We performed a prospective study in patients with renal involvement, in particular FNGN, due to AAV, to investigate whether specific clinical presentation, histology, and outcome of MPO-ANCA(+), PR3-ANCA(+), and ANCA(-) diseases support their definition as different entities. The gene discussed is PRTN3; the disease is anti-neutrophil cytoplasmic antibody-associated vasculitis.