By Merritt McKinney
NEW YORK, Sep 24 (Reuters Health) - Heredity plays a role in the gastrointestinal disorder irritable bowel syndrome, but family environment may have an equal or greater influence, researchers suggest.
"For irritable bowel syndrome at least, and possibly for similar disorders, how an individual learns to respond to physical sensations from those in their environment can be as, if not more, important to their experience of symptoms as their genetic inheritance," the study's lead author, Dr. Rona L. Levy at the University of Washington in Seattle, told Reuters Health.
Irritable bowel syndrome, or IBS, which affects women more often than men, causes abdominal pain, constipation, bloating and diarrhea. Stress, anxiety and depression can exacerbate IBS episodes. Increasing physical activity and adjusting the diet may relieve symptoms.
IBS tends to run in families, leading some researchers to suspect that a person's genes play a role in the development of the disorder.
Another potential cause of the disorder, according to Levy and her colleagues, is that a person's family environment may affect the odds of developing irritable bowel syndrome. According to this idea of "social learning," children of a parent with IBS might be influenced by how the parent deals with his or her own gastrointestinal symptoms.
In a study being published in the journal Gastroenterology, Levy's team set out to measure the influences of heredity and social learning on IBS.
The study included twins with the condition. The investigators compared the percentage of mothers of twins who also had IBS with the percentage of "co-twins" who also had the gastrointestinal disorder.
Levy and her co-authors hypothesized that if the percentage of mothers who had irritable bowel syndrome was higher than the percentage of fraternal, or nonidentical, co-twins who had the disorder, then there would be evidence of an environmental influence on IBS. They note that fraternal twins share about the same number of genes as mothers do with their children--twins or not.
The findings were based on more than 10,000 twins representing more than 6,000 sets of twins.
The researchers found that about 17% of identical twins with IBS had a twin with the disorder. Only about 8% of fraternal twins had a co-twin with IBS. Since identical twins share all the same genes but fraternal twins share just half, the higher rate in identical twins supports a role for heredity in the development of IBS, the authors conclude.
But the findings also support an important role for social learning. Identical twins were about as likely to have a mother with IBS as to have a twin with the ailment.
Fraternal twins with IBS were more likely to have a mother with the disorder than a twin. The likelihood that an identical twin had a mother with IBS was also higher than the chance that a fraternal twin had a twin with IBS.
"This supports a social learning contribution to IBS, because mothers share about the same number of genes with their children as (fraternal) twins share with each other," the authors conclude. "Yet the proportion of IBS twins who have mothers with IBS was significantly greater than the proportion of (fraternal) twins with IBS whose co-twins have IBS."
Levy told Reuters Health that the focus of future research should be on both preventing and treating IBS.
"From a preventative point of view, we need to address how individuals can learn when to respond, and when to not respond, to their physical sensations in a way that maximizes their health and well-being," she said. According to Levy, therapy should "focus on both cognitive and behavioral strategies to produce this outcome."
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