Long QT syndrome (LQTS) is an inherited ion channel disorder manifesting with prolongation of the cardiac repolarization phase and severe ventricular arrhythmias. The common KCNE1 D85N potassium channel variant prolongs QT interval by inhibiting IKs (KCNQ1) and IKr (KCNH2) currents and is therefore a suitable candidate for a modifier gene in LQTS.