A Simple Misspelling May Determine if a Certain Medication Will Work for You

Do you know how a medicine will work, or what the side effects are? Certainly, all you have to do is read the label. Wrong. Many people are surprised to learn that medicines may only work properly in a percentage of those who take them. What's more, whether or not people develop side effects — and if they do, which ones they'll get — varies widely. While many factors such as diet, environment, and the amount of exercise a person gets can help account for this variability in drug response, a key determinant is genes.

So-called pharmacogenetics research aims to unravel some of the biological reasons why people react so differently to medicines. In recent years, pharmacogenetics scientists have found many examples where a change in one or a few of the DNA "letters" that spell out genes can cause people to have different responses to medicines. For example, researchers have identified a group of cancer patients who had a bad reaction to a chemotherapy drug called irinotecan, which is used to treat a variety of solid tumors. The scientists found that these patients have two extra letters in the gene that instructs the body to make a protein that metabolizes irinotecan and other drugs. Because of this genetic difference, these people have much higher levels of irinotecan than most patients given the same dose.

When administered this medicine, patients with extra letters in the gene experienced dramatic drops in their white blood cell counts, making these patients more likely to develop a potentially life-threatening infection. The same patients also experienced severe diarrhea, which can cause dangerous fluid loss in people who are already very sick. Future genetic screening of patients may help avoid toxic side effects and help determine the precise dose of chemotherapy needed to treat their cancer.

Likewise with other drugs! It may be that a simple blood test to determine how your genes are spelled, will be able to tell the doctor which drugs to prescribe for you.