Targeted resequencing in epileptic encephalopathies identifies de novo mutations in CHD2 and SYNGAP1

Epilepsy as a Novel Phenotype of BPTF-Related Disorders

BACKGROUND

Neurodevelopmental disorder with dysmorphic facies and distal limb anomalies (NEDDFL) is associated to BPTF gene haploinsufficiency. Epilepsy was not included in the initial descriptions of NEDDFL, but emerging evidence indicates that epileptic seizures occur in some affected individuals. This study aims to investigate the electroclinical epilepsy features in individuals with NEDDFL.

METHODS

We enrolled individuals with BPTF-related seizures or interictal epileptiform discharges (IEDs) on electroencephalography (EEG). Demographic, clinical, genetic, raw EEG, and neuroimaging data as well as response to antiseizure medication were assessed.

RESULTS

We studied 11 individuals with a null variant in BPTF, including five previously unpublished ones. Median age at last observation was 9 years (range: 4 to 43 years). Eight individuals had epilepsy, one had a single unprovoked seizure, and two showed IEDs only. Key features included (1) early childhood epilepsy onset (median 4 years, range: 10 months to 7 years), (2) well-organized EEG background (all cases) and brief bursts of spikes and slow waves (50% of individuals), and (3) developmental delay preceding seizure onset. Spectrum of epilepsy severity varied from drug-resistant epilepsy (27%) to isolated IEDs without seizures (18%). Levetiracetam was widely used and reduced seizure frequency in 67% of the cases.

CONCLUSIONS

Our study provides the first characterization of BPTF-related epilepsy. Early-childhood-onset epilepsy occurs in 19% of subjects, all presenting with a well-organized EEG background associated with generalized interictal epileptiform abnormalities in half of these cases. Drug resistance is rare.

Comprehensive network modeling approaches unravel dynamic enhancer-promoter interactions across neural differentiation

BACKGROUND

Increasing evidence suggests that a substantial proportion of disease-associated mutations occur in enhancers, regions of non-coding DNA essential to gene regulation. Understanding the structures and mechanisms of the regulatory programs this variation affects can shed light on the apparatuses of human diseases.

RESULTS

We collect epigenetic and gene expression datasets from seven early time points during neural differentiation. Focusing on this model system, we construct networks of enhancer-promoter interactions, each at an individual stage of neural induction. These networks serve as the base for a rich series of analyses, through which we demonstrate their temporal dynamics and enrichment for various disease-associated variants. We apply the Girvan-Newman clustering algorithm to these networks to reveal biologically relevant substructures of regulation. Additionally, we demonstrate methods to validate predicted enhancer-promoter interactions using transcription factor overexpression and massively parallel reporter assays.

CONCLUSIONS

Our findings suggest a generalizable framework for exploring gene regulatory programs and their dynamics across developmental processes; this includes a comprehensive approach to studying the effects of disease-associated variation on transcriptional networks. The techniques applied to our networks have been published alongside our findings as a computational tool, E-P-INAnalyzer. Our procedure can be utilized across different cellular contexts and disorders.

Diagnostic utility of DNA methylation analysis in genetically unsolved pediatric epilepsies and CHD2 episignature refinement

Sequence-based genetic testing identifies causative variants in ~ 50% of individuals with developmental and epileptic encephalopathies (DEEs). Aberrant changes in DNA methylation are implicated in various neurodevelopmental disorders but remain unstudied in DEEs. We interrogate the diagnostic utility of genome-wide DNA methylation array analysis on peripheral blood samples from 582 individuals with genetically unsolved DEEs. We identify rare differentially methylated regions (DMRs) and explanatory episignatures to uncover causative and candidate genetic etiologies in 12 individuals. Using long-read sequencing, we identify DNA variants underlying rare DMRs, including one balanced translocation, three CG-rich repeat expansions, and four copy number variants. We also identify pathogenic variants associated with episignatures. Finally, we refine the CHD2 episignature using an 850 K methylation array and bisulfite sequencing to investigate potential insights into CHD2 pathophysiology. Our study demonstrates the diagnostic yield of genome-wide DNA methylation analysis to identify causal and candidate variants as 2% (12/582) for unsolved DEE cases.

Solving the Etiology of Developmental and Epileptic Encephalopathy with Spike-Wave Activation in Sleep (D/EE-SWAS)

OBJECTIVE

To understand the etiological landscape and phenotypic differences between 2 developmental and epileptic encephalopathy (DEE) syndromes: DEE with spike-wave activation in sleep (DEE-SWAS) and epileptic encephalopathy with spike-wave activation in sleep (EE-SWAS).

METHODS

All patients fulfilled International League Against Epilepsy (ILAE) DEE-SWAS or EE-SWAS criteria with a Core cohort (n = 91) drawn from our Epilepsy Genetics research program, together with 10 etiologically solved patients referred by collaborators in the Expanded cohort (n = 101). Detailed phenotyping and analysis of molecular genetic results were performed. We compared the phenotypic features of individuals with DEE-SWAS and EE-SWAS. Brain-specific gene co-expression analysis was performed for D/EE-SWAS genes.

RESULTS

We identified the etiology in 42/91 (46%) patients in our Core cohort, including 29/44 (66%) with DEE-SWAS and 13/47 (28%) with EE-SWAS. A genetic etiology was identified in 31/91 (34%). D/EE-SWAS genes were highly co-expressed in brain, highlighting the importance of channelopathies and transcriptional regulators. Structural etiologies were found in 12/91 (13%) individuals. We identified 10 novel D/EE-SWAS genes with a range of functions: ATP1A2, CACNA1A, FOXP1, GRIN1, KCNMA1, KCNQ3, PPFIA3, PUF60, SETD1B, and ZBTB18, and 2 novel copy number variants, 17p11.2 duplication and 5q22 deletion. Although developmental regression patterns were similar in both syndromes, DEE-SWAS was associated with a longer duration of epilepsy and poorer intellectual outcome than EE-SWAS.

INTERPRETATION

DEE-SWAS and EE-SWAS have highly heterogeneous genetic and structural etiologies. Phenotypic analysis highlights valuable clinical differences between DEE-SWAS and EE-SWAS which inform clinical care and prognostic counseling. Our etiological findings pave the way for the development of precision therapies. ANN NEUROL 2024.

Multicenter retrospective study of patients with PCDH19-related epilepsy: The first Hungarian cohort

OBJECTIVE

PCDH19-related epilepsy occurs predominantly in girls and is caused by pathogenic variant of the protocadherin-19 gene. The initial seizures usually develop in association with fever, begin on average at 15 months of age, and often occur in clusters. Autistic symptoms, intellectual disability, and sleep disturbance are often associated.

METHODS

In our retrospective, multicenter study, we reviewed clinical data of nine children with epilepsy genetically confirmed to be associated with PCDH19.

RESULTS

In the Hungarian patient population aged 0-18 years, the prevalence of PCDH19-related epilepsy was found to be lower (1/100000 live births in females) than the reported international data (4-5/100000 live births in females). Four of our nine patients had positive family history of epilepsy (cousins, sister, and mother). We assessed brain anomalies in three patients (in one patient focal cortical dysplasia and left anterior cingulate dysgenesis, and in two children right or left hippocampal sclerosis) and in another three cases incidentally identified benign alterations on brain MRI were found. The first seizure presented as a cluster in seven out of nine children. In seven out of nine cases occurred status epilepticus. Six out of nine children had autistic symptoms and only one child had normal intellectual development. Seven of our patients were seizure free with combined antiseizure medication (ASM). The most effective ASMs were levetiracetam, valproate, and clobazam.

SIGNIFICANCE

The prevalence of PCDH19-related epilepsy is presumably underestimated because of the lack of widely performed molecular genetic evaluations. Molecular genetic testing including PCDH19 pathogenic variants is recommended for female patients with an onset of seizures before the age of 3 years.

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.

Context-dependent hyperactivity in syngap1a and syngap1b zebrafish models of SYNGAP1-related disorder

Background and aims

SYNGAP1-related disorder (SYNGAP1-RD) is a prevalent genetic form of Autism Spectrum Disorder and Intellectual Disability (ASD/ID) and is caused by de novo or inherited mutations in one copy of the SYNGAP1 gene. In addition to ASD/ID, SYNGAP1 disorder is associated with comorbid symptoms including treatment-resistant-epilepsy, sleep disturbances, and gastrointestinal distress. Mechanistic links between these diverse symptoms and SYNGAP1 variants remain obscure, therefore, our goal was to generate a zebrafish model in which this range of symptoms can be studied.

