Our report is the third case of a homozygous recessive mutation in SCN4A found in CMS/congenital myopathy, and all 3 missense mutations are at arginine residues in the S4 segment of the domain IV voltage sensor (p.R1454W6, p.R1457H7, and p.R1460W). Here, SCN4A is linked to congenital myopathy with cores.