FAMILIAL VERSUS SPORADIC ANKYLOSING-SPONDYLITIS 2 DIFFERENT DISEASES

Objective. To define potential differences and the possible contributi on of susceptibility or severity genes in familial versus sporadic ank ylosing spondylitis (AS). Methods. Three hundred twenty patients with AS were studied: 160 who had first-degree relatives with AS (familial) and 160 age- and sex-matched controls who had no first-degree relativ e with the disease (sporadic). Disease expression in the two groups wa s evaluated using an index of physical, psychological, and social func tioning (the Arthritis Impact Measurement Scales [AIMS]) and an assess ment of spinal mobility. Results. Familial disease was significantly m ilder than sporadic disease as assessed by all measures, e.g., spinal mobility score (mean 4.08 versus 4.65, P < 0.038), AIMS overall impact score (mean 2.63 versus 3.59, P = 0.002), AIMS physical activity scor e (4.19 versus 5.10 [P = 0.004]), AIMS social function score (4.02 ver sus 4.60, P = 0.023), and AIMS pain score (4.15 versus 5.33, P = 0.002 ). Conclusion. The greater prevalence of AS in at-risk families may be explained by the occurrence of more AS ''susceptibility'' genes in th ose families, whereas the more severe disease, seen in patients with s poradic AS, is conferred by the presence of more ''severity'' genes th an ''susceptibility'' genes.