Intestinal-cell kinase and juvenile myoclonic epilepsy

No abstract available

Phenotype-genotype complexities: opening DOORS

Samuel F Berkovic, Jozef Gec

Nomenclature of Genetically Determined Myoclonus Syndromes:Recommendations of the International Parkinson and Movement Disorder Society Task Force

Genetically determined myoclonus disorders are a result of a large number of genes. They have wide clinical variation and no systematic nomenclature. With next-generation sequencing, genetic diagnostics require stringent criteria to associate genes and phenotype. To improve (future) classification and recognition of genetically determined movement disorders, the Movement Disorder Society Task Force for Nomenclature of Genetic Movement Disorders (2012) advocates and renews the naming system of locus symbols. Here, we propose a nomenclature for myoclonus syndromes and related disorders with myoclonic jerks (hyperekplexia and myoclonic epileptic encephalopathies) to guide clinicians in their diagnostic approach to patients with these disorders. Sixty-seven genes were included in the nomenclature. They were divided into 3 subgroups: prominent myoclonus syndromes, 35 genes; prominent myoclonus syndromes combined with another prominent movement disorder, 9 genes; disorders that present usually with other phenotypes but can manifest as a prominent myoclonus syndrome, 23 genes. An additional movement disorder is seen in nearly all myoclonus syndromes: ataxia (n = 41), ataxia and dystonia (n = 6), and dystonia (n = 5). However, no additional movement disorders were seen in related disorders. Cognitive decline and epilepsy are present in the vast majority. The anatomical origin of myoclonus is known in 64% of genetic disorders: cortical (n = 34), noncortical areas (n = 8), and both (n = 1). Cortical myoclonus is commonly seen in association with ataxia, and noncortical myoclonus is often seen with myoclonus-dystonia. This new nomenclature of myoclonus will guide diagnostic testing and phenotype classification. (c) 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society

A variant of KCC2 from patients with febrile seizures impairs neuronal Cl- extrusion and dendritic spine formation

Genetic variation in SLC12A5 which encodes KCC2, the neuron‐specific cation‐chloride cotransporter that is essential for hyperpolarizing GABAergic signaling and formation of cortical dendritic spines, has not been reported in human disease. Screening of SLC12A5 revealed a co‐segregating variant (KCC2‐R952H) in an Australian family with febrile seizures. We show that KCC2‐R952H reduces neuronal Cl− extrusion and has a compromised ability to induce dendritic spines in vivo and in vitro. Biochemical analyses indicate a reduced surface expression of KCC2‐R952H which likely contributes to the functional deficits. Our data suggest that KCC2‐R952H is a bona fide susceptibility variant for febrile seizures.Peer reviewe

A variant of KCC2 from patients with febrile seizures impairs neuronal Cl- extrusion and dendritic spine formation

Genetic variation in SLC12A5 which encodes KCC2, the neuron‐specific cation‐chloride cotransporter that is essential for hyperpolarizing GABAergic signaling and formation of cortical dendritic spines, has not been reported in human disease. Screening of SLC12A5 revealed a co‐segregating variant (KCC2‐R952H) in an Australian family with febrile seizures. We show that KCC2‐R952H reduces neuronal Cl− extrusion and has a compromised ability to induce dendritic spines in vivo and in vitro. Biochemical analyses indicate a reduced surface expression of KCC2‐R952H which likely contributes to the functional deficits. Our data suggest that KCC2‐R952H is a bona fide susceptibility variant for febrile seizures.Peer reviewe

Progressive Myoclonus Epilepsy Caused by a Homozygous Splicing Variant of SLC7A6OS

Exome sequencing was performed in 2 unrelated families with progressive myoclonus epilepsy. Affected individuals from both families shared a rare, homozygous c.191A > G variant affecting a splice site in SLC7A6OS. Analysis of cDNA from lymphoblastoid cells demonstrated partial splice site abolition and the creation of an abnormal isoform. Quantitative reverse transcriptase polymerase chain reaction and Western blot showed a marked reduction of protein expression. Haplotype analysis identified a similar to 0.85cM shared genomic region on chromosome 16q encompassing the c.191A > G variant, consistent with a distant ancestor common to both families. Our results suggest that biallelic loss-of-function variants in SLC7A6OS are a novel genetic cause of progressive myoclonus epilepsy. ANN NEUROL 2020Peer reviewe

