Gene controls pain threshold
Variations in a single gene may explain why some people can
withstand pain that would cause others to crumple.
The gene in question, which comes in two forms, makes an enzyme that
helps control the brain signals involved in pain response.
Everyone carries two copies of the gene, one inherited from each
parent.
A study of volunteers showed that those with two copies of one form of
the gene felt much more pain than those with two copies of the other.
People with one copy of each gene variation had a pain response
somewhere between the two.
The gene variants are known as "val" or "met". They make versions of
an enzyme called catechol-O-methyl transferase (COMT) which differ in
only the tiniest of ways.
Complex process
Lead researcher Dr Jon-Kar Zubieta, from the University of Michigan in
Ann Arbor, said: "Participants who had two copies of the val form
withstood quite a bit more pain than others in the study, while at the
same time reporting that they felt less pain and fewer pain-related
negative emotions.
"Our findings and those of other groups underlie the need to think about
pain as the result of complex interfaces between injury and our own
capacity to regulate its severity and significance.
"Examining and detailing the biochemistry of these processes can then
lead to more effective treatments."
The researchers used brain scans to trace the brain's pain responses in
29 volunteers.
Each was given carefully controlled salt-water injections in their jaw
muscles to induce pain.
Subjects rated their pain every 15 seconds during each scan and filled
out standardised questionnaires assessing how they felt.
The COMT enzyme breaks down chemicals such as dopamine which
transmit messages between brain cells.
Two copies of the "val" gene makes powerful COMT that mops up the
chemicals rapidly.
But two copies of the "met" form produce a weaker version of COMT
that is not so good at clearing away the chemicals.
It is thought that a build up of chemicals like dopamine suppresses the
activity of the brain's natural painkillers - the endogenous opioids.
The study found that volunteers with two copies of the "val" gene were
better able to break down dopamine and suffered less pain.
The research is published in the magazine Science.
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