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. The gene discussed is SCN4A; the disease is congenital myopathy with cores.