PRTN3 and anti-neutrophil cytoplasmic antibody-associated vasculitis: Anti-proteinase-3 (PR3-ANCA) and anti-myeloperoxidase (MPO-ANCA) antibodies are anti-neutrophil cytoplasmic antibodies (ANCA) which are useful markers for diagnosing ANCA-associated vasculitis (AAV) (1–4).