Genetic precision: New fields in genetic testing lend support to clinical effectiveness

July 1, 2008

Genetic testing is used to predict or diagnose a disease for an individual. It also makes possible the use of pharmacogenetics-the study of genetic variation that translates to differing response to drugs-to align drug treatment for maximum effectiveness. The emerging field of pharmacogenetics has opened up a new world of personalized treatment and evidence-based medicine.

IN MAY, PRESIDENT BUSH signed the Genetic Information Nondiscrimination Act, which protects Americans against discrimination based on their genetic information in the context of health insurance and employment. The news should ease patients' worry that genetic information intended for personalized medicine might be used by health insurers in setting premiums or by employers in hiring decisions.

Genetic testing is used to predict or diagnose a disease for an individual. It also makes possible the use of pharmacogenetics-the study of genetic variation that translates to differing response to drugs-to align drug treatment for maximum effectiveness. The emerging field of pharmacogenetics has opened up a new world of personalized treatment and evidence-based medicine.

Carol Reed, MD, executive vice president and chief medical officer for Clinical Data Inc., in Newton, Mass., which provides pharmacogenomics services, says that pharmacogenetic application enables treatment to be based on science, not trial and error. Genetic markers help indicate drug response rates, which leads to patient safety, better outcomes and reduced costs.

"The business model has not been one of targeting therapeutics but rather finding compounds to bring to market," he says. "And diagnostics have not been value-based."

He also notes that since as many as 93% of physicians were educated before the human genome was mapped in 2003, they are not familiar with the role genetics plays in therapeutic solutions.

WARFARIN STUDIES

"Once we let the genome out of the bottle in 2003, we have been looking at ways to bring more precision to prescribing," says Robert Epstein, MD, chief medical officer for Medco Health Solutions.

The PBM began a partnership with Mayo Collaborative Services to evaluate how genetic testing can predict the rate at which patients metabolize the drug warfarin, used to prevent blood clots and bleeding. One-third of patients receiving warfarin metabolize it atypically. If the dosing is not matched to the individual's ability to metabolize the drug (depending on variants of the genes CYP2C9 and VKORC1), there can be a risk of serious bleeding or a risk of stroke. According to FDA, warfarin is the second most common drug (after insulin) implicated in emergency room visits for adverse drug events.

Medco's goal is to help physicians prescribe the most appropriate dose of the medication for a particular patient-something that has routinely been an issue of trial and error because of the drug's narrow therapeutic window for optimum dosing. The ongoing research is evaluating genetic testing results from more than 1,000 patients starting on warfarin.

Prior to the study, Medco claims indicated that as many as 22% of new starts on warfarin were hospitalized within six months for blood clots because of an incorrect dose of the drug.

"The need for proper dosing is even more critical than I had imagined," Dr. Epstein says. He anticipates that results from the study will heighten physicians' awareness of potential dosing problems and encourage them to make changes based on genetics.

Dr. Epstein also applauds the new labeling for warfarin, which provides information on how people with certain genetic differences may respond to the drug, and helps physicians prescribe the correct dose.