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Crohn's disease has strong genetic link: study

Last Updated: 2007-04-16 10:07:37 -0400 (Reuters Health)

WASHINGTON (Reuters) - Scientists have identified a handful of genes that increase the risk of developing Crohn's disease, confirming that the often debilitating inflammatory bowel disease has a strong genetic component.

U.S. and Canadian researchers scanned the entire genome -- all 22,000 genes -- of about 6,000 people. Approximately half had Crohn's disease and half did not, they reported in the medical journal Nature Genetics.

Previous studies identified two genes involved in the disease.

"I think at this point we have probably up to about eight or nine genes, depending on how you define it," said Dr. John Rioux of the Montreal Heart Institute and the Universite de Montreal, who led the team of investigators.

The researchers said the findings showed genetics play a crucial role in the disease, although environmental factors also are involved. For example, smoking raises one's risk.

Pinpointing the genes that predispose people to Crohn's disease, the researchers said, could help lead to new ways to treat it.

The disease, most commonly diagnosed in people between the ages of 20 and 30, can cause abdominal pain, diarrhea, rectal bleeding, weight loss and arthritis. Chronic intestinal inflammation may necessitate the removal of sections of intestine.

"We have been working toward this for over 10 years to try to put all the pieces together," Rioux said in a telephone interview. "To finally get to this stage where we can look at the entire genome and actually discover a handful of genes, it's very, very gratifying."

Scientists previously had some indications of a genetic component to Crohn's disease. It tends to run in families and is more common in certain ethnic groups, especially people of central and eastern European Jewish descent.

Experts think faulty responses to the microbes that live in the human digestive system somehow cause the immune system to attack the lining of the digestive tract, making it decay and become inflamed.

Rioux said some of the genes identified as risk factors are involved in the body's defense against microbes.

Crohn's disease, named after Dr. Burrill Crohn who described it in 1932, may also be referred to as ileitis or enteritis. While it can affect any area from the mouth to the anus, it most often affects the lower part of the small intestine, known as the ileum.

Up to three quarters of people with Crohn's disease eventually will require surgery to relieve symptoms that do not respond to medications or to correct complications like intestinal blockage, perforation, abscess and bleeding.

It can be hard to diagnose because symptoms are similar to other intestinal ailments such as irritable bowel syndrome and ulcerative colitis.

It is largely a disease of the developed world and is found principally in the United States and Europe, according to the Crohn's and Colitis Foundation of America.

In the United States alone, up to 1 million people have Crohn's disease and ulcerative colitis, about evenly split between the two, the group said.

The study relied on the Human Genome Project, a map of the human DNA, which is available free to anyone on the Internet. Researchers can compare the DNA of Crohn's disease patients to this DNA map to see how one person differs from another.

Date Posted: April 17, 2007