MPO and anti-neutrophil cytoplasmic antibody-associated vasculitis: Interestingly, MPO-ANCA-associated vasculitides are more common in Asian countries than in the USA or Europe, where 80% of AAV is PR-3 ANCA [6, 7] and ANCA-positive, while anti-MPO-negative patients with MPA most often have antibody specificity for PR3 [3].