What Is Charcot-Marie-Tooth Disease?
Charcot-Marie-Tooth disease (CMT) is an inherited peripheral nerve disorder. The peripheral nerves are located on the surface of the brain and the spinal cord. These nerves connect the central nervous system to the rest of the body. The disease was named after the physicians who discovered it in 1886: Jean-Martin Charcot, Pierre Marie, and Henry Tooth. This condition is sometimes called hereditary motor and sensory neuropathy, or personal muscular atrophy.
According to the National Institute of Neurological Disorders and Stroke, Charcot-Marie-Tooth disease is one of the most common inherited neurological disorders, affecting one out of every 2,500 people in the U.S. (NINDS, 2011)
What Causes CMT?
CMT is a congenital disease. This means you inherit the condition from one or both of your parents, and it’s present at birth. The condition is caused by one or more defective genes. The defects disturb the function and structure of peripheral nerve sheaths and axons (the insulating layers around nerves).
In some rare cases, people may be born with Charcot-Marie-Tooth disease spontaneously, without inheriting a defective gene from their parents.
There are five main types of CMT, and each has its own cause:
- CMT1 is caused by a duplication of a gene on chromosome 17 or by inheriting a mutated gene. This gene is responsible for instructing the body on how to make proteins that generate the nerve’s protective myelin sheath. This is the most common type of CMT.
- CMT2 results from a defect in the peripheral nerve cell’s axon. This is caused by a defect in the mitofusin 2 gene.
- CMT3, also called Dejerine-Sottas disease, is caused by a mutation in the P0 or PMP-22 gene. This type of CMT disease is rare.
- CMT4 is caused by several gene mutations. These genes include GDAP1, MTMR13, MTMR2, SH3TC2, NDG1, EGR2, PRX, FDG4, and FIG4. CMTX is caused by a point mutation in the connexin-32 protein on the X chromosome.
What Are the Symptoms of Charcot-Marie-Tooth Disease?
Symptoms of CMT normally occur in adolescence, but they can appear as late as mid-adulthood. CMT affects the nerves that control voluntary muscle activities.
Common symptoms include:
- weak legs
- difficulty standing
- frequent tripping
- difficulty walking
- high stepping when walking
Physical signs include:
- foot deformity
- inverted lower legs
As CMT progresses, you may experience difficulty moving your fingers, hands, wrists, feet and tongue.
To diagnose Charcot-Marie-Tooth disease, the doctor will order tests that help to determine the cause of your nerve damage and how much damage is present. These tests include a nerve condition study, electromyography, nerve biopsy, and genetic testing.
Genetic testing is used to check for defects in the genes that cause CMT. This is performed using a sample of blood.
An electromyography test is performed by inserting a thin needle into your muscle. This needle is attached to a wire that connects to a machine. The doctor will ask you to flex and then relax the muscle, while the machine measures the muscle’s electrical activity.
A nerve biopsy is performed by a surgeon. This procedure involves removing a piece of a nerve from your calf for testing. This nerve sample is examined for the appearance of CMT.
The function of electrical signals in your nerves can be tested using a nerve conduction study. This test is conducted by placing small electrodes on your skin and transmitting a small amount of electricity to the electrodes. A weak response may indicate CMT.
Physical therapy is a common treatment for people with CMT. Physical therapy involves many stretches and light exercises. This therapy helps to increase muscle strength and prevent atrophy (muscle loss).
People with a loss of function in their extremities may be given assistive devices to help them grab, reach, and push objects.
Orthopedic devices, such as braces and splints, are given to prevent injuries due to weak legs and to increase stability. Thumb splints are available for people having difficulty grabbing items.
If you have a severe foot deformity, surgery may be needed to correct it.