Familial aggregation of inflammatory bowel disease in a Mediterranean area.

To evaluate familial aggregation of inflammatory bowel disease (IBD) in the Mediterranean area and to estimate the disease risk in first degree relatives. 427 patients with IBD were consecutively interviewed in order to obtain a complete pedigree of first degree relatives. Sufficient information was obtained in 98% of 2,685 family members. The prevalence ratio of IBD in family members was estimated and compared to the prevalence ratio of IBD in general population; the ratio was then standardized by age since the prevalence of the disease is age-dependent. The lifetime risk was assessed by the Kaplan Meier method. Thirty index cases (7%) had at least one affected first degree relative. As compared with the general population, first degree relatives of the 427 patients with IBD had a 4.38-fold increase in the age corrected risk of having the same disease. The Kaplan-Meier curve showed a higher risk at 25 years of age for offsprings (3%) than for parents (1%) and siblings (1%) whereas the crude ratio showed a higher risk for siblings (1.9%) compared to parents (0.8%) and offsprings (1%). In the Mediterranean area, the familial prevalence of IBD is higher than in the general population and comparable to North European rates.