Any atrial heart septal defect in which the cause of the disease is a mutation in the GATA6 gene. The disease is atrial septal defect 9 (MONDO_0013770, a Monarch Disease Ontology term). Also known as: ASD9, GATA6 atrial heart septal defect, atrial heart septal defect caused by mutation in GATA6, atrial heart septal defect type 9, atrial septal defect type 9.