Familial atrioventricular septal defect

A spectrum of septal defects involving the atrial septum; ventricular septum; and the atrioventricular valves (tricuspid valve; bicuspid valve). These defects are due to incomplete growth and fusion of the endocardial cushions which are important in the formation of two atrioventricular canals, site of future atrioventricular valves.