Loss-of-function variants of SCN4A cause CMS [79,81,270], whereas gain-of-function variants of SCN4A cause hyperkalemic periodic paralysis [271], hypokalemic periodic paralysis [271], potassium-aggravated myotonia congenita [272], and paramyotonia congenita [273]. This evidence concerns the gene SCN4A and congenital myasthenic syndrome.