SCN5A and familial long QT syndrome: The corresponding LQTS subtypes LQT1 (KCNQ1), LQT2 (KCNH2) and LQT3 (SCN5A) account for 40–55 %, 30–35 % and 5–10 % of all LQTS cases, with different molecular mechanisms leading to QTc prolongation.