Charcot-Marie-Tooth disease
What is Charcot-Marie-Tooth disease?
Charcot-Marie-Tooth disease is a hereditary disorder marked by slowly progressive muscle weakness in the feet, lower legs, hands and forearms, and a mild loss of sensation in limbs, fingers, and toes. The weakness results from the degeneration of nerves that stimulate muscle rather than from a degenerative process in the muscle tissue itself.
The disorder, named for 3 physicians who first identified it in 1886, is also known as peroneal muscular atrophy because it primarily affects the peroneal muscles, which are located in the lower leg. There are now thought to be at least 2 types of the disease — hypertrophic and neuronal — that differ to some degree in severity.
How disabling is the disease?
In both types of Charcot-Marie-Tooth disease, there is normal life expectancy, limited disability, and very slow progression of the disease. Some patients, however, experience rapid progression and severe disability.
What are the early symptoms?
The first symptoms of Charcot-Marie-Tooth disease are usually foot deformities (high arch and flexed toes) and difficulty in walking caused by these structural changes. Typically, the knees have to be raised higher than normal to lift feet off the ground. There is also a tendency to sprain ankles and some difficulty in maintaining balance while standing.
How does the disease progress?
As the disorder advances, muscles in the lower legs and sometimes lower third of the thighs become weak and reduced in size (atrophic). Hands and forearms are affected in later stages, and fine manipulatory acts may become difficult. In addition, the sense of touch is somewhat diminished in the limbs and extremities.
What is the age of onset?
Because of the slow progression of the disease, its onset is often difficult to determine. Generally some foot deformity occurs before age 20 in the hypertrophic type. In the neuronal type, symptoms usually develop later, in early adult life or middle age.
In what other ways do the hypertrophic and neuronal types differ?
The small muscles of the hand are more affected in the hypertrophic type than they are in the neuronal, and sensory changes are more pronounced. This form of Charcot-Marie-Tooth disease is also characterised by enlarged (hypertrophic) nerves and by degeneration of the sheath of fatty material (myelin) that insulates many of the body's nerve fibres.
The neuronal form of Charcot-Marie-Tooth disease affects lower limb functions more than the hypertrophic form, and there is comparatively greater loss of muscle bulk below the knee. Weakness in the ankles and feet is also likely to be more severe in the neuronal type.
How does a person get Charcot-Marie-Tooth disease?
The disease is usually inherited as a dominant trait in both the hypertrophic and neuronal types. This means that it is only necessary for one parent to carry the defective gene for the disease to be transmitted. It also means that this parent will have the disease, although he or she might be unaware of it if the disorder is very mild with no apparent symptoms. There is a 50 per cent chance that a child will inherit the disorder if either parent carries the gene. Male and female children are equally affected.
How is Charcot-Marie-Tooth disease diagnosed?
Diagnosis is usually made through a physical examination that includes tests of muscle function and sensory responses, supplemented with a laboratory test (electromyogram) that measures the electrical activity of muscle cells. In addition, a complete family medical history is taken to determine if the patient's disorder is an inherited one. In some cases, nerve and muscle biopsies may be done to enable the physician to confirm the diagnosis, especially when symptoms are very mild and family history of the disease is not apparent. Both electromyography and muscle biopsy tests help to distinguish between the hypertrophic and neuronal types of the disorder.
Is there any cure or treatment?
There is no known cure for Charcot-Marie-Tooth disease. However, foot deformities can be treated with carefully fitted shoes and proper foot care. A regular programme of moderate exercise can build up muscles and increase the mobility of joints.
What research is being done?
Scientists are exploring the basic areas of nerve function, development, degeneration, and of nerve muscle interaction to uncover the underlying pathological process in Charcot-Marie -Tooth disease. Fundamental defects of lipid (fat) metabolism have been found in several inherited neuromuscular diseases that are clinically similar to Charcot-Marie-Tooth disease, and the possibility that this abnormality may also be of significance in Charcot-Marie-Tooth disease is under investigation.
Last Reviewed: 13 June 2007
