Genetic Testing Disease Risk Profiling Drug Metabolism

You’ve probably watched your doctor write prescriptions on many occasions. Whether your primary healthcare provider uses an old-fashioned notepad or e-mails the prescription to the nearest pharmacy, you probably know that the dosage recommendations usually stem from your weight, sex, general and liver health, and possibly your age.

How Genes Influence Drug Effectiveness

Some medications can have different effects on different people. For example, warfarin, marketed under the name Coumadin, often helps thin blood in clot-prone patients. However, in some people it can cause dangerous internal bleeding.

Codeine, a narcotic painkiller, is usually effective, but for some it has no impact on their level of pain. For others, it might prove dangerous even at normal dosing levels.

A doctor might prescribe phenytoin for patients who have problems with seizures. Phenytoin is a commonly used drug and usually works well, but a few people find their seizures increase when they begin taking it.

Even very common allergy medications like Allegra can have different effects on different people. Diabetics and cancer patients can also find that their treatments vary in effectiveness. A rare mutation can cause a fatal reaction to even one dose of Camptosar, a drug used to fight cancer.

In the field of mental health, doctors usually find that they need to make frequent adjustments to prescription dosages of antidepressants like Paxil, Prozac and Zoloft. Clearly, a person’s individual metabolism affects how well he or she responds to these drugs.

DNA Genetic Testing

Until fairly recently, no one understood why these and other drugs worked well on most people while not helping some and hurting others. Now, scientists and doctors are learning that a patient’s probable reaction to certain medications can be revealed through DNA. DNA genetic testing can become a valuable new source of knowledge for doctors and patients.

How DNA Genetic Testing Works

DNA genetic testing is very easy to purchase if you want to find out whether or not a specific drug might be dangerous. The lab sends a kit. You use their cotton swabs to wipe the inside of your cheek, depositing your genetic material on the swab. After you mail in the swabs, the lab performs the tests. Results are usually ready within two weeks – sometimes faster if you pay an additional fee.

The lab looks at particular parts of your DNA that are responsible for producing enzymes that metabolize different drugs. Different enzymes metabolize different drugs, so the test you get is dependent on the drug you’re concerned about. By looking for specific mutations that can lead to factors affecting drug metabolism, the lab can often predict whether you’ll have a bad reaction to a certain medication.

Genetic testing for Coumadin risks can even save a person’s life if he or she is a poor metabolizer of the drug — a condition that affects about 10 percent the population.

Effectiveness of DNA Genetic Testing

Genetic testing for drug effectiveness isn’t always reliable. Experts currently recommend against genetic testing for antidepressants in particular, since so few studies exist on the test’s success rate for these drugs.

Until there are more clinical studies on testing’s effect on the accuracy of drug prescription and effectiveness, there is little point to the tests. As doctors and scientists gather more knowledge about how genetic testing can help, they might decide that it’s a worthwhile tool for formulating prescriptions.

Resources

Genelex (2008). DNA drug reaction testing. Retrieved September 18, 2008, from the Genelex Web site: http://www.healthanddna.com/drug-safety/dna-drug-reaction-testing.html.

Hsu, Andro (2008). Expert group discourages genetic testing for antidepressant dosage. Retrieved September 18, 2008, from the Spittoon Web site: http://spittoon.23andme.com/2008/01/10/expert-group-discourages-genetic-testing-for-antidepressant-dosage/.