Singapore: Researchers have found 71 new human genes associated with Crohn's disease and ulcerative colitis, two chronic inflammatory bowel diseases (IBD) that affect the small and large (colon) 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 from the US, 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 in the US. The results were published in Nature.

The first phase of the genome-wide association studies involved combining 15 previously reported datasets of people with Crohn's disease, 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, which is 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 who had been recruited from 11 research centers. A total of 60,828 samples were genotyped from 20,076 people with Crohn's disease, 15,307 people with ulcerative colitis, and 25,445 people who did not have either disease.

As a result of these scans, 71 new genes strongly associated with IBD were identified, including many also associated with other inflammatory diseases such as ankylosing spondylitis (spine inflammation) and the skin disorder psoriasis. It also appears that these IBD-variants have evolved in regions responsible for resisting mycobacterial infections, which are microbes that cause diseases such as tubercolosis and leprosy.