Breast Cancer Gene May Beget Itself

Study suggests women with BRCA-1 mutation twice as likely to have girls

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By
HealthDay Reporter

(HealthDay is the new name for HealthScout News.)

TUESDAY, Aug. 19, 2003 (HealthDayNews) -- As if having a higher risk of breast or ovarian cancer weren't enough, Spanish researchers have now discovered that families with specific genetic mutations for these diseases may give birth to more girls, thus passing on the vulnerability.

But even if borne out in future studies, however, these preliminary findings have little relevance for the average woman, according to an American expert.

"It's an interesting observation. I don't think it has a great deal of clinical impact for patients," says Dr. Noah Kauff, clinical assistant physician on the clinical genetic service and the gynecology service at Memorial Sloan-Kettering Cancer Center in New York City.

Women with mutations in either the BRCA-1 and BRCA-2 genes are at greater risk of being diagnosed with breast or ovarian cancer. Scientists have speculated that the BRCA-1 gene may have a role in a process called x-inactivation, which occurs shortly after fertilization.

"The X chromosome has more genetic information than the Y chromosome, and humans actually have very little tolerance for extra, or not enough, genetic material," Kauff explains. "In order that there is not too much genetic material, one of the X chromosomes becomes inactivated." This, of course, happens in the female embryo, because females have two X chromosomes while males have an X and a Y chromosome.

The researchers, all based at Hospital Clinico San Carlos in Madrid, Spain, looked at the ratio of girls and boys in 68 Spanish families who had either of the BRCA-1 or BRCA-2 mutations, or both. To qualify for the study, each family had to have had at least three cases of breast cancer and/or ovarian cancer in two generations.

Families with the BRCA-1 gene had twice as many female births. By contrast, families with only the BRCA-2 gene had roughly equal proportions of boys and girls, according to the study, which appears in the Aug. 20 issue of the Journal of the American Medical Association.

"It at least provides further support that BRCA-1 may have to do with inactivation of the X chromosomes, and therefore, some sex selection," Kauff says. "They're speculating that one reason you might see an overrepresentation of females is because if the process doesn't work correctly, it actually may result in selection against males."

But another explanation has to do with the way the research was conducted. All of the families included in the study had to have histories of breast and/or ovarian cancers.

"People who present for the full sequence of genetic testing frequently have a strong family history of cancer, but because BRCA-1 is predominantly associated with cancers in women, if you have a family with a preponderance of men, they would not come to the attention of cancer researchers," Kauff says.

In other words, the families included in the study had already self-selected themselves.

Even if the results were borne out in future studies, the significance would still be largely theoretical, at least for the time being.

"It would just give us more insight into the roles of BRCA-1, but it probably doesn't give us a huge amount of useful clinical information for a woman who's facing an inherited risk of breast cancer," Kauff says. "It's hard to say where this information is going to lead."

"We have to ask ourselves what are we going to do with this information," adds Dr. Jay Brooks, chief of hematology/oncology at the Ochsner Clinic Foundation in Baton Rouge, La. "We many times want to translate this into a clinical solution very quickly, and we may not be able to do that. Plus, it has to be confirmed."

More information

For more on BRCA-1 and BRCA-2, visit the National Center for Biotechnology Information or the National Cancer Institute.

SOURCES: Noah Kauff, M.D., clinical assistant physician, clinical genetic service and gynecology service, Memorial Sloan-Kettering Cancer Center, New York City; Jay Brooks, M.D., chief of hematology/oncology, Ochsner Clinic, Baton Rouge, La.; Aug. 20, 2003, Journal of the American Medical Association

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