KCNH2 and familial long QT syndrome: It should benoted that the KCNQ1, KCNH2, andSCN5A genes, mutations in which cause LQTS 1, 2 and 3,respectively, are so-called “major” LQTS genes, and mutations inthem imply a high probability of congenital LQTS and is important for riskstratification (see below).