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Feeling No Pain: New Form of Rare Gene Disorder Decoded

Mason Inman
for National Geographic News
December 13, 2006
 
"I have super powers," a girl named Megan whispers to her doctor on a recent episode of the TV show Grey's Anatomy.

That's her explanation for how she's able to withstand nasty gashes and being hit with a baseball bat—all without feeling any pain.

Megan actually has a rare genetic disorder that renders her insensitive to pain. And although she is a fictional character, her problem is real.

Across the world about a few hundred people suffer from one of a variety of diseases that make them completely unable to feel pain from the time they're born.

Now a new form of this disorder has been recognized among people from northern Pakistan, and scientists have tracked down the mutated gene responsible for the condition.

Their study, published today in the journal Nature, could help researchers gain a better understanding of how pain works and may help them develop new painkillers with fewer side effects.

(Related news: "Toxic Snail Venoms Yielding New Painkillers, Drugs" (June 14, 2005)

Faulty Gene

Among people who are born without pain sensations, the classic case of the disorder is called congenital insensitivity to pain with anhidrosis (lack of sweating).

These patients usually have a variety of physical ailments, including slight mental retardation.

Only a handful of sufferers are like the TV character Megan, without major symptoms beyond a loss of pain.

Researchers discovered the latest version of the disorder when they spotted a young street performer in Pakistan.

"They came across him in the market, sticking daggers through his arms," said John Wood, a professor at University College London in England and a member of the research team.

From talking to the locals the researchers were able to find six other people from three families in the same region who also had the disease.

These people were able to feel hot and cold, sense pressure, and could tell sharp objects touching their skin from blunt ones.

They were all deemed to be of at least average intelligence. But none of them felt any pain.

Surprisingly, the families were unrelated, but all of the afflicted members had mutations to the same gene (get an overview of human genetics).

The culprit gene encodes a protein that forms part of a channel that allows electrically charged particles to cross the surface of nerve cells.

"This channel is undoubtedly crucial for human pain perception," Wood said.

The mutation stopped the protein from working, the study showed. This apparently prevented a certain type of nerve cell from passing on signals that tell the brain when something is painful.

Learning by Example

Early childhood can be treacherous for people with complete insensitivity to pain.

They can gnaw endlessly on their tongues and fingers during teething, stick their fingers in their eyes, or suffer major injuries without noticing.

The six people studied for the Nature paper all had permanent injuries to their lips or tongues from biting themselves when they were young.

The boy who clued researchers to their presence in Pakistan died after jumping off a house before his fourteenth birthday.

But eventually sufferers can learn what to avoid doing even without pain as a guide.

Paola Sandroni, a neurologist at the Mayo Clinic in Rochester, Minnesota, who was not a member of the research team, had a patient with a nearly identical disorder to the Pakistani subjects.

This patient was very unusual, because he was 20 years old before he was diagnosed with a nerve disorder.

When he was a toddler he complained to his mother that some kids had roughed him up and hurt his feelings. What he didn't mention was that he also had broken his arm.

But eventually, Sandroni said, "he learned by using his intellect and experience of watching others."

He once shocked himself while working on some wiring, for example.

"His arm started jumping, and he felt nothing," Sandroni related.

"He thought it was pretty funny, actually … Then he said, Oh, maybe I shouldn't be touching these wires. So he pulled his hand away and noticed that he had a burn."

When Sandroni reported the diagnosis earlier this year, she couldn't find reports of any other patients with the set of symptoms.

But, she says, the new cases in Pakistan sound very similar.

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