KCNA3 and familial long QT syndrome: The recognition that both drug induced and the LQT2 form of congenital LQTS affect the IKr channel has suggested that some patients who have drug induced LQTS may have a predisposing forme fruste of congenital LQTS, the hypothesis being that their underlying defect makes them susceptible to TdP when repolarization is further impaired by administration of drugs which decrease potassium channel function [62-65].