Colon cancer risk traced to common ancestor

LONDON (Reuters) - A married couple who sailed to America from England around 1630 are the reason why thousands of people in the United States are at higher risk of a hereditary form of colon cancer, researchers said on Wednesday.

Using a genetic fingerprint, a U.S. team traced back a so-called founder genetic mutation to the couple found among two large families currently living in Utah and New York.

Cancer researchers at the Huntsman Cancer Institute in Utah did not name the families but said thousands of people across the country may have the mutation that spread widely as the couple's descendants branched apart over many generations.

"The fact that this mutation can be traced so far back in time suggests it could be carried by many more families in the United States than is currently known," said Deb Neklason, who led the study. "In fact, this founder mutation might be related to many colon cancer cases in the United States."

Colorectal cancer is the third-leading cause of cancer death in the United States. It will affect 153,000 Americans in 2008, according to the American Cancer Society, and will kill 52,000.

Family history, smoking and diet are all linked with colorectal cancer but experts are still struggling to identify the causes that underlie most cases.

An estimated less than 1 percent of these cases are due to this particular genetic mutation, according to the study published in Clinical Gastroenterology and Hepatology.

The U.S. team first focused on the Utah branch of the family -- numbering about 5,000 people today -- 14 years ago because its members had an unusually high risk of colon cancer.

Because the family was Mormon, the researchers were able to mine a wealth of genealogical information taken from detailed church records over the years that is now part of a large genetics database in Utah, Neklason said.

While most of the records in the study related to the Utah part of the family, the researchers eventually identified the New York branch as well.

"We just know about these two branches of the family," Neklason said. "The significance of it going so far back is there are probably many branches of the family out there that aren't aware of the mutation."

In the study, the team identified the mutation that causes a condition called attenuated familial adenomatous polyposis (AFAP), which makes people more prone to developing polyps that can cause colon cancer.

Without proper treatment, people with this mutation have a greater than 2 in 3 risk of developing colon cancer by age 80, compared to about 1 in 24 for the general population. Early treatment, however, can just about eliminate this risk.

"This study highlights that you need to pay attention to your family history," Neklason said. "With intervention to remove the polyps, the risk goes to near nothing."

(Reporting by Michael Kahn; Editing by Janet Lawrence)