KCNQ1 and familial long QT syndrome: To date, about 1000 mutations in 13 LQTS-susceptibility genes have been identified; however, only three of these genes, namely KCNQ1 (encoding KvLQT1 channel α-subunit, conducting IKs), KCNH2 (encoding hERG channel α-subunit, conducting IKr), and SCN5A (encoding Nav1.5 channel α-subunit, conducting INa), account by themselves for ~75% of all cases (5).