In Sweden, two LQT1 founder mutations, KCNQ1 Y111C [17, 18] and KCNQ1 R518* [19], with an estimated population prevalence of 1:4000 to 1:7000 and 1:2000 to 1:4000 [17, 19, 20], respectively, account for >25% of index cases with molecularly defined LQTS [21]. The gene discussed is KCNQ1; the disease is familial long QT syndrome.