A significant association of HLA-DRB1*0901 with MPA (P = 0.0037, OR = 2.44) and MPO-AAV (P = 0.0014, OR = 2.44) was demonstrated in 50 MPA and 64 MPO-ANCA AAV cases compared with 265 controls in a Japanese cohort (25). This evidence concerns the gene HLA-DRB1 and microscopic polyangiitis.