Any atrioventricular septal defect in which the cause of the disease is a mutation in the GATA6 gene. The disease is Monarch Disease Ontology id MONDO_0013769 (atrioventricular septal defect 5). Also known as: GATA6 atrioventricular septal defect, atrioventricular septal defect caused by mutation in GATA6, atrioventricular septal defect type 5.