While c-ANCA or p-ANCA are detected by immunofluorescence, a separate test is needed to detect proteinase 3 (PR3)-ANCA or myeloperoxidase (MPO)-ANCA, and is mandatory for the diagnosis of ANCA-associated vasculitis (AAV) [7]. The gene discussed is MPO; the disease is anti-neutrophil cytoplasmic antibody-associated vasculitis.