Posted on 02/22/2003 11:40:20 AM PST by ChemistCat
WASHINGTON (AP) — Inheriting a variation in a single gene can determine whether a person will be a wimp or a stoic when it comes to handling pain. University of Michigan neuroscientists put healthy young adults inside a brain scanner, made them hurt — just temporarily — and proved that carriers of the ``stoic'' gene version really can tolerate more pain.
The discovery emphasizes the need to customize pain treatment and might even allow doctors to soon try predicting which patients will respond to a certain kind of medication.
People's perceptions of pain are tremendously variable. A substantial blow to one person may seem trivial to another; likewise, pain medication that helps one patient may do nothing for the next.
The new research shows how much people suffer is due partly to a gene that helps regulate how many natural painkillers, called endorphins, the body produces.
The gene produces an enzyme called COMT that metabolizes the neurochemical dopamine, which acts as a signal messenger between brain cells.
Everyone has two copies of this gene, one inherited from each parent — but they can inherit forms that differ by one amino acid. The COMT gene that contains the amino acid methionine, or met, is less active than if it contained the amino acid valine, or val.
Dr. Jon-Kar Zubieta injected the jaw muscles of 29 healthy young adults with enough salt water to make them really ache, simulating a painful condition called temporomandibular joint syndrome, or TMJ. Using a PET scanner, Zubieta measured how their brain cells reacted while the volunteer victims rated, every 15 seconds, how much they hurt during the 20-minute pain cycle.
People who had two copies of the val-COMT gene were stoics. They withstood significantly greater saline doses than other volunteers while rating the resulting pain as less bothersome, Zubieta reports in Friday's edition of the journal Science.
The PET scans verified that response: Painkilling endorphins were much more active in these people's brains.
In contrast, people with two copies of the met-COMT gene suffered the most pain from the smallest saline injections — and had far less natural painkiller action.
People who inherited both a met and val gene copy tolerated pain at levels between the two extremes.
A quarter of the U.S. population carries the ``stoic'' gene variation while another quarter has the gene variant that makes them supersensitive to pain, Zubieta estimates.
Why would a gene that regulates dopamine also affect painkilling endorphins? Too much dopamine in the brain reduces endorphin content, Zubieta explained. People with the double-val gene make a very potent COMT enzyme that clears out dopamine rapidly, triggering more endorphin production, while people with the double-met gene have the opposite reaction.
It's an important discovery, said neurobiologist Adron Harris of the University of Texas at Austin, who has long studied why men and women tolerate pain differently.
One reason: When standard pain medications fail, antidepressants that target dopamine sometimes relieve severe, chronic pain. But there has been no way to predict who might benefit. The new research suggests a simple gene test might soon solve that problem, Harris said.
``Certainly the need to individualize pain treatment ... is great, and is now done mostly by trial and error,'' he said. ``This (research) is really getting to molecular medicine or genetic medicine, where you're using the genotype to predict which drug would be best for the person.''
Pain response clearly depends on more than a single gene, Zubieta cautioned. For example, in another study, he found women tolerate pain better during the time of the menstrual cycle when estrogen levels are highest.
And Zubieta's ultimate goal isn't just to predict pain tolerance, but to understand what combination of genetics and other factors make certain people more vulnerable to painful diseases, like the joint-afflicting fibromyalgia that tends to strike women.
This ought to interest anyone who has fibromyalgia, CFS, or other chronic-pain diseases. Maybe a lot of people with the same tissue abnormalities we have just don't suffer from it like we do? It also might be of interest to the military, if there's a connection between pain response and performance under fire. Perhaps elite units might be comprised only of pre-screened stoics who can be counted on to keep going despite serious wounds?
Wouldn't it be ironic if we learned that all the past 200 years' do-goodism regarding criminals was worthless, and that by simply making the violent criminal feel pain more keenly, his behavior could be drastically changed?
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