It was demonstrated that ANCA serotyping distinguishes distinct classes of ANCA disease: PR3-ANCA-associated vasculitis (PR3-AAV), MPO-ANCA-associated vasculitis (MPO-AAV), and ANCA-negative vasculitis (reviewed by Reference [45]). The gene discussed is MPO; the disease is anti-neutrophil cytoplasmic antibody-associated vasculitis.