Placebo effect related to genetics

Researchers in the US have found evidence that suggests the placebo effect is dependent on patient’s genes.

The placebo effect can be described as an improvement in health or behaviour not attributable to a medication or invasive treatment. An example of a placebo could be a sugar table given to a patient instead of one containing active ingredients. It has been a highly researched area and a medical mystery for over 70 years.

New research, published in PLoS ONE this week, shows how the extent of people's placebo responses may be explained by genetic differences that vary the amount of dopamine in their brains.

This was assessed using a gene called Catechol-O-Methyltransferase (COMT).  A person can have a number of variants of the COMT gene; met/met, met/val or val/val. People with the met/met variant have four times more dopamine available in their prefrontal cortex (an area of the brain that is linked to cognition, personality expression, decision making, and social behaviour) than those with the val/val variant.

Paper author Dr Kathryn Hall, proposed that if dopamine is involved in the placebo effect, then a person’s COMT type would determine their response.

This proposal was tested by looking back at a 2008 clinical trial, which investigated the placebo effect in patients with irritable bowel syndrome (IBS).  Hall and colleagues were then able to find patients genotypes from their blood samples.

They found that as the copies of met in the COMT gene increased, so did the placebo response ("presumably because more dopamine was available", says Hall). In some cases met/met carriers showed 6 times the improvement in symptoms than those val/val carriers.

Hall says their results suggest "met/met is a genetic marker for the placebo response and val/val is a marker for non-response".

"With this new research, we may now be able to use a person's genetic makeup to predict whether or not they will respond to a placebo,"

This has important implications for patient care, and will also help researchers design and carry out more cost-effective clinical drug trials.

A fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. Full medical glossary
A common name for the large and/or small intestines. Full medical glossary
The outer region of an organ. Full medical glossary
A type of neurotransmitter - chemicals that help the communication between nerve cells (neurons). Full medical glossary
The basic unit of genetic material carried on chromosomes. Full medical glossary
Relating to the genes, the basic units of genetic material. Full medical glossary
irritable bowel syndrome, a combination of abdominal pain and constipation, diarrhoea, or bouts of each that occur in the absence of any other diagnosed disease Full medical glossary
otitis media Full medical glossary