KCNH2 and long QT syndrome 3: The three most common subtypes include LQT1, which is caused by mutations in the KCNQ1 (IKs potassium channel [Kv7.1]) gene; LQT2, which results from mutations in the KCNH2 (IKr potassium channel [Kv11.1]) gene; and LQT3, which is associated with mutations in the SCN5A gene (Ina sodium channel [NaV1.5]) [6].