Familial incidence of Crohn's disease in The Netherlands and a review of the literature.

A detailed family history of first-degree relatives of 400 unrelated Dutch patients with Crohn's disease revealed a second case among first-degree relatives in 32 families (8%). The most frequently observed positive relationship was among siblings. In two families, three children had Crohn's disease. One pair of concordant monozygotic twins was found; in the other pair of monozygotic twins, only one was affected by the disease. None of the five dizygotic twin pairs was found to be concordant for Crohn's disease. The results of the present study, together with those published in the medical literature, support a hereditary predisposition for Crohn's disease.