FYI: Charcot-Marie-Tooth Disorder (CMT)

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  1. MemoryLane

    MemoryLane Member

    Charcot-Marie-Tooth disease (CMT) is one of the most common inherited neurological disorders, affecting approximately 1 in 2,500 people in the United States. The disease is named for the three physicians who first identified it in 1886 - Jean-Marie-Charcot and Pierre Marie in Paris, France, and Howard Henry Tooth in Cambridge, England. CMT, also known as hereditary motor and sensory neuropathy (HMSN) or peroneal muscular atrophy, comprises a group of disorders that affect peripheral nerves. The peripheral nerves lie outside the brain and spinal cord and supply the muscles and sensory organs in the limbs. Disorders that affect the peripheral nerves are called peripheral neuropathies.


    From the National Institutes of Health - The National Institute of Neurological Disorders and Stroke

    Charcot-Marie-Tooth Disease Fact Sheet:


    What is Charcot-Marie-Tooth Disorder?

    Charcot-Marie-Tooth disorder (CMT) is an inherited neurological disease characterized by a slowly progressive degeneration of the muscles in the foot, lower leg, hand, and forearm, and a mild loss of sensation in the limbs, fingers, and toes. The first sign of CMT is generally a high arched foot or gait disturbances. Other symptoms of the disorder may include foot bone abnormalities such as high arches and hammer toes, problems with hand function and balance, occasional lower leg and forearm muscle cramping, loss of some normal reflexes, occasional partial sight and/or hearing loss, and, in some patients, scoliosis (curvature of the spine). CMT is a disorder of genetic heterogeneity, in which mutations in different genes can produce the same clinical symptoms. In CMT, there are not only different genes but different patterns of inheritance. The most common type, CMT1A, is inherited in an autosomal dominant pattern. This means that if one parent has CMT there is a 50 percent chance of passing the disease on to each child. Other types are autosomal recessive or sex-linked CMT. Each type is characterized by symptoms ranging from severe weakness and wasting of leg and hand muscles to very mild symptoms or no symptoms at all. Full expression of CMT's clinical symptoms generally occurs by age 30. The more severe symptoms are related to an earlier age of onset.


    What are the symptoms of Charcot-Marie-Tooth disease?

    The neuropathy of CMT affects both motor and sensory nerves. A typical feature includes weakness of the foot and lower leg muscles, which may result in foot drop and a high-stepped gait with frequent tripping or falls. Foot deformities, such as high arches and hammertoes (a condition in which the middle joint of a toe bends upwards) are also characteristic due to weakness of the small muscles in the feet. In addition, the lower legs may take on an "inverted champagne bottle" appearance due to the loss of muscle bulk. Later in the disease, weakness and muscle atrophy may occur in the hands, resulting in difficulty with fine motor skills. Although sensory nerves are also involved, patients rarely notice significant numbness or pain.

    Onset of symptoms is most often in adolescence or early adulthood, however presentation may be delayed until mid-adulthood. The severity of symptoms is quite variable in different patients and some people may never realize they have the disorder. Progression of symptoms is very gradual. CMT is not fatal and people with most forms of CMT have a normal life expectancy.


    What are the types of Charcot-Marie-Tooth disease?

    There are many forms of CMT disease. The principal types include CMT1, CMT2, CMT3, CMT4, and CMTX. CMT1 is the most frequent and results from abnormalities in the myelin sheath. There are three main types of CMT1. CMT1A is an autosomal dominant disease resulting from a duplication of the gene on chromosome 17 that carries the instructions for producing the peripheral myelin protein-22 (PMP-22). The PMP-22 protein is a critical component of the myelin sheath. An overabundance of this gene causes the structure and function of the myelin sheath to be abnormal. Patients experience weakness and atrophy of the muscles of the lower legs beginning in adolescence; later they experience hand weakness and sensory loss. Interestingly, a different neuropathy distinct from CMT1A called hereditary neuropathy with predisposition to pressure palsy (HNPP) is caused by a deletion of one of the PMP-22 genes. In this case abnormally low levels of the PMP-22 gene result in episodic, recurrent demyelinating neuropathy. CMT1B is an autosomal dominant disease caused by mutations in the gene that carries the instructions for manufacturing the myelin protein zero (P0) which is another critical component of the myelin sheath. Most of these mutations are point mutations, meaning a mistake occurs in only one letter of the DNA genetic code. To date, scientists have identified more than 30 different point mutations in the P0 gene. As a result of abnormalities in P0, CMT1B produces symptoms similar to those found in CMT1A. The gene defect that causes CMT1C, which also has symptoms similar to those found in CMT1A, has not yet been identified.


