showed that the novel mutation affected the structure of the KMT5B pre-SET domain, mainly in the α-helix region. According to the American College of Medical Genetics and Genomics (ACMG) guidelines, this type of variant was eventually determined to be likely pathogenic (PVS1+PM2_P).

Conclusions

Our investigation expands the mutation spectrum of KMT5B to help us to better understand KMT5B-related neurodevelopmental disorder.

The omics era: a nexus of untapped potential for Mendelian chromatinopathies

The OMICs cascade describes the hierarchical flow of information through biological systems. The epigenome sits at the apex of the cascade, thereby regulating the RNA and protein expression of the human genome and governs cellular identity and function. Genes that regulate the epigenome, termed epigenes, orchestrate complex biological signaling programs that drive human development. The broad expression patterns of epigenes during human development mean that pathogenic germline mutations in epigenes can lead to clinically significant multi-system malformations, developmental delay, intellectual disabilities, and stem cell dysfunction. In this review, we refer to germline developmental disorders caused by epigene mutation as "chromatinopathies". We curated the largest number of human chromatinopathies to date and our expanded approach more than doubled the number of established chromatinopathies to 179 disorders caused by 148 epigenes. Our study revealed that 20.6% (148/720) of epigenes cause at least one chromatinopathy. In this review, we highlight key examples in which OMICs approaches have been applied to chromatinopathy patient biospecimens to identify underlying disease pathogenesis. The rapidly evolving OMICs technologies that couple molecular biology with high-throughput sequencing or proteomics allow us to dissect out the causal mechanisms driving temporal-, cellular-, and tissue-specific expression. Using the full repertoire of data generated by the OMICs cascade to study chromatinopathies will provide invaluable insight into the developmental impact of these epigenes and point toward future precision targets for these rare disorders.

Expansion of the Genotypic and Phenotypic Spectrum of ASH1L-Related Syndromic Neurodevelopmental Disorder

Pathogenic ASH1L variants have been reported in probands with broad phenotypic presentations, including intellectual disability, autism spectrum disorder, attention deficit hyperactivity disorder, seizures, congenital anomalies, and other skeletal, muscular, and sleep differences. Here, we review previously published individuals with pathogenic ASH1L variants and report three further probands with novel ASH1L variants and previously unreported phenotypic features, including mixed receptive language disorder and gait disturbances. These novel data from the Brain Gene Registry, an accessible repository of clinically derived genotypic and phenotypic data, have allowed for the expansion of the phenotypic and genotypic spectrum of this condition.

Variants in ZFX are associated with an X-linked neurodevelopmental disorder with recurrent facial gestalt

Pathogenic variants in multiple genes on the X chromosome have been implicated in syndromic and non-syndromic intellectual disability disorders. ZFX on Xp22.11 encodes a transcription factor that has been linked to diverse processes including oncogenesis and development, but germline variants have not been characterized in association with disease. Here, we present clinical and molecular characterization of 18 individuals with germline ZFX variants. Exome or genome sequencing revealed 11 variants in 18 subjects (14 males and 4 females) from 16 unrelated families. Four missense variants were identified in 11 subjects, with seven truncation variants in the remaining individuals. Clinical findings included developmental delay/intellectual disability, behavioral abnormalities, hypotonia, and congenital anomalies. Overlapping and recurrent facial features were identified in all subjects, including thickening and medial broadening of eyebrows, variations in the shape of the face, external eye abnormalities, smooth and/or long philtrum, and ear abnormalities. Hyperparathyroidism was found in four families with missense variants, and enrichment of different tumor types was observed. In molecular studies, DNA-binding domain variants elicited differential expression of a small set of target genes relative to wild-type ZFX in cultured cells, suggesting a gain or loss of transcriptional activity. Additionally, a zebrafish model of ZFX loss displayed an altered behavioral phenotype, providing additional evidence for the functional significance of ZFX. Our clinical and experimental data support that variants in ZFX are associated with an X-linked intellectual disability syndrome characterized by a recurrent facial gestalt, neurocognitive and behavioral abnormalities, and an increased risk for congenital anomalies and hyperparathyroidism.

