When analysing all patients with MPA, HLA-DRB1*04:04 was the strongest associated allele (p=8.6×10−12, OR=3.9 (95% CI 2.6 to 5.8)), followed by the SNPs rs34784936 and rs35874654, but with weaker signals of association compared with MPO-AAV (online supplemental table 5). Here, MPO is linked to microscopic polyangiitis.