SCN5A and familial long QT syndrome: Mutations in three genes are responsible for the vast majority of LQTS cases in humans, namely KCNQ1 encoding Kv7.1 channel α-subunit (LQT1, 35% of cases), KCNH2 encoding Kv11.1 channel α-subunit (LQT2, 30% of cases), and SCN5A encoding Nav1.5 Na+ channel α-subunit (LQT3, 10% of cases).