Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease characterized by necrotizing small-vessel inflammation, and it is associated with the presence of myeloperoxidase (MPO)-ANCA or proteinase 3 (PR3)-ANCA. The gene discussed is MPO; the disease is anti-neutrophil cytoplasmic antibody-associated vasculitis.