Antineutrophil cytoplasmic antibodies (ANCA) directed against proteinase 3 (PR3) and myeloperoxydase (MPO) are strongly associated with primary systemic vasculitis, including granulomatosis with polyangiitis, microscopic polyangiitis, and eosinophilic granulomatosis with polyangiitis.1,2 Although, ANCA have also been described in other conditions, especially connective-tissue diseases, inflammatory bowel diseases, malignancies, and drug-induced vasculitis.3 Here, PRTN3 is linked to microscopic polyangiitis.