Charcot-Marie-Tooth disease type 2 (CMT2) is an inherited nerve disorder that damages the long fibers (axons) connecting your brain and spinal cord to your muscles and sensory organs. This distinguishes it from the more common type 1, which damages the protective coating around those fibers. The result is progressive weakness and numbness that typically starts in the feet and lower legs, then gradually moves to the hands. CMT2 generally does not shorten life expectancy, but it worsens over time and can significantly affect mobility and daily activities.
How CMT2 Differs From Type 1
All forms of Charcot-Marie-Tooth disease affect the peripheral nerves, the wiring that carries signals between the brain and the rest of the body. In CMT1, the problem is in the myelin sheath, an insulating layer that wraps around nerve fibers and helps signals travel quickly. In CMT2, the nerve fibers themselves are damaged directly. Think of it like an electrical cable: type 1 is a problem with the rubber coating, while type 2 is a problem with the copper wire inside.
This difference shows up clearly on nerve conduction tests, which measure how fast electrical signals travel through your nerves. Normal nerve conduction velocity is above 40 to 45 meters per second. In CMT1, signals slow dramatically to below 35 m/s because the damaged insulation forces signals to crawl. In CMT2, signals still travel at relatively normal speeds (above 45 m/s), but the signals are weaker because fewer nerve fibers are intact. This is one of the key ways doctors distinguish between the two types.
What Causes CMT2
CMT2 is genetic, passed down in families through mutations in any of more than a dozen different genes. Each mutation defines a subtype. The most common is CMT2A, caused by mutations in a gene called MFN2, which accounts for roughly 20% of all CMT2 cases. MFN2 provides instructions for a protein involved in mitochondrial function, the energy-producing structures inside cells. When this gene is mutated, mitochondria inside nerve cells clump together and can’t travel properly along the length of the axon. Since peripheral nerves can stretch over three feet long, their far ends depend on a steady supply of mitochondria to keep functioning. When that supply is disrupted, the longest nerve fibers fail first, which is why symptoms begin in the feet and hands.
Other subtypes are rarer and involve different genes. CMT2B (RAB7 gene) tends to cause predominantly sensory problems. CMT2D (GARS gene) often presents as a mostly motor syndrome, primarily affecting the hands. CMT2E involves a gene called NEFL, while CMT2F and CMT2L involve heat shock proteins. Because so many genes can cause CMT2, genetic testing sometimes requires working through several possibilities before identifying the specific mutation.
Symptoms and How They Progress
Muscle weakness typically starts in the feet and lower legs during the teenage years or early adulthood, though symptoms can appear at any age. The earliest and most noticeable sign for many people is foot drop, a difficulty lifting the front of the foot that causes a high-stepping gait and frequent tripping. Over time, the muscles of the lower legs waste away, sometimes creating a characteristic “inverted champagne bottle” shape where the calves narrow while the thighs remain normal-sized.
As the disease progresses, weakness can spread to the hands and forearms, making fine motor tasks like buttoning a shirt or writing more difficult. Foot deformities are common, including high arches and hammertoes (toes that curl downward), caused by the uneven pull of weakened muscles. Some people develop scoliosis or joint contractures, where muscles or tendons shorten and limit movement around a joint.
Sensory symptoms play a larger role in CMT2 than many people expect. About 75% of CMT2 patients experience “positive” sensory symptoms like tingling, burning, or nerve pain, compared to only 20% of those with CMT1. For roughly a third of CMT2 patients, sensory symptoms are actually what brings them to a doctor in the first place. Those whose disease begins with sensory problems tend to have a later onset, with a median age around 57, compared to a median of 25 for those who present with motor weakness first. Reduced ability to feel temperature, vibration, or the position of your limbs in space (proprioception) is also common and contributes to balance problems.
Some forms of CMT2 can also cause speech difficulties or breathing problems due to nerve damage affecting those muscles, though this is less typical.
How CMT2 Is Diagnosed
Diagnosis usually begins with a physical exam and family history, since the disease runs in families. Doctors look for characteristic signs: weakness in the feet, reduced reflexes, sensory loss in a “stocking-glove” pattern (affecting areas a sock or glove would cover), and visible muscle wasting.
Nerve conduction studies are the primary test for distinguishing CMT2 from other types. In CMT2, the speed of nerve signals remains near normal, but the strength of the signal (measured as compound muscle action potential amplitude) is reduced. Electromyography can reveal that motor units, the groups of muscle fibers controlled by a single nerve, are reduced in number even in muscles that still appear to function well. Research has found that this loss of motor units can extend into proximal muscles like the upper arm, suggesting the nerve damage is more widespread than the visible symptoms might indicate.
Genetic testing confirms the specific subtype. Doctors typically test for MFN2 mutations first, since CMT2A is the most common form. If that comes back negative, testing expands to other known genes depending on the clinical picture. A person with primarily sensory symptoms might be tested for RAB7 mutations, while someone with hand-dominant weakness might be tested for GARS.
Managing CMT2 Day to Day
There is currently no cure or disease-modifying treatment for CMT2. Management focuses on maintaining function, reducing discomfort, and adapting to changes as they occur.
Physical therapy is the cornerstone of care. Strength training targeting the hips, thighs, and knees has been shown to improve functional ability and the speed at which people can perform daily tasks. Both strength-focused and endurance-focused exercise programs show benefits. The goal is not to reverse nerve damage but to keep the muscles that still have intact nerve supply as strong as possible and to compensate for areas of weakness.
Orthotic devices play an important role for many people with CMT2. Ankle-foot orthoses (AFOs), which are lightweight braces worn inside shoes, help control foot drop, improve walking balance, and reduce tripping. Rigid plastic AFOs tend to improve both posture control and walking mechanics, while more flexible elastic designs help with the dynamic aspects of movement. For milder foot problems like high arches and foot pain, simpler shoe inserts may be sufficient. Night splints worn on the ankles can improve range of motion by a few degrees over several weeks, helping to prevent the gradual tightening of calf muscles that many people experience.
Neuropathic pain, the burning or shooting sensations caused by nerve damage, can be managed with medications. Surgical correction of severe foot deformities is sometimes considered when bracing alone is not enough to maintain functional walking.
Long-Term Outlook
CMT2 progresses slowly in most people, though the rate varies between subtypes and even between family members who carry the same mutation. Early-onset cases, those appearing in childhood, tend to cause more significant disability over time. Most people with CMT2 remain ambulatory throughout their lives, though many eventually need braces, walking aids, or other assistive devices. Life expectancy is typically normal, and many people with CMT2 work, exercise, and live independently with appropriate adaptations.