MILWAUKEE – Researchers have pinpointed a damaged gene that doubles the risk of familial breast cancer in a small percentage of women, a new study shows.

Experts say the findings won’t change patient care, but may provide comfort to women who develop the disease despite not having the commonly mutated BRCA1 and BRCA2 genes.

“Unraveling why women get breast cancer is complex,” said Mary Ann Gilligan, an associate professor of medicine at the Medical College of Wisconsin who was not involved in the study.

“This study gives us a small piece of the puzzle toward explaining risk, but it’s not the answer,” said Gilligan, who practices at Froedtert Hospital in Milwaukee.

About 5 percent to 10 percent of breast cancers are caused by inherited mutations in a single gene. Women with mutations in BRCA1 or BRCA2 have about an 80 percent chance of getting breast cancer in their lifetimes.

Other genes – TP53, CHEK2 and ATM – also have been identified, but the combination of all known genes only account for about 25 percent of inherited risk.

The new study looked at a gene called BRIP1 in women with a family history of breast cancer, but who didn’t have either of the BRCA genes.

BRIP1 is a DNA repair gene that can lead to uncontrollable cell growth if it’s not functioning properly.

Among the 1,212 British women with breast cancer, nine had a truncated, or severely damaged, BRIP1 gene. There were two severe mutations among the 2,081 patients without breast cancer.

The researchers concluded that the mutated gene increased risk for breast cancer from 8 percent to 16 percent by age 70, thus only explaining another small piece of risk.

The findings are published in the journal Nature Genetics.

“There are likely to be several different genes, each with small effects, which will be acting together and with other non-genetic factors to cause familial clustering of cancer,” said Nazneen Rahman, author of the study and a professor of cancer genetics at The Institute of Cancer Research in the United Kingdom.

“Moreover mutations in this gene are present in only one in one thousand of the population,” she said. “We will need to find out more about which women with BRIP1 mutations develop cancer, and why, before testing can be offered.”

Currently, there’s no way to screen women for the mutation, Gilligan said.

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