KCNH2 and long QT syndrome 3: Although mutations of 17 different genes have been currently identified in clinically diagnosed LQTS, > 90% of genotype-positive cases involve three genes only, i.e. KCNQ1 (encoding Kv7.1 channel α-subunit, conducting the slow delayed rectifier potassium current IKs; LQT1), KCNH2 [Kv11.1 (also named hERG, human ether-à-go-go-related gene K+-channel) conducting the rapid delayed rectifier potassium current IKr; LQT2], and SCN5A (Nav1.5, conducting the sodium current INa; LQT3) (El-Sherif et al., 2017).