(Hereditary Motor and Sensory Neuropathies; HMSNs)
DefinitionCharcot-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 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 the teen years. It is the most common type of CMT.
- 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.
- 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:
- Delayed ability to walk due to weakness of the leg muscles closest to the trunk
- Severe sensory problems
- Hearing loss
- 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.
CausesCMT is caused by defects in specific genes.
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Risk FactorsThe primary risk factor for developing CMT is having family members with this disease.
SymptomsUsually, 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
- High arched heels
- Decreased sensation in the feet and legs
- 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 in the lower extremities—can spread to the upper extremities later in life
- Reduced ability to detect hot and cold, vibration, and position
- Difficulty writing, fastening buttons and zippers, and handling small objects
- Delay in learning how to walk—Type III
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