Saturday science subject: The placebo gene

— 1:00 PM on December 6, 2008

Are some of us genetically predisposed to get better when given sugar pills instead of actual medication? The findings of a study by Tomas Furmark and his colleagues at the University of Uppsala in Sweden certainly suggest so. As the New Scientist reports, the double-blind study involved 25 people suffering from social anxiety disorder. Here's what happened:

Participants had to give a speech at the start and end of an eight-week treatment - which unbeknownst to them and their doctors, was actually a placebo. . . . Ten volunteers responded to the placebo much better than the rest. By the end of the experiment, their anxiety scores had halved, whereas the others' stayed the same. Brain scans also showed that activity in the amygdala, the brain's "fear" centre, had dropped by 3 per cent.

To see if there were genetic differences between responders and non-responders, Furmark screened them for a variant of the gene for tryptophan hydroxylase-2, which makes the brain chemical, serotonin. Previous studies suggested that people with two copies of a particular "G" variant are less anxious in standard "fear" tests. Sure enough 8 of the 10 responders had two copies, while none of the non-responders did (Journal of Neuroscience (DOI: 10.1523/JNEUROSCI.2534-08.2008).

According to the New Scientist, Furmark expects the same gene may affect pain disorders, depression, and other phobias, since those also involve the amygdala—but he stresses that "only further studies will reveal whether the gene influences the placebo effect more generally."

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