Scientists have identified a handful of genes that boost the risk of developing Crohn’s disease, confirming that the often debilitating inflammatory bowel ailment has a strong genetic component.
The researchers scanned the entire genome — all 22,000 genes — of about 6,000 people. About half had Crohn’s disease and half did not, they reported on Sunday in the journal Nature Genetics.
Previous studies had 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 John Rioux of the Montreal Heart Institute and the University of Montreal, who led the team of Canadian and U.S. researchers.
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.
“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 -- the body’s natural defenses -- 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 ability to deal with microbes.
Crohn’s disease, named after Dr. Burrill Crohn who described it in 1932, causes inflammation of the digestive system. It is also called 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 all the human DNA that is freely available to anyone on the Internet. Researchers can compare the DNA of patients to the map version to see where one person differs from another.