Definition

Charcot-Marie-Tooth (CMT) disease is a group of genetic disorders that affects movement and feeling in the limbs. The disease progresses slowly and causes damage to the peripheral nerves. These nerves control muscles and transmit sensation.

CMT is classified as follows:

  • Type I (demyelinating)—This type affects the coating of the nerve called the myelin sheath, causing nerve impulses to travel more slowly. It usually occurs in childhood or the teen years. It is the most common type of CMT.
    • Type III—Also called Dejerine-Sottas disease, this is a rare, severe, early onset form of CMT. It is sometimes considered to be a subtype of CMT Type I. Symptoms may include:
    • Type IV (demyelinating autosomal recessive)—This is similar to Type I, but often less severe. It is less likely to be inherited by an affected individual's children.
  • Type II (axonal)—This type affects the part of the nerve called the axons. Although the speed is normal, the size or amount of impulses is less than normal. This type of CMT is less common and occurs after the teen years.

Causes

CMT is caused by defects in genes that produce proteins involved in the structure and function of the nerve axon or the myelin sheath. The mutation is usually inherited. Some forms occur when only one copy of the abnormal gene is inherited while other forms occur when both copies are inherited. Some other forms are inherited due to an abnormal x-linked chromosome.

Nerve Cell

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Risk Factors

The primary risk factor for developing CMT is having family members with this disease.

Symptoms

Symptoms and symptom severity depend on the type of disease. Symptoms usually begin before age 20. The first sign of CMT is often a high arched foot or difficulty walking. Other symptoms may include:

  • Flexed toes
  • Difficulty holding the foot up in a horizontal position
  • Slapping the feet on the floor when walking
  • Muscle cramping, weakness, and wasting in the lower extremities—can spread to the upper extremities later in life
  • Decreased sensation in the feet and legs
  • Problems with balance
  • Type III symptoms:
    • Delayed ability to walk due to weakness of the leg muscles closest to the trunk
    • Severe sensory problems
    • Hearing loss

Diagnosis

You may be asked about your symptoms and medical history. A physical exam will be done.

You may have nerve and muscle functions tested. This can be done with:

Your doctor may need to test your DNA. This can be done with a blood test.

Treatment

Although there is no cure for CMT, treatment may help to improve function, coordination, and mobility. Treatment is also vital to protect against injury due to muscle weakness and reduced sensation. Treatment may include:

  • Physical and occupational therapy
  • Moderate exercise
  • Braces on the lower legs
  • Shoe inserts to correct foot deformity
  • Foot care and routine exams with a foot specialist
  • Orthopedic surgery

Prevention

There are no known ways to prevent CMT. If you have CMT or have risk factors, you may want to talk to a genetic counselor before deciding to have children.