Although c-ANCA (with proteinase 3 specificity) mostly appear in Wegener’s granulomatosis (80-90% of ANCA-positive GPA patients), and p-ANCA (directed against myeloperoxidase) are mainly found in microscopic polyangiitis, 10-20% of ANCA-positive GPA patients have increased p-ANCA levels. This evidence concerns the gene MPO and granulomatosis with polyangiitis.