Feel no pain, for real: mutation appears to underlie rare sensation disorder in a Pakistani family.

Scientists have tracked down a genetic mutation that makes some members of an unusual Pakistani family fail to sense pain.

Although pain can be agonizing, it does serve a useful function--it teaches people and animals to avoid dangerous situations and forces them to attend to wounds. However, a handful of people have genetic conditions that prevent them from feeling pain. This rare lack of sensation is often detrimental; people with the condition can be unaware of having suffered significant injuries.

Several years ago, medical geneticist C. Geoffrey Woods of the University of Cambridge in England and his colleagues began working with children from a family in northern Pakistan in which several members can't sense pain. The team's first research subject, a 10-year-old boy, was well known in his community for street performances in which he placed knives through his arms and walked on hot coals. Despite tissue damage, he apparently felt no discomfort.

Wondering what could cause this boy and other family members to lack pain sensation, woods' group scanned the genomes of six of the other children who were affected by the condition. The researchers searched for genetic quirks that weren't shared by family members with normal pain sensation. The team eventually zeroed in on mutations in SCN9A, a gene that encodes part of a cell-surface channel that lets sodium into pain-sensing nerve cells as part of signal propagation.

In separate experiments, the researchers tested how these mutations might affect the sodium channel's function. The team caused kidney cells, which don't naturally have the channel, to display either the normal or the mutant channels on their surfaces. When the scientists stimulated the cells with electric current, the normal sodium channels opened and sodium ions flooded into the cells. In contrast, electric current didn't open the mutant channels.

The researchers say in the Dec. 14 Nature that people with such mutations in their SCN9A genes probably have a similar loss of sodium-channel function in their pain-sensing nerve cells. However, these cells' membranes also contain sodium channels that aren't affected by the mutation, so the team isn't sure why the affected individuals feel no pain.

"This paper shows that rare diseases can still be of great importance because of the insights they give into biological and developmental processes," Woods says. He notes that continuing to study the Pakistani family members could lead to a better understanding of the general mechanisms behind pain.

People with some types of chronic pain have on their pain-sensing nerve cells an abnormally high number of sodium channels containing the protein encoded by SCN9A, according to research by Yale University neurologist Stephen G. Waxman. In a commentary that accompanies the Nature report by Woods' team, Waxman adds that if researchers could craft a drug to make these channels inactive, as they are in the Pakistani family members, they could help millions of people worldwide who suffer from chronic pain.

"This research could give pharmaceutical companies a valuable lead," Waxman predicts.