SCN5A and familial long QT syndrome: QT prolongation in LQTS might arise from prolongation of action potential duration due to either loss of function in slowly (KCNQ1 mutation in LQT1) or rapidly (KCNH2 mutation in LQT2) acting potassium outward current during phase 3 or to gain of function in late sodium inward current during the late plateau phase (SCN5A mutation in LQT3) [30].