BK channel properties correlate with neurobehavioral severity in three <i>KCNMA1</i>-linked channelopathy mouse models.

Abstract

KCNMA1 forms the pore of BK K⁺ channels, which regulate neuronal and muscle excitability. Recently, genetic screening identified heterozygous <i>KCNMA1</i> variants in a subset of patients with debilitating paroxysmal non-kinesigenic dyskinesia, presenting with or without epilepsy (PNKD3). However, the relevance of <i>KCNMA1</i> mutations and the basis for clinical heterogeneity in PNKD3 has not been established. Here, we evaluate the relative severity of three <i>KCNMA1</i> 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 <i>Kcnma1</i>^N999S/WT and <i>Kcnma1</i>^D434G/WT transgenic mice but not <i>Kcnma1</i>^H444Q/WT mice. In a novel behavioral test for paroxysmal dyskinesia, the more severely affected <i>Kcnma1</i>^N999S/WT mice became immobile after stress. This was abrogated by acute dextroamphetamine treatment, consistent with PNKD3-affected individuals. Homozygous <i>Kcnma1</i>^D434G/D434G mice showed similar immobility, but in contrast, homozygous <i>Kcnma1</i>^H444Q/H444Q mice displayed hyperkinetic behavior. These data establish the relative pathogenic potential of patient alleles as N999S>D434G>H444Q and validate <i>Kcnma1</i>^N999S/WT mice as a model for PNKD3 with increased seizure propensity.