Variants of the SCN4A gene encoding human Nav1.4 (hNav1.4), expressed in the skeletal muscle, are associated with autosomal-dominantly inherited muscle diseases such as sodium channel myotonia, paramyotonia congenita, hyperkalemic periodic paralysis, and hypokalemic periodic paralysis [4, 5]. The gene discussed is SCN4A; the disease is hypokalemic periodic paralysis.