Colon Cancer Seen Linked to Bloom Gene

Mutation Slightly Raises Risk for Carriers, Researchers Find

By Ross Schneiderman

Published August 15, 2003, issue of August 15, 2003.
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Ashkenazi Jews are two to three times more likely to develop colon cancer if they carry the gene for Bloom syndrome, according to a September 2002 study by American and Israeli researchers.

Dr. Kenneth Offit, senior author of the study and chief of the clinical genetics service at Memorial Sloan-Kettering Cancer Center in New York, said that the researchers arrived at the conclusion after they found that Jews of Eastern European descent diagnosed with colon cancer were two to three times more likely to have a single mutation of the BLM gene. Having two copies of the mutation means an individual has Bloom syndrome, one of the so-called Jewish genetic diseases.

“For these individuals there is a very slight increase for colon cancer on the order of two times,” Offit said. He added that the finding was “of a great scientific interest” and that it will “help give us a better understanding of the origin of colon cancer.” The study of more than 3,000 Ashkenazi Jews was first reported in the journal Science.

Despite the apparent danger, Offit stressed that he does not recommend doing routine clinical testing. “In theory, all colon cancer can be prevented,” he said. “If you can remove the polyps [pre-cancerous lesions], you can prevent colon cancers. You can see the polyps by having a colonoscopy every five years.”

Colonoscopy, Offit explained, gives the doctor the ability to visualize the entire colon and is thus the recommended method of detection. He added that getting the procedure done regularly “is the most important thing to do if you are a person with a family history of the malignancy.”

“We had thought in the past that increasing your fiber and decreasing your fat would decrease your chances of getting colon cancer,” he said. “But now that evidence isn’t so strong, although those things make sense for other reasons.”

Some recent evidence has shown that taking aspirin can be helpful, according to Offit. But, he said, that is also still being researched.

Some 148,000 new cases of colon cancer are diagnosed each year, 56,000 of which are fatal. The malignancy is the third leading cause of cancer death in the United States.

Offit said that the researchers found no evidence of links between single mutations of the BLM gene and other forms of cancer associated with Bloom syndrome. Before arriving at their conclusion, the multinational team of scientists analyzed DNA from 1,244 Ashkenazi Jews with colon cancer and 1,839 who did not have the disease.

A mutation of both copies of the culprit gene causes Bloom syndrome, a disease that greatly increases an individual’s likelihood of developing cancer, lung disease and diabetes, and can be characterized by a number of other physical conditions, including small stature, low birth weight, infertility and rashes upon exposure to the sun. According to the Web site for the Chicago Center for Jewish Genetic Disorders, there is currently no effective treatment for the disease, and the mean age of death from it is 27, usually cancer-related.

Offit said that although the disease afflicts people in all ethnic groups, it is most common in Ashkenazi Jews, among whom one in 120 are carriers of the disease. Carriers do not have Bloom syndrome but can pass it on to their progeny if the other parent also has a single mutated copy of BLM. If two carriers have a child together, there is a 25% chance that the child will have Bloom syndrome and a 50% chance that the child will be a carrier of the disease.

Prenatal carrier screening for Bloom syndrome is available. However, Offit does not recommend screening for the gene as a way to guard against colon cancer because of the option of colonoscopy. “Genetic testing is a very important thing. You have to think of other family members involved,” he said. “You have to think of discrimination by their insurance company or employer.”

Past research by numerous scientists indicates that the BLM gene is linked to DNA repair. A team of University of North Carolina at Chapel Hill scientists found that in fruit flies the BLM gene “has a specific function of repairing DNA breaks, such as those that occur after exposure to X-rays,” according to Jeff Sekelsky, an assistant professor of biology and a faculty member with the UNC program in molecular biology and biotechnology, in a January 2003 press release.

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