A new gene mutation linked to Crohn's disease and ulcerative colitis has been identified by US and Canadian experts.
Scientists have long suspected a genetic link
The fault is in a gene receptor present in healthy people without inflammatory bowel disease but rare in those with the condition.
The receptor's protein, interleukin-23 (IL-23), is known to regulate chronic inflammation and help fight bacterial infections.
The Science Express study authors say the finding is a target for new drugs.
Inflammatory bowel diseases tend to run in families and scientists have long suspected a genetic component. Other mutations have already been found, but more are thought to exist.
The researchers performed a genome-wide scan of more than 1,000 people with and without Crohn's disease to look for variations of the DNA sequence that might be related to inflammatory bowel disease.
They found three variations - two that were already known, and one new one.
The new variation found in the IL-23 receptor was particularly intriguing because it was more common in people without disease than those with it, rather than the other way round.
One of the study's author's Dr Judy Cho, from the Department of Medicine and Genetics at Yale University, said: "We appear to have identified a gene variant that protects against development of IBD.
"It causes us to think about the genetics of health as well as the genetics of the disease.
"One mutation appears to offer significant protection from IBD, and will be a crucial target for drugs that might better manage Crohn's disease and ulcerative colitis."
In the UK, a large-scale study to find genes for a dozen common disorders, including Crohn's disease, run by the Welcome Trust Case Control Consortium, is close to completion.
One of those involved in the research, Professor Christopher Mathew, of the Complex Disease Genetics Group at King's College London, said the work in Science suggested the IL-23 gene played a "key role" in the inflammatory response.
He said there was hope that identifying genes for these common disorders would lead to new and more effective forms of therapy.