Just a quick preface: I am NOT a licensed physician. I am a high school student who enjoys researching interesting medical phenomena. I just enjoy writing about medicine and science!
Congenital Insensitivity to Pain with Anhidrosis, commonly known as CIPA, is a rare genetic disorder of the nervous system which prevents the feeling of pain or temperature. CIPA is inherited in an autosomal recessive pattern and is caused by mutations in the NTRK1 gene. The NTRK1 gene provides the instructions for making a receptor protein called the neurotrophic tyrosine kinase-1 receptor or NTRK1 receptor protein. The NTRK1 receptor is found on the surface of sensory neurons which transmit pain, temperature, and touch sensations. It belongs to a group of nerve growth factor receptors whose ligands, a protein located on the surface of the cell involved in interpreting and carrying signals inside a cell, include neurotrophins. Neurotrophins are a group of proteins that help to regulate development, maintenance, and function of the nervous system. The NTRK1 receptor protein’s job is to bind to another protein called NGFβ. The NGFβ protein is responsible for initiating signaling pathways inside a cell. Specifically the bond between the NTRK1 receptor protein and the NGFβ protein, causes neurons to grow, mature, and to differentiate. The specific bond also plays a role in pain sensation. Unfortunately it is not known what the bind signals specifically, but signalling can help sensory neurons grow and differentiate. In patients with CIPA, mutations in the NTRK1 gene lead to a protein that is unable to transmit signals. As a result of a lack of signaling, neurons then die via apoptosis:
the death of cells that occurs as a part of the growth of an organism. It is this loss of sensory neurons that causes the inability for CIPA patients to feel pain. CIPA patients also lose the nerves that lead to sweat glands which causes anhidrosis, the inability to sweat and thus an inability for patients to maintain their body temperature. This is because humans use evaporative cooling from sweat in order to maintain body temperature. The loss of pain manifests itself in many very serious symptoms. Symptoms of CIPA include unintentional self-mutilation, slow healing of bone and skin injuries, repeated trauma can lead to bone infections like osteomyelitis or Charcot joints, high fevers or hyperpyrexia due to their inability to sweat, febrile seizures, many have lichenification or thicker leather-like skin, hypotrichosis where patches of hair on the scalp doesn't grow, and finally half of all CIPA patients are emotionally or intellectually
disabled. As a result of the plethora of symptoms that CIPA patients experience, the real life implications are drastic. CIPA patients, because of their inability to feel pain, must check every part of themselves constantly every day for indications of injury
as they don’t experience any pain to indicate a potential injury. Patients with CIPA often have to live an overly cautious and protected lifestyle in order to prevent more injury and damage. Also, most patients with CIPA don't live past the age of twenty five. There is also no cure, and treatment only consists of controlling body temperature and treating self inflicted injuries. This partly comes as a result of the sheer rarity of this condition, there are not enough cases to even calculate an incidence but some experts say that the incidence is something like one in one hundred and twenty five million.
Sources:
https://ghr.nlm.nih.gov/condition/congenital-insensitivity-to-pain-with-anhidrosis#
https://www.omim.org/entry/191315
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2758233/
https://ghr.nlm.nih.gov/gene/NGF
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3564101/
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