The placebo effect has puzzled scientists for years. Why do patients experience a temporary relief in symptoms without the administration of biologically active substances? According to scientists of the Harvard Medical School in Boston the susceptibility to placebos may be partly based on specific genetic variants. These results were published in a review in Trends in Molecular Medicine.
An increasing number of studies indicates that neurotransmitters in the brain may be involved in the placebo response. Especially dopamine and opioid pathways have been postulated to participate. However, these systems do not function alike in all people because of genetic variation. For example, the binding affinity of a dopamine receptor changes if it has only one different amino acid.
For the review, the researchers included placebo-controlled drug studies with additional information on gene associations. The resulting data showed that high dopamine levels and a strong placebo effect were connected to a specific gene variant. These insights should be considered in future drug trials, the scientists recommend, because understanding the genetic constitution of the study population may allow more precise measurements of drug efficacy.
"Understanding the collection of genes related to placebo responses opens possibilities to improving patients' responses to clinical care and pharmaceuticals", says lead author dr. Kathryn Hall, researcher at Beth Israel Deaconess Medical Center. This holds especially for drugs that affect the neurotransmitter pathways involved in the placebo effect.
Of note, the authors add that it would be simplistic to attribute the whole placebo response to genetic factors. Personal expectations, experiences, disease characteristics and the interaction with the medical staff are at least as important.
Sources: Eurekalert and Trends in Molecular Medicine.
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