HLA-DRB1*04:04 has been associated with RA, where a particularly strong association with residue 74 was revealed.44 An overlap syndrome of AAV and RA has been described, mainly featuring AAV with MPO-ANCA.45 46 In light of the current findings, this overlap syndrome may plausibly be an effect of shared genetic predisposition between RA and MPO-AAV. This evidence concerns the gene MPO and rheumatoid arthritis.