Lundby et al. [55] demonstrated that the Q147R mutation in KCNQ1 represents a ‘loss-of-function’ KCNQ1 mutation (molecular substrate for AF) when co-expressed with KCNE1, but a ‘gain-of-function’ mutation when co-expressed with KCNE2, alone or with KCNE1 (molecular substrate for QT prolongation). This evidence concerns the gene KCNQ1 and atrial fibrillation.