In the LQTS subcohort, 26 index cases were genetically analyzed, identifying a total of 62 genetic variants in 24 of them: 18 in genes with a definitive clinical validity to LQTS (KCNH2, KCNQ1, SCN5A, and CALM1), 1 in a gene with a moderate clinical validity (CACNA1C), 1 in a gene with limited clinical validity (KCNE1), 4 in a gene with disputed clinical validity (ANK2) and 17 in genes with no association to LQTS. Here, SCN5A is linked to familial long QT syndrome.