<b>Abbreviations:</b> GPA = granulomatosis with polyangiitis, EGPA = eosinophilic granulomatosis with polyangiitis, MPA = Microscopic polyangiitis, ANCA = Anti-neutrophil cytoplasmic antibodies, c-ANCA = ANCA to proteinase-3, p-ANCA = ANCA to myeloperoxidase, ELISAs = antigen-specific enzyme-linked immunosorbent assays, ENT = ear, nose, throat, CP = cyclophosphamide, NSAIDs = nonsteroidal anti-inflammatory drugs, AZA = azathioprine, GC = glucocorticoids. This evidence concerns the gene MPO and granulomatosis with polyangiitis.