These autoantibodies are divided into two main groups: cytoplasmic (c-ANCA) which confers antigen specificity for proteinase 3 and is associated with Wegener's granulomatosis and perinuclear (p-ANCA) which reacts against myeloperoxidase (MPO) and is mainly associated with microscopic polyangiitis (MPA) and Churg-Strauss syndrome. The gene discussed is MPO; the disease is microscopic polyangiitis.