A newly discovered breast cancer gene mutation doubles a woman's risk of breast cancer, U.K. researchers report.

That's a significant risk -- but not nearly as big as the 10- to 20-fold risk conferred by the already known BRCA1 and BRCA2 mutations, note Nazneen Rahman, MD, PhD, and colleagues at the Institute of Cancer Research in Sutton, England.

The newly discovered mutation, BRIP1, carries about the same risk as the already known CHEK2 and ATM gene mutations. Like the scarier BRCA mutations, all of these genes are involved in DNA repair.

Most likely, BRIP1, CHEK2, and ATM mutations only cause cancer in combination with each other or with environmental factors, the researchers report.

Stay tuned: All of the breast cancer gene mutations found so far explain only 25 percent of inherited breast cancer risk. That means Rahman and other geneticists still have a lot of work to do before they can predict who will inherit breast cancer and who won't.

The findings appear in the advance online edition of Nature Genetics.

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SOURCE: Seal, S. Nature Genetics, advance online edition published Oct. 8, 2006.