Anticipation in inflammatory bowel disease: a phenomenon caused by an accumulation of confounders

Inflammatory bowel disease (IBD) has a definite genetic component as documented by epidemiological and linkage evidence. It shows an earlier onset of disease in children of affected patients than in their parents. This has lead to speculations about genetic anticipation in this disorder. 2,007 IBD patients with sporadic disease and 472 multiplex familial cases (including 103 affected parents and 99 children of affected patients) were evaluated with a multi-item questionnaire as part of a study of inflammatory bowel disease genetics. The Mann-Whitney U-test and the general linear model were used for analysis. Clinical characteristics such as presence of fistulae, stenoses, extraintestinal manifestations, and other parameters, which are related to the severity of the disease, were found to be similar between familial and sporadic cases of IBD (corrected P > or = 0.31 for all tests). The mean-age-of onset in children of affected patients was 19.4 years earlier than in their parents. However, the age of the parental cohort was significantly higher (27 years) and the diagnostic interval also longer (1.7 years). If these confounders are corrected in a general linear model, no significant difference is evident for the age-of-onset between the groups (P > or = 0.52). There is no evidence for genetic anticipation in inflammatory bowel disease. The absence of genetic anticipation is consistent with the clinical similarity of familial and sporadic inflammatory bowel disease. This finding justifies the primary genetic analysis of familial disease under the assumption that their genetic background will be representative for all presentations of IBD.