New Gene Defect Leading to Colon Cancer Found

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 1 in 4 cases of inherited colon cancer in Ashkenazi Jews--those of Eastern European ancestry, who constitute more than 95% of this country’s 6 million Jews. It can be detected with a newly available $200 blood test, which some geneticists predict will 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 to detect cancer in its earliest stages. The disease is easily prevented or cured when growths are removed early.

“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.

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 also predisposes to cancer, not by directly causing tumor formation but by making the gene unstable and vulnerable to carcinogens.

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