Thursday, December 14, 2006

Rare Gene Brings Life Without Pain

(HealthDay News) -- A rare genetic mutation makes it impossible for an otherwise healthy carrier to feel pain, researchers report.

The mutation -- discovered in three related families in northern Pakistan -- advances the understanding of the genetic basis of pain and might lead to new pain treatments, the international team said.

The findings are published in the Dec. 14 issue of Nature.

"Occasionally, rare genetic diseases can teach us lessons about more common disorders," explained Dr. Stephen G. Waxman, chairman of neurology and director of the Neuroscience and Regeneration Research Center at Yale University and author of an accompanying journal commentary.

Individuals with the rare genetic mutation cannot feel any pain but have otherwise completely normal sensory functions.

One case the researchers studied involved a 10-year-old Pakistani street performer born with the genetic mutation. In his act, he placed knives through his arms and walked on burning coals.

The boy later died on his 14th birthday from injuries he suffered after jumping off a roof.

The Pakistani discovery "really illustrates the pivotal effect that one molecule can have [on pain]," Waxman said. "We do not yet have a cure for common pain, but we hope that there will be a totally new class of drugs to treat pain."

"This paper shows that rare diseases can still be of great importance because of the insights they give into biological and developmental processes," the study's lead researcher, Dr. Geoffrey Woods, from the Department of Medical Genetics and the University of Cambridge Institute for Medical Research, U.K., said in a prepared statement.

Among the three related families the researchers studied, six relatives had not felt pain at any time in their lives. Neurological examinations found no evidence of motor or sensory disease. The affected individuals could still feel a number of sensations, including touch, warm and cold temperature, tickle and pressure.

Pain is not all bad, experts say. In fact, it is a survival mechanism that enables people to be aware of and minimize damage to tissues. The researchers noted that all of the carriers of the mutant gene showed signs of a variety of injuries -- including wounds to their lips and/or tongues from biting themselves when young.

Woods's group found that a mutation in a gene called SCN9A causes a loss of function in the "voltage-gated sodium channel" it encodes. Sodium channels are proteins that excite nerve cells. Though the precise function of this channel is unclear, it appears to play a part in exciting sensory neurons.

"The work of Geoff Woods and his team has provided us with an exciting new target for pain-killing drugs," coauthor Dr. John Wood, from University College London, said in a prepared statement. "Potentially, this is as important as the identification of the morphine receptors. It is fascinating that this same gene, when mutated to encode a hyperactive channel, has also been found to contribute to ongoing pain in some heritable human disorders," he said.

Since people with mutations in SCN9A are otherwise healthy, the researchers hope that compounds that block sodium channel functioning could become effective analgesics.

But Waxman stressed that the Pakistani mutation is not the only one associated with pain.

"We came across a rare genetic disorder called erythromelalgia, also called 'man on fire syndrome,' " Waxman said. "These are people who have pain to any mild warmth. Going into a warm room, putting on a pair of socks, exercise -- that triggers severe burning pain. They describe it as if hot lava were poured onto their hands and feet."

It turns out that families that have this syndrome have a mutation in one of the sodium channels, Waxman said. "This mutation causes this channel to have enhanced function," he said.

Knowing the basis for the problem, it might be possible to develop a drug to treat it, Waxman said. "One could develop drugs that turn down or turn off the channel," he said.

Another expert says that this study confirms the genetic link to how we experience pain.
"There is tremendous variability based on genotype in response to painful stimuli," said Dr. Rollin Gallagher, the director of pain management at the Philadelphia VA Medical Center and a professor of psychiatry and anesthesiology at the University of Pennsylvania School of Medicine.

This study substantiates what is seen clinically, Gallagher said. "It shows the difference in individuals in their opioid receptors. This also gives us a direction for research and suggests that treatments can be found to treat sodium channel defects," he said.

More information
More more on pain, head to the U.S. National Institutes of Health Pain Consortium.

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