MPO and microscopic polyangiitis: MPA and MPO-AAV are more prevalent in East Asian populations, as compared with populations of European descent.1 2 Accordingly, classical HLA alleles have been investigated in Japanese and Chinese cases with these subtypes of AAV, revealing a genetic predisposition tagged by the HLA-DRB1*09:01-HLA-DQB1*03:03/03:02 haplotypes.18 20–22 In contrast, studies of classical HLA alleles in European cases with MPA/MPO-AAV are lacking.