SCN5A and familial long QT syndrome: In the five largest LQTS population surveys that have been published to date, involving the five most common LQTS-causing genes (KCNQ1, KCNH2, SCN5A, KCNE1 and KCNE2), the mutation yield was 72%, 51%, 50%, 36%, and 32%, respectively (Table 4)[8,12-15].