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, 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, consistent with stress-induced immobility episodes observed in 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.
