Sex ratio in the spondyloarthropathies and its relationship to phenotypic expression, mode of inheritance and age at onset.

OBJECTIVE

To investigate the interrelated effect of phenotypic expression [i.e., primary ankylosing spondylitis (1 degree AS) or disease secondary to psoriasis (Ps) AS or inflammatory bowel disease (IBD)AS], age at onset, sex and inheritance of responsible genes in AS.

METHODS

Three studies were performed to evaluate 1949 subjects with AS. Subgroups of the patients were formed for each study depending on disease type (1 degree AS = 1695; Ps AS = 173; IBD AS = 81), nature of inheritance or age at onset of AS symptoms. These groups were further subdivided to assess the effect of sex.

RESULTS

The sex ratio of the entire group was 2.6:1 in favor of men. However, IBD AS had an equal sex distribution as does IBD alone. By contrast, Ps, which has an equal sex ratio as a lone event or in association with arthritis, resulted in a male dominance of 4.1:1 when it occurred as Ps AS. Women with IBD AS had a significantly younger onset compared to women with 1 degree AS [mean onset 21.7 years (SD 6.65) vs mean onset 24.4 years (SD 9.79), respectively; p = 0.019]. A younger age at onset was found in women with familial disease [mean 22.2 years (SD 7.55)] compared with the mean onset of sporadic disease in women [24.5 years (SD 10.0); p = 0.0059]. There was a progressive fall in the sex ratio as the age at onset increased (p = 0.053). For example: M:F ratio of < 20 years old was 3:1 compared to 1.8:1 for those with an onset of > 40 years.

CONCLUSION

Sex ratio and age at onset are influenced both by each other and such factors as disease type and familial versus sporadic occurrence. These data help provide a predictable pattern of disease in spondyloarthropathy.