A new Mayo Clinic study found strong familial aggregation of irritable bowel syndrome (IBS), suggesting a possible genetic basis for the disorder. Results of the research will be presented Tuesday, May 23, in Los Angeles at Digestive Disease Week® 2006.

IBS affects nearly one in five American adults, and the disorder accounts for more than one of every 10 doctor visits in the United States. It is characterized by abdominal pain or cramping and changes in bowel function, including bloating, gas, diarrhea and constipation.

“Because we don’t understand the causes for the symptoms of IBS, it is difficult to identify a definitive therapy,” says Yuri Saito, M.D., Mayo Clinic gastroenterologist and the study’s lead investigator. “This study was one of the first steps in getting at the root of the problem and determining whether there could be a genetic basis for the disorder.”

The study population included 50 patients with irritable bowel syndrome who were seen in gastroenterology clinics, as well as a control group of 53 age-, gender-, and race-matched patients seen at general medicine clinics in 2004 and 2005. Surveys asking about gastrointestinal symptoms were then mailed to over 400 of their first-degree relatives. Family comparisons of the relatives showed that 70 percent of patients with IBS had at least one affected family member. In contrast, only 43 percent of the control group families had an affected family member.

“While it is too early to say that there is a genetic cause for IBS, this research is a step in the right direction and gives us the foundation to analyze genetic patterns,” says Dr. Saito. The next step in her team’s research is to identify 500 families affected by IBS, as well as 500 control families, and develop in-depth family modeling to determine whether genetic and/or environmental patterns exist. The ultimate goal of the research is to identify a molecular base of the abnormality in order to develop more definitive treatment programs for patients with IBS.

Dr. Saito points out that the study also identified the importance of gathering IBS symptom data directly from family members, as patients typically underestimated the frequency of IBS-type symptoms in their relatives. Individuals with IBS estimated that 20 percent of their first-degree relatives had IBS, while those relatives who participated in the study self-reported that 46 percent were actually affected by the disorder. Likewise, the control group estimated that 4 percent of their first-degree relatives had IBS, but when the relatives themselves were surveyed, 25 percent were affected.

“It is not surprising that individuals underestimated the frequency of IBS in their relatives, since gastrointestinal symptoms are not something that many people feel comfortable discussing,” says Dr. Saito. “This simply emphasizes the need for direct data collection from family members in any family study of IBS.”

Co-authors of this paper include Nicholas Talley, M.D., Ph.D.; Janice Zimmerman; W. Scott Harmsen; Mariza de Andrade, Ph.D.; Michael Camilleri, M.D.; G. Richard Locke III, M.D.; and Gloria Petersen, Ph.D., all of Mayo Clinic in Rochester, Minn.

Mayo Clinic