Examining the classical alleles, we noted that HLA-B∗27, a risk allele for another arthritic disease, ankylosing spondylitis (MIM 106300),33 demonstrated the lowest p value for PsA versus PsC association (p = 1.2 × 10−4; Figure 4; Table S4) but much less significantly than HLA-B Glu45. This evidence concerns the gene HLA-B and pancreatic serous cystadenoma.