Autism spectrum disorder recurrence, resulting of germline mosaicism for a CHD2 gene missense variant

Clinical analysis of five CHD2 gene mutations in Chinese children with epilepsy

INTRODUCTION

Increasing evidence reveals critical roles for CHD2 in children with developmental and epileptic encephalopathy.

OBJECTIVES

The aim was to present clinical analysis results of five cases with CHD2 mutations and 157 reported cases with non-copy number variations (non-CNV) of CHD2.

METHODS

This study recruited pediatric epilepsy patients with CHD2 mutations and clinical data from November 2016 to October 2023 in the Linyi People's Hospital, China. Whole-exome and gene panel sequencing were employed to find mutations. The HGMD and PubMed databases were examined for documented cases that had CHD2 mutations.

RESULTS

This study reports five cases with CHD2 mutations: c.3543T > A, c.1850A > G, c.2536C > T, c.4233_4236del, c.3782G > C. Three novel mutations (c.3543T > A, c.1850A > G, c.2536C > T) have never been reported. c.4233_4236del has been reported in three cases, indicating that this locus may be a mutation hotspot. c.3782G > C has been reported in one case. All five patients had seizures before the age of four. Three patients had varying degrees of developmental delay, and four patients had varying degrees of intellectual disability. All of them had controlled seizures after Valproic acid (VPA) monotherapy or VPA in combination with other medications. Furthermore, we reviewed 157 reported cases having non-CNV mutations of CHD2. Most mutations of these cases were de novo. Epilepsy, developmental delay, and intellectual disability were the typical clinical phenotypes. We also found a significant clustering of the mutations near the C-terminus of the CHD2 protein (P < 0.001).

CONCLUSION

This study reports new CHD2 genotypes and analyzes reported CHD2 mutation cases. Given its significance in epileptic encephalopathies, research on the CHD2 gene may provide new insights into epileptogenesis.

Low-grade parental gonosomal mosaicism in CHD2 siblings with Smith-Magenis-like syndrome

Loss-of-function CHD2 (chromodomain helicase DNA-binding protein 2) mutations are associated with a spectrum of neurodevelopmental disorders often including early-onset generalized seizures, photosensitivity, and epileptic encephalopathies. Patients show psychomotor delay/intellectual disability (ID), autistic features, and behavior disorders, such as aggression and impulsivity. Most reported cases are sporadic with description of germline mosaicism only in two families. We detect the first case of parental gonosomal CHD2 mosaicism disclosed by two brothers showing mild ID, born to healthy parents. The eldest brother has a history of drug-controlled generalized tonic-clonic seizures and displays sleep disorder and aggressive behavior suggestive of Smith-Magenis syndrome (SMS). Analysis of brothers' DNAs by next-generation sequencing (NGS) custom gene panel for pediatric epilepsy and/or ID disclosed in both the same pathogenic CHD2 variant. Additional NGS experiment on genomic DNA from parents' peripheral blood and from buccal swab raised the suspicion of low-grade gonosomal mosaicism in the unaffected mother subsequently confirmed by digital polymerase chain reaction (dPCR). This report underlines as worthwhile CHD2 screening in individuals presenting ID/developmental delay, with/without epilepsy, and behavior and sleep disorders suggestive of SMS. Detecting a CHD2 variant should prime testing probands' parents by NGS coupled to dPCR on different tissues to exclude/confirm gonosomal mosaicism and define the recurrence risk.

CHD2 pathogenic nonsense variant in a three-generation family with variable phenotype and a paracentric inversion 16: Case report

Chromosomal inversions are usually balanced structural chromosomal rearrangements that do not have an impact on the clinical phenotype of a carrier. The main clinical consequence of inversions is the risk for unbalanced gametes and offspring with severe phenotypes. Rarely though, inversions are associated with a phenotype, mainly due to submicroscopic Copy Number Variants (CNVs) or disruption at the breakpoints of a functionally important gene and/or genomic elements. In this study, a paracentric inversion of chromosome 16 [inv(16)(q22.3q24.1)] was identified in a three-generation family with discordant phenotypes with/without epilepsy and/or intellectual impairment, as well as with an unaffected carrier. This finding was confirmed by fluorescence in situ hybridization (FISH). Genetic investigation, initially with chromosomal microarray (CMA), did not reveal any copy number variants. Finally, Clinical Exome Sequencing (CES), detected the presence of a pathogenic nonsense variant (rs797044912) in the Chromodomain Helicase DNA-binding protein 2 (CHD2) gene [NM_001271.4:c.5035C>T p.(Arg1679Ter)]. CHD2 pathogenic variants have been associated with Developmental and Epileptic Encephalopathy-94 (DEE-94), a rare yet severe condition, characterized by developmental delay, seizures with an early onset, intellectual impairment, autism spectrum disorder, and sometimes behavioral issues. Family testing showed that the variant segregated with phenotypic heterogeneity in the affected individuals and appears to be causative. To the best of our knowledge, this is the first CHD2 pathogenic variant segregating in a three-generation family and the fourth familial case reported. These results further support our previous findings that familial, balanced rearrangements with discordant phenotypes in the same family are, in the vast majority, coincidental.

