In North American and European populations, ANCAs in patients with GPA are mostly the c-ANCA type (with a cytoplasmic labeling pattern on immunofluorescence) and show proteinase 3 (PR3) specificity on enzyme-linked immunosorbent assay (ELISA), whereas patients with MPA and EGPA show predominantly p-ANCA (with a perinuclear labeling pattern on immunofluorescence) and myeloperoxidase (MPO) specificity on ELISA. This evidence concerns the gene MPO and microscopic polyangiitis.