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Human Leukocyte Antigen B*27 (subtypes B*2701-2724) is a class I surface antigen encoded by the B locus in the major histocompatibility complex (MHC) on chromosome 6. It presents microbial antigens to T-cells and is strongly associated with certain immunity diseases (SpA spondyloarthropathies). In the general population, about 8% Caucasian, 4% African, 2-9% Chinese, and 0.1-0.5% Japanese have the HLA-B27 antigen. In Northern Scandinavia (Lapland), 24% of people are HLA-B27 positive while 1.8% have ankylosing spondylitis (AS). Mystery The relationship between HLA-B27 and many diseases has not yet been fully elucidated. Though it is associated with a wide range of pathology, it does not appear to be the sole mediator in development of disease. For example, while nearly all people with ankylosing spondylitis (AS) are HLA-B27 positive, only a fraction of people with HLA-B27 ever develop AS. This raises two important questions: why don't all HLA-B27 positive people develop AS, and why do some (although rarely) people who are HLA-B27 negative develop it? The literature is inconclusive, though several theories have been suggested and research continues.
Associated pathology In addition to its connection with AS, HLA-B27 is implicated in Reiter's syndrome, certain eye disorders such as acute anterior uveitis, iritis, Behçet's Disease, psoriatic arthritis and inflammatory bowel disease. Reiter's syndrome then again, is statistically associated with AS.
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