Neurodevelopmental functions of CHD8: new insights and questions

Heterozygous, de novo, loss-of-function variants of the CHD8 gene are associated with a high penetrance of autism and other neurodevelopmental phenotypes. Identifying the neurodevelopmental functions of high-confidence autism risk genes like CHD8 may improve our understanding of the neurodevelopmental mechanisms that underlie autism spectrum disorders. Over the last decade, a complex picture of pleiotropic CHD8 functions and mechanisms of action has emerged. Multiple brain and non-brain cell types and progenitors appear to be affected by CHD8 haploinsufficiency. Behavioural, cellular and synaptic phenotypes are dependent on the nature of the gene mutation and are modified by sex and genetic background. Here, I review some of the CHD8-interacting proteins and molecular mechanisms identified to date, as well as the impacts of CHD8 deficiency on cellular processes relevant to neurodevelopment. I endeavour to highlight some of the critical questions that still require careful and concerted attention over the next decade to bring us closer to the goal of understanding the salient mechanisms whereby CHD8 deficiency causes neurodevelopmental disorders.

Increased burden of rare protein-truncating variants in constrained, brain-specific and synaptic genes in extremely impulsively violent males with antisocial personality disorder

The genetic correlates of extreme impulsive violence are poorly understood, and there have been few studies that have characterized a large group of affected individuals both clinically and genetically. We performed whole exome sequencing (WES) in 290 males with the life-course-persistent, extremely impulsively violent form of antisocial personality disorder (APD) and analyzed the spectrum of rare protein-truncating variants (rPTVs). Comparisons were made with 314 male controls and publicly available genotype data. Functional annotation tools were used for biological interpretation. Participants were significantly more likely to harbor rPTVs in genes that are intolerant to loss-of-function variants (odds ratio [OR] 2.06; p < 0.001), specifically expressed in brain (OR 2.80; p = 0.036) and enriched for those involved in neurotransmitter transport and synaptic processes. In 60 individuals (20%), we identified rPTVs that we classified as clinically relevant based on their clinical associations, biological function and gene expression patterns. Of these, 37 individuals harbored rPTVs in 23 genes that are associated with a monogenic neurological disorder, and 23 individuals harbored rPTVs in 20 genes reportedly intolerant to loss-of-function variants. The analysis presents evidence in support of a model where presence of either one or several private, functionally relevant mutations contribute significantly to individual risk of life-course-persistent APD and reveals multiple individuals who could be affected by clinically unrecognized neuropsychiatric Mendelian disease. Thus, Mendelian diseases and increased rPTV burden may represent important factors for the development of extremely impulsive violent life-course-persistent forms of APD irrespective of their clinical presentation.

Novel germline variants in KMT2C in Chinese patients with Kleefstra syndrome-2

Kleefstra syndrome (KLEFS) refers to a rare inherited neurodevelopmental disorder characterized by intellectual disability (ID), language and motor delays, behavioral abnormalities, abnormal facial appearance, and other variable clinical features. KLEFS is subdivided into two subtypes: Kleefstra syndrome-1 (KLEFS1, OMIM: 610253), caused by a heterozygous microdeletion encompassing the Euchromatic Histone Lysine Methyltransferase 1 (EHMT1) gene on chromosome 9q34.3 or pathogenic variants in the EHMT1 gene, and Kleefstra syndrome-2 (KLEFS2, OMIM: 617768), caused by pathogenic variants in the KMT2C gene. More than 100 cases of KLEFS1 have been reported with pathogenic variants in the EHMT1 gene. However, only 13 patients with KLEFS2 have been reported to date. In the present study, five unrelated Chinese patients were diagnosed with KLEFS2 caused by KMT2C variants through whole-exome sequencing (WES). We identified five different variants of the KMT2C gene in these patients: c.9166C>T (p.Gln3056*), c.9232_9247delCAGCGATCAGAACCGT (p.Gln3078fs*13), c.5068dupA (p.Arg1690fs*10), c.10815_10819delAAGAA (p.Lys3605fs*7), and c.6911_6912insA (p.Met2304fs*8). All five patients had a clinical profile similar to that of patients with KLEFS2. To analyze the correlation between the genotype and phenotype of KLEFS2, we examined 18 variants and their associated phenotypes in 18 patients with KLEFS2. Patients carrying KMT2C variants presented with a wide range of phenotypic defects and an extremely variable phenotype. We concluded that the core phenotypes associated with KMT2C variants were intellectual disability, facial dysmorphisms, language and motor delays, behavioral abnormalities, hypotonia, short stature, and weight loss. Additionally, sex may be one factor influencing the outcome. Our findings expand the phenotypic and genetic spectrum of KLEFS2 and help to clarify the genotype-phenotype correlation.

