Granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA) are systemic small-vessel vasculitides, often associated with positive antineutrophil cytoplasmic antibodies (ANCA) targeting either proteinase 3 (PR3) or myeloperoxidase (MPO). Here, PRTN3 is linked to granulomatosis with polyangiitis.