CMT, or Charcot-Marie-Tooth disease, is the most common inherited nerve disorder, affecting roughly 1 in 3,300 people worldwide and an estimated 150,000 in the United States. It damages the peripheral nerves, the long cables that connect your brain and spinal cord to your muscles and sensory organs. The result is progressive weakness and numbness that typically starts in the feet and hands and slowly works its way inward over years.
Despite its name (taken from the three physicians who first described it in 1886), CMT is not a single disease. It’s a family of genetic conditions with several types, each affecting nerves in a slightly different way. It is not life-threatening, and most people with CMT have a normal life expectancy.
How CMT Damages Nerves
Peripheral nerves have two key parts: the axon, which is the long fiber that carries electrical signals, and myelin, a fatty insulating layer wrapped around it that speeds those signals along. CMT attacks one or both of these structures, depending on the type.
In Type 1 CMT (CMT1), the myelin sheath is abnormal. Without proper insulation, nerve signals travel more slowly and the underlying nerve fiber can deteriorate over time. In Type 2 (CMT2), the axon itself is damaged, which weakens the strength of nerve signals even though they may travel at a normal speed. Some forms, classified as “intermediate,” affect both the myelin and the axon simultaneously. Type 4 (CMT4) can damage either structure but follows a different inheritance pattern, and Type X (CMTX) is caused by mutations on the X chromosome.
What Causes It
CMT is genetic. The most common form, CMT1A, is caused by having an extra copy of a gene called PMP22 on chromosome 17. This gene tells cells how to build a protein used in the myelin sheath. With a duplicate gene, cells overproduce that protein, and the excess overwhelms the cell’s ability to process it properly. The result is a buildup of nonfunctional protein that destabilizes myelin, leading to its gradual breakdown.
Most forms of CMT1 and CMT2 follow an autosomal dominant inheritance pattern, meaning a child needs only one copy of the altered gene (from one parent) to develop the condition. CMT4 is autosomal recessive, requiring a copy from both parents. CMTX follows X-linked inheritance, which typically means males are affected more severely because they have only one X chromosome.
Symptoms and How They Progress
CMT usually appears in adolescence or early adulthood, though some people notice symptoms in childhood and others not until middle age. The disease is progressive, meaning symptoms slowly worsen over time, but the pace varies widely from person to person.
The earliest and most recognizable signs tend to show up in the feet and lower legs:
- High arches or very flat feet. The muscle imbalances caused by CMT often pull the foot into an abnormally high arch (a condition called pes cavus), though some people develop flat feet instead.
- Hammer toes. Weakened muscles in the foot allow the toes to curl upward or clench, sometimes causing painful rubbing against shoes.
- Foot drop. Weakness in the muscles that lift the front of the foot makes it hard to clear the ground while walking, leading to tripping or a high-stepping gait.
- Numbness and reduced sensation. Loss of feeling in the feet and lower legs can make it difficult to detect injuries or temperature changes.
As the disease progresses, weakness and numbness can spread to the hands and forearms, making fine motor tasks like buttoning a shirt or writing more difficult. Muscle wasting in the lower legs can give them a characteristic “inverted champagne bottle” appearance, where the calves are noticeably thinner than the thighs. Walking becomes increasingly awkward, and balance problems are common. That said, most people with CMT remain ambulatory throughout their lives.
How CMT Is Diagnosed
Diagnosis typically starts with a neurological exam, where a doctor checks muscle strength, reflexes, and sensation. Two electrical tests help confirm the diagnosis. Nerve conduction studies measure how fast electrical signals travel through your nerves; delayed or weak responses point toward CMT. Electromyography (EMG) uses a thin needle inserted into a muscle to measure its electrical activity during contraction, revealing which muscles are affected.
A genetic blood test can identify the specific gene mutation responsible. This is valuable not only for confirming the diagnosis but also for family planning, since CMT can be passed to children. Genetic testing also helps rule out other causes of nerve damage that can look similar to CMT.
Managing the Condition
There is no cure for CMT, but a combination of bracing, physical therapy, and sometimes surgery can significantly improve daily function and comfort.
Orthotics and Bracing
Shoe inserts (orthotics) are often the first step, with the goal of getting the ankle and hindfoot into as close to normal alignment as possible. When inserts aren’t enough, ankle-foot orthoses (AFOs) provide more support. For someone whose main issue is foot drop, an off-the-shelf carbon fiber AFO can work well. If the ankle also leans inward or outward when standing, a custom-fitted plastic AFO with a hinged ankle joint offers better correction and helps with walking on uneven ground, stairs, and driving.
Physical and Occupational Therapy
Therapy focuses on maintaining flexibility, strengthening muscles that still function well, and learning movement strategies that reduce fall risk. Occupational therapy can help with hand weakness by introducing adaptive tools for tasks like opening jars or typing.
Surgery
Surgery is generally reserved for cases where bracing can no longer correct the foot’s position. If the Achilles tendon has become so tight that you’re essentially walking on your toes, a tendon-lengthening procedure may be considered. Surgeons can also transfer tendons from stronger areas of the foot to weaker ones, for example, moving a tendon from the inside of the foot to the outside of the ankle to improve stability, or to the top of the foot to help with lifting it during walking.
Modern surgical approaches favor bone-cutting and reshaping (osteotomy) over fusion, which tends to cause arthritis and pain years later. Straightening hammer toes surgically is possible but less commonly recommended unless they’re causing blisters or corns from shoe friction. Recovery from a major foot reconstruction takes six to nine months, including a hospital stay, casting, and physical therapy.
Medications to Avoid
People with CMT need to be aware that certain medications can severely worsen nerve damage. The Charcot-Marie-Tooth Association revised its neurotoxic drug list in 2023 and flagged two cancer drugs as significant risks. Vincristine, a chemotherapy agent, carries a manufacturer warning against use in people with the demyelinating form of CMT. Its neurotoxic effects can cause severe, sometimes irreversible worsening of symptoms. Paclitaxel, another chemotherapy drug, is also a concern because it can cause peripheral neuropathy on its own and may compound the nerve damage already present in CMT. If you have CMT and ever need cancer treatment, making sure your oncologist knows about your diagnosis is critical.
Living With CMT Long-Term
CMT progresses slowly enough that most people adapt gradually. The condition does not shorten your lifespan. Many people with CMT work, exercise, and live independently throughout their lives, though the specific accommodations they need tend to increase over time. Ankle sprains, falls, and foot pain are common ongoing challenges, and cold temperatures often make numbness worse.
Because CMT is inherited, genetic counseling can help families understand the odds of passing it on. If one parent has an autosomal dominant form, each child has a 50 percent chance of inheriting the condition. For autosomal recessive forms like CMT4, both parents must carry the gene, and each child has a 25 percent chance of being affected.