atrial fibrillation, familial, 9 (Monarch Disease Ontology identifier MONDO_0013513) is any familial atrial fibrillation in which the cause of the disease is a mutation in the KCNJ2 gene. Also known as: KCNJ2 familial atrial fibrillation, atrial fibrillation, familial, type 9, familial atrial fibrillation caused by mutation in KCNJ2.