SCN4B and familial long QT syndrome: The latter is caused by variants in genes encoding ion channels or associated proteins and contains long QT syndrome (LQTS) for which the genes KCNQ1, KCNH2, SCN5A, CAV3, GPD1-L, SNTA1, SCN1B, SCN2B, SCN3B, and SCN4B are of great importance (mutations in the first three genes explain 80–90% of LQTS with the remaining genes having rare mutations [27]).