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Gene Mapping for Healthy People No 'Crystal Ball'

Mapping Fails to Predict Most Diseases: Study

By Charlene Laino
WebMD Health News

Reviewed by Laura J. Martin, MD

April 2, 2012 (Chicago) -- Mapping a person's whole genome cannot, for the most part, accurately predict the medical problems in a healthy person's future, a new study suggests.

As the price of full-genome mapping comes down, many healthy people are wondering if it's worth their while to see if they can find any future health problems tucked away in their DNA. According to this study, they may want to save their money.

This doesn't mean gene mapping is not valuable. Mapping the DNA of individuals has led to a new understanding of many diseases and led to many new treatments. And in some families with strong histories of cancer or another disease, it can be extremely informative, says researcher Bert Vogelstein, MD, professor of oncology at the Johns Hopkins Kimmel Cancer Center.

In general, though, gene mapping "is not a crystal ball. A fortune teller who uses [gene mapping] to predict a person's risk of disease would go out of business," he tells WebMD.

The findings were presented here at the annual meeting of the Association for Cancer Research and published online in the journal Science Translational Medicine.

Gene Mapping Not Always Informative

Gene mapping, or whole-genome sequencing, catalogs all of the genes that a person inherits from each parent, looking for alterations in DNA that can affect susceptibility to cancer and other diseases.

Using data on 24 diseases from more than 50,000 identical twins in five countries, Vogelstein and colleagues analyzed the power of sequencing to determine an individual's risk of disease.

Results showed that for 23 of the 24 diseases, most people would get a negative result from a whole-genome scan, suggesting their lifetime risk of the disease is low.

But that could mean their risk is only slightly lower than that of the general population, which could be substantial, Vogelstein says. "A negative test is not a free pass," he says.

Gene mapping could theoretically identify three-fourths of people who may develop four of the 24 diseases studied -- heart disease in men, autoimmune thyroid disease, type 1 diabetes, and Alzheimer's disease, the analysis showed.

In the case of Alzheimer's disease, for example, the research suggests that a whole-genome map would identify most people with at least a 10% lifetime risk of developing the disease. Still, "a 10% risk for disease does not imply that this disease will be his or her major health problem," Vogelstein cautions.

What limits the usefulness of genes to predict disease? Contrary to what most people think, environment plays only a small role in changing your genes, Vogelstein says. "Much more important are random mistakes in genes that occur when cells divide," a process that starts in the womb, but can also occur anytime throughout life, he says.

Whole Genome Testing: Experts Comment

The key to fighting cancer and other disease remains routine checkups, early screening tests, and a healthy lifestyle that includes not smoking and maintaining your ideal weight, among other strategies, Vogelstein says.

Timothy Rebbeck, PhD, of the University of Pennsylvania Perelman School of Medicine in Philadelphia, notes that the current findings only apply to healthy people, and that gene mapping can be beneficial for identifying inherited illnesses or for finding the best treatments for people who are already sick.

"For someone who has disease, whole-genome sequencing can be extremely valuable," he says.

Louis M. Weiner, MD, director of the Georgetown Lombardi Comprehensive Cancer Center in Washington, D.C., says that the study offers "a cautionary tale not to rush into using new technology" until its benefits and limitations are understood.

Whole-genome testing, which cost several hundred thousand dollars only a few years ago, can now be performed for $1,000 to $3,000, though it varies form company to company.

Vogelstein receives royalties on sales of technologies or products related to the study.

SOURCES: American Association for Cancer Research Meeting 2012, Chicago, March 31-April 4, 2012. Bert Vogelstein, MD, professor of oncology, Johns Hopkins Kimmel Cancer Center, Baltimore. Timothy Rebbeck, PhD, professor of epidemiology, University of Pennsylvania Perelman School of Medicine, Philadelphia. Louis M. Weiner, MD, director, Georgetown Lombardi Comprehensive Cancer Center, Washington, D.C. Vogelstein B. Science Translational Medicine, published online April 2, 2012. Colditz, G. Science Translational Medicine, published online March 28, 2012.

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