Methods

We used CRISPR/Cas9 to introduce frameshift mutations in the syngap1a and syngap1b zebrafish duplicates (syngap1ab) and validated these stable models for Syngap1 loss-of-function. Because SYNGAP1 is extensively spliced, we mapped splice variants to the two zebrafish syngap1a and b genes and identified mammalian-like isoforms. We then quantified locomotory behaviors in zebrafish syngap1ab larvae under three conditions that normally evoke different arousal states in wild-type larvae: aversive, high-arousal acoustic, medium-arousal dark, and low-arousal light stimuli.

Results

We show that CRISPR/Cas9 indels in zebrafish syngap1a and syngap1b produced loss-of-function alleles at RNA and protein levels. Our analyses of zebrafish Syngap1 isoforms showed that, as in mammals, zebrafish Syngap1 N- and C-termini are extensively spliced. We identified a zebrafish syngap1 α1-like variant that maps exclusively to the syngap1b gene. Quantifying locomotor behaviors showed that syngap1ab mutant larvae are hyperactive compared to wild-type but to differing degrees depending on the stimulus. Hyperactivity was most pronounced in low arousal settings, and hyperactivity was proportional to the number of mutant syngap1 alleles.

Limitations

Syngap1 loss-of-function mutations produce relatively subtle phenotypes in zebrafish compared to mammals. For example, while mouse Syngap1 homozygotes die at birth, zebrafish syngap1ab-/- survive to adulthood and are fertile, thus some aspects of symptoms in people with SYNGAP1-Related Disorder are not likely to be reflected in zebrafish.

Conclusion

Our data support mutations in zebrafish syngap1ab as causal for hyperactivity associated with elevated arousal that is especially pronounced in low-arousal environments.

Comprehensive network modeling approaches unravel dynamic enhancer-promoter interactions across neural differentiation

Background

Increasing evidence suggests that a substantial proportion of disease-associated mutations occur in enhancers, regions of non-coding DNA essential to gene regulation. Understanding the structures and mechanisms of regulatory programs this variation affects can shed light on the apparatuses of human diseases.

Results

We collected epigenetic and gene expression datasets from seven early time points during neural differentiation. Focusing on this model system, we constructed networks of enhancer-promoter interactions, each at an individual stage of neural induction. These networks served as the base for a rich series of analyses, through which we demonstrated their temporal dynamics and enrichment for various disease-associated variants. We applied the Girvan-Newman clustering algorithm to these networks to reveal biologically relevant substructures of regulation. Additionally, we demonstrated methods to validate predicted enhancer-promoter interactions using transcription factor overexpression and massively parallel reporter assays.

Conclusions

Our findings suggest a generalizable framework for exploring gene regulatory programs and their dynamics across developmental processes. This includes a comprehensive approach to studying the effects of disease-associated variation on transcriptional networks. The techniques applied to our networks have been published alongside our findings as a computational tool, E-P-INAnalyzer. Our procedure can be utilized across different cellular contexts and disorders.

Comprehensive phenotypes of patients with SYNGAP1-related disorder reveals high rates of epilepsy and autism

OBJECTIVE

To delineate the comprehensive phenotypic spectrum of SYNGAP1-related disorder in a large patient cohort aggregated through a digital registry.

METHODS

We obtained de-identified patient data from an online registry. Data were extracted from uploaded medical records. We reclassified all SYNGAP1 variants using American College of Medical Genetics criteria and included patients with pathogenic/likely pathogenic (P/LP) single nucleotide variants or microdeletions incorporating SYNGAP1. We analyzed neurodevelopmental phenotypes, including epilepsy, intellectual disability (ID), autism spectrum disorder (ASD), behavioral disorders, and gait dysfunction for all patients with respect to variant type and location within the SynGAP1 protein.

RESULTS

We identified 147 patients (50% male, median age 8 years) with P/LP SYNGAP1 variants from 151 individuals with data available through the database. One hundred nine were truncating variants and 22 were missense. All patients were diagnosed with global developmental delay (GDD) and/or ID, and 123 patients (84%) were diagnosed with epilepsy. Of those with epilepsy, 73% of patients had GDD diagnosed before epilepsy was diagnosed. Other prominent features included autistic traits (n = 100, 68%), behavioral problems (n = 100, 68%), sleep problems (n = 90, 61%), anxiety (n = 35, 24%), ataxia or abnormal gait (n = 69, 47%), sensory problems (n = 32, 22%), and feeding difficulties (n = 69, 47%). Behavioral problems were more likely in those patients diagnosed with anxiety (odds ratio [OR] 3.6, p = .014) and sleep problems (OR 2.41, p = .015) but not necessarily those with autistic traits. Patients with variants in exons 1-4 were more likely to have the ability to speak in phrases vs those with variants in exons 5-19, and epilepsy occurred less frequently in patients with variants in the SH3 binding motif.

SIGNIFICANCE

We demonstrate that the data obtained from a digital registry recapitulate earlier but smaller studies of SYNGAP1-related disorder and add additional genotype-phenotype relationships, validating the use of the digital registry. Access to data through digital registries broadens the possibilities for efficient data collection in rare diseases.

Epigenomic tomography for probing spatially defined chromatin state in the brain

Spatially resolved epigenomic profiling is critical for understanding biology in the mammalian brain. Single-cell spatial epigenomic assays were developed recently for this purpose, but they remain costly and labor intensive for examining brain tissues across substantial dimensions and surveying a collection of brain samples. Here, we demonstrate an approach, epigenomic tomography, that maps spatial epigenomes of mouse brain at the scale of centimeters. We individually profiled neuronal and glial fractions of mouse neocortex slices with 0.5 mm thickness. Tri-methylation of histone 3 at lysine 27 (H3K27me3) or acetylation of histone 3 at lysine 27 (H3K27ac) features across these slices were grouped into clusters based on their spatial variation patterns to form epigenomic brain maps. As a proof of principle, our approach reveals striking dynamics in the frontal cortex due to kainic-acid-induced seizure, linked with transmembrane ion transporters, exocytosis of synaptic vesicles, and secretion of neurotransmitters. Epigenomic tomography provides a powerful and cost-effective tool for characterizing brain disorders based on the spatial epigenome.

NUS1 Variants Cause Lennox-Gastaut Syndrome Related to Unfolded Protein Reaction Activation

NUS1 encodes the Nogo-B receptor, a critical regulator for unfolded protein reaction (UPR) signaling. Although several loss-of-function variants of NUS1 have been identified in patients with developmental and epileptic encephalopathy (DEE), the role of the NUS1 variant in Lennox-Gastaut syndrome (LGS), a severe child-onset DEE, remains unknown. In this study, we identified two de novo variants of NUS1, a missense variant (c.868 C > T/p.R290C) and a splice site variant (c.792-2 A > G), in two unrelated LGS patients using trio-based whole-exome sequencing performed in a cohort of 165 LGS patients. Both variants were absent in the gnomAD population and showed a significantly higher observed number of variants than expected genome-wide. The R290C variant was predicted to damage NUS1 and decrease its protein stability. The c.792-2 A > G variant caused premature termination of the protein. Knockdown of NUS1 activated the UPR pathway, resulting in apoptosis of HEK293T cells. Supplementing cells with expression of wild-type NUS1, but not the mutant (R290C), rescued UPR activation and apoptosis in NUS1 knockdown cells. Compared to wild-type Drosophila, seizure-like behaviors and excitability in projection neurons were significantly increased in Tango14 (homolog of human NUS1) knockdown and Tango14R290C/+ knock-in Drosophila. Additionally, abnormal development and a small body size were observed in both mutants. Activated UPR signaling was also detected in both mutants. Thus, NUS1 is a causative gene for LGS with dominant inheritance. The pathogenicity of these variants is related to the UPR signaling activation, which may be a common pathogenic mechanism of DEE.

Molecular and phenotypical findings of a novel de novo SYNGAP1 gene variant in an 11-year-old Iranian boy with intellectual disability

OBJECTIVE

Intellectual developmental disorder (IDD) type 5 is an autosomal dominant (AD) disorder and is characterized by intellectual disability (ID), psychomotor developmental delay, variable autism phenotypes, microcephaly, and seizure. IDD can be caused by mutations in the SYNGAP1 gene, which encodes a Ras GTPase-activating protein. This study revealed a novel de novo nonsense variant in SYNGAP1. The identification of such variants is essential for genetic counseling in patients and their families.

