Hyperkalemic Periodic Paralysis Caused by a Mutation in the Sodium Channel SCN4A Gene

Abstract

Hyperkalemic periodic paralysis (HyperPP) is an autosomal dominant muscle sodium channelopathy characterized by recurrentepisode of reversible paralysis with concomitant hyperkalemia. The diagnosis of HyperPP is suggested by a history of attacks ofparalysis, positive family history, and the presence of myotonia. A 19-year-old man presented with recurrent generalized limbweakness since childhood. The paralysis often followed by fatigue, exercise, and fasting. His parents were clinically unaffectedand had never experienced paralytic symptoms. Electromyographic evaluation demonstrated myotonic discharge. Directsequencing of SCN4A exon 24 revealed a heterozygous A>G transition at nucleotide 4774, resulting in the substitution of amethionine by a valine at codon 1592 (Met1592Val). We report a patient with HyperPP confirmed by Met1592Val mutation inSCN4A gene.