KCNQ1 and atrial fibrillation: To further characterize the functional consequences of this KCNQ1 AF risk allele, we analyzed the electrophysiological properties of patient-specific cardiomyocytes differentiated from induced pluripotent stem cells (iPSC-CMs) obtained from 2 distantly related (9 meioses separation) heterozygous KCNQ1 R231H mutation carriers with a young-onset AF phenotype compared to a healthy, non-carrier first-degree relative sibling control and an unrelated control subject.