METHODS

Exome sequencing implicated the causative variant. Sanger sequencing and cosegregation analyses were used to confirm the variant. Multiple in silico analysis tools were applied to interpret the variant using the American College of Medical Genetics and Genomics and the Association for Molecular Pathology guidelines.

RESULTS

The de novo NM_006772.3(SYNGAP1):c.3685C>T variant was identified in an 11-year-old boy with severe intellectual disability, neurodevelopmental delay, speech disorder, ataxia, specific dysmorphic facial features, and aggressive behavior.

CONCLUSION

The current study findings expand the existing knowledge of variants in SYNGAP1 that have been previously associated with nonsyndromic intellectual disability and autism, extending the spectrum of phenotypes associated with this gene. The data have implications for genetic diagnosis and counseling in similar phenotypic presentations.

Interactions between Ras and Rap signaling pathways during neurodevelopment in health and disease

The Ras family of small GTPases coordinates tissue development by modulating cell proliferation, cell-cell adhesion, and cellular morphology. Perturbations of any of these key steps alter nervous system development and are associated with neurological disorders. While the underlying causes are not known, genetic mutations in Ras and Rap GTPase signaling pathways have been identified in numerous neurodevelopmental disorders, including autism spectrum, neurofibromatosis, intellectual disability, epilepsy, and schizophrenia. Despite diverse clinical presentations, intersections between these two signaling pathways may provide a better understanding of how deviations in neurodevelopment give rise to neurological disorders. In this review, we focus on presynaptic and postsynaptic functions of Ras and Rap GTPases. We highlight various roles of these small GTPases during synapse formation and plasticity. Based on genomic analyses, we discuss how disease-related mutations in Ras and Rap signaling proteins may underlie human disorders. Finally, we discuss how recent observations have identified molecular interactions between these pathways and how these findings may provide insights into the mechanisms that underlie neurodevelopmental disorders.

Novel syndromic neurodevelopmental disorder caused by de novo deletion of CHASERR, a long noncoding RNA

Genes encoding long non-coding RNAs (lncRNAs) comprise a large fraction of the human genome, yet haploinsufficiency of a lncRNA has not been shown to cause a Mendelian disease. CHASERR is a highly conserved human lncRNA adjacent to CHD2-a coding gene in which de novo loss-of-function variants cause developmental and epileptic encephalopathy. Here we report three unrelated individuals each harboring an ultra-rare heterozygous de novo deletion in the CHASERR locus. We report similarities in severe developmental delay, facial dysmorphisms, and cerebral dysmyelination in these individuals, distinguishing them from the phenotypic spectrum of CHD2 haploinsufficiency. We demonstrate reduced CHASERR mRNA expression and corresponding increased CHD2 mRNA and protein in whole blood and patient-derived cell lines-specifically increased expression of the CHD2 allele in cis with the CHASERR deletion, as predicted from a prior mouse model of Chaserr haploinsufficiency. We show for the first time that de novo structural variants facilitated by Alu-mediated non-allelic homologous recombination led to deletion of a non-coding element (the lncRNA CHASERR) to cause a rare syndromic neurodevelopmental disorder. We also demonstrate that CHD2 has bidirectional dosage sensitivity in human disease. This work highlights the need to carefully evaluate other lncRNAs, particularly those upstream of genes associated with Mendelian disorders.

Validation of targeted next-generation sequencing panels in a cohort of Polish patients with epilepsy: assessing variable performance across clinical endophenotypes and uncovering novel genetic variants

Introduction

Targeted Next-Generation Sequencing Panels (TNGSP) have become a standard in global clinical practice. Instead of questioning the necessity of next-generation sequencing in epilepsy patients, contemporary large-scale research focuses on factors such as the size of TNGSP, the comparative advantages of exome or genome-wide sequencing over TNGSP, and the impact of clinical, electrophysiological, and demographic variables on genetic test performance. This study aims to elucidate the demographic and clinical factors influencing the performance of TNGSP in 138 Polish patients with epilepsy, recognizing the pivotal role of genetic testing in guiding patient management and therapy.

Methods

A retrospective analysis was conducted on patients from a genetic clinic in Poznań, Poland, who underwent commercial gene panel studies at Invitae Corporation (USA) between 2020 and 2022. Patient groups were defined based on the age of onset of the first epileptic seizures, seizure type, gender, fever dependence of seizures, presence of intellectual disability or developmental delay, abnormalities in MRI, and the presence of dysmorphic features or congenital malformations. Seizure classification followed the 2017 ILAE criteria.

Results

Among the 138 patients, 30 (21.7%) exhibited a pathogenic or likely pathogenic variant, with a distribution of 20.7% in males and 22.5% in females. Diagnostic performance correlated with the patient's age at the onset of the first seizure and the type of seizure. Predominant variants were identified in the SCN1A, PRRT2, CDKL5, DEPDC5, TSC2, and SLC2A1 genes. Additionally, 12 genes (CACNA1A, SCN2A, GRIN2A, KCNQ2, CHD2, DYNC1H1, NEXMIF, SCN1B, DDX3X, EEF1A2, NPRL3, UBE3A) exhibited single instances of damage. Notably, novel variants were discovered in DEPDC5, SCN1A, TSC2, CDKL5, NPRL3, DYNC1H1, CHD2, and DDX3X.

Discussion

Identified variants were present in genes previously recognized in both European and non-European populations. A thorough examination of Variants of Uncertain Significance (VUSs), specifically focusing on gene copy number changes, may unveil more extensive chromosomal aberrations. The relatively frequent occurrence of pathological variants in X chromosome-linked genes in girls warrants further investigation, challenging the prevailing notion of male predominance in X-linked epilepsy.

A novel de novo frameshift variant in the CHD2 gene related to intellectual and developmental disability, seizures and speech problems

BACKGROUND

The chromodomain helicase DNA-binding protein 2 (CHD2) is a member of the ATP-dependent chromatin remodelling family of proteins, which are critical for the assembly and regulation of chromatin. De novo variants and deletions in the CHD2 gene have been associated with childhood-onset developmental and epileptic encephalopathies type 94 (DEE 94). This study reports a novel deleterious de novo heterozygous frameshift insertion variant in the CHD2 gene.

METHODS

The causative variant was diagnosed using whole-exome sequencing. Sanger sequencing and cosegregation analysis were applied to confirm the candidate variant. Multiple in silico analysis tools were employed to interpret the variant using the American College of Medical Genetics and Genomics and the Association for Molecular Pathology guidelines.

RESULTS

A de novo deleterious variant, NM_001271.4:c.1570dup (NP_001262.3:p.Ser524PhefsTer30), in the CHD2 gene, was identified in a 16-year-old boy with an intellectual and developmental disability, seizures and speech problems. The de novo occurrence of the variant was confirmed by segregation analysis in the family.

CONCLUSION

The findings of this study expand the existing knowledge of variants of the CHD2 gene and provide a detailed phenotype associated with this gene. These data could have implications for genetic diagnosis and counselling in similar conditions. Moreover, this information could be useful for therapeutic purposes, including the proper administration of medication to control epilepsy.

Genetic etiology of progressive pediatric neurological disorders

BACKGROUND

The aim of the study was to characterize molecular diagnoses in patients with childhood-onset progressive neurological disorders of suspected genetic etiology.

METHODS

We studied 48 probands (age range from newborn to 17 years old) with progressive neurological disorders of unknown etiology from the largest pediatric neurology clinic in Finland. Phenotypes included encephalopathy (54%), neuromuscular disorders (33%), movement disorders (11%), and one patient (2%) with hemiplegic migraine. All patients underwent whole-exome sequencing and disease-causing genes were analyzed.

RESULTS

We found 20 (42%) of the patients to have variants in genes previously associated with disease. Of these, 12 were previously reported disease-causing variants, whereas eight patients had a novel variant on a disease-causing gene: ATP7A, CHD2, PURA, PYCR2, SLC1A4, SPAST, TRIT1, and UPF3B. Genetics also enabled us to define atypical clinical presentations of Rett syndrome (MECP2) and Menkes disease (ATP7A). Except for one deletion, all findings were single-nucleotide variants (missense 72%, truncating 22%, splice-site 6%). Nearly half of the variants were de novo.

CONCLUSIONS

The most common cause of childhood encephalopathies are de novo variants. Whole-exome sequencing, even singleton, proved to be an efficient tool to gain specific diagnoses and in finding de novo variants in a clinically heterogeneous group of childhood encephalopathies.

IMPACT

Whole-exome sequencing is useful in heterogeneous pediatric neurology cohorts. Our article provides further evidence for and novel variants in several genes. De novo variants are an important cause of childhood encephalopathies.

