Background and Aims: Crohn's disease has a bimodal age distribution of disease onset diagnosis. The peaks (20 and 50 years) may represent different phenotypes or different genetic and/or environmental influences between younger- and older-onset individuals. The aim of this study was to examine the influences of age at diagnosis of Crohn's disease on disease site, type, and course. Methods: Records of 552 consecutive patients with Crohn's disease were reviewed retrospectively. Results: Younger age at diagnosis (younger than 20 years), compared with an older age (40 years or older), was associated with a greater prevalence of a family history of Crohn's disease (29.9% vs. 13.6%), greater small bowel involvement (88.7% vs. 57.5%), more structuring disease (45.8% vs. 28.8%), and a higher frequency of surgery (70.6% vs. 55.3%). Older age at diagnosis was associated with a greater prevalence of colonic disease (84.8% vs. 71.2%) and the inflammatory subtype (54.5% vs. 34.4%). A conditional logistic regression analysis confirmed an independent effect of age at diagnosis on ileal disease and surgery for intractable disease. Conclusions: In Crohn's disease, early age at diagnosis is associated with more complicated disease and a greater likelihood of having affected relatives. Stratification of Crohn's disease by age at diagnosis provides support for the concept of genetic heterogeneity.
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