Iwasa et al. (2000) were the first to report on the c.1673A > G single nucleotide polymorphism (“SNP”) in the SCN5A gene, which is responsible for the replacement of histidine (H) with arginine (R) at position 558 of the NaV1.5 protein (p.His558Arg or H558R), in relation to familial LQTS. Here, SCN5A is linked to familial long QT syndrome.