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.

Adult Phenotype of SYNGAP1-DEE

Background and Objectives

SYNGAP1 variants are associated with rare developmental and epileptic encephalopathies (DEEs). Although SYNGAP1-related childhood phenotypes are well characterized, the adult phenotype remains ill-defined. We sought to investigate phenotypes and outcomes in adults with SYNGAP1 variants and epilepsy.

Methods

Patients 18 years or older with DEE carrying likely pathogenic and pathogenic (LP/P) SYNGAP1 variants were recruited through physicians' practices and patient organization groups. We used standardized questionnaires to evaluate current seizures, medication use, sleep, gastrointestinal symptoms, pain response, gait, social communication disorder and adaptive skills of patients. We also assessed caregiver burden.

Results

Fourteen unrelated adult patients (median: 21 years, range: 18-65 years) with SYNGAP1-DEE were identified, 11 with novel and 3 with known LP/P SYNGAP1 de novo variants. One patient with a partial exon 3 deletion had greater daily living skills and social skills than others with single-nucleotide variants. Ten of 14 (71%) patients had drug-resistant seizures, treated with a median of 2 antiseizure medications. All patients (100%) had abnormal pain processing. Sleep disturbances, social communication disorders, and aggressive/self-injurious behaviors were each reported in 86% of patients. Only half of adults could walk with minimal or no assistance. Toileting was normal in 29%, and 71% had constipation. No adult patients could read or understand verbal material at a sixth-grade level or higher. Aggressive/self-injurious behaviors were leading cause of caregiver burden. The oldest patient was aged 65 years; although nonambulant, she had walked independently when younger.

Discussion

Seventy-one percent of patients with SYNGAP1-DEEs continue to have seizures when adults. Nonseizure comorbidities, especially aggression and self-injurious behaviors, are major management challenges in adults with SYNGAP1-DEE. Only 50% of adults can ambulate with minimal or no assistance. Almost all adult patients depend on caregivers for many activities of daily living. Prompt diagnostic genetic testing of adults with DEE can inform clinical care and guide outcomes of precision therapies.

Movement Disorders in Patients With Genetic Developmental and Epileptic Encephalopathies

BACKGROUND AND OBJECTIVES

Movement disorders (MDs) are underrecognized in the developmental and epileptic encephalopathies (DEEs). There are now more than 800 genes implicated in causing the DEEs; relatively few of these rare genetic diseases are known to be associated with MDs. We identified patients with genetic DEEs who had MDs, classified the nature of their MDs, and asked whether specific patterns correlated with the underlying mechanism.

METHODS

We classified the type of MDs associated with specific genetic DEEs in a large international cohort of patients and analyzed whether specific patterns of MDs reflected the underlying biological dysfunction.

RESULTS

Our cohort comprised 77 patients with a genetic DEE with a median age of 9 (range 1-38) years. Stereotypies (37/77, 48%) and dystonia (34/77, 44%) were the most frequent MDs, followed by chorea (18/77, 23%), myoclonus (14/77, 18%), ataxia (9/77, 12%), tremor (7/77, 9%), and hypokinesia (6/77, 8%). In 47% of patients, a combination of MDs was seen. The MDs were first observed at a median age of 18 months (range day 2-35 years). Dystonia was more likely to be observed in nonambulatory patients, while ataxia was less likely. In 46% of patients, therapy was initiated with medication (34/77, 44%), deep brain stimulation (1/77, 1%), or intrathecal baclofen (1/77, 1%). We found that patients with channelopathies or synaptic vesicle trafficking defects were more likely to experience dystonia; whereas, stereotypies were most frequent in individuals with transcriptional defects.

DISCUSSION

MDs are often underrecognized in patients with genetic DEEs, but recognition is critical for the management of these complex neurologic diseases. Distinguishing MDs from epileptic seizures is important in tailoring patient treatment. Understanding which MDs occur with different biological mechanisms will inform early diagnosis and management.

Identifying the mechanism of action of the Kv7 channel opener, retigabine in the treatment of epilepsy

Epilepsy is characterized by recurrent epileptic seizures caused by high levels of neuronal excitability in the brain. Voltage-sensitive K+ channels (Kv) of the Kv7 (KCNQ) family encoded by the KCNQ gene are involved in a wide range of cellular processes, i.e., KCNQ2 and KCNQ3 channels mediate M-currents to inhibit neuronal excitability and reduce transmitter release throughout the nervous system. Thus, as a positive allosteric modulator (or opener) of KCNQ channels, retigabine has been the only clinically approved anti-seizure medication that acts on the KCNQ channels. This review discusses the biochemical mechanisms about how retigabine acts on Kv7 channels, significance in neuronal pathophysiology, preclinical efficacy, and clinical stage of development. Additional efforts are being made to emphasize the possible benefits and drawbacks of retigabine compared to currently available medications for treatment-resistant epilepsy.

Customized targeted massively parallel sequencing enables the identification of novel pathogenic variants in Tunisian patients with developmental and epileptic encephalopathy

OBJECTIVE

To develop a high-throughput sequencing panel for the diagnosis of developmental and epileptic encephalopathy in Tunisia and to clarify the frequency of disease-causing genes in this region.

METHODS

We developed a custom panel for next-generation sequencing of the coding sequences of 116 genes in individuals with developmental and epileptic encephalopathy from the Tunisian population. Segregation analyses and in silico studies have been conducted to assess the identified variants' pathogenicity.

RESULTS

We report 12 pathogenic variants in SCN1A, CHD2, CDKL5, SZT2, KCNT1, GNAO1, PCDH19, MECP2, GRIN2A, and SYNGAP1 in patients with developmental and epileptic encephalopathy. Five of these variants are novel: "c.149delA, p.(Asn50MetfsTer26)" in CDKL5; "c.3616C > T, p.(Arg1206Ter)" in SZT2; "c.111_113del, p.(Leu39del)" in GNAO1; "c.1435G>C, p.(Asp479His)" in PCDH19; and "c.2143delC, p.(Arg716GlyfsTer10)" in SYNGAP1. Additionally, for four of our patients, the genetic result facilitated the choice of the appropriate treatment.

SIGNIFICANCE

This is the first report of a custom gene panel to identify genetic variants implicated in developmental and epileptic encephalopathy in the Tunisian population as well as the North African region (Tunisia, Egypt, Libya, Algeria, Morocco) with a diagnostic rate of 30%. This high-throughput sequencing panel has considerably improved the rate of positive diagnosis of developmental and epileptic encephalopathy in the Tunisian population, which was less than 15% using Sanger sequencing. The benefit of genetic testing in these patients was approved by both physicians and parents.

Identification and functional characterization of de novo variant in the SYNGAP1 gene causing intellectual disability

Background: Intellectual disability (ID) is defined by cognitive and social adaptation defects. Variants in the SYNGAP1 gene, which encodes the brain-specific cytoplasmic protein SYNGAP1, are commonly associated with ID. The aim of this study was to identify novel SYNGAP1 gene variants in Chinese individuals with ID and evaluate the pathogenicity of the detected variants. Methods: Whole exome sequencing (WES) was performed on 113 patients diagnosed with ID. In the study, two de novo variants in SYNGAP1 were identified. Sanger sequencing was used to confirm these variants. Minigene assays were used to verify whether the de novo intronic variant in SYNGAP1 influenced the normal splicing of mRNA. Results: Two de novo heterozygous pathogenic variants in SYNGAP1, c.333del and c.664-2A>G, were identified in two ID patients separately. The c.333del variant has been reported previously as a de novo finding in a child with ID, while the c.664-2A>G variant was novel de novo intronic variant, which has not been reported in the literature. Functional studies showed that c.664-2A>G could cause aberrant splicing, resulting in exon 7 skipping and a 16bp deletion within exon 7. Conclusion: We identified two de novo pathogenic heterozygous variants in SYNGAP1 in two patients with ID, among which the c.664-2A>G variant was a novel de novo pathogenic variant. Our findings further enrich the variant spectrum of the SYNGAP1 gene and provide a research basis for the genetic diagnosis of ID.

