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Researchers Discover 71 New Human Genes Associated With Bowel Diseases

Findings may lead to better, more-targeted treatments (Nov. 1)

Researchers have found 71 new human genes associated with Crohn's disease and ulcerative colitis — two chronic inflammatory bowel diseases (IBDs) that affect the small and large intestines of nearly 2.5 million people worldwide. This study brings the total number of known genes associated with IBD to 163.

The study was conducted by a consortium of researchers in the U.S., Canada, and Europe. It was funded in part by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) IBD Genetics Consortium, at the National Institutes of Health (NIH). The results were published in the November 1 issue of Nature.

The first phase of the genome-wide association studies involved combining 15 previously reported datasets of people with Crohn’s disease or ulcerative colitis, and unaffected controls (people who did not have either disease). This analysis covered common genetic variants throughout the genome.

Researchers then analyzed the DNA samples using the Immunochip — a new technique to validate and confirm genes associated with diseases. This analysis provided more complete coverage of variants in genes functioning in the immune system, and associated with other immune disorders. The analysis scanned DNA samples of people from 15 countries. A total of 60,828 samples were genotyped from 20,076 people with Crohn's disease, from 15,307 people with ulcerative colitis, and from 25,445 people who did not have either disease.

These scans identified 71 new genes strongly associated with IBD, including many also associated with other inflammatory diseases, such as ankylosing spondylitis and psoriasis. It also appears that these IBD variants have evolved in regions responsible for resisting mycobacterial infections, such as tubercolosis and leprosy.

The exact cause of IBD is still unclear. Researchers believe an unknown factor or agent triggers an abnormal reaction by the body’s immune system. The most common signs of the disease are diarrhea and abdominal pain. IBD tends to run in families and is more likely to be diagnosed in young adults. People of Jewish heritage, particularly Ashkenazi Jews who are of Eastern European descent, have an increased risk of developing the disease.

Further analysis revealed that of the 163 genes associated with IBD, 110 are associated with Crohn’s disease and ulcerative colitis; 30 are specific to Crohn’s; and 23 are specific to ulcerative colitis.

"These findings are only the beginning,” said Robert W. Karp, PhD, project officer for NIDDK's IBD Genetics Consortium. “We expect new approaches like systems biology will provide a more complete picture of the genetic pathways involved with IBD. In turn, the greater level of detail will help us develop better, more-targeted treatments."

Source: NIH, November 1, 2012.

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