KCNQ5 and familial long QT syndrome: Although remarkable genetic heterogeneity is observed in LQTS, KCNQ1 (LQT1) and KCNH2 (LQT2), which encode potassium channel proteins, and SCN5A (LQT3), encoding a sodium channel protein, are foremost in importance, in that more than 90% of LQTS patients with identified mutations carry variants in these genes18.