KCNH2 and familial long QT syndrome: Mutations in at least 17 genes have been associated with LQTS, with LQTS type 1 (LQT1) (KCNQ1 gene), LQTS type 2 (LQT2) (KCNH2 gene), and LQTS type 3 (LQT3) (SCN5A gene) accounting for ∼80%–90% of genotype-positive cases.6