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Genetic Defect Doubles Colon Cancer Risk, Researchers Find

By Rick Weiss
The Washington Post

Researchers have discovered a new kind of genetic defect that doubles a person's risk of colon cancer and is present in one of every 17 American Jews, making it the most common cancer-associated mutation ever identified in any ethnic population.

The mutation, apparently rare in non-Jews, appears to be responsible for about one in four cases of inherited colon cancer in Ashkenazi Jews - those of Eastern European ancestry, who constitute more than 95 percent of this country's 6 million Jewish people. It can be detected with a newly available $200 blood test, which some geneticists predicted would quickly become one of the more commonly used genetic tests.

Doctors called the discovery a major advance since a positive blood test can alert people to the need for regular colon examinations, called colonoscopies, which can detect colon cancer in its earliest stages. The disease is easily prevented or cured when growths in the colon are spotted early and removed.

"This is perhaps the best example yet of a situation where a genetic test will not only detect a significant number of folks at increased risk, but in a circumstance where you have something to offer them in the way of an intervention," said Francis Collins, chief of the National Human Genome Research Institute.

At the same time, experts expressed concern that federal protections against genetic discrimination still are not fully in place, even as the number and value of genetic tests grows. Several said they hoped the discovery would spur the passage of legislation, recently endorsed by President Clinton, to protect people against the misuse of genetic information by health insurers and others.

"Despite the potential benefits of this testing there still are substantial risks for people, including insurance discrimination and the likelihood of adverse psychological effects for the individual or family members," said Caryn Lerman, director of cancer genetics at Georgetown University's Lombardi Cancer Center. "For an individual to make an informed decision and weigh the risks and benefits adequately, informed consent and pretest genetic counseling would have to be offered."

The new work, led by Bert Vogelstein of the Howard Hughes Medical Institute at Johns Hopkins University in Baltimore, focused on a stretch of DNA called the APC gene. Scientists have known since 1991 that mutations in that gene can lead to colon cancer. The new work shows that a less dramatic kind of genetic variation in the APC gene, called a polymorphism, also predisposes to cancer - not by directly causing tumor formation but by making the gene unstable and prone to further damage by carcinogens.

Researchers said the identification of the new kind of cancer-promoting glitch could help them find the underlying causes of other kinds of cancers in different populations.

"We always assumed polymorphisms are harmless variations," Vogelstein said, like spellings of the word "color" and "colour" in America and England. "Now people are going to be going back and looking at all these to see what else they may be doing."

The new research, which appears in the September issue of Nature Genetics, involved genetic analyses of blood or tissue samples taken from about 1,000 Ashkenazi Jews.