NDMs comprise a heterogeneous group of neuromuscular disorders caused by mutations of skeletal muscle chloride channels (CLCN1) and sodium channels (SCN4A), and include myotonia congenita, paramyotonia congenital (PMC), potassium-aggravated myotonia or sodium channel myotonia, and hyperkalemic periodic paralysis (HYPP) [1–3]. The gene discussed is SCN4A; the disease is hyperkalemic periodic paralysis.