Diagnostic Utility of Genome-wide DNA Methylation Analysis in Genetically Unsolved Developmental and Epileptic Encephalopathies and Refinement of a CHD2 Episignature

Sequence-based genetic testing currently identifies causative genetic variants in ∼50% of individuals with developmental and epileptic encephalopathies (DEEs). Aberrant changes in DNA methylation are implicated in various neurodevelopmental disorders but remain unstudied in DEEs. Rare epigenetic variations ("epivariants") can drive disease by modulating gene expression at single loci, whereas genome-wide DNA methylation changes can result in distinct "episignature" biomarkers for monogenic disorders in a growing number of rare diseases. Here, we interrogate the diagnostic utility of genome-wide DNA methylation array analysis on peripheral blood samples from 516 individuals with genetically unsolved DEEs who had previously undergone extensive genetic testing. We identified rare differentially methylated regions (DMRs) and explanatory episignatures to discover causative and candidate genetic etiologies in 10 individuals. We then used long-read sequencing to identify DNA variants underlying rare DMRs, including one balanced translocation, three CG-rich repeat expansions, and two copy number variants. We also identify pathogenic sequence variants associated with episignatures; some had been missed by previous exome sequencing. Although most DEE genes lack known episignatures, the increase in diagnostic yield for DNA methylation analysis in DEEs is comparable to the added yield of genome sequencing. Finally, we refine an episignature for CHD2 using an 850K methylation array which was further refined at higher CpG resolution using bisulfite sequencing to investigate potential insights into CHD2 pathophysiology. Our study demonstrates the diagnostic yield of genome-wide DNA methylation analysis to identify causal and candidate genetic causes as ∼2% (10/516) for unsolved DEE cases.

Neurodevelopmental deficits and cell-type-specific transcriptomic perturbations in a mouse model of HNRNPU haploinsufficiency

Heterozygous de novo loss-of-function mutations in the gene expression regulator HNRNPU cause an early-onset developmental and epileptic encephalopathy. To gain insight into pathological mechanisms and lay the potential groundwork for developing targeted therapies, we characterized the neurophysiologic and cell-type-specific transcriptomic consequences of a mouse model of HNRNPU haploinsufficiency. Heterozygous mutants demonstrated global developmental delay, impaired ultrasonic vocalizations, cognitive dysfunction and increased seizure susceptibility, thus modeling aspects of the human disease. Single-cell RNA-sequencing of hippocampal and neocortical cells revealed widespread, yet modest, dysregulation of gene expression across mutant neuronal subtypes. We observed an increased burden of differentially-expressed genes in mutant excitatory neurons of the subiculum-a region of the hippocampus implicated in temporal lobe epilepsy. Evaluation of transcriptomic signature reversal as a therapeutic strategy highlights the potential importance of generating cell-type-specific signatures. Overall, this work provides insight into HNRNPU-mediated disease mechanisms and provides a framework for using single-cell RNA-sequencing to study transcriptional regulators implicated in disease.

Case report: Off-label use of low-dose perampanel in a 25-month-old girl with a pathogenic SYNGAP1 variant

Introduction

Preclinical studies in a mouse model have shown that SYNGAP1 haploinsufficiency results in an epilepsy phenotype with excessive GluA2-AMPA insertion specifically on the soma of fast-spiking parvalbumin-positive interneurons associated with significant dysfunction of cortical gamma homeostasis that was rescued by perampanel (PER), an AMPA receptor blocker. In this single case, we aimed to investigate the presence of dysregulated cortical gamma in a toddler with a pathogenic SYNGAP1 variant and report on the effect of low-dose PER on electroencephalogram (EEG) and clinical profile.

Methods

Clinical data from physician's clinic notes; genetic testing reports; developmental scores from occupational therapy, physical therapy, speech and language therapy evaluations; and applied behavioral analysis reports were reviewed. Developmental assessments and EEG analysis were done pre- and post-PER.

Results

Clinically, the patient showed improvements in the developmental profile and sleep quality post-PER. EEG spectral power analysis in our patient revealed a loss of gamma power modulation with behavioral-state transitions similar to what was observed in Syngap1+/- mice. Furthermore, the administration of low-dose PER rescued the dysfunctional cortical gamma homeostasis, similar to the preclinical study. However, as in the epileptic mice, PER did not curb epileptiform discharges or clinical seizures.

Conclusion

Similar to the Syngap1+/- mice, cortical gamma homeostasis was dysregulated in the patient. This dysfunction was rescued by PER. These encouraging results necessitate further validation of gamma dysregulation as a potential translational EEG biomarker in SYNAP1-DEE. Low-dose PER can be explored as a therapeutic option through clinical trials.

hdWGCNA identifies co-expression networks in high-dimensional transcriptomics data

Biological systems are immensely complex, organized into a multi-scale hierarchy of functional units based on tightly regulated interactions between distinct molecules, cells, organs, and organisms. While experimental methods enable transcriptome-wide measurements across millions of cells, popular bioinformatic tools do not support systems-level analysis. Here we present hdWGCNA, a comprehensive framework for analyzing co-expression networks in high-dimensional transcriptomics data such as single-cell and spatial RNA sequencing (RNA-seq). hdWGCNA provides functions for network inference, gene module identification, gene enrichment analysis, statistical tests, and data visualization. Beyond conventional single-cell RNA-seq, hdWGCNA is capable of performing isoform-level network analysis using long-read single-cell data. We showcase hdWGCNA using data from autism spectrum disorder and Alzheimer's disease brain samples, identifying disease-relevant co-expression network modules. hdWGCNA is directly compatible with Seurat, a widely used R package for single-cell and spatial transcriptomics analysis, and we demonstrate the scalability of hdWGCNA by analyzing a dataset containing nearly 1 million cells.

Early recognition of characteristic conventional and amplitude-integrated EEG patterns of seizures in SCN2A and KCNQ3-related epilepsy in neonates

PURPOSE

Early recognition of seizures in neonates secondary to pathogenic variants in potassium or sodium channel coding genes is crucial, as these seizures are often resistant to commonly used anti-seizure medications but respond well to sodium channel blockers. Recently, a characteristic ictal amplitude-integrated electroencephalogram (aEEG) pattern was described in neonates with KCNQ2-related epilepsy. We report a similar aEEG pattern in seizures caused by SCN2A- and KCNQ3-pathogenic variants, as well as conventional EEG (cEEG) descriptions.

METHODS

International multicentre descriptive study, reporting clinical characteristics, aEEG and cEEG findings of 13 neonates with seizures due to pathogenic SCN2A- and KCNQ3-variants. As a comparison group, aEEGs and cEEGs of neonates with seizures due to hypoxic-ischemic encephalopathy (n = 117) and other confirmed genetic causes affecting channel function (n = 55) were reviewed.

RESULTS

In 12 out of 13 patients, the aEEG showed a characteristic sequence of brief onset with a decrease, followed by a quick rise, and then postictal amplitude attenuation. This pattern correlated with bilateral EEG onset attenuation, followed by rhythmic discharges ending in several seconds of post-ictal amplitude suppression. Apart from patients with KCNQ2-related epilepsy, none of the patients in the comparison groups had a similar aEEG or cEEG pattern.

DISCUSSION

Seizures in SCN2A- and KCNQ3-related epilepsy in neonates can usually be recognized by a characteristic ictal aEEG pattern, previously reported only in KCNQ2-related epilepsy, extending this unique feature to other channelopathies. Awareness of this pattern facilitates the prompt initiation of precision treatment with sodium channel blockers even before genetic results are available.

Sleep disturbances in autism spectrum disorder: Animal models, neural mechanisms, and therapeutics

Sleep is crucial for brain development. Sleep disturbances are prevalent in children with autism spectrum disorder (ASD). Strikingly, these sleep problems are positively correlated with the severity of ASD core symptoms such as deficits in social skills and stereotypic behavior, indicating that sleep problems and the behavioral characteristics of ASD may be related. In this review, we will discuss sleep disturbances in children with ASD and highlight mouse models to study sleep disturbances and behavioral phenotypes in ASD. In addition, we will review neuromodulators controlling sleep and wakefulness and how these neuromodulatory systems are disrupted in animal models and patients with ASD. Lastly, we will address how the therapeutic interventions for patients with ASD improve various aspects of sleep. Together, gaining mechanistic insights into the neural mechanisms underlying sleep disturbances in children with ASD will help us to develop better therapeutic interventions.

Chromosome Microarray Analysis for the Investigation of Deletions in Pediatric Movement Disorders: A Systematic Review of the Literature

Background

Chromosome microarray analysis (CMA) can detect copy number variants (CNV) beyond the resolution of standard G-banded karyotyping. De novo or inherited microdeletions may cause autosomal dominant movement disorders.

Objectives

The purpose of this study was to analyze the clinical characteristics, associated features, and genetic information of children with deletions in known genes that cause movement disorders and to make recommendations regarding the diagnostic application of CMA.

