Aggregation of symptoms of abdominal pain or bowel disturbance has been described in the families of patients with irritable bowel syndrome (IBS).
This may be due to environmental factors, including learned responses to abdominal symptoms or a genetic contribution to the etiology of IBS.
Dr Imtiyaz and colleagues from England determined the relative contribution of genetic factors to IBS by evaluating IBS symptoms in monozygotic and dizygotic twins.
The investigators identified a total of 4480 unselected twin pairs from a national volunteer twin register.
The investigative team asked the twin pairs to complete a validated questionnaire with IBS defined by the Rome II criteria.
|The prevalence of IBS was 17% in monozygotic and 16% in dizygotic twins|
|American Journal of Gasroenterology|
A total of 5032 subjects replied, giving a 56% response rate.
Of these, the research team reported that 1870 complete twin pairs were evaluable.
The evaluable twin pairs included 888 monozygotic pairs of which 82 were male pairs with a mean age 51 and dizygotic pairs with 69 male pairs and a mean age of 52.
The team found that the prevalence of IBS was 17% in monozygotic and 16% in dizygotic twins.
The investigators observed no significant difference in casewise concordance rates between the monozygotic and dizygotic twins.
Logistic regression analysis conducted by the team, revealed that decreasing age and increasing psychosomatic score were independently associated with IBS.
The team used multifactorial liability threshold modelling, which suggested that a combination of unique and shared environmental factors provided the best model for IBS.
In contrast, the investigative team showed that somatization was moderately heritable.
Dr Imtiyaz's team concludes, “Genetic factors are of little or no influence on IBS where the predominant influences appear to be environmental.”