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.