Strain‐dependence of seizures in a mouse model of a Kcnb1 mutant

Abstract

KCNB1 encodes the Kv2.1 voltage‐gated potassium channel α subunit. Pathogenic variants in KCNB1 cause a neurodevelopmental disorder that includes infant onset epilepsy characterized by multiple seizure types, global developmental delay, and cognitive, motor and behavioral impairments. The KCNB1‐G379R mutation was identified by clinical whole exome sequencing in a patient with global developmental delay, refractory seizures, and abnormal EEG with background slowing, multifocal spikes, and polyspikes. A mouse model of this mutation was generated using CRISPR/Cas9 genome editing. The Kcnb1G379R mutant mouse displays spontaneous seizures, reduced thresholds to induced seizures, and neurobehavioral abnormalities compared to wildtype (WT) littermates. Genetic modifiers are non‐pathogenic alleles that affect penetrance and severity of disease. Modifiers influence phenotype expression in monogenic disorders and can confer protective or risk effects. In mouse models, strain‐dependent severity of disease‐causing genotypes suggests the presence of modifier loci. For Kcnb1G379R, we surveyed strain‐dependence of phenotypes in F1 and F2 crosses with 6 inbred strains. Our objective was to evaluate the influence of strain background on spontaneous seizures and induced seizure thresholds in the Kcnb1G379R mouse model. Kcnb1G379R mice isogenic on the C57BL/6J (B6) background (B6.Kcnb1G379R) sometimes exhibit spontaneous seizures upon transfer to a clean cage. To determine if these spontaneous seizures are affected by strain background, we systematically evaluated spontaneous seizures in homozygous Kcnb1G379R/G379R F2 offspring from crosses with PWK/PhJ, C3H/FeJ, NOD/ShiLtJ, LP/J, and DBA/2J. Over a 6‐week period, a blinded observer moved mice individually to a clean cage and observed for spontaneous seizures (n=12/sex and genotype). Kcnb1G379R/G379R mice on the [B6xDBA/2J]F2 background had no spontaneous seizures, compared to 9/24 B6.Kcnb1G379R/G379R with spontaneous seizures in at least one observation. A similar number (8/24) of [B6xNOD/ShiLtJ]F2 mice had spontaneous seizures, while a lower proportion of [B6xLP/J]F2, [B6xPWK/PhJ]F2, and [B6xC3H/FeJ]F2 mice had spontaneous seizures (2/24). A subset of mice had seizures in multiple observations over the course of the 6 weeks. B6.Kcnb1G379R mice have reduced latency to seizures induced by flurothyl compared to WT littermates. At 10–12 weeks of age, F2 mice were evaluated for latency to flurothyl‐induced seizures, as well as severity. B6.Kcnb1G379R/G379R homozygotes had reduced latency and increased severity relative to WT littermates. [B6xC3H/FeJ]F2 and [B6xLP/J]F2 homozygous Kcnb1G379R/G379R mutants had reduced latency, but decreased severity compared to WT and heterozygous littermates. Variable strain‐dependent susceptibility to spontaneous and induced seizures suggest the presence of modifier alleles that influence the Kcnb1G379R phenotype. Future genetic mapping will localize modifier loci that influence seizure susceptibility.Support or Funding InformationSupported by NIH/NINDS R01 NS053792This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.