The way in which people perceive physical and emotional pain is partly due to variations in a single gene, according to a team of US researchers. The gene, which comes in two different versions, makes a brain chemical known as COMT. People with one form of COMT are particularly sensitive to pain, whereas those with the other form tend to be more stoic. People who inherit both versions, one from each parent, have an intermediate response to pain. 'This is the first time a gene has been linked to particular changes both to the chemical systems of the brain and behaviour', said team leader Dr Jon-Kar Zubieta, of the University of Michigan, Ann Arbor.
The COMT (catechol-O-methyl transferase) protein is responsible for mopping up another brain chemical called dopamine, which is produced by the brain when the body senses pain. But animal studies show that too much dopamine can interfere with the brain's production of its own natural painkilling substances. COMT exists in two different forms: the 'val' form and the less efficient 'met' form, which mops up dopamine more slowly.
The researchers studied the effect of these two different versions of COMT on the pain threshold of 29 volunteers by injecting salt water into their jaws. They then asked them to record their level of pain every 15 seconds, whilst carrying out brain scans to measure brain chemical activity. They found that participants with two copies of the val form of COMT broke down dopamine more quickly, withstood more pain and suffered less emotional distress than others in the study.
The research, published in last week's Science, 'is helping tell us how important individual differences are in the experience of pain and other significant stressors' said Zubieta.