SCN4A and Thomsen and Becker disease: The NDMs are comprised of myotonia congenita (MC) due to mutations in the skeletal muscle chloride channel gene CLCN1 encoding CLC-1 as well as paramyotonia congenita (PMC) and sodium channel myotonia (SCM) caused by mutations in the skeletal muscle sodium channel gene SCN4A encoding Nav1.4 [3].