DNA Testing Not So Potent for Prevention, Study Says

When scientists developed the ability to catalog a person's genes, many hailed  whole genome sequencing as modern medicine's best tool to predict  and prevent  serious diseases, such as  cancer. But according to a new study, whole genome sequencing is not the magic bullet for prevention - at least not yet.

A team of researchers   from Johns Hopkins Kimmel Cancer Center found that the test fails to provide solid predictive evidence for a large portion of people. The findings were published online today in the journal Science Translational Medicine.

"From a public health perspective, basically, it's a reality check. It tells us what will we be able to do, and what won't we be able to do with whole genome sequencing," said Dr. Bert Vogelstein, co-director of the Hopkins' Ludwig Center for Cancer Biology Research in Baltimore, and an author of the study.

The researchers analyzed data from thousands of identical twins, noting how many of them had developed any of 24 different diseases, including cancer and autoimmune, cardiovascular, genitourinary, neurological and obesity-related disorders.

Vogelstein said data from identical twins, who share the same genome, give scientists an opportunity to study the genetic components of disease. If the genome was the determining factor for common diseases, then the number of twins who have a certain disease that their twin also has could  show how well whole genome sequencing could predict an individual's disease risk, he said.

Using what they knew about how many of the twins developed certain disorders, the researchers created a mathematical model to calculate the capacity of whole genome sequencing to predict the risk of each disease.   

They found that the majority of people would receive negative results for 23 of the 24 diseases, even though the risk of developing 19 of them in people who tested negative would still be 50 to 80 percent of the risk in the general population. The researchers reported that the best case scenario would mean that 90 percent of people tested would be alerted to a clinically significant predisposition to at least one disease.

Vogelstein told ABC News that the study found that whole genome sequencing is not a perfect predictor of a person's future health.

"In some cases people may find it useful, but others will decide that it's less useful," Vogelstein said. "All we're trying to do is provide the limits so people will know what they're paying for and what the capacity is of these tests."

A number of private labs provide whole genome sequencing services for about $3,000 per genome, but prices are dropping  as the technology improves.

Dr. Ronald Crystal, chairman  of genetic medicine at Weill Cornell Medical College in New York City, said the tests are still a valuable way to test for the risk of certain diseases that have definite genetic links, such as  Alzheimer's disease or type 1 diabetes. But for many diseases, for example  cancer, which are shaped by a symphony of genetic, environmental and behavioral risk factors, scientists still need much more research before learning what genetic results mean for a specific individual's risk.

"In terms of disease prevention, what we tell patients now still holds:  Don't smoke, don't do drugs, don't be obese, eat sensibly and exercise," Crystal said.