March 31, 2011

VU experts explore promises, pitfalls of gene testing field

VU experts explore promises, pitfalls of gene testing field

A mere 10 years after the first draft of the human genome sequence was completed, scientists and companies are delivering some of the first fruits of that achievement to patients and consumers.

At Vanderbilt University Medical Center, for example, patients scheduled for cardiac catheterization are tested for a genetic variation to determine which blood thinner they should receive. Tumors from patients with lung cancer and melanoma are screened for mutations that make them vulnerable to specific targeted therapies.

The flip side of this scientific revolution is direct-to-consumer genetic testing. For roughly $300, consumers can send some saliva or a swab of cheek cells for DNA analysis, and get a report that predicts their risk for developing certain diseases.

But just how accurate is genetic testing? How is it affecting people's lives?

Those questions were at the forefront of a workshop, “DNA Testing and You,” sponsored last Friday, March 25, by the Vanderbilt Center for Human Genetics Research and featuring several center investigators.

Holli Dilks, Ph.D., research assistant professor of Molecular Physiology & Biophysics, urged consumers to have a healthy dose of skepticism.
“You have to remember that extreme care must be taken in preparing these (DNA) samples, processing them, analyzing them and interpreting the output,” Dilks said.

“These technologies are not fully automated … Therefore humans are involved at many different steps in the process.”

Dana Crawford, Ph.D., assistant professor of Molecular Physiology & Biophysics, said she was concerned about the inclusion of the breast cancer (BRCA) genes in one of the consumer kits, because only 5 percent to 10 percent of breast cancers are inherited.

If the genetic tests come back negative for BRCA mutations associated with increased breast cancer risk, she asked, “will this lead to fewer mammograms … does it give you a false sense of security?”

Much of the discussion focused on age-related macular degeneration (AMD), the leading cause of vision loss and legal blindness in people over age 60.

Jonathan Haines, Ph.D., who directs the Center for Human Genetics Research, has been a leader in identifying genetic variations that increase the risk of AMD. He and his colleagues' work led to the development of a genetic test for the disease.

To be useful in the clinic, however, genetic tests must demonstrate a high degree of sensitivity and specificity, said Kylee Spencer, Ph.D., research instructor of Molecular Physiology & Biophysics.

That means they pick out people who are truly at high risk for the disease while weeding out the false positives.

Genetic testing “is really in its infancy,” agreed Milam Brantley, M.D., Ph.D., assistant professor of Ophthalmology and Visual Science and a retinal specialist.

Yet the field is maturing rapidly. To help doctors find the latest information that may benefit their patients, the Vanderbilt-Ingram Cancer Center recently launched a personalized cancer decision support tool called “My Cancer Genome.”

The tool catalogs genetic mutations associated with various cancers, highlights “genotype-driven” clinical trials and summarizes the comparative effectiveness of targeted therapies.

“This is really cool,” Brantley said. “It's another step of bringing genetics to everybody.”