Moreover, some mutations in the SCN5A gene cause the biophysical defects, or may be in associationed with an increased risk of sudden cardiac death. R1193Q polymorphism (CGG>CAG, refSNP ID rs41261344) in the SCN5A gene is the cause of approximately 13% of patients with LQTS. It seems that R1193Q polymorphism is a functional substitution that disrupts sodium channel function, and consequently increases susceptibility to LQTS . R1193Q polymorphism is a non-conservative missense mutation, a replacement of arginine with glutamine at position 1193, that results in the inactivation of the sodium channel current.