CIPA (congenital insensitivity to pain with anhidrosis) is caused by mutations in a single gene called NTRK1, which prevents pain-sensing and temperature-sensing neurons from surviving during fetal development. The result is a person born without the ability to feel pain or regulate body temperature through sweating. It is extremely rare, inherited in an autosomal recessive pattern, and affects nearly every aspect of daily life.
The Gene Behind CIPA
The NTRK1 gene provides instructions for building a receptor protein that sits on the surface of certain neurons. This receptor’s job is to bind with a signaling protein called nerve growth factor (NGF). When NGF locks onto the receptor, it sends a survival signal into the cell, telling it to grow, divide, and stay alive. In CIPA, mutations in NTRK1 produce a receptor that cannot transmit those signals. Without that survival cue, the neurons self-destruct through a process called apoptosis, a form of programmed cell death that normally helps the body prune unnecessary cells during development.
The neurons that die off are specifically the ones responsible for carrying pain and temperature signals from the body to the brain, along with the sympathetic nerves that control sweat glands. Other types of neurons, those involved in movement, vision, hearing, and most touch sensation, are not dependent on this particular signaling pathway and develop normally.
Why Pain Sensation Is Completely Absent
Pain signals normally travel from the skin, muscles, and organs through specialized sensory neurons whose cell bodies sit in clusters along the spinal cord called dorsal root ganglia. In people with CIPA, these NGF-dependent sensory neurons never make it past early development. They die before they can form functioning connections. This means there is no pathway to carry pain or temperature information to the brain at all. It is not that the brain ignores pain signals; the wiring simply does not exist.
This is different from conditions where pain signals are generated but the brain fails to interpret them. In CIPA, the peripheral hardware is missing entirely.
Why Sweating Fails
The sweat glands themselves are physically present in people with CIPA. The problem is that the nerves connecting to those glands, sympathetic postganglionic neurons, are also dependent on NGF signaling for survival. When those nerves die during development, the sweat glands lose their instructions to activate. The glands exist but have no way to receive the “start sweating” command. This is why the condition is called anhidrosis: the body cannot cool itself through perspiration, even when core temperature climbs dangerously high.
How CIPA Is Inherited
CIPA follows an autosomal recessive inheritance pattern, meaning a child must inherit two defective copies of the NTRK1 gene, one from each parent, to develop the condition. Parents who carry one mutated copy and one working copy are completely unaffected and show no symptoms. When two carriers have a child, there is a 25% chance the child will have CIPA, a 50% chance the child will be an asymptomatic carrier, and a 25% chance the child will inherit no mutated copies at all.
Because carriers show no signs of the condition, most families have no idea they carry the mutation until a child is born with CIPA. The condition is more common in populations where specific founder mutations have been identified. A particular splice-site mutation is common among Japanese, Korean, and Chinese populations. A different mutation has been traced to Israeli Bedouin communities, and another to Turkish families. These founder variants reflect cases where a single ancestral mutation spread through a relatively closed population over generations.
What CIPA Does to the Body Over Time
The inability to feel pain might sound like a superpower, but it removes the body’s most important alarm system. Without pain, injuries go unnoticed and untreated, leading to a cascade of complications that worsen with age.
Young children with CIPA frequently bite their tongues, lips, and fingers before they understand the concept of self-harm, sometimes severely enough to cause tissue loss or amputation of fingertips. Burns from hot food, bathwater, and surfaces are common because there is no reflex to pull away. Fractures occur frequently. In a radiological study of 20 individuals with CIPA, every single patient had fractures in their extremities. Close to 50% also had chronic bone infections (osteomyelitis) and progressive joint destruction, particularly in older children. Dislocations were less common, occurring in fewer than 15% of cases.
Wound healing is notably slow in CIPA, and because injuries often go undetected for days, infections have time to take hold. Corneal ulcers can develop because the eye lacks the protective pain reflex that normally triggers blinking or tearing in response to irritation. Skin changes are also widespread: thickened palms, malformed nails, dry skin, and patchy hair loss on the scalp.
The Danger of Overheating
Because sweating is the body’s primary cooling mechanism, the inability to sweat creates a life-threatening vulnerability to heat. People with CIPA can experience dangerously high fevers (hyperpyrexia) from physical activity, warm environments, or even mild illness. These episodes of overheating can trigger seizures, particularly in infants and young children. Recurrent fevers are often one of the earliest signs that lead to a CIPA diagnosis, sometimes before the painlessness becomes obvious to caregivers.
Managing temperature requires constant environmental awareness: staying in cool spaces, avoiding prolonged physical exertion in warm weather, and using external cooling methods like wet cloths or cooling vests. For families raising a child with CIPA, monitoring body temperature becomes a daily routine.
Neurological and Behavioral Effects
CIPA affects more than just pain and sweating. Many people with the condition have intellectual disabilities, and roughly half exhibit hyperactivity or emotional instability. These neurological features are thought to stem from the broader role that NGF signaling plays in brain development, not just in peripheral nerve survival. Low muscle tone (hypotonia) is also common, and some individuals are diagnosed with autism spectrum disorder.
How CIPA Differs From Other Pain Insensitivity Conditions
CIPA is classified as hereditary sensory and autonomic neuropathy type IV (HSAN IV), one of at least six related but distinct conditions. The closest relative is HSAN V, which also involves an inability to feel pain but preserves the ability to sweat. That distinction is clinically significant because people with HSAN V face far less risk of life-threatening overheating.
Another related condition, congenital indifference to pain, is fundamentally different. People with that condition can detect pain signals but do not have the normal emotional or behavioral reaction to them. In CIPA, the sensory neurons are physically gone. The signals never reach the brain in the first place. Riley-Day syndrome (HSAN III), seen almost exclusively in people of Eastern European Jewish descent, involves autonomic dysfunction including excessive sweating, essentially the opposite of CIPA’s anhidrosis, along with a different set of sensory and digestive problems.
Genetic testing for NTRK1 mutations confirms a CIPA diagnosis and distinguishes it from these overlapping conditions.