6

Pain is an unpleasant experience that involves both physical and psychological components. Feeling pain is quite adaptive because it makes us aware of an injury, and it motivates us to remove ourselves from the cause of that injury. In addition, pain also makes us less likely to suffer additional injury because we will be gentler with our injured body parts.

However, there are some individuals born without the ability to feel pain. This very rare genetic disorder is known as congenital insensitivity to pain (a.k.a. CIPA or congenital analgesia). While those with congenital analgesia can detect differences in temperature and pressure, they cannot experience pain. As a result, they often suffer significant injuries. Young children often have serious mouth and tongue injuries because they have bitten themselves repeatedly. CIPA generally results in an early death, due to either overheating (the A in CIPA is anhidrosis, an inability to sweat to cool oneself) or to repeated injury (e.g., chewing off your tongue and lips, twisting the skin off your hand trying to open a jar). CIPA is an inherited disease which happens when you get 2 defective copies of the SCN9A gene, which codes for a sub-unit of the Na+ channels in nociceptors. This results in these receptors not forming properly and a failure to send pain signals to the brain.

References:

Gerbrich E. van den Bosch, Martin G. A. Baartmans, Paul Vos, Jan Dokter, Tonya White, Dick Tibboel Pediatrics May 2014, 133 (5) e1381-e1387; DOI: 10.1542/peds.2013-2015.