An Updated Review on the Significance of DNA and Protein Methyltransferases and De-methylases in Human Diseases: From Molecular Mechanism to Novel Therapeutic Approaches

Epigenetic mechanisms are crucial in regulating gene expression. These mechanisms include DNA methylation and histone modifications, like methylation, acetylation, and phosphorylation. DNA methylation is associated with gene expression suppression; however, histone methylation can stimulate or repress gene expression depending on the methylation pattern of lysine or arginine residues on histones. These modifications are key factors in mediating the environmental effect on gene expression regulation. Therefore, their aberrant activity is associated with the development of various diseases. The current study aimed to review the significance of DNA and histone methyltransferases and demethylases in developing various conditions, like cardiovascular diseases, myopathies, diabetes, obesity, osteoporosis, cancer, aging, and central nervous system conditions. A better understanding of the epigenetic roles in developing diseases can pave the way for developing novel therapeutic approaches for affected patients.

A novel 11 base pair deletion in KMT2C resulting in Kleefstra syndrome 2

BACKGROUND

Haploinsufficiency of the Lysine Methyltransferase 2C (KMT2C) gene results in the autosomal dominant disorder, Kleefstra syndrome 2. It is an extremely rare neurodevelopmental condition, with 14 previous reports describing varied clinical manifestations including dysmorphic features, delayed psychomotor development and delayed growth.

METHODS

Here, we describe a female with global developmental delay, attention deficit disorder, dyspraxia, short stature and subtle non-specific dysmorphic features. To identify causative mutations, whole exome sequencing was performed on the proband and her younger brother with discrete clinical presentation.

RESULTS

Whole exome sequencing identified a novel de novo heterozygous 11 bp deletion in KMT2C (c.1759_1769del), resulting in a frameshift mutation and early termination of the protein (p.Gln587SerfsTer7). This variant is the second-most N-terminal reported mutation, located 4171 amino acids upstream of the critical enzymatically active SET domain (required for chromatin modification and histone methylation).

CONCLUSION

The majority of the other reported mutations are frameshift mutations upstream of the SET domain and are predicted to result in protein truncation. It is thought that truncation of the SET domain, results functionally in an inability to modify chromatin through histone methylation. This report expands the clinical and genetic characterisation of Kleefstra syndrome 2.

A. Epigenetic regulation of craniofacial development and disease

BACKGROUND

The formation of the craniofacial complex relies on proper neural crest development. The gene regulatory networks (GRNs) and signaling pathways orchestrating this process have been extensively studied. These GRNs and signaling cascades are tightly regulated as alterations to any stage of neural crest development can lead to common congenital birth defects, including multiple syndromes affecting facial morphology as well as nonsyndromic facial defects, such as cleft lip with or without cleft palate. Epigenetic factors add a hierarchy to the regulation of transcriptional networks and influence the spatiotemporal activation or repression of specific gene regulatory cascades; however less is known about their exact mechanisms in controlling precise gene regulation.

AIMS

In this review, we discuss the role of epigenetic factors during neural crest development, specifically during craniofacial development and how compromised activities of these regulators contribute to congenital defects that affect the craniofacial complex.

Structural basis of nucleosomal H4K20 recognition and methylation by SUV420H1 methyltransferase

Histone lysine methyltransferase SUV420H1, which is responsible for site-specific di-/tri-methylation of histone H4 lysine 20 (H4K20), has crucial roles in DNA-templated processes, including DNA replication, DNA damage repair, and chromatin compaction. Its mutations frequently occur in human cancers. Nucleosomes containing the histone variant H2A.Z enhance the catalytic activities of SUV420H1 on H4K20 di-methylation deposition, regulating early replication origins. However, the molecular mechanism by which SUV420H1 specifically recognizes and deposits H4K20 methyl marks on nucleosomes remains poorly understood. Here we report the cryo-electron microscopy structures of SUV420H1 associated with H2A-containing nucleosome core particles (NCPs), and H2A.Z-containing NCPs. We find that SUV420H1 makes extensive site-specific contacts with histone and DNA regions. SUV420H1 C-terminal domain recognizes the H2A-H2B acidic patch of NCPs through its two arginine anchors, thus enabling H4K20 insertion for catalysis specifically. We also identify important residues increasing the catalytic activities of SUV420H1 bound to H2A.Z NCPs. In vitro and in vivo functional analyses reveal that multiple disease-associated mutations at the interfaces are essential for its catalytic activity and chromatin state regulation. Together, our study provides molecular insights into the nucleosome-based recognition and methylation mechanisms of SUV420H1, and a structural basis for understanding SUV420H1-related human disease.