Methods

Clinical cases published in English were identified in scientific databases (PubMed, ClinVar, and DECIPHER) from January 1998 to July 2019 following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Cases with deletions or microdeletions greater than 300 kb were selected. Information collected included age, sex, movement disorders, associated features, and the size and location of the deletion. Duplications or microduplications were not included.

Results

A total of 18.097 records were reviewed, and 171 individuals were identified. Ataxia (30.4%), stereotypies (23.9%), and dystonia (21%) were the most common movement disorders. A total of 16% of the patients demonstrated more than one movement disorder. The most common associated features were intellectual disability or developmental delay (78.9%) and facial dysmorphism (57.8%). The majority (77.7%) of microdeletions were smaller than 5 Mb. We find no correlation between movement disorders, their associated features, and the size of microdeletions.

Conclusions

Our results support the use of CMA as an investigational test in children with movement disorders. As the majority of identified articles were case reports and small case series (low quality), future efforts should focus on larger prospective studies to examine the causation of microdeletions in pediatric movement disorders.

Brain somatic mosaicism in epilepsy: Bringing results Back to the clinic

Over the past decade, there has been tremendous progress in understanding brain somatic mosaicism in epilepsy in the research setting. Access to resected brain tissue samples from patients with medically refractory epilepsy undergoing epilepsy surgery has been key to making these discoveries. In this review, we discuss the gap between making discoveries in the research setting and bringing results back to the clinical setting. Current clinical genetic testing mainly uses clinically accessible tissue samples, like blood and saliva, and can detect inherited and de novo germline variants and potentially non-brain-limited mosaic variants that have resulted from post-zygotic mutation (also called "somatic mutations"). Methods developed in the research setting to detect brain-limited mosaic variants using brain tissue samples need to be further translated and validated in the clinical setting, which will allow post-resection brain tissue genetic diagnoses. However, obtaining a genetic diagnosis after surgery for refractory focal epilepsy, when brain tissue samples are available, is arguably "too late" to guide precision management. Emerging methods using cerebrospinal fluid (CSF) and subdural electroencephalogram (SEEG) depth electrodes hold promise for establishing genetic diagnoses pre-resection without the need for actual brain tissue. In parallel, development of curation rules for interpreting the pathogenicity of mosaic variants, which have unique considerations compared to germline variants, will assist clinically accredited laboratories and epilepsy geneticists in making genetic diagnoses. Returning results of brain-limited mosaic variants to patients and their families will end their diagnostic odyssey and advance epilepsy precision management.

GABRG2 Variants Associated with Febrile Seizures

Febrile seizures (FS) are the most common form of epilepsy in children between six months and five years of age. FS is a self-limited type of fever-related seizure. However, complicated prolonged FS can lead to complex partial epilepsy. We found that among the GABAA receptor subunit (GABR) genes, most variants associated with FS are harbored in the γ2 subunit (GABRG2). Here, we characterized the effects of eight variants in the GABAA receptor γ2 subunit on receptor biogenesis and channel function. Two-thirds of the GABRG2 variants followed the expected autosomal dominant inheritance in FS and occurred as missense and nonsense variants. The remaining one-third appeared as de novo in the affected probands and occurred only as missense variants. The loss of GABAA receptor function and dominant negative effect on GABAA receptor biogenesis likely caused the FS phenotype. In general, variants in the GABRG2 result in a broad spectrum of phenotypic severity, ranging from asymptomatic, FS, genetic epilepsy with febrile seizures plus (GEFS+), and Dravet syndrome individuals. The data presented here support the link between FS, epilepsy, and GABRG2 variants, shedding light on the relationship between the variant topological occurrence and disease severity.

Clocking Epilepsies: A Chronomodulated Strategy-Based Therapy for Rhythmic Seizures

Epilepsy is a neurological disorder characterized by hypersynchronous recurrent neuronal activities and seizures, as well as loss of muscular control and sometimes awareness. Clinically, seizures have been reported to display daily variations. Conversely, circadian misalignment and circadian clock gene variants contribute to epileptic pathogenesis. Elucidation of the genetic bases of epilepsy is of great importance because the genetic variability of the patients affects the efficacies of antiepileptic drugs (AEDs). For this narrative review, we compiled 661 epilepsy-related genes from the PHGKB and OMIM databases and classified them into 3 groups: driver genes, passenger genes, and undetermined genes. We discuss the potential roles of some epilepsy driver genes based on GO and KEGG analyses, the circadian rhythmicity of human and animal epilepsies, and the mutual effects between epilepsy and sleep. We review the advantages and challenges of rodents and zebrafish as animal models for epileptic studies. Finally, we posit chronomodulated strategy-based chronotherapy for rhythmic epilepsies, integrating several lines of investigation for unraveling circadian mechanisms underpinning epileptogenesis, chronopharmacokinetic and chronopharmacodynamic examinations of AEDs, as well as mathematical/computational modeling to help develop time-of-day-specific AED dosing schedules for rhythmic epilepsy patients.

Neurodevelopmental and Epilepsy Phenotypes in Individuals With Missense Variants in the Voltage-Sensing and Pore Domains of KCNH5

BACKGROUND AND OBJECTIVES

KCNH5 encodes the voltage-gated potassium channel EAG2/Kv10.2. We aimed to delineate the neurodevelopmental and epilepsy phenotypic spectrum associated with de novo KCNH5 variants.

METHODS

We screened 893 individuals with developmental and epileptic encephalopathies for KCNH5 variants using targeted or exome sequencing. Additional individuals with KCNH5 variants were identified through an international collaboration. Clinical history, EEG, and imaging data were analyzed; seizure types and epilepsy syndromes were classified. We included 3 previously published individuals including additional phenotypic details.

RESULTS

We report a cohort of 17 patients, including 9 with a recurrent de novo missense variant p.Arg327His, 4 with a recurrent missense variant p.Arg333His, and 4 additional novel missense variants. All variants were located in or near the functionally critical voltage-sensing or pore domains, absent in the general population, and classified as pathogenic or likely pathogenic using the American College of Medical Genetics and Genomics criteria. All individuals presented with epilepsy with a median seizure onset at 6 months. They had a wide range of seizure types, including focal and generalized seizures. Cognitive outcomes ranged from normal intellect to profound impairment. Individuals with the recurrent p.Arg333His variant had a self-limited drug-responsive focal or generalized epilepsy and normal intellect, whereas the recurrent p.Arg327His variant was associated with infantile-onset DEE. Two individuals with variants in the pore domain were more severely affected, with a neonatal-onset movement disorder, early-infantile DEE, profound disability, and childhood death.

DISCUSSION

We describe a cohort of 17 individuals with pathogenic or likely pathogenic missense variants in the voltage-sensing and pore domains of Kv10.2, including 14 previously unreported individuals. We present evidence for a putative emerging genotype-phenotype correlation with a spectrum of epilepsy and cognitive outcomes. Overall, we expand the role of EAG proteins in human disease and establish KCNH5 as implicated in a spectrum of neurodevelopmental disorders and epilepsy.

Precision medicine for developmental and epileptic encephalopathies in Africa-strategies for a resource-limited setting

PURPOSE

Sub-Saharan Africa bears the highest burden of epilepsy worldwide. A presumed proportion is genetic, but this etiology is buried under the burden of infections and perinatal insults in a setting of limited awareness and few options for testing. Children with developmental and epileptic encephalopathies (DEEs) are most severely affected by this diagnostic gap in Africa, because the rate of actionable findings is highest in DEE-associated genes.

METHODS

We tested 234 genetically naive South African children diagnosed with/possible DEE using gene panels, exome sequencing, and chromosomal microarray. Statistical comparison of electroclinical features in children with and children without candidate variants was performed to identify characteristics most likely predictive of a positive genetic finding.

RESULTS

Of the 41 (of 234) children with likely/pathogenic variants, 26 had variants supporting precision therapy. Multivariate regression modeling highlighted neonatal or infantile-onset seizures and movement abnormalities as predictive of a positive genetic finding. We used this, coupled with an emphasis on precision medicine outcomes, to propose the pragmatic "Think-Genetics" strategy for early recognition of a possible genetic etiology.

CONCLUSION

Our findings emphasize the importance of an early genetic diagnosis in DEE. We designed the Think-Genetics strategy for early recognition, appropriate interim management, and genetic testing for DEE in resource-constrained settings.

