Two separate scientific groups say they have discovered a second major breast cancer susceptibility gene.
In today's issue of the journal Nature, an international team of scientists reports it has isolated a large part of the gene, called BRCA2.
And in Salt Lake City, Myriad Genetics Inc., a genetic testing company, says it has identified the entire gene in collaboration with researchers at the University of Utah and the University of Pennsylvania.
"Myriad scientists have cloned . . . the complete sequence of this gene," the company said in a statement, adding that it would publish the sequence on an Internet database today.
Mutations in BRCA2 are believed to cause about 45 percent of hereditary breast cancers - including the rare cases that occur in men. Together, BRCA2 and BRCA1, which was discovered last year, may account for up to 90 percent of all inherited breast cancers.
Inherited cancers make up 5 percent to 10 percent of the 182,000 breast cancer cases diagnosed each year in the United States. But women who carry a mutated gene have an 80 percent lifetime risk of developing breast cancer.
Like BRCA1, the newfound gene seems to suppress cancer when it is working normally. But when BRCA2 is defective, this protection is undermined.
Everyone inherits two copies of BRCA2, one from each parent. If one copy is defective when inherited, and the remaining copy is damaged by environmental or other triggers, the woman is left defenseless against breast cancer.
The BRCA2 discovery is sure to intensify debate over testing for predisposition to breast cancer. BRCA2 is much larger than the enormous BRCA1 gene, so developing an inexpensive, reliable test to search for mutations along the entire gene will be difficult.
Both genes can mutate in an undetermined number of ways - some of which do not disrupt the function of the gene - so patients should be counseled about the limitations of a test.
More than 100 mutations have been found so far in BRCA1.
"We found six mutations in BRCA2," said P. Andrew Futreal of Duke University Medical Center in Durham, N.C., a lead author of the paper published in Nature by a team of 38 researchers from around the world. "It's going to take some time, I'd guess a year or two, to get the whole thing figured out. In my opinion, the most appropriate place for testing right now is in research."
