HLA-B27

introduction

Human Leukocyte Antigen (HLA) B27 is a class I surface antigen encoded by the B locus in the major histocompatibility complex (MHC) on chromosome 6 and presents antigenic peptides (derived from self and non-self antigens) to T cells.
it is strongly associated with ankylosing spondylitis (AS) and other spondyloarthopathies.

varies markedly in the general population.
8% of Caucasians
- 24% of those in northern Scandinavia (Lapland), while 1.8% have associated ankylosing spondylitis (AS).
4% of North Africans,
2-9% of Chinese
0.1-0.5% of persons of Japanese

90% of people with ankylosing spondylitis (AS) are HLA-B27 positive, but only a fraction of people with HLA-B27 ever develop AS
60-80% of people with reactive arthritis (Reiter's syndrome)
60% of people with spondylitis associated with inflammatory bowel disease (IBD)
60% of people with psoriatic spondylitis
- HLA-B27 is associated with the pustular form of psoriasis
- the association of HLA-B27 in peripheral psoriatic arthritis is weak
- in the presence of spondylitis associated with psoriasis, 60-70% of these cases are HLA-B27 positive
up to 50% of people who develop isolated anterior uveitis
- 18-32% of all anterior uveitis cases in western countries and for 6-13% of all anterior uveitis cases in Asia
- B27 positive patients tend to have 1st episode aged 20-40 years whereas B27 negative patients tend to be older at 1st presentation
20-25% of people with Undifferentiated spondyloarthropathy (USpA)