In medical terms, CMT stands for Charcot-Marie-Tooth disease, the most common inherited nerve disorder in the world. It affects roughly 1 in 3,300 people, with an estimated 150,000 living with it in the United States alone. CMT is a group of genetic conditions that damage the peripheral nerves, the wiring that connects your brain and spinal cord to your muscles and sensory organs in your arms, hands, legs, and feet.
How CMT Affects Your Nerves
Your peripheral nerves have two key parts: the axon, which carries electrical signals, and the myelin sheath, an insulating layer that helps those signals travel quickly. Different forms of CMT target one or both of these structures. When the myelin breaks down, signals slow dramatically. When the axon itself is damaged, signals weaken or fail to reach their destination at all. Either way, the result is progressive muscle weakness and sensory loss, primarily in the legs and feet, and sometimes in the hands and arms.
CMT affects both motor nerves (which control movement) and sensory nerves (which relay touch, temperature, and pain). This dual impact is why the condition is also called hereditary motor and sensory neuropathy.
Common Symptoms
CMT typically starts in the feet and lower legs before progressing to the hands and forearms. Early signs often appear in childhood or young adulthood, though some forms show up later. The most recognizable symptoms include:
- Foot deformities: High arches, curled toes (hammer toes), and feet that turn inward are hallmarks of CMT. These develop gradually as certain muscles weaken while others stay relatively strong.
- Muscle wasting: The calves and lower legs lose bulk over time, sometimes giving the legs a distinctive “inverted champagne bottle” shape.
- Tripping and balance problems: Weakness in the muscles that lift the front of the foot (called foot drop) makes it hard to clear the ground while walking.
- Numbness and reduced sensation: You may lose the ability to feel temperature changes, pain, or vibration in your feet and hands.
- Hand weakness: Fine motor tasks like buttoning a shirt or writing can become difficult as the condition progresses to the upper limbs.
The severity varies enormously. Some people have mild symptoms they barely notice, while others experience significant disability. In rare cases, CMT can also involve cranial nerves or affect other organ systems.
What Causes It
CMT is genetic. It’s caused by mutations in genes responsible for building and maintaining the peripheral nerves. More than 50 genes have been linked to CMT so far, but a handful account for the vast majority of cases.
The single most common cause is a duplication of a gene called PMP22, which produces a protein essential for the myelin sheath. This one mutation accounts for about 62% of all genetically confirmed cases. Three other genes (GJB1, MFN2, and MPZ) together explain another 24%. Everything else is rare, each responsible for fewer than 1 to 2% of cases.
Most forms of CMT follow an autosomal dominant inheritance pattern, meaning you only need one copy of the mutated gene (from one parent) to develop the condition. X-linked and autosomal recessive forms also exist. Roughly 10% of cases involving the PMP22 duplication arise as new, spontaneous mutations, so a family history isn’t always present.
Major Types of CMT
CMT is classified into several types based on which part of the nerve is affected, the inheritance pattern, and the age symptoms begin. The two most common are CMT1 and CMT2.
CMT1 is a demyelinating form, meaning the myelin sheath deteriorates. Nerve conduction studies in people with CMT1 typically show signals traveling at 15 to 35 meters per second in the upper limbs, far below the normal speed of over 45 meters per second. CMT1 is the most prevalent subtype, affecting roughly 10.6 per 100,000 people. It usually begins in childhood or adolescence.
CMT2 affects the axon directly rather than the myelin. Nerve signals may travel at closer to normal speeds, but the signals themselves are weaker. CMT2 tends to appear later and can be harder to distinguish from other nerve conditions on initial testing.
CMTX is an X-linked form that shows up differently in men and women. Men are generally more severely affected. Nerve conduction speeds in CMTX tend to fall in an intermediate range, between 35 and 45 meters per second. CMT4 covers the autosomal recessive forms, which are less common overall but more prevalent in populations where marriages between close relatives are frequent. Some forms cause severe symptoms beginning in infancy.
How CMT Is Diagnosed
Diagnosis usually starts with a neurological exam. A doctor will look for telltale signs like high arches, hammer toes, muscle wasting in the lower legs, and reduced reflexes. They’ll also ask about family history, since CMT runs in families more often than not.
Nerve conduction studies are a key next step. These tests measure how fast and how strongly electrical signals travel through your peripheral nerves. The speed of the signal helps classify which type of CMT you have. Signals under 35 meters per second point toward a demyelinating form. Speeds in the 35 to 45 range suggest an intermediate type. Normal speeds with weak signal strength suggest an axonal form like CMT2.
Genetic testing confirms the diagnosis and identifies the specific mutation. Testing typically starts with the PMP22 duplication since it’s by far the most common cause. If that comes back negative, the next genes tested depend on the nerve conduction results, family history, and how the symptoms have progressed. In children, doctors generally stick to nerve conduction studies and genetic testing rather than more invasive procedures like needle testing of the muscles.
Treatment and Daily Management
There is no cure for CMT, but the condition can be managed effectively enough that many people maintain a high degree of independence throughout their lives. CMT does not typically shorten life expectancy.
Physical therapy is central to managing CMT. A regular program of low-impact exercise and stretching helps maintain muscle strength, flexibility, and balance. The goal is to keep muscles from tightening into permanent contractures, which limit joint movement. Starting physical therapy early and sticking with it makes a meaningful difference over time.
Bracing is another cornerstone. Ankle-foot orthoses (lightweight braces worn inside shoes) compensate for foot drop and improve walking stability. Modern designs are far less bulky than older versions, and many are barely visible under clothing. For hand weakness, occupational therapists can recommend adaptive tools and techniques that make daily tasks easier.
Surgery becomes an option when foot or ankle deformities are severe enough that bracing alone can’t correct them. Procedures may loosen tight tendons, realign bones, or stabilize joints. These aren’t routine for every person with CMT, but they can significantly improve mobility when needed.
Most people with CMT will never need a wheelchair. However, those with severe forms or older adults with advanced progression may benefit from a scooter or wheelchair for longer distances. The progression of CMT is slow, often measured in decades rather than years, giving people time to adapt and plan as their needs change.