Approximately 75% of LQTS is caused by pathogenic variants in the potassium ion channel subunits KCNQ1 (LQT1, 35%) and KCNH2 (LQT2, 30%), and the sodium ion channel subunit SCN5A (LQT3, 10%). The gene discussed is KCNQ1; the disease is familial long QT syndrome.