BK channel properties correlate with neurobehavioral severity in three KCNMA1-linked channelopathy mouse models

Abstract

KCNMA1 forms the pore of BK K+ channels, which regulate neuronal and muscle excitability. Recently, genetic screening identified heterozygous KCNMA1 variants in a subset of patients with debilitating paroxysmal non-kinesigenic dyskinesia, presenting with or without epilepsy (PNKD3). However, the relevance of KCNMA1 mutations and the basis for clinical heterogeneity in PNKD3 has not been established. Here we evaluate the relative severity of three KCNMA1 patient variants in BK channels, neurons, and mice. In heterologous cells, BKN999S and BKD434G channels displayed gain-of-function (GOF) properties, whereas BKH444Q channels showed loss-of-function (LOF) properties. The relative degree of channel activity was BKN999S > BKD434G > WT > BKH444Q. BK currents and action potential firing were increased, and seizure thresholds decreased, in Kcnma1N999S/WT and Kcnma1D434G/WT transgenic mice but not Kcnma1H444Q/WT mice. In a novel behavioral test for paroxysmal dyskinesia, the more severely affected Kcnma1N999S/WT mice became immobile after stress, consistent with stress-induced immobility episodes observed in PNKD3 patients. Homozygous Kcnma1D434G/D434G mice showed similar immobility, but in contrast, homozygous Kcnma1H444Q/H444Q mice displayed hyperkinetic behavior. These data establish the relative pathogenic potential of patient alleles as N999S > D434G > H444Q and validate Kcnma1N999S/WT mice as a model for PNKD3 with increased seizure propensity.

Effect of an autism-associated KCNMB2 variant, G124R, on BK channel properties

“…In addition to reporting the patient phenotype, a basic functional investigation of the G124R mutation β2 on BK channel activity in physiological K + conditions revealed limited gain-of-function (GOF) effects on activation and deactivation gating kinetics (speeding activation and slowing deactivation). This kinetic effect is similar in nature, although smaller in magnitude, with two other KCNMA1 mutations that cause seizures and dyskinesia ( Moldenhauer et al, 2020 ; Park et al, 2022 ). Some of these KCNMA1 channelopathy patients also have autism and learning disability, but ASD and intellectual/learning diagnoses are not exclusive to the GOF population and are additionally found in patients harboring loss-of-function variants (LOF) and variants of uncertain significance (VUS) ( Bailey et al, 2019 ; Heim et al, 2020 ; Miller et al, 2021 ).…”