Anti-neutrophil cytoplasmic autoantibody-associated vasculitis (AAV) is a systemic autoimmune disease characterized by destructive vascular inflammation, which is associated with autoantibodies directed against the neutrophil granule proteins myeloperoxidase (MPO) or proteinase 3 (PR3). The gene discussed is MPO; the disease is anti-neutrophil cytoplasmic antibody-associated vasculitis.