Functional correlates of clinical phenotype and severity in recurrent SCN2A variants

In SCN2A-related disorders, there is an urgent demand to establish efficient methods for determining the gain- (GoF) or loss-of-function (LoF) character of variants, to identify suitable candidates for precision therapies. Here we classify clinical phenotypes of 179 individuals with 38 recurrent SCN2A variants as early-infantile or later-onset epilepsy, or intellectual disability/autism spectrum disorder (ID/ASD) and assess the functional impact of 13 variants using dynamic action potential clamp (DAPC) and voltage clamp. Results show that 36/38 variants are associated with only one phenotypic group (30 early-infantile, 5 later-onset, 1 ID/ASD). Unexpectedly, we revealed major differences in outcome severity between individuals with the same variant for 40% of early-infantile variants studied. DAPC was superior to voltage clamp in predicting the impact of mutations on neuronal excitability and confirmed GoF produces early-infantile phenotypes and LoF later-onset phenotypes. For one early-infantile variant, the co-expression of the alpha(1) and beta(2) subunits of the Na(v)1.2 channel was needed to unveil functional impact, confirming the prediction of 3D molecular modeling. Neither DAPC nor voltage clamp reliably predicted phenotypic severity of early-infantile variants. Genotype, phenotypic group and DAPC are accurate predictors of the biophysical impact of SCN2A variants, but other approaches are needed to predict severity. A comprehensive biophysical analysis of disease-associated mutations in the voltage-gated sodium channel gene, SCN2A, suggests that dynamic action potential clamp may be a better predictor than voltage clamp of how these mutations alter neuronal excitability, though other approaches are needed to predict severity

A case-control collapsing analysis identifies epilepsy genes implicated in trio sequencing studies focused on de novo mutations

Trio exome sequencing has been successful in identifying genes with de novo mutations (DNMs) causing epileptic encephalopathy (EE) and other neurodevelopmental disorders. Here, we evaluate how well a case-control collapsing analysis recovers genes causing dominant forms of EE originally implicated by DNM analysis. We performed a genome-wide search for an enrichment of "qualifying variants" in protein-coding genes in 488 unrelated cases compared to 12,151 unrelated controls. These "qualifying variants" were selected to be extremely rare variants predicted to functionally impact the protein to enrich for likely pathogenic variants. Despite modest sample size, three known EE genes (KCNT1, SCN2A, and STXBP1) achieved genome-wide significance (p<2.68×10−6). In addition, six of the 10 most significantly associated genes are known EE genes, and the majority of the known EE genes (17 out of 25) originally implicated in trio sequencing are nominally significant (p<0.05), a proportion significantly higher than the expected (Fisher’s exact p = 2.33×10−17). Our results indicate that a case-control collapsing analysis can identify several of the EE genes originally implicated in trio sequencing studies, and clearly show that additional genes would be implicated with larger sample sizes. The case-control analysis not only makes discovery easier and more economical in early onset disorders, particularly when large cohorts are available, but also supports the use of this approach to identify genes in diseases that present later in life when parents are not readily available

Detection of microchromosomal aberrations in refractory epilepsy: a pilot study

ABSTRACT -Seizures often occur in patients with microchromosomal aberrations responsible for moderate to severe intellectual disability. We hypothesised that epilepsy alone could be caused by microdeletions or microduplications, which might also relate to epilepsy refractory to medication. Chromosomes from 20 subjects with epilepsy and repeated failure of antiepileptic medication were examined using molecular methods. Firstly, the 41 subtelomeric regions were scanned using fluorescence in situ hybridization and multiplex ligationdependent probe amplification. Secondly, a genome-wide scan was carried out using oligonucleotide-array comparative genome hybridisation on two platforms: Nimblegen and Agilent. Two aberrations (2/20) were identified: a recurrent microdeletion at 15q13.3 previously characterised in patients with seizures that generally respond to medication, and a novel 1.15 Mb microchromosomal duplication at 10q21.2 also present in the unaffected mother. We conclude that gene content of microchromosomal aberrations is not a major cause of refractory seizures, but that microchromosomal anomalies are found in an appreciable fraction of such cases