SCN5A and familial long QT syndrome: To date at least 15 genes have been identified to be responsible for different subtypes of the syndrome3,4, with the first three LQTS (LQT1-3, caused by mutations in KCNQ1, KCNH2, and SCN5A genes, respectively) being the most common and accounting for approximately 75% of genotype-positive LQTS population3.