SCN4A and congenital myopathy: Compound heterozygous or homozygous loss-of-function NaV1.4 variants (including the previously reported Val1442Met variant) cause myasthenic syndrome and congenital myopathy.12, 14 Some of these patients need respiratory support.12, 14 These observations support the notion that disrupted sodium channel function in the respiratory muscles can contribute to life-threatening events.