Inflammatory bowel disease in 67 families each with three or more affected first-degree relatives

Background & Aims: Some families have multiple members with inflammatory bowel disease (IBD). Do clinical features of familiar differ from sporadic cases? Is there concordance between affected family members? Do environmental factors affect familial clustering? Methods: In 67 families, each with three or more first-degree relatives with IBD, the 213 affected family members were interviewed, and their case records were reviewed, Results: The clinical manifestations of familial cases did not differ from IBD reported ire a large series, There was concordance for type of disease (P < 0.001) but not greater than expected concordance for age at diagnosis, site and extent of disease, or transmural aggressiveness of Crohn's disease, A significant association between smoking with Crohn's disease and nonsmoking with ulcerative colitis was found (P < 0.001), even in families with both disorders. The intervals between diagnosis of successive family cases varied so greatly that a single etiologic factor with a constant latent period seems to be unlikely, When IHD affected successive generations, parents were diagnosed at a later age than the children (P < 0.001) and after the child in 12 of 49 cases, Conclusions: Analysis has not identified any clinically significant differences between familiar and sporadic cases of IBD, Tobacco smoking affects disease type in familial cases.