Congenital insensitivity to pain

Congenital insensitivity to pain (CIP), also known as congenital analgesia, is one or more rare conditions where a person cannot feel (and has never felt) physical pain. The conditions described here are separate from the HSAN group of disorders, which have more specific signs and etiology.

Presentation
For patients with this disorder, cognition and sensation are otherwise normal; for instance patients can still feel discriminative touch (though not always temperature ), and there are no detectable physical abnormalities.

Children with this condition often suffer oral cavity damage both in and around the oral cavity (such as having bitten off the tip of their tongue) or fractures to bones. Unnoticed infections and corneal damage due to foreign objects in the eye are also seen. Because the child cannot feel pain they may not respond to problems, thus being at a higher risk of more severe diseases or otherwise.

In some people with this disorder, there may be a mild intellectual disability, as well as an impaired corneal reflex.

Causes
In some cases, this disorder can be in the voltage-gated sodium channel SCN9A (NaV1.7). Patients with such mutations are congenitally insensitive to pain and lack other neuropathies. There are three mutations in SCN9A: W897X, located in the P-loop of domain 2; I767X, located in the S2 segment of domain 2; and S459X, located in the linker region between domains 1 and 2. This results in a truncated non-functional protein. NaV1.7 channels are expressed at high levels in nociceptive neurons of the dorsal root ganglia. As these channels are likely involved in the formation and propagation of action potentials in such neurons, it is expected that a loss of function mutation in SCN9A will lead to abolished nociceptive pain propagation.

Hansen's Disease, an infectious illness, can result in the progressive destruction of the nerves; the disease can be passed on to offspring, sometimes remaining dormant except for nerve damage. This scenario can mimic the truly hereditary diseases described above.

Types of congenital pain indifference
There are generally two types of non-response exhibited.
 * Insensitivity to pain means that the painful stimulus is not even perceived: a patient cannot describe the intensity or type of pain.
 * Indifference to pain means that the patient can perceive the stimulus, but lacks an appropriate response: they will not flinch or withdraw when exposed to pain.

Incidence
The disorder is primarily found in homogeneous societies.

For example, it is found in Vittangi, a village in Kiruna Municipality in northern Sweden, where nearly 40 cases have been reported.

Also, Ashkenazi Jews have been found to have a higher risk, though it is still unusual.

In the Media
In Stieg Larsson's Millennium series, former boxer Paolo Roberto discovers that Ronald Niederman was born with congenital analgesia and is therefore, as he describes "invulnerable" physically. ("He just keeps on going!") Even so, Roberto continues that his inability to perceive pain is a severe danger because Niederman has no way of understanding when his body is being put in mortal danger by way of punches, blows, burns, or even gunshots. It is suggested that human awareness of painful stimuli is an evolutionarily necessary component of vulnerability to injury and death.

The Grey's Anatomy Episode Sometimes a Fantasy features a young girl named Megan Clover that suffers from congenital analgesia believing herself to be a superhero.

The episode of House, M.D. entitled Insensitive also features a young girl who suffers from congenital analgesia, making her sickness extremely difficult to diagnose--a situation exacerbated by her refusal to cooperate until House treats her mother for injuries sustained in the car crash that brought them to the hospital in the first place.