The difference between those who can tolerate pain and those who can’t may come down to a slight variation within a single gene.

According to researchers at the University and the National Institute of Alcohol and Alcoholism, a new study indicates that a person’s pain threshold may be inherited.

The study shows variation in the gene that encodes the enzyme catechol-O-methyl transferase has a significant effect on pain tolerance and pain-related emotions of individuals.

“This research is the first of its kind to build bridges between behavioral effects, brain circuits and genetics,” said Stanley Watson, co-director of the Mental Health Research Institute.

The gene that encodes the COMT enzyme expresses itself either as valine or methionine alleles. All people receive one of these alleles from each parent.

The study tested the pain thresholds and pain-related emotional responses of 29 individuals by injecting a carefully controlled amount of salt-water into the jaw muscle to stimulate temporomandibular joint pain disorder, and then watching the brain react using brain-imaging technology. Subjects also answered questionnaires on how the pain made them feel.

Results showed that individuals with two copies of the “met” allele withstood less pain and reported feeling more pain-related negative emotions than those with two copies of the “val” allele. Those who had one copy of each responded to pain somewhere in the middle.

“The beauty of the gene is that it is so frequent,” said neuroscientist and the lead author of the study Jon-Kar Zubieta. “Fifty percent of the population has both alleles, 25 percent has two copies of the met allele and 25 percent has two copies of the val allele.”

The COMT enzyme metabolizes the brain chemicals dopamine and noradrenaline. Those with two copies of the val allele are able to metabolize the dopamine better than a person with two copies of the met allele. If enough dopamine is not metabolized, the brain reduces the production of enkephalins or painkillers.

What began as a study to better understand why women were more prone to conditions like TMJ, fibromyalgia and depression now has the data to explore a whole new field of study, Watson said.

“The possibility now exists for medical treatment and medicine to become more personalized – treating individuals on the basis of their own physical and emotional responses,” Watson said.

He added that in the future, the research could provide the tools to treat veterans of war who have been traumatized.

“We’re making the point that it is not enough to look at genes and behavior – we must look at the brain,” Zubieta said. “To fully understand humans, we must understand that which regulates over our every thought and sensation.”

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