Congenital insensitivity to pain

Congenital insensitivity to pain (or congenital analgia) is a rare condition where a person cannot feel (and has never felt) physical pain.

Presentation
Cognition and sensation is otherwise normal; for instance they can still feel discriminative touch (though not always temperature), and there is no detectable physical abnormality.

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 can not 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 slight mental retardation, as well as an impaired corneal reflex.

Causes
There are some cases where the condition is caused by increased production of endorphins in the brain, in which case naloxone may be used as treatment. This treatment does not always work.

In some cases, this disorder can be caused by mutations 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.

One of the side effects of Hansen's Disease is the progressive destruction of the nerves; this can be passed on to offspring, remaining dormant except for nerve insensitivity.

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.