In a population-based prospective study, microscopic polyangiitis (MPA) and myeloperoxidase (MPO) -ANCA-positive AAV (MPO-AAV) were the predominant subtypes (>80%) in Japan, while granulomatosis with polyangiitis (GPA) and proteinase 3 (PR3) -ANCA-positive AAV (PR3-AAV) were the predominant subtypes (>60%) in the UK [1]. The gene discussed is MPO; the disease is microscopic polyangiitis.