PRTN3 and anti-neutrophil cytoplasmic antibody-associated vasculitis: This observation, together with the strong association of GPA with PRTN3 (which encodes the autoantigen of PR3-ANCA) and with SERPINA1 (encoding α1-antitrypsin, the major system able to catabolise PR3), suggested a central role of the autoantigen in the generation of ANCA and in the pathogenesis of AAV.