Think about the last time you accidentally grabbed the handle of a hot pan without wearing an oven mitt. You wish you hadn’t felt that searing pain, right? Now imagine walking around on a broken leg that you don't know is broken. You're feeling no pain. Imagine how much damage you could do to your body if pain never warned you that something was seriously wrong.

That's the case for people with the incredibly rare condition known as congenital insensitivity to pain. They feel no pain, whether they have a minor blister or a leg fracture. In severe cases, “they mutilate the lips as they do not sense when they bite the skin around their mouths,” Lucy Norcliffe-Kaufmann, an assistant professor of physiology and neuroscience at NYU Langone Medical Center, tells mental_floss.

No one likes pain, but it is an incredibly useful warning system. Without it, your mind doesn't recognize an injury, and you won't take steps to remove yourself from its cause. Patients with this condition have been known to develop terrible infections, unintentionally mutilate themselves, and wear away their joints.

By now you must be starting to appreciate the sensation you felt—and maybe the expletive you yelled—when you last stubbed your toe on the coffee table.

The key to unlocking the mechanisms behind this condition, researchers are finding, lies in genetics. A team led by C. Geoffrey Woods of the University of Cambridge recently published a study in Nature Genetics that identified 10 new mutations present on the gene PRDM12 among 158 people from 11 families who all suffer from some form of congenital pain insensitivity.

The researchers believe these mutations, coupled with others previously discovered on the genes SCN9A and SCN11A, cause an inability to feel pain and, in some cases, to distinguish between hot and cold temperatures. Woods’ team concludes that mutations in PRDM12 cause developmental defects in a person’s nociception, or ability of the nervous system to translate pain from its source to the brain. 

Treatment for those with congenital insensitivity to pain is currently limited, and most patients must be cautiously supervised at all times to keep them from unintentionally hurting themselves. New findings in this field could not only help develop new treatments for them, but also potentially lead to new ways to address more common chronic pain conditions, which affect millions.

“Understanding how rare diseases are expressed sheds light on how normal physiology works,” Norcliffe-Kaufmann explains. “Knowing a specific mutation and how this changes our ability to sense pain may help us find new targets for the development of [painkillers].”