Why do some people feel pain more than others? Scientists discovered a major gene that could help answer that question and could someday lead to new ways to treat chronic pain, according to a recent study published in the journal Nature Medicine. Pain and pain-reducing drugs evoke widely varying responses in people, but little is known about the genetics of pain sensitivity, scientists said.

Studies were conducted on lab mice, which exhibited significant differences in pain hypersensitivity after surgically induced nerve pain. Mice with low pain sensitivity were found to carry a gene with a mutation of a pain receptor called P2X7. The mutation impaired the formation of pores that normally permit large molecules to pass through the receptor. The researchers don't know what these large molecules are or how they are associated with pain.

Experiments showed that pore formation was unimpaired in mice with high pain sensitivity. By administering a compound that blocked or disabled pore formation but didn't affect other receptor functions, researchers prevented and reversed hypersensitivity in these mice. The experiments were carried out in Montreal and Toronto, and replicated in a U.S. lab.

Researchers conducted genetic tests to see if pain sensitivity in people was associated with the P2X7 mutation. These tests were done on 354 Israeli women who had undergone breast-cancer surgery; 743 osteoarthritis patients; and 586 control subjects in North Carolina. Results showed subjects with lower pain sensitivity carried the mutation. Treatments that block pore formation on this receptor but allow smaller molecules to pass through may improve pain control in patients genetically at risk for chronic pain, with fewer side effects, researchers said.

Caveat: The research was carried out in mice and on DNA samples from human subjects.