KCNH2 and familial long QT syndrome: Strong genotype–phenotype relationships have been found for the three main types of LQTS (ie, LQT1, LQT2, and LQT3), with more benign and malignant variants identified.8–10 The most common mutations associated with each genotype include LQT1 on KvLQT1 (alpha subunit on IKs potassium channel protein), LQT2 on HERG (IKr potassium channel protein), and LQT3 on SCN5A (cardiac sodium channel), respectively; all three can cause abnormally prolonged ventricular repolarization.11