KCNQ1 and long QT syndrome 1: The congenital long-QT syndrome (LQTS) type 1 (LQT-1) is associated with life-threatening arrhythmias and sudden cardiac death because of impaired cardiac repolarization due to mutations of the KCNQ1 gene encoding for the slow component of the repolarizing rectifier potassium currents (IKr).