Genetic information as self-fulfilling prophecy

If the TV ads are at all effective, plenty of people will be getting the gift of their genetic tests this Christmas. These tests frequently allow people to explore their inherited tendencies toward health problems and, in some cases, may suggest lifestyle changes to ward off future problems—although studies have indicated that few people do.

However, DNA test results can also cause issues that wouldn’t otherwise be there. Genetic information can exert a potent placebo effect—or the opposite, the nocebo effect, wherein if you think that something can harm you, it in fact does. And the potency of this effect has not been studied until now.

Experimental ethics

Some psychologists at Stanford wondered if the perception of genetic risk could actually increase people’s risk, independent of their actual genetic risk. In other words, could simply learning that you have a genetic propensity for something elicit physiological changes akin to really having that propensity, regardless of whether you have it? The team designed experiments to find out.

First, they recruited a couple hundred research subjects into a “personal health study” in which the participants were told that they would have genetic profiles done and then learn about which exercises and diets were best suited to them. The researchers obtained a sample of the participants’ DNA to find out their true genetic status for two easily measurable physiological parameters: how much they could run on a treadmill or how full they got after eating a meal. But they didn’t tell the participants their results. Researchers then measured that parameter by feeding the participants or putting them on a treadmill, providing a baseline reading.

A week later, the same participants were invited back. At this point, the researchers lied to half of the people about their genetic risk, while telling the controls the truth. They had both groups run on the treadmill or eat the same meal again. Then they told the participants the truth about the genetic results.

If lying about genetic tests sounds ethically… questionable, the researchers know. They dealt with their reservations in a few ways. First, the researchers focused on genetic risk information for obesity; they figured that learning you are at risk would obviously suck, but it’s not like they were telling people they were at risk for cancer or Alzheimer’s. Second, they only allowed the participants to hold the wrong idea about their genes for an hour, just long enough for the researchers to assay the effect of the misinformation on behavior and physiology.

Finally, the team notes that “the potentially iatrogenic [induced inadvertently by medical care] effects of learning one’s genetic risk are already occurring at scale.” One in twenty-five American adults have already purchased personalized genetic test results; we might as well study how this information is impacting them.

Food and fitness

The first genetic variant sequenced was one associated with reduced exercise capacity. Those told that they had the high risk genotype—regardless of whether they did—got off the treadmill quicker and didn’t breathe as efficiently as they had the previous week, before they got their DNA test results. Those told they had the protective variant ran for longer before reporting feeling hot or that the workout was hard, compared to their baseline workout the week before.