Background and aims: To explore the change in risk among 1st degree relatives of ulcerative colitis (UC) and Crohn's disease (CD) for development of concordant disease in an incidence cohort followed for ten years. Furthermore, we wanted to compare familial and sporadic cases regarding clinical characteristics and the course of the disease.
Methods: This population-based study included 421 patients with UC and 197 with CD enrolled from 1990 to 1994. Clinical characteristics and the number of 1st degree relatives of the patients were recorded continuously during ten years.
Results: Age at diagnosis in CD patients (OR=0.95, 95% CI: 0.93-0.98) and cumulative relapse rate in UC patients (OR=4.91, 95% CI=1.16, 20.75) were significantly associated to familial clustering. Based on the calculated population prevalence of CD (262/100000) and UC (505/100000), the age-adjusted risk for development of concordant disease was 25.9 and 8.6 among siblings and parents of CD, respectively. In UC, the corresponding risks were 8.6 and 1.5. In the course of ten years the increase in risk was observed only among siblings (28%) and parents (97%) of UC, in contrast to no increase in CD. Moreover, the concordance for UC was high in three generations.
Conclusions: Our study confirmed the importance of genetic influence on the development of CD. Within an observation period of ten years, the increased concordance and relapse rate in familial UC, might point to a larger genetic component in UC than previously suggested.