KCNH2 and familial long QT syndrome: LQT1, LQT2, and LQT3 are distinct subtypes of LQTS, with LQT1 caused by variants in the KCNQ1 gene, LQT2 caused by variants in the KCNH2 gene, and LQT3 caused by variants in the SCN5A gene, highlighting different affected ion channels and underlying mechanisms contributing to prolonged QT interval and arrhythmia susceptibility (54).