Around one in a million people worldwide are thought to be born without a sense of pain.
Although this may sound great at first, the rare condition, known as congenital insensitivity to pain (CIP), leaves sufferers at risk of self-inflicted injuries and often leads to reduced lifespan.
But scientists may now be one step closer to finding a solution to the condition after discovering a possible genetic cause for it.
A team of researchers lead by scientists at The University of Cambridge studied the condition in 11 affected families in Europe and Asia.
The researchers were able to pinpoint the cause of the condition to variants of the gene PRDM12.
They found that people who suffered from CIP had inherited mutated PRDM12 genes from both their mother and their father.
Family members who inherited a mutated PRDM12 gene from just one parent were able to experience pain as usual.
"PRDM12 had previously been implicated in the modification of chromatin, a small molecule that attaches to our DNA and acts like a switch to turn genes on and off (an effect known as epigenetics)," a statement from The University of Cambridge explains.
"The researchers showed that all the genetic variants of PRDM12 in the CIP patients blocked the gene's function."
Teenager Ashlyn Blocker is just one of the CIP sufferers who has been found to have two defective copies of genes.
Blocker feels no pain and has sustained injuries in the past due to the condition. As a child, she put her hand in boiling water without feeling any discomfort.
"Everyone in my class asks me about it, and I say, ‘I can feel pressure, but I can’t feel pain’,” Blocker said, according to The Independent.
Gabby Gingras is another teenager who suffers from CIP. She appeared on the The Oprah Winfrey Show in 2005 when she was five years old with her parents.
The audience heard of how she'd mutilated three of her fingers from chewing on them. She also poked and scratched at her eyes constantly, forcing doctors to remove one and leaving her legally blind.
Gabby Gingras in 2005
Gingras and her parents returned to the show last year when she was 14 years old.
Her father told Oprah that although she has a better sense of her limitations, his daughter has still injures herself without knowing it.
"She came home from school one day and said, 'my back feels funny,'" he recalled.
"We felt on her back and felt a bump and felt it was warm... [Doctors] took an x-ray and they came back and said that her back was broken."
Commenting on the latest study, Professor Geoff Woods from the Cambridge Institute for Medical Research at the University of Cambridge said: "The ability to sense pain is essential to our self-preservation, yet we understand far more about excessive pain than we do about lack of pain perception.
"Both are equally important to the development of new pain treatments – if we know the mechanisms that underlie pain sensation, we can then potentially control and reduce unnecessary pain."
The study is published in the online journal Nature.
21 Rare Diseases
[H/T: The Independent ]