A congenital myasthenic syndrome with ptosis, bulbar weakness, respiratory difficulties, and prolonged episodes of weakness more typical for periodic paralysis has been associated with missense mutations of SCN4A that cause a LOF by markedly enhancing channel inactivation.5, –, 7 More recently, congenital myopathy with neonatal hypotonia has been reported in patients with null mutations in SCN4A. Here, SCN4A is linked to Congenital myasthenic syndromes.