KCNH2 and long QT syndrome 1: This is due to a chaperone effect of KCNQ1-WT that helps to enhance the membrane localization of KCNH2. We measured the E4031 (a specific blocker of the rapid activating delayed rectifier potassium channel (IKr))-sensitive IKr density in hiPSC-CMs from the LQT1 patient and control, and observed no difference between them (data not shown).