GATA4 and familial atrioventricular septal defect: It remains unclear if the GATA4 G296S mutation has a role in formation of the endocardial cushions but one family member with the G296S mutation did have an atrioventricular septal defect [12] and other non-related individuals with GATA4 mutations have atrioventricular septal defects [13].