In the growing population of patients with congenital heart defects (CHD), while arrhythmias are not a major issue for children, they are a leading complication during adulthood. My hypothesis is that the origin of some life-threatening arrhythmias in adult, lies in cardiac structural and electrophysiological development. Thus, studying causes of CHDs may reveal key steps, mis-regulated in adult patients with CHD, leading to arrhythmias.Cardiac development and adult electrical function are finely regulated by transcription factors (TFs). Mutations in TFs have previously been linked to patients with CHD who are developing arrhythmias in adulthood. Hamamy syndrome is a newly described rare disease with CHD and rhythm disorders, caused by a mutation in IRX5 TF. In adult mice, Irx5 is known to regulate cardiac electrical function.I hypothesize that IRX5 mutation in Hamamy-affected patients, leads to misregulation of heart development, promoting arrhythmic events during adulthood.I already generated induced pluripotent stem (iPS) cells from Hamamy patients and a transgenic mouse expressing the Irx5 mutation.The project will be focused on three aims: 1. Characterizing the cardiac cellular function altered by IRX5 mutation, using iPS-derived cardiomyocytes; 2. Identifying cardiac structural and electrophysiological defects in the transgenic mouse; 3. Understanding the syndrome’s molecular mechanism.This study will provide immediate insight into understanding fundamental processes by which some arrhythmias in the adult originate in cardiac development. It may also help unveil the mechanism of age-related increase of arrhythmias in the general population. Finally, it will illustrate the ability of human iPS cell technology to model the abnormal functional phenotype of an inherited cardiac disorder. As such, it represents a promising model to study disease mechanisms, optimize patient care (personalized medicine), and aid in the development of new therapies.