Extra-intestinal manifestations associated with irritable bowel syndrome: a twin study

Background: Little is known about the role of genetic and environmental factors in irritable bowel syndrome. Various extra-intestinal manifestations are more prevalent in cases than in controls. Genetic effects may be important in the liability to develop functional bowel disorders. Aims: To evaluate the associations of irritable bowel syndrome with several disorders co-morbid with the condition, using both a case-control design and a co-twin control design, Methods: A sample of 850 Swedish twin pairs, aged 18-85 years, was contacted for a telephone interview. Through a diagnostic algorithm, 72 unrelated cases of irritable bowel syndrome and 216 age- and gender-matched controls were identified. Fifty-eight twin pairs discordant for irritable bowel syndrome were evaluated in co-twin analyses. Results: Renal problems (odds ratio (OR) = 3.3; confidence interval (CI), 1.3-8.2), obesity (OR = 2.6; CI, 1.0-6.4), underweight in the past (OR = 2.4; CI, 1.1-6.4), gluten intolerance (OR = 9.0; CI, 1.4-60.1), rheumatoid arthritis (OR = 3.2; CI, 1.1-9.4) and poor self-rated health (OR = 1.8; CI, 1.0-3.2) were significantly associated with irritable bowel syndrome. In the co-twin analyses, the only factors maintaining significance were renal and recurrent urinary tract problems. Conclusions: The association between irritable bowel syndrome and renal and urinary tract problems does not reflect a genetic or familial mediation. Eating disorders in childhood represent a familial-environmental influence on irritable bowel syndrome, whereas the association with rheumatoid arthritis and perhaps gluten intolerance probably reflects genetic mediation.