One of the most interesting findings in our study is that the haplotype carrying DRB1*13:02, which we have reported to have protective association against RA [16] and SLE [17], is also protective against MPA and MPO-AAV, suggesting that this haplotype carries a common protective allele with shared efficacy against different autoimmune diseases. This evidence concerns the gene HLA-DRB1 and rheumatoid arthritis.