Interestingly, while ERAP1 was associated with ankylosing spondylitis only in HLA-B*27-positive individuals, ERAP2 was associated with this disease independently from HLA-B*27 (17, 18, 26, 56–58), which may suggest it participates in another activity in addition to peptide trimming (see the next section). This evidence concerns the gene ERAP2 and ankylosing spondylitis.