NEW YORK — The discovery that a genetic mutation relatively common among Ashkenazi Jews makes them predisposed to colon cancer has prompted alarm — and the search for more information.
“We’ve been flooded with calls,” said Jill Brensinger, a genetic counselor at Johns Hopkins University’s Hereditary Colorectal Cancer Registry in Baltimore.
Her department’s telephone message apologizes for long-term busy signals.
Researchers at Johns Hopkins found that a genetic defect doubling a person’s risk of colon cancer is present in about 360,000 American Jews, or 6 percent of the population, making it the most common cancer-causing mutation ever identified in an ethnic population.
Jews of Ashkenazi, or Eastern European, heritage comprise 95 percent of the more than 5 million Jews in the United States.
Colon cancer is the third most common type of cancer in the United States and will likely kill about 55,000 men and women this year.
The new finding raises questions about why so many genetic mutations are being found in the Ashkenazi Jewish population. It also raises questions about the value and risks of genetic testing, especially for a disease that is often preventable.
The discovery was made by a team of researchers at the Howard Hughes Medical Institute of Johns Hopkins. The findings appear in the September issue of the journal Nature Genetics.
The scientists analyzed blood and tissue samples taken from about 1,000 Ashkenazi Jews and concluded that Jews who carry the genetic mutation have doubled other Ashkenazi Jews’ odds — a 16 to 30 percent chance — of getting colon cancer.
Some in the health field warned of overestimating the chances that Ashkenazi Jews will get colon cancer, citing initial reports that mutations BRCA1 and BRCA2 conferred a 70 to 80 percent chance that Jews with those genes will get breast cancer.
Those estimates were reduced in more recent studies, which put the rate at closer to 50 percent.
This finding marks the third time in as many years that Ashkenazi Jews have been singled out with discoveries about genetic mutations causing potentially fatal diseases. The two other discoveries both revolved around breast cancer genes.
“I have trouble myself figuring out why we keep finding mutations so much in Ashkenazi Jews,” said Mark Skolnik, chief scientific officer at Myriad Genetics, a Salt Lake City laboratory.
“Why should this happen in Ashkenazim and not other populations? The answer is that we don’t understand.
“The mystery is not that there’s a specific mutation in a specific population. That’s to be expected. The mystery is that they’re so frequent” among Ashkenazi Jews, he said.
The breast cancer discoveries illuminate growing concerns about the privacy of genetic test results and the way that information might be used by medical insurance companies and employers to discriminate against those whose genes deem them predisposed to serious disease.
The colon cancer discovery has prompted the same concerns, but with a twist.
Even if a woman is tested and found to have the breast cancer mutations, there is little she can do. She can change her diet and exercise habits, which can somewhat reduce her chances of being stricken with cancer. But short of having a prophylactic mastectomy, or amputation, that is all.
In contrast, colon cancer can be detected very early and, in many cases, it can be prevented with periodic colonoscopies.
The uncomfortable and unloved procedure involves inserting a long viewing device up the rectum into the large intestine to search for and remove pre-cancerous growths called polyps.
The test is generally recommended for people over 50, but could enable people with the genetic predisposition to monitor their colons starting at even an earlier age.
But Brensinger of Johns Hopkins said that only people who have a parent, child or sibling with the disease are encouraged to have colonoscopies prior to age 50.
Because the discovery’s ramifications have not yet been explored, it is not clear yet whether health professionals will encourage genetic testing for all Ashkenazi Jews.
Only Johns Hopkins currently offers the test for the genetic mutation particular to Ashkenazi Jews. But more of the country’s several dozen genetic testing labs are expected to begin doing it in the next month or two.
Johns Hopkins began offering the test on Tuesday. At $200, the test is cheap compared to the breast cancer gene test, which costs $2,400. Only a single genetic base must be examined for the colon cancer test in contrast to 17,500 genetic bases for the breast cancer mutation, Skolnik said.