More than 15 forms of LQTS have been described, but most cases fall into 3 subgroups: Long QT syndrome type 1 (LQTS1): loss of function mutation of gene KCNQ1, which encodes an adrenergic-sensitive Kv7.1 channel responsible for the slow outward potassium current (IKs) Long QT syndrome type 2 (LQTS2): loss of function mutation of gene KCNH2, which encodes the hERG channel responsible for the rapid outward potassium current (IKr) Long QT syndrome type 3 (LQTS3): gain-of-function mutation of gene SCN5A, which encodes the Nav1.5 channel responsible for the inward sodium current (INa).