Mutations of SCN4A are consequently associated with a range of neuromuscular phenotypes without systemic involvement, including autosomal‐dominant myotonia, and/or periodic paralysis, and autosomal recessive congenital myasthenia and congenital myopathy.1, 2, 3 Respiratory and laryngeal muscle compromise is common in affected infants and children and can cause life‐threatening respiratory impairment including recurrent apneas.4 The autosomal‐dominant SCN4A disorders such as myotonia are episodic. The gene discussed is SCN4A; the disease is congenital myopathy with cores.