SCN4A and Congenital myasthenic syndromes: Mutations in Nav1.4 have been associated with various neuromuscular disorders, including SCN4A-related myotonia, paramyotonia congenita of von Eulenburg, congenital myasthenic syndrome, hypokalemic periodic paralysis type 2, hyperkalemic periodic paralysis and normokalemic periodic paralysis [17,18].