Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) describes a group of rare vasculitides that, for the majority of patients, are associated with the presence of ANCA against one of two (auto)antigens: proteinase-3 (PR3-ANCA) or myeloperoxidase (MPO-ANCA).1 AAV comprises granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic GPA (EGPA), with PR3-ANCA and MPO-ANCA frequently associated, respectively, with GPA and MPA. This evidence concerns the gene MPO and eosinophilic granulomatosis with polyangiitis.