There are four clinical entities in this group: microscopic polyangiitis (MPA) which is frequently associated with MPO-ANCA, granulomatosis associated with polyangiitis (GPA, formerly known as Wegener’s granulomatosis) which is frequently associated with PR3-ANCA, eosinophilic granulomatosis associated with polyangiitis (also known as Churg Strauss syndrome) and the single organ limited vasculitis [1]. The gene discussed is MPO; the disease is microscopic polyangiitis.