LQTS is diagnosed in the presence of either a QTc ≥ 480 ms, a LQTS risk score > 3 (a diagnostic score including several items regarding ECG, clinical history and family history), or an unequivocally pathogenic mutation in one of the LQTS-associated genes, such as loss-of-function variants of KCNQ1 (LQTS1) or KCNH2 (LQTS2) or gain-of-function variants of SCN5A (LQTS3) [1,6]. The gene discussed is SCN5A; the disease is familial long QT syndrome.