March 25, 2008

Identical Genes From Parents May Raise Cancer Risk

TUESDAY, March 25 (HealthDay News) -- People who have two identical copies of certain genes -- one inherited from the mother and one from the father -- seem to be at greater risk of developing a number of common types of cancer, research shows.

Although the findings need to be validated in more studies, there could be significant implications for patient care, experts say.

"This could represent a new way to do cancer risk-assessment. I suspect this will be added into routine clinical testing," said Dr. Charis Eng, senior author of the paper published in the March 26 issue of the Journal of the American Medical Association. "This is truly 'genetics to keep healthy people healthy,' " she said.

Eng, who is director of the Genomic Medicine Institute at the Cleveland Clinic Foundation, noted that by the time such tests wind their way into clinical practice, doctors should also have more preventative and screening tools at their disposal.

Unlike many currently available genetic tests -- such as those for the BRCA1 and 2 genes thought to play a role in breast cancer -- these anticipated tests could be applicable to everybody, not just people at high risk for a particular malignancy.

Similarly, the new findings suggest that more than 5 percent of all cancers are linked to heredity, the researchers said.

Previously, Eng had noticed that a high level of germline cells (those containing genetic material that can be passed on to children) were homogenous, meaning that two copies of the same gene were identical. Her team was studying heterozygosity, but these cells were "maddeningly homogenous," she said. At first, she attributed the pattern to bad luck, but after years of finding the same thing, she decided it couldn't be a coincidence.

So, Eng and her colleagues decided to look at 400 genetic markers scattered throughout the genome in 385 breast, prostate and head and neck cancer patients and in people without cancer.

All patients were of the same ethnic group.

"Lo and behold, in 16 markers, let's call them 'hot spots,' there were high frequencies of homozygosity compared to the controls," Eng said.

The association was then validated in patients with lung cancer. This time, they streamed through 250,000 markers across the human genome and found that cancer patients were more likely to have homozygosity in the same 16 markers.

"We are saying that lack of genetic diversity or uniformity in hot spots in 16 places seems to be associated with common cancers," Eng said. "This is a novel means of cancer predisposition."

"We don't know the mechanism yet," she added. "Right now, it's an association."

The study authors have postulated that this homozygosity occurs at "common" fragile sites on the genome, sites that are susceptible to DNA damage. These are to be distinguished from "rare" fragile sites that are also sensitive to such damage but are more likely to be associated with less common cancers.

More information

For more on different types of cancer, visit the U.S. National Cancer Institute.

SOURCES: Charis Eng, M.D., Ph.D., director, Genomic Medicine Institute, Cleveland Clinic Foundation; March 26, 2008, Journal of the American Medical Association
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