Which environmental factors are involved in the etiology of ankylosing spondylitis (AS)?

Updated: Jul 17, 2018
  • Author: Lawrence H Brent, MD; Chief Editor: Herbert S Diamond, MD  more...
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Answer

AS does not develop in every person who is HLA-B27 positive; thus, it is clear that environmental factors are important. Even first-degree relatives who are HLA-B27 positive do not uniformly develop the disease. In fact, only 15-20% of such individuals develop the disease.

HLA-B27–positive transgenic rats develop an illness similar to a spondyloarthropathy, with manifestations that include sacroiliitis, enthesitis, arthritis, skin and nail lesions, ocular inflammation, cardiac inflammation, and inflammation of the gastrointestinal and male genitourinary tracts. [44] The severity of the clinical disease correlates with the number of copies of HLA-B27 expressed in the transgenic animal.

HLA-B27–positive transgenic rats that are raised in a germ-free environment do not develop clinical disease. Once introduced into a regular environment (ie, non–germ-free) and exposed to bacteria, the rats develop clinical manifestations of spondyloarthropathy. [45, 46]

Patients with AS may experience exacerbations after trauma. However, no scientific studies support trauma as a cause of AS.


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