Irritable bowel syndrome in twins: Heredity and social learning both contribute to etiology

Background & Aims: Heredity has been suggested to explain the finding that irritable bowel syndrome (IBS) tends to run in families. Research in this area has been limited. The aim of the present study was to assess the relative contribution of genetic and environmental (social learning) influences on the development of IBS by comparing concordance rates in monozygotic and dizygotic twins to concordance between mothers and their children. Methods: Questionnaires soliciting information on the occurrence of more than 80 health problems, including IBS, in self and other family members were sent to both members of 11,986 twin pairs. Results: Analysis is based on 10,699 respondents representing 6060 twin pairs. Concordance for IBS was significantly greater (P = 0.030) in monozygotic (17.2%) than in dizygotic (8.4%) twins, supporting a genetic contribution to IBS. However, the proportion of dizygotic twins with IBS who have mothers with IBS (15.2%) was greater than the proportion of dizygotic twins with IBS who have co-twins with IBS (6.7%, P < 0.001), and logistic regression analysis showed that having a mother with IBS and having a father with IBS are independent predictors of irritable bowel status (P < 0.001); both are stronger predictors than having a twin with IBS. Addition of information about the other twin accounted for little additional predictive power. Conclusions: Heredity contributes to development of IBS, but social learning (what an individual learns from those in his or her environment) has an equal or greater influence.