Hypokalemic periodic paralysis: an autosomal dominant muscle disorder caused by mutations in a voltage-gated calcium channel.

Hypokalemic periodic paralysis (hypoPP) is an autosomal dominant disorder characterized by acute attacks of muscle weakness concomitant to a drop in blood potassium levels. Recent molecular work has shown that hypoPP is due to mutations in a skeletal muscle voltage-gated calcium channel: the dihydropyridine receptor (DHP receptor). Mutations affect segments S4 of domains II and IV, changing an arginine in position 528 and 1239 into an histidine, or an histidine or a glycine respectively. Surprisingly, expressing in vitro mutants channels in a non-muscular environment resulted in functional calcium channels with minor modifications in electrophysiological properties. Expressing mutant channels in a muscular environment or transgenic mice might help to bridge the gap between the knowledge of the molecular defect and the understanding of the pathophysiology of the disease.