Detection of Modified Histones from Oral Mucosa of a Patient with DYT-KMT2B Dystonia

Introduction

DYT-KMT2B is a rare childhood-onset, hereditary movement disorder typically characterized by lower-limb dystonia and subsequently spreads into the craniocervical and laryngeal muscles. Recently, KMT2B-encoding lysine (K)-specific histone methyltransferase 2B was identified as the causative gene for DYT-KMT2B, also known as DYT28. In addition to the fact that many physicians do not have sufficient experience or knowledge of hereditary dystonia, the clinical features of DYT-KMT2B overlap with those of other hereditary dystonia, and limited clinical biomarkers make the diagnosis difficult.

Methods

Histone proteins were purified from the oral mucosa of patients with de novo KMT2B mutation causing premature stop codon, and then trimethylated fourth lysine residue of histone H3 (H3K4me3) which was catalyzed by KMT2B was analyzed by immunoblotting with specific antibody. We further analyzed the significance of H3K4me3 in patients with DYT-KMT2B using publicly available datasets.

Results

H3K4me3 histone mark was markedly lower in the patient than in the control group. Additionally, a reanalysis of publicly available datasets concerning DNA methylation also demonstrated that KMT2B remained inactive in DYT-KMT2B.

Discussion

Although only one case was studied due to the rarity of the disease, the reduction of H3K4me3 in the patient's biological sample supports the dysfunction of KMT2B in DYT-KMT2B. Together with informatics approaches, our results suggest that KMT2B haploinsufficiency contributes to the DYT-KMT2B pathogenic process.

Rare de novo gain-of-function missense variants in DOT1L are associated with developmental delay and congenital anomalies

Misregulation of histone lysine methylation is associated with several human cancers and with human developmental disorders. DOT1L is an evolutionarily conserved gene encoding a lysine methyltransferase (KMT) that methylates histone 3 lysine-79 (H3K79) and was not previously associated with a Mendelian disease in OMIM. We have identified nine unrelated individuals with seven different de novo heterozygous missense variants in DOT1L through the Undiagnosed Disease Network (UDN), the SickKids Complex Care genomics project, and GeneMatcher. All probands had some degree of global developmental delay/intellectual disability, and most had one or more major congenital anomalies. To assess the pathogenicity of the DOT1L variants, functional studies were performed in Drosophila and human cells. The fruit fly DOT1L ortholog, grappa, is expressed in most cells including neurons in the central nervous system. The identified DOT1L variants behave as gain-of-function alleles in flies and lead to increased H3K79 methylation levels in flies and human cells. Our results show that human DOT1L and fly grappa are required for proper development and that de novo heterozygous variants in DOT1L are associated with a Mendelian disease.

Identification of two novel autism genes, TRPC4 and SCFD2, in Qatar simplex families through exome sequencing

This study investigated the genetic underpinnings of autism spectrum disorder (ASD) in a Middle Eastern cohort in Qatar using exome sequencing. The study identified six candidate autism genes in independent simplex families, including both four known and two novel autosomal dominant and autosomal recessive genes associated with ASD. The variants consisted primarily of de novo and homozygous missense and splice variants. Multiple individuals displayed more than one candidate variant, suggesting the potential involvement of digenic or oligogenic models. These variants were absent in the Genome Aggregation Database (gnomAD) and exhibited extremely low frequencies in the local control population dataset. Two novel autism genes, TRPC4 and SCFD2, were discovered in two Qatari autism individuals. Furthermore, the D651A substitution in CLCN3 and the splice acceptor variant in DHX30 were identified as likely deleterious mutations. Protein modeling was utilized to evaluate the potential impact of three missense variants in DEAF1, CLCN3, and SCFD2 on their respective structures and functions, which strongly supported the pathogenic natures of these variants. The presence of multiple de novo mutations across trios underscored the significant contribution of de novo mutations to the genetic etiology of ASD. Functional assays and further investigations are necessary to confirm the pathogenicity of the identified genes and determine their significance in ASD. Overall, this study sheds light on the genetic factors underlying ASD in Qatar and highlights the importance of considering diverse populations in ASD research.