In the far majority of clinically definite LQTS cases mutations in LQTS genes are found, with KCNQ1  (LQT1),KCNH2  (LQT2), andSCN5A   (LQT3) as the most common LQTS genes, accounting for ≈90% of all genotype-positive cases [97, 114]. This evidence concerns the gene KCNH2 and familial long QT syndrome.