SCN4A/Nav1.4 is predominantly expressed in skeletal muscles, and mutations in Nav1.4 are associated with multiple skeletal muscle disorders including myotonia, paramyotonia congenita (PC), hyper or hypokalemic periodic paralysis (hyperPP or hypoPP), and congenital myasthenic syndrome (CMS). Here, SCN4A is linked to paramyotonia congenita of Von Eulenburg.