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

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, BK(N999S) and BK(D434G) channels displayed gain-of-function (GOF) properties, whereas BK(H444Q) channels showed loss-of-function (LOF) properties. The relative degree of channel activity was BK(N999S) > BK(D434G)>WT > BK(H444Q). BK currents and action potential firing were increased, and seizure thresholds decreased, in Kcnma1(N999S/WT) and Kcnma1(D434G/WT) transgenic mice but not Kcnma1(H444Q/WT) mice. In a novel behavioral test for paroxysmal dyskinesia, the more severely affected Kcnma1(N999S/WT) mice became immobile after stress. This was abrogated by acute dextroamphetamine treatment, consistent with PNKD3-affected individuals. Homozygous Kcnma1(D434G/D434G) mice showed similar immobility, but in contrast, homozygous Kcnma1(H444Q/H444Q) mice displayed hyperkinetic behavior. These data establish the relative pathogenic potential of patient alleles as N999S>D434G>H444Q and validate Kcnma1(N999S/WT) mice as a model for PNKD3 with increased seizure propensity.