KCNQ1 and familial long QT syndrome: Hermans et al. (2020) demonstrated QTc cutoffs >480 ms had the poorest performance with regards to diagnostic accuracy for both the study cohort (Amsterdam data) and external cohort (Leuven data), that being 62% and 52%, respectively, in individuals with LQTS (LQT1, LQT2, LQT3) compared to genotype negative family member controls.