Familial Mediterranean fever and seronegative arthritis.

Familial Mediterranean fever (FMF) is characterized by recurrent, self-limited episodes of polyserositis, with articular involvement also being a common manifestation. The pattern and joint predilection of arthritis show many similarities to those of spondyloarthritis. Moreover, case series suggest an increased prevalence of ankylosing spondylitis or spondyloarthritis among FMF patients. FMF is caused by mutations in the MEFV gene encoding pyrin, which is believed to be involved in regulation of interelukin-1β activation. Recent studies conducted in populations with a high background carrier rate of MEFV variants have reported an increased frequency of M694V among AS patients with no personal or family history of FMF. These findings are of interest, as both candidate gene and genome-wide association studies suggest that the interleukin-1 cytokine pathway may be implicated in the pathogenesis of ankylosing spondylitis. Therefore, association of M694V with ankylosing spondylitis can be recognized as a geographic region-specific risk factor affecting a common inflammatory pathway in the disease pathogenesis.