The researchers said they have linked genetic variations in 163 regions of the human genome with a heightened risk of developing inflammatory bowel disease (IBD). Of those regions, 71 are newly discovered.
IBD comprises a group of chronic, autoimmune digestive disorders that affect 2.5 million people worldwide. Symptoms include abdominal pain and diarrhoea and patients typically require lifelong treatment with drug therapy. Many also require surgery to repair tissue damage caused by the disease.
How the study was done
In this study, researchers analysed data from about 34 000 people who took part in 15 previous studies of either Crohn's disease or ulcerative colitis. They also examined data from genome-wide scans of more than 41,000 DNA samples from Crohn's disease and ulcerative colitis patients collected at 11 centres around the world.
In addition to confirming that 92 regions of the human genome identified in previous studies are associated with a significant risk for the two illnesses, the new study linked 71 new regions to IBD.
The regions pinpointed in this study overlap those linked with other autoimmune diseases and suggest that IBD results from overactive immune defence systems that evolved to combat serious bacterial infections, the researchers said.
The findings appear in the journal Nature.
"Until this point we have been studying the two main forms of IBD - Crohn's disease and ulcerative colitis - separately," co-lead author Judy Cho, professor of gastroenterology and genetics at Yale School of Medicine, said in a Yale news release. "We created this study based on what seems to be a vast amount of genetic overlap between the two disorders."
The new study reveals "a genetic balancing act between [the immune system] defending against bacterial infection and attacking the body's own cells," co-lead author Jeffrey Barrett of the Wellcome Trust Sanger Institute in Cambridge, England, said in the news release. "Many of the regions we found are involved in sending out signals and responses to defend against bad bacteria. If these responses are over-activated, we found it can contribute to the inflammation that leads to IBD."
How the digestive system works
The U.S. National Institute of Diabetes and Digestive and Kidney Diseases has more about Crohn's disease.
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