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Wednesday, September 7, 2016

ASSOCIATIONS BETWEEN HLA AND DISEASES


Some of the deformities that occur during rheumatic disease

Some of the deformities that occur during rheumatic disease



Rheumatic diseases


The best known of these associations and the most striking to date is between B27 and ankylosing spondylitis, a seronegative arthritis of unknown etiology occurring predominantly in males and affecting the lumbodorsal spine, the sacroiliac,and sometimes the peripheral joints.

In the Caucasian population, B27 is present in 85% to 95% of patients compared to only 6% to 10% of control populations.  B27 is also associated with the disease in other ethnic groups such as the Japanese or African-Americans, despite a low frequency of B27 in these populations.

Neither B27 nor ankylosing spondylitis is present in African blacks and the Australian aborigines. By contrast, in British Columbia 10% of the adult male, Haida Indians have sacroiliitis, whereas the frequency of B27 is 51% in the Haida population and 100% of the few ankylosing spondylitis patients tested.

For individuals with B27, the relative risk of ankylosing spondylitis is about 200 times that of B27 and that prevalence of ankylosing spondylitis is much higher than generally accepted. 

In addition to ankylosing spondylitis, the frequency of B27 is increased in a large of patients with other types of arthritis:Reiter's syndrome, acute anterior uveitis, juvenile rheumatoid arthritis, and acute arthritis following specific infections such as a Salmonella, Shigella or Yersinia. 

Although different pathogens seem responsible for each of these diseases, they probably have a common pathogenetic mechanism involving perhaps B27 directly or close linked susceptibility gene. Evidence is accumulating for immunological cross-reactivity between B27 and antigen in gram-negative bacteria.

Unlike the other forms of arthritis,adult rheumatoid arthritis is not associated with B27 but with HLA-Dw4. The fact that rheumatoid arthritis has a susceptibility gene different from the other forms of arthritis suggests that this disorder is probably a distinct disease.

The absence of a strong familial incidence of rheumatoid arthritis suggests that environmental factors override genetic susceptibility.


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