Placebo genes?

From Ars Technica

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.

That is, they were looking for a placebo effect of genetic information.  It’s not a ridiculous idea that there could be one. The placebo effect is a real phenomenon (at least in some settings) and there’s no obvious reason why it should work with pills and injections but not genetic information.  And I’m in favour of the principle that giving people health information (that they didn’t ask for) is an intervention that should be evaluated like any other. However, I’m not entirely convinced.

There were two experiments. One saw that people told they had a bad-at-exercise gene variant were worse at exercise.  The other saw that people told they had a staying-hungry gene variant stayed more hungry after drinking a nutrition shake. What the story (and the research paper) makes a lot of, though, is that physiological measurements changed too. It wasn’t all in the participants’ minds (or even all in their brains).

One issue is that the evidence isn’t all that strong (especially given the publication filtering it takes to get into the media) — even though the observed differences were surprisingly large. That makes it likely more that chance contributed to the results. Also, to the extent we’re seeing random variation in exercise or in hungriness we’d expect to see the same variation in biochemical measurements. If the explanation isn’t a placebo effect, the physiological differences are exactly what you’d expect.

It’s also worth noting that the biochemical difference seen in the hunger experiment (in something called glucagon-like-peptide-1) isn’t one of the differences that have been reported for the gene in question (at least in the references given). The researchers looked for a biochemical difference that had been seen for the gene (in ghrelin), and didn’t see it.  It would have been interesting to see whether information about the hunger-related gene affected exercise capacity — if there’s something there, is it somewhat specific or is it general to being told ‘bad genes’?

Even without necessarily believing the specific conclusions of the research, though, it’s another reminder that the evidence for health benefits of most sorts of genetic information is surprisingly weak.