So far, mutations in 17 genes have been associated with LQTS [75, 78]: (1) three genes were classified as definitive genes for typical LQTS (KCNQ1, KCNH2, and SCN5A), (2) four genes with a strong evidence for causality in LQTS with atypical features (CALM1, CALM2, CALM3, and TRDN), (3) one gene with a moderate level evidence for causing this disease (CACNA1C), and (4) nine genes as having limited or disputed evidence as LQTS-causative genes (AKAP9, ANK2, CAV3, KCNE1, KCNE2, KCNJ2, KCNJ5, SCN4B, and SNTA1) [78]. The gene discussed is KCNJ5; the disease is familial long QT syndrome.