A review of studies into the placebo effect published last week suggests that there may be up to 11 different genes involved in an individual’s response. This indicates that the placebo response is a much more complex phenotype than originally thought.
The “Placebome” refers to the genetic factors influencing the effect. While a third of the population are placebo responders, the variation in response can be vast, from slight to significant improvement. The 11 placebo-linked genes are largely involved in neurotransmitter pathways such as endocannabinoids, serotonin and opioids.
One such pathway involves the catechol-O-methyltransferase (COMT) gene, responsible for generating the enzyme that breaks down dopamine. In 2012, Kathryn Hall, lead author of the recent review, and her team discovered that possessing two mutant alleles of this gene has been linked to higher levels of dopamine in the body and consequently an increased placebo susceptibility in Irritable Bowel Syndrome (IBS) patients. It has also been found that placebos and drugs may involve the same pathways, therefore altering one another’s responses.
Genetic screening could potentially be used in the future to assess the likely effect of placebos on certain patients. It could then be applied to create personalised therapeutic treatments. However, Tomas Furmark, who first discovered a placebo-associated gene, believes there is a long way to go before these practical applications become possible.
Personality traits such as extroversion and being open to new experiences may also have an influence on level of response, further highlighting the complexity of the placebo effect. Evidence from the review, however, suggests that placebos are likely to play a far greater role in healthcare than previously thought.