Expanding the genetic and phenotypic spectrum of CHD2-related disease: From early neurodevelopmental disorders to adult-onset epilepsy

CHD2 encodes the chromodomain helicase DNA-binding protein 2, an ATP-dependent enzyme that acts as a chromatin remodeler. CHD2 pathogenic variants have been associated with various early onset phenotypes including developmental and epileptic encephalopathy, self-limiting or pharmacoresponsive epilepsies and neurodevelopmental disorders without epilepsy. We reviewed 84 previously reported patients carrying 76 different CHD2 pathogenic or likely pathogenic variants and describe 18 unreported patients carrying 12 novel pathogenic or likely pathogenic variants, two recurrent likely pathogenic variants (in two patients each), three previously reported pathogenic variants, one gross deletion. We also describe a novel phenotype of adult-onset pharmacoresistant epilepsy, associated with a novel CHD2 missense likely pathogenic variant, located in an interdomain region. A combined review of previously published and our own observations indicates that although most patients (72.5%) carry truncating CHD2 pathogenic variants, CHD2-related phenotypes encompass a wide spectrum of conditions with developmental delay/intellectual disability (ID), including prominent language impairment, attention deficit hyperactivity disorder and autistic spectrum disorder. Epilepsy is present in 92% of patients with a median age at seizure onset of 2 years and 6 months. Generalized epilepsy types are prevalent and account for 75.5% of all epilepsies, with photosensitivity being a common feature and adult-onset nonsyndromic epilepsy a rare presentation. No clear genotype-phenotype correlation has emerged.

CHD2-related epilepsy: novel mutations and new phenotypes

The aim of this report was to refine the genotypes and phenotypes of chromodomain helicase DNA-binding protein 2 (CHD2)-related epilepsy. Seventeen patients with CHD2 mutations were enrolled. CHD2 mutations were identified by application of next-generation sequencing of epilepsy or whole exome sequencing. Sixteen mutations were identified, among which 15 have not yet been reported. Thirteen mutations were de novo. Age at seizure onset ranged from 3 months to 10 years 5 months. Seizures observed were generalized tonic-clonic, myoclonic, atonic, atypical absence, focal, and myoclonic-atonic. Epileptic spasms occurred in two patients. Developmental disability was present in 14 patients. Autism features were observed in seven patients. Video electroencephalogram was abnormal in 15 patients. Five patients were diagnosed with non-specific epileptic encephalopathy, two with epilepsy with myoclonic-atonic seizures, two with Lennox-Gastaut syndrome, two with febrile seizures plus, and one with West syndrome. Seizures were controlled in nine patients. Q1392TfsX17 may be a hot-spot mutation of CHD2. West syndrome was observed as a new phenotype of CHD2 mutation. The severity of the phenotypes of CHD2 mutations ranged from mild febrile seizures to severe epileptic encephalopathy. WHAT THIS PAPER ADDS: Q1392TfsX17 maybe the hot-spot mutation of CHD2. West syndrome could be a new phenotype of CHD2 mutation.

Chromatin remodeling dysfunction extends the etiological spectrum of schizophrenia: a case report

BACKGROUND

The role of deleterious copy number variations in schizophrenia is well established while data regarding pathogenic variations remain scarce. We report for the first time a case of schizophrenia in a child with a pathogenic mutation of the chromodomain helicase DNA binding protein 2 (CHD2) gene.

