These diseases are classified as anti-neutrophil cytoplasmic antibody–associated vasculitis (AAV) on the basis of their association with anti-neutrophil cytoplasmic antibodies (ANCA) that target proteinase 3 (PR3) or myeloperoxidase (MPO) antigens [1]. This evidence concerns the gene MPO and anti-neutrophil cytoplasmic antibody-associated vasculitis.