KCNH2 and long QT syndrome 3: Approximately 90% of LQT cases are linked to mutations in the KCNQ1 (type 1 LQT; LQT1), KCNH2 (type 2 LQT; LQT2), and SCN5A (type 3 LQT; LQT3) genes, and about 45% of these cases are caused by changes in the potassium channels KCNQ1 and KCNH2 (5, 6).