A Novel Mutation in the Gene for the Adult Skeletal Muscle Sodium Channel α-Subunit (SCN4A) That Causes Paramyotonia Congenita of von Eulenburg

Abstract
PARAMYOTONIA congenita (PMC) is an autosomal dominant muscular disease characterized by paradoxical and cold-induced myotonia.1 Paramyotonia congenita has been subdivided into PMC of von Eulenburg (Mendelian Inheritance in Man [MIM 168300])—accompanied by cold-induced paralysis—and PMC without cold paralysis (MIM 168350). Hyperkalemic periodic paralysis (MIM 170500) is also a dominantly inherited disease in which periodic paralysis is associated with hyperkalemia. Because hyperkalemic periodic paralysis can occur in some families with PMC, it has been suggested that the 2 diseases share a common etiologic basis. In fact, PMC and hyperkalemic periodic paralysis have been genetically mapped to the same locus on chromosome 17q23-25,2,3 and various missense mutations in the gene for the subunit of the skeletal muscle sodium channel (SCN4A) at this locus have been identified as causative mutations for both diseases.4-7 Furthermore, other autosomal dominant myotonias characterized by potassium sensitivity (potassium-aggravated myotonia) have also been demonstrated to be caused by mutations in the SCN4A gene.8-18