Exome sequencing as first-tier genetic testing in infantile-onset pharmacoresistant epilepsy: diagnostic yield and treatment impact

Pharmacoresistant epilepsy presenting during infancy poses both diagnostic and therapeutic challenges. We aim to identify diagnostic yield and treatment implications of exome sequencing (ES) as first-tier genetic testing for infantile-onset pharmacoresistant epilepsy. From June 2016 to December 2020, we enrolled patients with infantile-onset (age ≤ 12 months) pharmacoresistant epilepsy. 103 unrelated patients underwent ES. Clinical characteristics and changes in management due to the molecular diagnosis were studied. 42% (43/103) had epilepsy onset within the first month of life. After ES as first-tier genetic testing, 62% (64/103) of the cases were solved. Two partially solved cases (2%; 2/103) with heterozygous variants identified in ALDH7A1 known to cause autosomal recessive pyridoxine dependent epilepsy underwent genome sequencing (GS). Two novel large deletions in ALDH7A1 were detected in both cases. ES identified 66 pathogenic and likely pathogenic single nucleotide variants (SNVs) in 27 genes. 19 variants have not been previously reported. GS identified two additional copy number variations (CNVs). The most common disease-causing genes are SCN1A (13%; 13/103) and KCNQ2 (8%; 8/103). Eight percent (8/103) of the patients had treatable disorders and specific treatments were provided resulting in seizure freedom. Pyridoxine dependent epilepsy was the most common treatable epilepsy (6%; 6/103). Furthermore, 35% (36/103) had genetic defects which guided gene-specific treatments. Altogether, the diagnostic yield is 64%. Molecular diagnoses change management in 43% of the cases. This study substantiates the use of next generation sequencing (NGS) as the first-tier genetic investigation in infantile-onset pharmacoresistant epilepsy.

Identification of novel mendelian disorders of the epigenetic machinery (MDEMs) associated functional mutations and neurodevelopmental disorders

BACKGROUND

Mendelian disorders of the epigenetic machinery (MDEMs) are a newly identified group of neurodevelopmental disorders (NDDs) and multiple congenital anoMalies caused by mutations in genes encoding components of the epigenetic machinery. Many studies have shown that MDEM-associated mutations may disrupt the balance between chromatin states and trigger dysplasia.

AIM

To help eight Chinese families with neurodevelopmental disorders acquire a definitive diagnosis.

METHODS

In this study, we used whole-exome sequencing (WES) to diagnose eight unrelated Chinese families with NDDs. We also verified the potential pathogenic variants by Sanger sequencing and analyzed the changes in gene expression along with histone methylation modifications.

RESULTS

Eight variants of six epigenetic machinery genes were identified, six of which were novel. Six variants were pathogenic (P) or likely pathogenic (LP), while two novel missense variants (c.5113T>C in CHD1 and c.10444C>T in KMT2D) were classified to be variants of uncertain significance (VUS). Further functional studies verified that c.5113T>C in CHD1 results in decreased protein levels and increased chromatin modifications (H3K27me3). In addition, c.10444C>T in KMT2D led to a significant decrease in mRNA transcription and chromatin modifications (H3K4me1). Based on experimental evidence, these two VUS variants could be classified as LP.

CONCLUSION

This study provided a definitive diagnosis of eight families with NDDs and expanded the mutation spectrum of MDEMs, enriching the pathogenesis study of variants in epigenetic machinery genes.

Exome sequencing for patients with developmental and epileptic encephalopathies in clinical practice

AIM

To assess the clinical utility of exome sequencing for patients with developmental and epileptic encephalopathies (DEEs).

METHOD

Over 2 years, patients with DEEs were recruited for singleton exome sequencing. Parental segregation was performed where indicated.

RESULTS

Of the 103 patients recruited (54 males, 49 females; aged 2 weeks-17 years), the genetic aetiology was identified in 36 out of 103 (35%) with management implications in 13 out of 36. Exome sequencing revealed pathogenic or likely pathogenic variants in 30 out of 103 (29%) patients, variants of unknown significance in 39 out of 103 (38%), and 34 out of 103 (33%) were negative on exome analysis. After the description of new genetic diseases, a molecular diagnosis was subsequently made for six patients or through newly available high-density chromosomal microarray testing.

INTERPRETATION

We demonstrate the utility of exome sequencing in routine clinical care of children with DEEs. We highlight that molecular diagnosis often leads to changes in management and informs accurate prognostic and reproductive counselling. Our findings reinforce the need for ongoing analysis of genomic data to identify the aetiology in patients in whom the cause is unknown. The implementation of genomic testing in the care of children with DEEs should become routine in clinical practice.

WHAT THIS PAPER ADDS

The cause was identified in 35% of patients with developmental and epileptic encephalopathies. KCNQ2, CDKL5, SCN1A, and STXBP1 were the most frequently identified genes. Reanalysis of genomic data found the cause in an additional six patients. Genetic aetiology was identified in 41% of children with seizure onset under 2 years, compared to 18% with older onset. Finding the molecular cause led to management changes in 36% of patients with DEEs.

Phenotype and genotype analyses of Chinese patients with autosomal dominant mental retardation type 5 caused by SYNGAP1 gene mutations

Background: Autosomal dominant mental retardation type 5 (MRD5), a rare neurodevelopmental disorder (NDD) characterized by intellectual disability (ID), developmental delay (DD), and epilepsy predominantly, is caused by a heterozygous mutation in the SYNGAP1 gene. SYNGAP1 mutations have been rarely reported in the Chinese population. Here, we present an investigation of SYNGAP1 mutations in a clinical cohort with ID and DD in Shandong, a northern province in China, to further explore the genotype and phenotype correlations. Methods: A retrospective study was conducted on 10 children with SYNGAP1 mutations presenting ID, DD, and epilepsy who were diagnosed between January 2014 and May 2022. Clinical data and genetic tests were collected. Treatment and regular follow-ups were carried out to pay close attention to the prognosis of the patients. Results: We described 10 unrelated affected individuals with SYNGAP1 mutations, displaying ID, DD, epilepsy, or seizures. All mutations of SYNGAP1 in the 10 patients were de novo, except patient 3 whose father was unavailable, including five nonsense mutations, two frameshift mutations, two splicing mutations, and one codon deletion. Among these mutations, five were novel and the other five were previously reported. Significantly, all patients with epilepsy were sensitive to anti-seizure drugs, especially sodium valproate. Furthermore, rehabilitation training seemed to exert a more improved effect on motor development than language development for the patients. Conclusion The 10 patients carrying SYNGAP1 mutations were diagnosed as MRD5. Five novel genetic mutations were found, which expanded the mutational spectrum of the SYNGAP1 gene. The identification of these mutations in this study helps explore the relationship between genotypes and phenotypes and contributes to genetic counseling and therapeutic intervention for patients with MRD5.

Association of respiratory failure with inhibition of NaV1.6 in the phrenic nerve

As part of a drug discovery effort to identify potent inhibitors of NaV1.7 for the treatment of pain, we observed that inhibitors produced unexpected cardiovascular and respiratory effects in vivo. Specifically, inhibitors administered to rodents produced changes in cardiovascular parameters and respiratory cessation. We sought to determine the mechanism of the in vivo adverse effects by studying the selectivity of the compounds on NaV1.5, NaV1.4, and NaV1.6 in in vitro and ex vivo assays. Inhibitors lacking sufficient NaV1.7 selectivity over NaV1.6 were associated with respiratory cessation after in vivo administration to rodents. Effects on respiratory rate in rats were consistent with effects in an ex vivo hemisected rat diaphragm model and in vitro NaV1.6 potency. Furthermore, direct blockade of the phrenic nerve signaling was observed at exposures known to cause respiratory cessation in rats. Collectively, these results support a significant role for NaV1.6 in phrenic nerve signaling and respiratory function.

Reversibility and therapeutic development for neurodevelopmental disorders, insights from genetic animal models

Neurodevelopmental Disorders (NDDs) encompass a broad spectrum of conditions resulting from atypical brain development. Over the past decades, we have had the fortune to witness enormous progress in diagnosis, etiology discovery, modeling, and mechanistic understanding of NDDs from both fundamental and clinical research. Here, we review recent neurobiological advances from experimental models of NDDs. We introduce several examples and highlight breakthroughs in reversal studies of phenotypes using genetically engineered models of NDDs. The in-depth understanding of brain pathophysiology underlying NDDs and evaluations of reversibility in animal models paves the foundation for discovering novel treatment options. We discuss how the expanding property of cutting-edge technologies, such as gene editing and AAV-mediated gene delivery, are leveraged in animal models for the therapeutic development of NDDs. We envision opportunities and challenges toward faithful modeling and fruitful clinical translation.

