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A Novel Genetic Variant in MBD5 Associated with Severe Epilepsy and Intellectual Disability: Potential Implications on Neural Primary Cilia.

ABSTRACT: Disruptions in the MBD5 gene have been linked with an array of clinical features such as global developmental delay, intellectual disability, autistic-like symptoms, and seizures, through unclear mechanisms. MBD5 haploinsufficiency has been associated with the disruption of primary cilium-related processes during early cortical development, and this has been reported in many neurodevelopmental disorders. In this study, we describe the clinical history of a 12-year-old child harboring a novel MBD5 rare variant and presenting psychomotor delay and seizures. To investigate the impact of MBD5 haploinsufficiency on neural primary cilia, we established a novel patient-derived cell line and used CRISPR-Cas9 technology to create an isogenic control. The patient-derived neural progenitor cells revealed a decrease in the length of primary cilia and in the total number of ciliated cells. This study paves the way to understanding the impact of MBD5 haploinsufficiency in brain development through its potential impact on neural primary cilia.

SUBMITTER: Martins M

PROVIDER: S-EPMC10454663 | biostudies-literature | 2023 Aug

REPOSITORIES: biostudies-literature

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A Novel Genetic Variant in MBD5 Associated with Severe Epilepsy and Intellectual Disability: Potential Implications on Neural Primary Cilia.

Martins Mariana M Oliveira Ana Rafaela AR Martins Solange S Vieira José Pedro JP Perdigão Pedro P Fernandes Ana Rita AR de Almeida Luís Pereira LP Palma Paulo Jorge PJ Sequeira Diana Bela DB Santos João Miguel Marques JMM Duque Frederico F Oliveira Guiomar G Cardoso Ana Luísa AL Peça João J Seabra Catarina Morais CM

International journal of molecular sciences 20230809 16

Disruptions in the MBD5 gene have been linked with an array of clinical features such as global developmental delay, intellectual disability, autistic-like symptoms, and seizures, through unclear mechanisms. MBD5 haploinsufficiency has been associated with the disruption of primary cilium-related processes during early cortical development, and this has been reported in many neurodevelopmental disorders. In this study, we describe the clinical history of a 12-year-old child harbori ...[more]

PMID: 37628781

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Project description:ObjectiveThe phenotypic and genotypic spectrum of adult patients with epilepsy and intellectual disability (ID) is less clear than in children. We investigated an adult patient cohort to further elucidate this and inform the genetic testing approach.MethodsFifty-two adult patients (30 male, 22 female) with epilepsy, at least mild ID and no known genetic or acquired cause were included and phenotyped. Variants identified through exome sequencing were evaluated using ACMG criteria. Identified variants were compared with commercially available gene panels. Cluster analysis of two features, age at seizure onset and age at ascertainment of cognitive deficits, was performed.ResultsMedian age was 27 years (range 20-57 years) with median seizure onset at 3 years and median ascertainment of cognitive deficits at 1 year. Likely pathogenic/pathogenic variants were identified in 16/52 patients (31%) including 14 (27%) single nucleotide variants and 2 (4%) copy number variants. Simulated yield of commercial gene panels varied between 13% in small (≤144 genes) and 27% in large panels (≥1478 genes). Cluster analysis (optimal number 3 clusters) identified a cluster with early seizure onset and early developmental delay (developmental and epileptic encephalopathy, n = 26), a cluster with early developmental delay but late seizure onset (ID with epilepsy, n = 16) and a third cluster with late ascertainment of cognitive deficits and variable seizure onset (n = 7). The smaller gene panels particularly missed the genes identified in the cluster with early ascertainment of cognitive deficits and later onset of epilepsy (0/4) as opposed to the cluster with developmental and epileptic encephalopathy (7/10).SignificanceOur data indicates that adult patients with epilepsy and ID represent a heterogeneous cohort that includes grown-up patients with DEE but also patients with primary ID and later onset of epilepsy. To maximize diagnostic yield in this cohort either large gene panels or exome sequencing should be used.

Project description:ObjectiveHeterozygous variants in KCNQ2 or, more rarely, KCNQ3 genes are responsible for early-onset developmental/epileptic disorders characterized by heterogeneous clinical presentation and course, genetic transmission, and prognosis. While familial forms mostly include benign epilepsies with seizures starting in the neonatal or early-infantile period, de novo variants in KCNQ2 or KCNQ3 have been described in sporadic cases of early-onset encephalopathy (EOEE) with pharmacoresistant seizures, various age-related pathological EEG patterns, and moderate/severe developmental impairment. All pathogenic variants in KCNQ2 or KCNQ3 occur in heterozygosity. The aim of this work was to report the clinical, molecular, and functional properties of a new KCNQ3 variant found in homozygous configuration in a 9-year-old girl with pharmacodependent neonatal-onset epilepsy and non-syndromic intellectual disability.MethodsExome sequencing was used for genetic investigation. KCNQ3 transcript and subunit expression in fibroblasts was analyzed with quantitative real-time PCR and Western blotting or immunofluorescence, respectively. Whole-cell patch-clamp electrophysiology was used for functional characterization of mutant subunits.ResultsA novel single-base duplication in exon 12 of KCNQ3 (NM_004519.3:c.1599dup) was found in homozygous configuration in the proband born to consanguineous healthy parents; this frameshift variant introduced a premature termination codon (PTC), thus deleting a large part of the C-terminal region. Mutant KCNQ3 transcript and protein abundance was markedly reduced in primary fibroblasts from the proband, consistent with nonsense-mediated mRNA decay. The variant fully abolished the ability of KCNQ3 subunits to assemble into functional homomeric or heteromeric channels with KCNQ2 subunits.SignificanceThe present results indicate that a homozygous KCNQ3 loss-of-function variant is responsible for a severe phenotype characterized by neonatal-onset pharmacodependent seizures, with developmental delay and intellectual disability. They also reveal difference in genetic and pathogenetic mechanisms between KCNQ2- and KCNQ3-related epilepsies, a crucial observation for patients affected with EOEE and/or developmental disabilities.

Dataset Information

A Novel Genetic Variant in MBD5 Associated with Severe Epilepsy and Intellectual Disability: Potential Implications on Neural Primary Cilia.

Publications

A Novel Genetic Variant in <i>MBD5</i> Associated with Severe Epilepsy and Intellectual Disability: Potential Implications on Neural Primary Cilia.

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