Pathogenic variants in one of the three major genes associated with LQTS, namely, KCNQ1, KCNH2, and SCN5A, account for most of the mutation-positive cases (5, 6): 40–55% of patients have LQTS type 1 (LQT1) due to loss-of-function variants in KCNQ1, which encodes the α-subunit of the K+-channel KV7.1, generating the repolarizing outward K+-current IKs (3). This evidence concerns the gene SCN5A and familial long QT syndrome.