KCNH2 and Prolonged QT interval: The underlying genetic defects of long QT syndrome were first described in the 1990s, identifying three genes (KCNQ1, KCNH2, and SCN5A) that encoded ion channel proteins (KvLQT1, hERG, and NaV 1.5) responsible for transmembrane ion currents critical to cardiac depolarization and repolarization.