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The gene might not play a role in our response to treatment for all conditions, and the experiment involved only a small number of people. Nonetheless, the discovery is a milestone in the quest to understand this phenomenon, which often blurs the results of clinical trials "To our knowledge, it's the first time anyone has linked a gene to the placebo effect," says Tomas Furmark of Uppsala University in Sweden.
He and his colleagues recruited 25 people with an exaggerated fear of public humiliation, otherwise known as social anxiety disorder. 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: link).
Furmark believes the effect of the gene may extend to other conditions where the amygdala is involved, such as phobias, pain disorders and even depression. However, he cautions that only further studies will reveal whether the gene influences the placebo effect more generally.
Echoing Furmark's caution is Fabrizio Benedetti of the University of Turin, Italy. "We know that there's not a single placebo effect but many." Some may work through genetics, he adds, others through the expectation of a reward.
Edzard Ernst of the Complementary Medicine Peninsula Medical School in Exeter, UK, agrees the results need to be replicated and tested in several clinical settings.
But I smell a decoy. Genes are getting the "blame" for a host of issues that are possibly, even probably, due more to other factors - environmental toxins, lifestyle, mental state, etc.
I suspect that genes expression is being used as the scapegoat to divert attention from the real villians.
When I see as much attention directed towards how gene expression is controlled by outside factors - stress, toxins, etc. - then I'll take these gene reports more seriously.