Finally, although EGPA is classified as ANCA-associated vasculitis (AAV), only ~40% of patients with EGPA test ANCA-positive, with the presence of anti-myeloperoxidase antibodies being more common than anti-proteinase 3 antibodies in serum (24). This evidence concerns the gene PRTN3 and anti-neutrophil cytoplasmic antibody-associated vasculitis.