HLA-B and psoriatic arthritis: Among thousands of HLA class I alleles identified, only a few are linked to certain diseases, including HLA-B*51 for BD, HLA-B27 for the spondylarthritis family (ankylosing spondylitis (AS), psoriatic arthritis, reactive arthritis, arthritis associated with inflammatory bowel disease (IBD)), HLA-C06:02 for psoriasis, and HLA-A29:02 for birdshot chorioretinopathy.