    What causes Charcot-Marie-Tooth disease?

    A nerve cell communicates information to distant targets by sending electrical signals down a long, thin part of the cell called the axon. In order to increase the speed at which these electrical signals travel, the axon is insulated by myelin, which is produced by another type of cell called the Schwann cell. Myelin twists around the axon like a jelly-roll cake and prevents dissipation of the electrical signals. Without an intact axon and myelin sheath, peripheral nerve cells are unable to activate target muscles or relay sensory information from the limbs back to the brain.

    CMT is caused by mutations in genes that produce proteins involved in the structure and function of either the peripheral nerve axon or the myelin sheath. Although different proteins are abnormal in different forms of CMT disease, all of the mutations affect the normal function of the peripheral nerves. Consequently, these nerves slowly degenerate and lose the ability to communicate with their distant targets. The degeneration of motor nerves results in muscle weakness and atrophy in the extremities (arms, legs, hands, or feet), and the degeneration of sensory nerves results in a reduced ability to feel heat, cold, and pain.

    The gene mutations in CMT disease are usually inherited. Each of us normally possesses two copies of every gene, one inherited from each parent. Some forms of CMT are inherited in an autosomal dominant fashion, which means that only one copy of the abnormal gene is needed to cause the disease. Other forms of CMT are inherited in an autosomal recessive fashion, which means that both copies of the abnormal gene must be present to cause the disease. Still other forms of CMT are inherited in an X-linked fashion, which means that the abnormal gene is located on the X chromosome. The X and Y chromosomes determine an individual's sex. Individuals with two X chromosomes are female and individuals with one X and one Y chromosome are male. In rare cases the gene mutation causing CMT disease is a new mutation which occurs spontaneously in the patient's genetic material and has not been passed down through the family.


    How is Charcot-Marie-Tooth disease diagnosed?

    Diagnosis of CMT begins with a standard patient history, family history, and neurological examination. Patients will be asked about the nature and duration of their symptoms and whether other family members have the disease. During the neurological examination a physician will look for evidence of muscle weakness in the arms, legs, hands, and feet, decreased muscle bulk, reduced tendon reflexes, and sensory loss. Doctors look for evidence of foot deformities, such as high arches, hammertoes, inverted heel, or flat feet. Other orthopedic problems, such as mild scoliosis or hip dysplasia, may also be present. A specific sign that may be found in patients with CMT1 is nerve enlargement that may be felt or even seen through the skin. These enlarged nerves, called hypertrophic nerves, are caused by abnormally thickened myelin sheaths.

    If CMT is suspected, the physician may order electrodiagnostic tests for the patient. This testing consists of two parts: nerve conduction studies and electromyography (EMG). During nerve conduction studies, electrodes are placed on the skin over a peripheral motor or sensory nerve. These electrodes produce a small electric shock that may cause mild discomfort. This electrical impulse stimulates sensory and motor nerves and provides quantifiable information that the doctor can use to arrive at a diagnosis. EMG involves inserting a needle electrode through the skin to measure the bioelectrical activity of muscles. Specific abnormalities in the readings signify axon degeneration. EMG may be useful in further characterizing the distribution and severity of peripheral nerve involvement.

    If all other tests seem to suggest that a patient has CMT, a neurologist may perform a nerve biopsy to confirm the diagnosis. A nerve biopsy involves removing a small piece of peripheral nerve through an incision in the skin. This is most often done by removing a piece of the nerve that runs down the calf of the leg. The nerve is then examined under a microscope. Patients with CMT1 typically show signs of abnormal myelination. Specifically, "onion bulb" formations may be seen which represent axons surrounded by layers of demyelinating and remyelinating Schwann cells. Patients with CMT2 usually show signs of axon degeneration.

