British scientists have found a rare genetic mutation the blocks pain in humans. They say if a drug can mimic it, the result could be a new class of painkillers with few side effects, if any. VOA's David McAlary reports from Washington.

University of Cambridge researcher Geoffrey Woods and colleagues found three related families from northern Pakistan who do not know what pain is.

"We've been looking at a group of children who don't feel any pain," said Geoffrey Woods. "They have never felt any pain of any type in their entire lives."

You may wish for the same protection, but pain is actually good for you. It is a sensation that causes us to withdraw from danger, like fire, and therefore prolongs survival. One of the Pakistani boys was not so lucky. Woods says the 14-year-old youth's freedom from pain allowed him to stick knives through his arms and walk on burning coals to the astonishment of onlookers, but eventually led to his death.

"We decided it was a disease because the first child we were going to study jumped off a roof and killed himself," he said. "He did that because he didn't feel pain, and because he didn't feel pain, he didn't avoid painful or damaging situations."

Woods and his colleagues hope that what they have since learned about the nervous systems of the boys' surviving relatives can be turned into a benefit for controlling pain. By studying the blood of these families, they found that a mutation in a single gene creates a protein that blocks nerve impulses conveying pain signals to the brain.

Woods outlined a theory on how the gene mutation works in an interview with Nature magazine, where the study is published.

"There are a number of proteins that sense tissue damage in our body of different types," explained Geoffrey Woods. "All are sensed, and a small sodium current leaks into a cell. That sodium current then needs to be amplified so it can be detected as a nerve impulse. It seems that our protein has that job. It takes all these small sodium signals and amplifies them so a nerve can detect them as a large voltage change."

Woods says if a drug could block this sodium channel as the natural protein does in the Pakistani families, it might be a total painkiller without side effects.

"These children and adults appear to be otherwise well," he noted. "There is nothing else wrong with their muscles, their intelligence, their sense of smell, the way they regulate their heart. Everything else seems to be fine. So potentially if you could block this channel in humans, you would have an analgesic that affects only pain."

He says in the end it might not be that simple, but the drug company Pfizer is trying to find out. It is already developing a product based on the new genetic target. The company says the drug should be ready for human tests in two years.