ANCA-associated vasculitis (AAV) encompasses a group of multisystem autoimmune diseases characterised by necrotising small-vessel vasculitis and the presence of circulating autoantibodies (ANCAs) directed against the neutrophil cytoplasmic antigens proteinase 3 (PR3) and myeloperoxidase (MPO). Here, MPO is linked to anti-neutrophil cytoplasmic antibody-associated vasculitis.