In this study, we evaluated the differences between MPO-ANCA(+), [proteinase 3 (PR3)-ANCA(+)], and ANCA(-) vasculitis in terms of clinical symptoms at presentation and severity of renal pathology; in addition, we prospectively assessed differences in response to treatment, the outcome of the disease, and rate of relapse in patients with necrotizing glomerulonephritis (NGN) due to AAV (5, 6). This evidence concerns the gene MPO and anti-neutrophil cytoplasmic antibody-associated vasculitis.