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http://www.nature.com/news/2006/061211/full/061211-11.html

 

Published online: 13 December 2006; | doi:10.1038/news061211-11

 

 

The mutation that takes away pain

 

*Studies of rare disorder shed light on pain mechanism.*

 

Michael Hopkin <http://www.nature.com/news/about/aboutus.html#Hopkin>

 

 

 

 

Tell me when it hurts: a mutation in a single gene can cause or inhibit pain.

 

/Punchstock /

 

Imagine being unable to feel any pain at all. For

a tiny handful of people, that is the reality —

and medical researchers have now pinpointed the

mutation that removes their ability to perceive painful sensations.

 

The study began when doctors in northern Pakistan

examined a remarkable group of related families

in which several individuals seem entirely

unaffected by pain. Their attention was first

attracted by one member of the clan, a locally

famous boy who performed street theatre involving

walking on burning coals and stabbing his arms with knives.

 

Although it sounds like a party trick, the

condition is devastating, as sufferers don't

learn to know their limits. The street-performing

boy killed himself on his fourteenth birthday

after jumping off a house roof. The researchers

studied six of his relatives, aged between 4 and

14 years. All had suffered many cuts and bruises,

and injuries to lips and tongue caused by biting

themselves; several had fractured bones without noticing.

 

This shows the importance of pain for our health

and survival, notes Geoffrey Woods of the

Cambridge Institute for Medical Research, UK, who

led the study. " Pain is there for a jolly good

reason — it stops us damaging ourselves, " he

says. For example, the pain from a broken arm or

sprained ankle encourages us to rest that body part while it recovers.

 

The children in the study had no such safety

check, causing them to be both graceless and

reckless. " One girl was continually knocked down

in the playground and just didn't mind at all, " Woods says.

 

*Nerve condition*

 

The researchers compared DNA samples from the six

children and found that they all share a mutation

in a gene called /SCN9A/, which is strongly

expressed in nerve cells. They report their

results in /Nature/^1

<http://www.nature.com/news/2006/061211/full/061211-11.html#B1> .

 

The /SCN9A/ gene encodes a 'sodium channel': one

of the structures that allows electrical charge

to flow into nerve cells, triggering a signal,

the researchers explain. Without this particular

type of sodium channel, the brain does not

receive any signal that the body has encountered a pain-causing stimulus.

 

The discovery answers the question of whether the

Pakistani subjects are truly unable to perceive

pain or simply indifferent to it. When the first

ever pain-free patient was examined in the early

twentieth century, some doctors thought that

perhaps the condition involved a malfunction in

the brain, rather than in the nerves.

 

The Pakistan patients did seem to understand the

concept of pain, and had picked up a knowledge of

situations in which other people experience it.

While being observed in a game of soccer, some of

the older children in the study even acted as if

in pain after being tackled. " Often, if you don't

look as if you feel pain people think you're odd, " Woods says.

 

*Oversensitive*

 

Mutations in /SCN9A/ are also involved at the

other end of the pain spectrum, another recent

study shows. Mutations that enhance, rather than

inhibit, the protein's activation are at the root

of paroxysmal extreme pain disorder, report

researchers led by Mark Gardiner of University

College London in the journal /Neuron/^2

<http://www.nature.com/news/2006/061211/full/061211-11.html#B2> .

 

It therefore seems that /SCN9A/ acts as a " major

trigger " of pain, says Woods. " It's amazing that

we missed it for so long and then out of the

woodwork come these two disorders, " he says.

 

This could offer potential new ways to treat

severe pain. Current methods, such as local

anaesthetics, are impractical, and constantly

taking opiate painkillers can lead to addiction.

Targeting /SCN9A/, perhaps through gene therapy,

could also help sufferers of constant extreme

pain from injuries, arthritis, spinal conditions or cancer.

 

But, as the Pakistani subjects showed, the new

discovery is of no use in tackling that perennial

human condition, emotional pain. " They can blush

and cry, and when they have flu they feel

unwell, " he says. " And they are hurt by rejection just the same as anyone. "

 

*Visit our newsblog

<http://blogs.nature.com/news/blog/2006/12/the_mutation_that_takes_away_p.html>

to read and post comments about this story.*

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