MPO and granulomatosis with polyangiitis: It is also worth emphasizing that racial differences are observed in the distribution of AAV serotypes in various populations, e.g., Caucasian patients diagnosed with GPA are mainly anti-ANCA-PR3-positive (65–75%), while in the Chinese population, the majority of patients with GPA show myeloperoxidase (MPO) positivity (71%) [29,30].