Sodium channel mutations in paramyotonia congenita and hyperkalemic periodic paralysis

Clinical and electrophysiological data have outlined a spectrum of similar yet distinct periodic paralyses, including potassium‐sensitive (hyperkalemic periodic paralysis [HYPP]) and temperature‐sensitive (paramyotonia congenita [PC]) forms. Recent work has revealed that these disorders result from allelic defects in the x‐subunit of the adult, human skeletal muscle sodium channel. We report an additional mutation, a leucine ‐ arginine substirution in the ss segment of domain 4 (L1433R), that results in the PC phenotype. Five other HYPP and PC families have been ascertained, and previously reported sodium channel mutations have been identified in each. Characterization of these mutartions and phenotypic variations in such familes will contribute to the understanding of sodium channel structure and function relationships, as well as channel malfunction in the periodic paralyses.