Charcot-Marie-Tooth Disease (Hereditary Motor and Sensory Neuropathies [HMSNs])

Definition

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

Causes

CMT is caused by defects in specific genes (genetic mutations) often inherited in an autosomal dominant pattern. This means that if one parent has CMT, each child has a 50% chance of inheriting the gene and the disease.

CMT can be classified in a number of ways:

• 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 adolescence and is the most common type of CMT.
• Type II (axonal)—This type affects the part of the nerve called 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 adolescence.
• Type III—Also called Dejerine-Sottas disease, this is a more rare, severe, early onset form of CMT. It is sometimes considered to be a subtype of CMT Type I. Symptoms may include:
  
  • Delayed ability to walk
  • Severe sensory problems
  • Hearing loss
• Type IV (demyelinating autosomal recessive)—This is similar to Type I, but often less severe. The inheritance pattern also makes it less likely to be inherited by an affected individual's children.

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition. The primary risk factor for developing CMT is having family members with this disease.

Symptoms

Usually, symptoms first appear in children and young adults. The first sign of CMT is often a high arched foot or difficulty walking. Other symptoms may include:

• Hammer toes
• Muscle cramping in legs and forearms
• Flexed toes
• Difficulty holding the foot up in a horizontal position
• Frequent sprained ankles and ankle fractures
• Problems with balance
• Muscle weakness and atrophy in the lower extremities
• Diminished ability to detect hot and cold, vibration, and position
• Difficulty writing, fastening buttons and zippers, and manipulating small objects
• Scoliosis

Diagnosis

The doctor will ask about your symptoms and medical history, and perform a physical exam. Tests may include:

• Nerve conduction study —a test that measures the speed and amplitude of nerve impulses in the extremities
• Electromyogram (EMG) —a test that records the electrical activity of muscle cells
• DNA blood test—to confirm certain types of CMT, even if there are no symptoms

Treatment

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

• Physical and occupational therapy
• Moderate exercise
• Lightweight lower leg braces
• Shoe inserts to correct foot deformity
• Vigilant podiatric care
• Orthopedic surgery

Prevention

There are no known ways to prevent CMT once a person is born with the condition. If you have CMT or risk factors for CMT, you may want to talk to a genetic counselor before deciding to have children.