Mutations in the sodium channel gene SCN4A encoding the Nav1.4 voltage-gated sodium channel are well-known causes of the skeletal muscle channelopathies: paramyotonia congenita (PMC), other forms of myotonia, and periodic paralyses (hyperkalemic periodic paralysis [HyperPP], normokalemic, and hypokalemic periodic paralysis). The gene discussed is SCN4A; the disease is paramyotonia congenita of Von Eulenburg.