CASE PRESENTATION

The proband was the second child of unrelated parents. Anxiety and sleep disorders appeared at the age of 10 months. He presented febrile seizures and, at the age of 8, two generalized tonic-clonic seizures. At the age of 10, emotional withdrawal emerged, along with a flat affect, disorganization and paranoid ideation, without seizures. He began to talk and giggle with self. Eventually, the patient presented daily auditory and visual hallucinations. The diagnosis of childhood onset schizophrenia (DSM V) was then evoked. Brain imaging was unremarkable. Wakefulness electroencephalography showed a normal background and some bilateral spike-wave discharges that did not explain the psychosis features. A comparative genomic hybridization array (180 K, Agilent, Santa Clara, CA, USA) revealed an 867-kb 16p13.3 duplication, interpreted as a variant of unknown significance confirmed by a quantitative PCR that also showed its maternal inheritance. Risperidone (1,5 mg per day), led to clinical improvement. At the age of 11, an explosive relapse of epilepsy occurred with daily seizures of various types. The sequencing of a panel for monogenic epileptic disorders and Sanger sequencing revealed a de novo pathogenic heterozygous transition in CHD2 (NM_001271.3: c.4003G > T).

CONCLUSIONS

This case underlines that schizophrenia may be, sometimes, underpinned by a Mendelian disease. It addresses the question of systematic genetic investigations in the presence of warning signs such as a childhood onset of the schizophrenia or a resistant epilepsy. It points that, in the absence of pathogenic copy number variation, the investigations should also include a search for pathogenic variations, which means that some of the patients with schizophrenia should benefit from Next Generation Sequencing tools. Last but not least, CHD2 encodes a member of the chromodomain helicase DNA-binding (CHD) family involved in chromatin remodeling. This observation adds schizophrenia to the phenotypic spectrum of chromodomain remodeling disorders, which may lead to innovative therapeutic approaches.

Autism-linked CHD gene expression patterns during development predict multi-organ disease phenotypes

Recent large-scale exome sequencing studies have identified mutations in several members of the CHD (Chromodomain Helicase DNA-binding protein) gene family in neurodevelopmental disorders. Mutations in the CHD2 gene have been linked to developmental delay, intellectual disability, autism and seizures, CHD8 mutations to autism and intellectual disability, whereas haploinsufficiency of CHD7 is associated with executive dysfunction and intellectual disability. In addition to these neurodevelopmental features, a wide range of other developmental defects are associated with mutants of these genes, especially with regards to CHD7 haploinsufficiency, which is the primary cause of CHARGE syndrome. Whilst the developmental expression of CHD7 has been reported previously, limited information on the expression of CHD2 and CHD8 during development is available. Here, we compare the expression patterns of all three genes during mouse development directly. We find high, widespread expression of these genes at early stages of development that gradually becomes restricted during later developmental stages. Chd2 and Chd8 are widely expressed in the developing central nervous system (CNS) at all stages of development, with moderate expression remaining in the neocortex, hippocampus, olfactory bulb and cerebellum of the postnatal brain. Similarly, Chd7 expression is seen throughout the CNS during late embryogenesis and early postnatal development, with strong enrichment in the cerebellum, but displays low expression in the cortex and neurogenic niches in early life. In addition to expression in the brain, novel sites of Chd2 and Chd8 expression are reported. These findings suggest additional roles for these genes in organogenesis and predict that mutation of these genes may predispose individuals to a range of other, non-neurological developmental defects.

Chromatin Remodeling Proteins in Epilepsy: Lessons From CHD2-Associated Epilepsy

The chromodomain helicase DNA-binding (CHD) family of proteins are ATP-dependent chromatin remodelers that contribute to the reorganization of chromatin structure and deposition of histone variants necessary to regulate gene expression. CHD proteins play an important role in neurodevelopment, as pathogenic variants in CHD1, CHD2, CHD4, CHD7 and CHD8 have been associated with a range of neurological phenotypes, including autism spectrum disorder (ASD), intellectual disability (ID) and epilepsy. Pathogenic variants in CHD2 are associated with developmental epileptic encephalopathy (DEE) in humans, however little is known about how these variants contribute to this disorder. Of the nine CHD family members, CHD2 is the only one that leads to a brain-restricted phenotype when disrupted in humans. This suggests that despite being expressed ubiquitously, CHD2 has a unique role in human brain development and function. In this review, we will discuss the phenotypic spectrum of patients with pathogenic variants in CHD2, current animal models of CHD2 deficiency, and the role of CHD2 in proliferation, neurogenesis, neuronal differentiation, chromatin remodeling and DNA-repair. We also consider how CHD2 depletion can affect each of these biological mechanisms and how these defects may underpin neurodevelopmental disorders including epilepsy.