Background: Little information is available about the familial aggregation of inflammatory bowel disease (IBD) in Asian populations. We therefore determined the risk of familial aggregation of IBD among first-degree relatives of patients with ulcerative colitis (UC) or Crohn's disease (CD) in an ethnically distinct Korean population.
Methods: Familial aggregation of IBD was evaluated in terms of family history, prevalence, lifetime risk, and population relative risk in first-degree relatives of 1440 unrelated patients with UC (n = 1043) or CD (n = 397).
Results: A positive first-degree family history of IBD was observed in 27 probands (1.88%): 21 of 1043 (2.01%) with UC and 6 of 397 (1.51%) with CD. The crude prevalence of IBD in first-degree relatives of probands with IBD was 0.31%. The lifetime risk of IBD was 0.54% in all first-degree relatives of IBD probands, 0.52% in UC probands, and 0.67% in CD probands, with overall lifetime relative risks of 0.12% in parents, 0.79% in siblings, and 1.43% in offspring. The age- and sex-adjusted population relative risk of IBD was 13.8 in first-degree relatives of probands with IBD.
Conclusions: Although a positive family history, prevalence, and lifetime risk of IBD among first-degree relatives of Korean IBD patients are much lower than among relatives of Western patients, the population relative risk in first-degree relatives is about equal in Koreans and Westerners. This finding indicates that a positive family history is an important risk factor for IBD in Koreans and in Westerners.