Any familial atrial fibrillation in which the cause of the disease is a mutation in the ABCC9 gene. The disease is atrial fibrillation, familial, 12 (MONDO_0013545, a Monarch Disease Ontology identifier). Also known as: ABCC9 familial atrial fibrillation, atrial fibrillation, familial, type 12, familial atrial fibrillation caused by mutation in ABCC9.