Congenital insensitivity to pain with anhidrosis (CIPA) has two characteristic features: the inability to feel pain and temperature, and decreased or absent sweating (anhidrosis). This condition is also known as hereditary sensory and autonomic neuropathy type IV. The signs and symptoms of CIPA appear early, usually at birth or during infancy, but with careful medical attention, affected individuals can live into adulthood.

An inability to feel pain and temperature often leads to repeated severe injuries. Unintentional self-injury is common in people with CIPA, typically by biting the tongue, lips, or fingers, which may lead to spontaneous amputation of the affected area. In addition, people with CIPA heal slowly from skin and bone injuries. Repeated trauma can lead to chronic bone infections (osteomyelitis) or a condition called Charcot joints, in which the bones and tissue surrounding joints are destroyed.

Normally, sweating helps cool the body temperature. However, in people with CIPA, anhidrosis often causes recurrent, extremely high fevers (hyperpyrexia) and seizures brought on by high temperature (febrile seizures).

In addition to the characteristic features, there are other signs and symptoms of CIPA. Many affected individuals have thick, leathery skin (lichenification) on the palms of their hands or misshapen fingernails or toenails. They can also have patches on their scalp where hair does not grow (hypotrichosis). About half of people with CIPA show signs of hyperactivity or emotional instability, and many affected individuals have intellectual disability. Some people with CIPA have weak muscle tone (hypotonia) when they are young, but muscle strength and tone become more normal as they get older.

Mutations in the NTRK1 gene cause CIPA. The NTRK1 gene provides instructions for making a receptor protein that attaches (binds) to another protein called NGFβ. The NTRK1 receptor is important for the survival of nerve cells (neurons).

The NTRK1 receptor is found on the surface of cells, particularly neurons that transmit pain, temperature, and touch sensations (sensory neurons). When the NGFβ protein binds to the NTRK1 receptor, signals are transmitted inside the cell that tell the cell to grow and divide, and that help it survive. Mutations in the NTRK1 gene lead to a protein that cannot transmit signals. Without the proper signaling, neurons die by a process of self-destruction called apoptosis. Loss of sensory neurons leads to the inability to feel pain in people with CIPA. In addition, people with CIPA lose the nerves leading to their sweat glands, which causes the anhidrosis seen in affected individuals.

Normal Function

The NTRK1 gene provides instructions for making a protein that is essential for the development and survival of nerve cells (neurons), especially those that transmit information about sensations such as pain, temperature, and touch (sensory neurons). The NTRK1 protein is found on the surface of cells, particularly sensory neurons. It acts as a kinase, which is an enzyme that changes the activity of other proteins by adding a cluster of oxygen and phosphorus atoms (a phosphate group) at specific positions. This process is called phosphorylation. The NTRK1 protein is turned on (activated) when another protein called nerve growth factor beta (NGFβ) attaches (binds) to it and signals the NTRK1 protein to phosphorylate itself (autophosphorylation). Then, the activated NTRK1 protein phosphorylates other proteins; this process is needed to transmit signals for cell growth and survival.

Health Conditions Related to Genetic Changes

Congenital insensitivity to pain with anhidrosis

Mutations in the NTRK1 gene cause congenital insensitivity to pain with anhidrosis (CIPA), a condition characterized by the inability to feel pain and decreased or absent sweating (anhidrosis). Many mutations in the NTRK1 gene are known to cause the condition. Many of the NTRK1 gene mutations lead to a protein that cannot be activated by phosphorylation, which means the mutated NTRK1 protein cannot transmit cell growth and survival signals to neurons. Without the proper signaling, neurons die by a process of self-destruction called apoptosis. Loss of sensory neurons leads to the inability to feel pain in people with CIPA. In addition, people with CIPA lose the nerves leading to their sweat glands, which causes the anhidrosis seen in affected individuals.

Cancers

Mutations in the NTRK1 gene are frequently found in people with a common type of thyroid cancer called papillary thyroid carcinoma. These mutations are acquired during a person's lifetime and are present only in certain cells. Such mutations are called somatic mutations. The mutations involved in papillary thyroid carcinoma occur when rearrangements of genetic material combine part of the NTRK1 gene with another gene. At least three other genes are known to be involved in these rearrangements: the TPM3 gene, the TPR gene, and the TFG gene. All of these genetic rearrangements create mutated proteins called TRK oncoproteins. Unlike normal NTRK1 protein, TRK oncoproteins do not have to be activated by binding to the NGFβ protein; they are always turned on. Constant activation of the protein signals for the cells to grow and divide continuously, which can lead to papillary thyroid carcinoma.

Other Names for This Gene

• high affinity nerve growth factor receptor
• MTC
• neurotrophic tyrosine kinase, receptor, type 1
• NTRK1_HUMAN
• p140-TrkA
• TRK
• Trk-A
• TRK1
• TRK1-transforming tyrosine kinase protein
• TRKA
• tyrosine kinase receptor A

Genomic Location

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

The long-term outlook (prognosis) for the hereditary sensory and autonomic neuropathy disorders is improving, and they are no longer considered only as diseases of childhood. The prognosis appears to depend on the degree of severity in each person, and the ability to control the complications of the disease. However, with careful medical attention, people with CIPA can live into adulthood.

The main problems are related to the high temperature and the bone problems that are present in CIPA. The disease may be fatal in the first years of life if hyperpyrexia (very high fever) is not properly managed, and it is the most frequently reported cause of death.

Orthopedic problems are also one of the most characteristic and serious complications of CIPA. In older children, osteomyelitis and bone and/or joint deformities require surgeries, which sometimes may need amputations.

CIPA is a rare condition; however, the prevalence is unknown.