Charcot Marie Tooth – A funny name, but for the estimated 2.6 million people worldwide who have CMT, including myself, it’s no laughing matter. CMT actually refers a group of genetic diseases that affect the peripheral nervous system. CMT affects about 1 person in 2500, making it considered to be a rare disease.
Symptoms of CMT are slowly progressive. They include foot bone abnormalities, muscle weakness and degeneration, problems with balance, and loss of some normal reflexes. Other symptoms of neuropathy include sensory loss and neuropathic sensations and pain. Some people with CMT experience muscle cramping. Scoliosis (curvature of the spine) is often associated with CMT. More rarely, respiratory difficulties occur.
These problems will most likely first be detected at the extremities, usually in the feet, then calves, then hands, and then progressing to the forearms. In some cases, people with CMT become wheelchair bound. Generally, the earlier a person begins experiencing symptoms of CMT, the more severe symptoms will become. CMT does not affect life expectancy, but can lead to significant disability.
Currently, the full genetic testing panel performed by Athena Diagnostics tests for 17 genetic subtypes of CMT, but there are a number of other genetic causes of CMT currently being investigated by researchers. While the mechanism behind the sub-types of CMT differs between diseases, the pattern of symptoms across forms is similar. At the same time, symptoms vary considerably in severity, age of onset, and presentation across people, even among people with the same type of CMT, and between people from the same family.
Most types of CMT can be inherited through just one dominant gene from one parent. There are also types of CMT that must be transmitted through receiving a recessive gene from both parents or carried on the sex chromosome (X-linked).
All types of CMT affect the peripheral nervous system, meaning the nerves that carry signals between the spine and body. If you think about nerves like electrical wires, the myelin sheath functions much like coating on a wire, while the “wire” is called the axon. The defective gene in a person with CMT affects the production of protein in the body that is necessary for proper functioning of either the myelin sheath or the axon.
There are two broad causes behind the symptoms of CMT. In about 70% of cases, the myelin sheath that coats the peripheral nerves starts to break down. Myelin (the “coating”) helps to speed up conduction of the nerve signal. As the myelin sheath breaks down, conduction slows down. Over time the axon deteriorates as well. The most common type of CMT, affecting about half of those diagnosed with CMT, is called CMT Type 1A. This type of CMT affects the myelin sheath and is inherited through a single gene from a parent.
In about 30% of cases, the axon (the “wire”) becomes directly affected. As the axon deteriorates, the nerve impulse can no longer travel along the axon as well, and symptoms arise.
Diagnosis of CMT will be likely to include a neurological exam from a neurologist, medical history, nerve conduction and electromyography (EMG) tests, and possibly genetic testing. Currently, no cure exists for any of the types of CMT, but research has been ongoing. Treatment may include orthotics, physical therapy, occupational therapy, surgery, and medication for neuropathic sensations. People with CMT should avoid certain medications that may increase symptoms. The Charcot Marie Tooth Association (CMTA) publishes a list of these medications.
The CMTA offers many other resources for those with CMT and raises money to provide grants to cutting-edge researchers through their STAR program. The Muscular Dystrophy also provides many resources for those with CMT, including access to medical care through the MDA Clinics.
Charcot Marie Tooth disease was named for the three physicians who first described CMT in 1886. Sometimes, CMT may be referred to as hereditary motor and sensory neuropathy (HMSN) or peroneal muscular atrophy (PMA). While more descriptive, these names do not appear to be used as often as that funny name, Charcot Marie Tooth, for this serious disease.
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Charcot Marie Tooth Association, (n.d.). An Overview of Charcot Marie Tooth Disorders. http://www.charcot-marie-tooth.org/about_cmt/overview.php . Retrieved 7/23/10.
Charcot Marie Tooth Association, (n.d.). Medical Alert. http://www.charcot-marie-tooth.org/med_alert.php . Retrieved 7/23/10.
Muscular Dystrophy Association (n.d.). Charcot-Marie-Tooth Disease. http://www.mda.org/disease/cmt.html . Retrieved 7/23/10.
Muscular Dystrophy Association (n.d.). Welcome to MDA. http://www.mda.org/disease/cmt.html . Retrieved 7/23/10.