WASHINGTON – Researchers have identified what they see as the leading cause of inherited colorectal cancer – a genetic abnormality that makes a person about nine times more likely to get the disease.

This trait may explain at least 10 percent and perhaps 15 to 20 percent of colorectal cancer cases, according to Ohio State University's Dr. Albert de la Chapelle, who helped lead the study published in the journal Science Thursday.

The researchers said in the future a simple blood test should be able to identify people with the trait so they can be screened regularly to catch colon and rectal cancer early when it is most treatable.

“We have identified what appears to be the main cause of inherited colorectal cancer,” Dr. Boris Pasche of Northwestern University and Northwestern Memorial Hospital in Illinois, who also helped lead the study, said in a telephone interview.

Colorectal cancer is the fourth most common type of cancer in men and the third most common in women worldwide, according to the American Cancer Society. Globally, about 1.2 million cases of colorectal cancer are diagnosed annually and the disease kills about 630,000 people, the organization said.

Experts believe that about a third of colorectal cancer cases are caused by genetics. Other risk factors include a diet high in fat and calories and low in fiber, obesity, a sedentary lifestyle, heavy drinking and smoking.

The study involved 242 people in central Ohio with colorectal cancer and 195 people who did not have it.

They found that people who had an abnormality related to a gene called TGFBR1 were 8.7 times as likely to develop colorectal cancer than those who did not have the trait.

“This makes it a strong risk factor,” de la Chapelle said.

COMMON TRAIT

Previous research had linked TGFBR1 to colorectal cancer risk, and the new study assessed the degree to which this abnormality in the gene increased one's risk.

The study indicates that 10 to 21 percent of people with colorectal cancer and 1 to 3 percent of the general population have the trait, which runs in families, de la Chapelle said.

The gene normally inhibits cell growth and also is involved in regulating the immune system, Pasche said.

Like other genes, people inherit two copies, one from the mother and the other from the father. But in people with this particular variation, one of the copies is less active than it should be, and this reduced activity may encourage colorectal cancer development.

The discovery is important because it could help identify people at high risk to ensure they get regular screening with methods such as colonoscopy and sigmoidoscopy that can find abnormal growths in the large intestine, the researchers said.

If caught early, colorectal cancer often can be cured but is usually fatal if it becomes advanced.

Pasche said a blood test for the trait could be available perhaps within a couple of years.

“People with known risk – those who have had a polyp or those who have a family member with colorectal cancer – should be tested for this trait. If it is found, it raises a red flag suggesting intensified surveillance, which in turn is likely to save lives,” de la Chapelle said by e-mail.

Previous research had identified other genetic traits that caused some cases of inherited colorectal cancer, but combined they accounted for only about 5 percent of cases.

(Editing by Maggie Fox and Vicki Allen)