The Pros and Cons of Genetic Testing

A $99 at-home test can detail our genome profile and assess our risk of contracting disease. But is that good news or bad news?

By Rita Rubin
Originally Posted On May 1, 2013


The era of personalized medicine is coming. As genetic profiling, also known as genome sequencing, gets better, cheaper and more widely available, more of us may one day know exactly which chronic diseases we're likely to contract, what medications we should avoid and even what type of diet we should follow. In just a few years, with such data in hand, our doctors might be able to identify our vulnerabilities and target treatments with a greater chance of success than ever before.

Perhaps the most reliable, and immediately actionable, component of the 23andMe data is its assessment of how our genes respond to certain drugs. For example, the company checks for genetic variations related to how well we metabolize clopidogrel (Plavix), which helps prevent blood clots that could cause heart attack or stroke, and warfarin (Coumadin), a blood-thinner that prevents and treats clots in the veins, lungs and heart.
Clopidogrel needs to be converted into its active form in the liver. Most of us have two functioning copies of the gene that carries the blueprints for the enzyme needed to activate the drug. But some of us have only one, and about 1 in 20 people have none. Those in the latter group are considered to be poor metabolizers of clopidogrel; for them, the drug works about as well as a sugar pill.
About a third of patients prescribed warfarin turn out to be more sensitive to the drug than expected, due in part to genetic mutations. This is why, in 2007, the Food and Drug Administration approved labeling on the drug that suggests doctors use genetic tests to optimize dosing. For people with a heightened sensitivity to warfarin's effects, a dose of the drug that is too high puts them at risk of potentially life-threatening internal bleeding. If a dose is too low, though, potentially lethal blood clots could form.
The Psychological Element

I'm not sure how I would have reacted if I had learned I had a genetic mutation increasing my risk of breast cancer. Experts remain concerned about the psychological impact of finding out that you're at high risk of a potentially fatal disease, especially when companies can send you the information via email without the context and advice your doctor could provide in person.

There's a threat to the health care system, some clinicians believe, in producing a legion of "patients in waiting" — otherwise healthy, asymptomatic people who have found out they may be at risk for chronic disease, then overload hospitals with demands for further testing and treatments that may not be necessary.

For patients with a risk of disease but no symptoms, the wisest action would be preventive steps, like changes in diet and lifestyle to ward off heart disease. But even with genetic data in hand, many of us may not take steps to improve our health. "I'm fairly comfortable with the conclusion that people don't freak out," Angrist says, "but neither are they likely to change their behavior."

Millions of us resist giving up cigarettes or fatty foods, despite the obvious health risks. When we find out that our genes make us even more susceptible to chronic disease than we thought, will we respond differently? That's one of the things we'll discover as genome sequencing goes mainstream.

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