According to researchers, a gene determines people's sensitivity to pain.In the study conducted on rats, the development of chronic pain could be prevented by blocking the expression of that particular gene after a nerve injury or inflammation. This could be a breakthrough in development of new painkillers.
"Studies in volunteers showed that about a quarter of them had the genetic variant that protects them from pain somewhat, and three percent carried two mutated copies that make them exceptionally insensitive to pain, " the researchers reported in the journal Nature Medicine.
"This is a completely new pathway that contributes to the development of pain," said Dr Clifford Woolf of Massachusetts General Hospital and Harvard Medical School in Boston, who led the research.
"The study shows that we inherit the extent to which we feel pain, both under normal conditions and after damage to the nervous system."
Chronic pain affects 1-in-5 adults or approximately 40 million Americans.
The gene involved is called GCH1 that codes for an enzyme GTP cyclohydrolase that is required for the synthesis of a chemical called tetrahydrobiopterin or BH4.
"Our results tell us that BH4 is a key pain-producing molecule - when it goes up, patients experience pain, and if it is not elevated, they will have less pain," Woolf said in a statement.
"The data also suggest that individuals who say they feel less pain are not just stoics but genuinely have inherited a molecular machinery that reduces their perception of pain. This difference results not from personality or culture, but real differences in the biology of the sensory nervous system."
Woolf and researchers in Germany and at the US National Institutes of Health said, "Rats with pain caused by nerve damage had higher levels of GCH1 gene activity and of BH4."
The rats appeared to be less sensitive to pain when injecting a drug blocked the enzyme GTP cyclohydrolase. On the other hand, augmented pain sensitivity was observed when BH4 was injected.
They conducted a study on 400 healthy individuals. They found that people with two copies of the protective version of "GCH1" were less sensitive to pain in tests, whereas those with only one copy had intermediate risk of developing chronic pain and those without any copy of the variant were at the highest risk.
"The drug used in the study, DAHP, is not very strong and is unlikely to be useful as a human medication, " said Woolf, who owns stock in a company called Solace Pharmaceuticals, which has licensed the findings for potential drug development.