    Genetic testing is available for some types of CMT and may soon be available for other types; such testing can be used to confirm a diagnosis. In addition, genetic counseling is available to parents who fear that they may pass mutant genes to their children.


    How is Charcot-Marie-Tooth disease treated?

    There is no cure for CMT, but physical therapy, occupational therapy, braces and other orthopedic devices, and even orthopedic surgery can help patients cope with the disabling symptoms of the disease.

    Physical and occupational therapy, the preferred treatment for CMT, involves muscle strength training, muscle and ligament stretching, stamina training, and moderate aerobic exercise. Most therapists recommend a specialized treatment program designed with the approval of the patient's physician to fit individual abilities and needs. Therapists also suggest entering into a treatment program early; muscle strengthening may delay or reduce muscle atrophy, so strength training is most useful if it begins before nerve degeneration and muscle weakness progress to the point of disability.

    Stretching may prevent or reduce joint deformities that result from uneven muscle pull on bones. Exercises to help build stamina or increase endurance will help prevent the fatigue that results from performing everyday activities that require strength and mobility. Moderate aerobic activity can help to maintain cardiovascular fitness and overall health. Most therapists recommend low-impact or no-impact exercises, such as biking or swimming, rather than activities such as walking or jogging, which may put stress on fragile muscles and joints.

    Many CMT patients require ankle braces and other orthopedic devices to maintain everyday mobility and prevent injury. Ankle braces can help prevent ankle sprains by providing support and stability during activities such as walking or climbing stairs. High-top shoes or boots can also give the patient support for weak ankles. Thumb splints can help with hand weakness and loss of fine motor skills. Assistive devices should be used before disability sets in because the devices may prevent muscle strain and reduce muscle weakening. Some CMT patients may decide to have orthopedic surgery to reverse foot and joint deformities.


    What research is being done?

    The NINDS supports research on CMT and other peripheral neuropathies in an effort to learn how to better treat, prevent, and even cure these disorders. Ongoing research includes efforts to identify more of the mutant genes and proteins that cause the various disease subtypes, efforts to discover the mechanisms of nerve degeneration and muscle atrophy with the hope of developing interventions to stop or slow down these debilitating processes, and efforts to find therapies to reverse nerve degeneration and muscle atrophy.

    One promising area of research involves gene therapy experiments. Research with cell cultures and animal models has shown that it is possible to deliver genes to Schwann cells and muscle. Another area of research involves the use of trophic factors or nerve growth factors, such as the hormone androgen, to prevent nerve degeneration.



    Organizations (They also have websites and email contacts)

    Charcot-Marie-Tooth Association (CMTA)
    2700 Chestnut Parkway
    Chester, PA 19013
    Tel: 610-499-9264 800-606-CMTA (2682)
    Fax: 610-499-7267


    Muscular Dystrophy Association
    3300 East Sunrise Drive
    Tucson, AZ 85718-3208
    Tel: 520-529-2000 800-572-1717
    Fax: 520-529-5300


    Neuropathy Association
    60 East 42nd Street
    Suite 942
    New York, NY 10165-0999
    Tel: 212-692-0662 800-247-6968
    Fax: 212-692-0668


    National Ataxia Foundation (NAF)
    2600 Fernbrook Lane
    Suite 119
    Minneapolis, MN 55447-4752
    Tel: 763-553-0020
    Fax: 763-553-0167



    Prepared by:
    Office of Communications and Public Liaison
    National Institute of Neurological Disorders and Stroke
    National Institutes of Health
    Bethesda, MD 20892

    NINDS health-related material is provided for information purposes only and does not necessarily represent endorsement by or an official position of the National Institute of Neurological Disorders and Stroke or any other Federal agency. Advice on the treatment or care of an individual patient should be obtained through consultation with a physician who has examined that patient or is familiar with that patient's medical history.

    All NINDS-prepared information is in the public domain and may be freely copied. Credit to the NINDS or the NIH is appreciated.

    Reviewed April 25, 2003


    [This Message was Edited on 05/14/2003]