A companion to the preclinical common data elements for genomics, transcriptomics, and epigenomics data in rodent epilepsy models. A report of the TASK3-WG4 omics working group of the ILAE/AES joint translational TASK force

The International League Against Epilepsy/American Epilepsy Society (ILAE/AES) Joint Translational Task Force established the TASK3 working groups to create common data elements (CDEs) for various preclinical epilepsy research disciplines. The aim of the CDEs is to improve the standardization of experimental designs across a range of epilepsy research-related methods. Here, we have generated CDE tables with key parameters and case report forms (CRFs) containing the essential contents of the study protocols for genomics, transcriptomics, and epigenomics in rodent models of epilepsy, with a specific focus on adult rats and mice. We discuss the important elements that need to be considered for genomics, transcriptomics, and epigenomics methodologies, providing a rationale for the parameters that should be collected. This is the first in a two-part series of omics papers with the second installment to cover proteomics, lipidomics, and metabolomics in adult rodents.

Mammalian Resilience Revealed by a Comparison of Human Diseases and Mouse Models Associated With DNA Helicase Deficiencies

Maintaining genomic integrity is critical for sustaining individual animals and passing on the genome to subsequent generations. Several enzymes, such as DNA helicases and DNA polymerases, are involved in maintaining genomic integrity by unwinding and synthesizing the genome, respectively. Indeed, several human diseases that arise caused by deficiencies in these enzymes have long been known. In this review, the author presents the DNA helicases associated with human diseases discovered to date using recent analyses, including exome sequences. Since several mouse models that reflect these human diseases have been developed and reported, this study also summarizes the current knowledge regarding the outcomes of DNA helicase deficiencies in humans and mice and discusses possible mechanisms by which DNA helicases maintain genomic integrity in mammals. It also highlights specific diseases that demonstrate mammalian resilience, in which, despite the presence of genomic instability, patients and mouse models have lifespans comparable to those of the general population if they do not develop cancers; finally, this study discusses future directions for therapeutic applications in humans that can be explored using these mouse models.

Epigenetic genes and epilepsy - emerging mechanisms and clinical applications

An increasing number of epilepsies are being attributed to variants in genes with epigenetic functions. The products of these genes include factors that regulate the structure and function of chromatin and the placing, reading and removal of epigenetic marks, as well as other epigenetic processes. In this Review, we provide an overview of the various epigenetic processes, structuring our discussion around five function-based categories: DNA methylation, histone modifications, histone-DNA crosstalk, non-coding RNAs and chromatin remodelling. We provide background information on each category, describing the general mechanism by which each process leads to altered gene expression. We also highlight key clinical and mechanistic aspects, providing examples of genes that strongly associate with epilepsy within each class. We consider the practical applications of these findings, including tissue-based and biofluid-based diagnostics and precision medicine-based treatments. We conclude that variants in epigenetic genes are increasingly found to be causally involved in the epilepsies, with implications for disease mechanisms, treatments and diagnostics.

Some (Syn)Gaps are Worse than Others: Deciphering The Role of Syngap Isoforms in Excitatory Synaptic Function

Endogenous Syngap Alpha Splice Forms Promote Cognitive Function and Seizure Protection

M Kilinc, V Arora, TK Creson, et al. eLife. 2022;11:e75707. doi:10.7554/eLife.75707.

Loss-of-function variants in SYNGAP cause a developmental encephalopathy defined by cognitive impairment, autistic features, and epilepsy. SYNGAP splicing leads to expression of distinct functional protein isoforms. Splicing imparts multiple cellular functions of SynGAP proteins through coding of distinct C-terminal motifs. However, it remains unknown how these different splice sequences function in vivo to regulate neuronal function and behavior. Reduced expression of SynGAP-α1/2 C-terminal splice variants in mice caused severe phenotypes, including reduced survival, impaired learning, and reduced seizure latency. In contrast, upregulation of α1/2 expression improved learning and increased seizure latency. Mice expressing α1-specific mutations, which disrupted SynGAP cellular functions without altering protein expression, promoted seizure, disrupted synapse plasticity, and impaired learning. These findings demonstrate that endogenous SynGAP isoforms with α1/2 spliced sequences promote cognitive function and impart seizure protection. Regulation of SynGAP-αexpression or function may be a viable therapeutic strategy to broadly improve cognitive function and mitigate seizure.

Polymerases and DNA Repair in Neurons: Implications in Neuronal Survival and Neurodegenerative Diseases

Most of the neurodegenerative diseases and aging are associated with reactive oxygen species (ROS) or other intracellular damaging agents that challenge the genome integrity of the neurons. As most of the mature neurons stay in G0/G1 phase, replication-uncoupled DNA repair pathways including BER, NER, SSBR, and NHEJ, are pivotal, efficient, and economic mechanisms to maintain genomic stability without reactivating cell cycle. In these progresses, polymerases are prominent, not only because they are responsible for both sensing and repairing damages, but also for their more diversified roles depending on the cell cycle phase and damage types. In this review, we summarized recent knowledge on the structural and biochemical properties of distinct polymerases, including DNA and RNA polymerases, which are known to be expressed and active in nervous system; the biological relevance of these polymerases and their interactors with neuronal degeneration would be most graphically illustrated by the neurological abnormalities observed in patients with hereditary diseases associated with defects in DNA repair; furthermore, the vicious cycle of the trinucleotide repeat (TNR) and impaired DNA repair pathway is also discussed. Unraveling the mechanisms and contextual basis of the role of the polymerases in DNA damage response and repair will promote our understanding about how long-lived postmitotic cells cope with DNA lesions, and why disrupted DNA repair contributes to disease origin, despite the diversity of mutations in genes. This knowledge may lead to new insight into the development of targeted intervention for neurodegenerative diseases.

CircRNAs in Xiang pig ovaries among diestrus and estrus stages

BACKGROUND

The fecundity of sows is a trait of major economic in pig industry. The molecular regulation of estrus cycles can affect the fecundity of female animals. Compared with the other pig breeds, Xiang pig exhibits the special estrus behaviors. CircRNAs are thought to involve in regulation of multiple biological processes. However, the potential roles of circRNAs in ovary regulation on Xiang pig estrus are largely unknown.

RESULTS

8,937 circRNAs were identified from eight libraries constructed from the ovarian samples of Xiang pig at estrus and diestrus stages by RNA sequencing method. Of which, 1,995 were high confidence circRNAs detected at least two junction reads in each ovary sample and seven circRNAs were validated by RT-PCR method. Furthermore, we identified 290 upregulated and 15 downregulated circRNAs in estrus ovaries. These differentially expressed circRNAs (DECs) derived from 273 host genes. And 207 miRNAs were identified to be targets sponged by 156 DECs with 432 binding sites, containing more than one miRNA binding site in each circRNA. Function enrichment analysis revealed that the host genes and the targets of miRNAs sponged by DECs were enriched in several reproduction-related signaling pathways, such as ovarian steroidogenesis, oocyte maturation, circadian rhythm, estrogen signaling pathway, GnRH signaling pathway, circadian entrainment, and oocyte meiosis. The circRNA-miRNA-mRNA networks revealed that 153 miRNAs interacting with 122 DECs and 86 miRNAs interacting with 84 DECs were involved in ovarian functions and ovarian circadian entrainment and circadian rhythm respectively. The DEC-miRNA-DEG (differentially expressed gene, DEG) networks associated with reproduction-related signaling pathways contained 22 DECs,18 miRNAs and 7 DEGs. 22 DECs were recognized as hub circRNAs during the estrus phase of Xiang pigs.

CONCLUSIONS

The circRNAs that function as miRNA sponges could play a key role in post-transcriptional regulation of gene expression during Xiang pig's estrus cycle.

Genetics and gene therapy in Dravet syndrome

Dravet syndrome is a well-established electro-clinical condition first described in 1978. A main genetic cause was identified with the discovery of a loss-of-function SCN1A variant in 2001. Mechanisms underlying the phenotypic variations have subsequently been a main topic of research. Various genetic modifiers of clinical severities have been elucidated through many rigorous studies on genotype-phenotype correlations and the recent advances in next generation sequencing technology. Furthermore, a deeper understanding of the regulation of gene expression and remarkable progress on genome-editing technology using the CRISPR-Cas9 system provide significant opportunities to overcome hurdles of gene therapy, such as enhancing Na_V1.1 expression. This article reviews the current understanding of genetic pathology and the status of research toward the development of gene therapy for Dravet syndrome. This article is part of the Special Issue "Severe Infantile Epilepsies".