GDF1 and familial atrioventricular septal defect: Both Alagille Syndrome 1 ALGS1 (MIM:118450) and Right Atrial Isomerism RAI (MIM:208530) not only share phenotypic similarities with TOF such as pulmonary stenosis (ALGS1) and complete atrioventricular septal defects (RAI), but also have disease genes in common with TOF, namely JAG1 and GDF1 (ref. [11]).