KCNH2 and Familial short QT syndrome: Genetic studies have shown that the pathogenesis of SQTS is related to abnormal cardiac ion channels that regulate the cardiac action potential (Table 1) [23], such as (1) functional gain mutations in the voltage-gated potassium channel subunit coding genes KCNH2, KCNJ2, and KCNQ1, resulting in shortened phase 3 repolarization; (2) loss-of-function mutations in the voltage-gated calcium channel subunit coding gene CACNA2D1, leading to a shortened QT interval, manifested as SQTS, and phenotype overlap with BrS [24].