Susceptibility to AS has been shown to be largely genetically determined, and it has been suggested that disease severity is at least partially determined by genetic factors. However, there is not much information on the contribution of genetic and environmental factors to disease severity. Researchers Sinead Brophy and colleagues from the Royal National Hospital for Rheumatic Diseases in Bath, England sought to determine patient characteristics that might explain the variability in outcomes in AS. Results were published in a recent issue of The Journal of Rheumatology.

Study Participants: 311 patients with AS (252 men, 81%) from the Royal National Hospital took part in the study.

Findings:

• Radiological change is an important outcome in AS because it is an objective sign that reflects the cumulative process of destruction over time in AS.
• Radiological hip involvement is significantly associated with higher scores of spinal radiological change.
• Outcome in patients with AS in terms of function and x-ray change can, in part, be predicted by clinical characteristics identifiable early in the disease course.
• Modifiable factors like exercise, occupation, and smoking on longterm x-ray outcome were not substantiated by the researchers' data.
• Age at onset of AS, site of first AS symptoms, positive family history, and associated inflammatory bowel disease were not associated with outcome.
• Cigarette smoking has been previously associated with worse outcome in AS and in psoriatic spondylitis. There was a significant interaction between smoking and psoriasis, such that patients with psoriasis who smoked had poorer function than either nonsmokers with psoriasis or nonsmokers without psoriasis.

Much of the variability in disease severity in AS remains unexplained. This study's data suggests that genetic factors have a greater influence than environmental factors on radiographical progression and disability in AS. They also believe that hormonal influences (as suggestive by the predictive value of male sex) may have a greater influence on outcome in AS than environmental factors. However, encouraging people not to smoke may help to preserve function in AS. Male sex, iritis, hip involvement, and higher disease activity scores appear to suggest a worse prognosis in AS. The researchers believe that targeting people with these risk factors early in the disease course with more aggressive therapies may improve their functional outcome and quality of life.

A limitation of the study is that it was based in a referral center where people with more severe AS may have been over-represented. Therefore, the results may not be generalized to all patients with AS, and it is possible that environmental variables (like occupation or exercises) could have important effects in people with milder disease.