Charcot Marie Tooth disease, also known as hereditary sensory and motor neuropathies, is a group of disorders that damages the peripheral nerves. Peripheral nerves act as a connecting medium between the central nervous system (brain and spinal cord) and the muscles and the sensory cells that help in detection of sensation including touch, heat, pain, and sound. The severity of symptoms leads to progressive worsening of the peripheral nerves resulting in alteration or loss of sensations and atrophy of muscles of various affected parts of the body, mostly, the feet, legs, and hands. Although the disease can occur at any point in life, it is most commonly seen in adolescence and early adulthood.(1)
How Does Charcot Marie Tooth Affect The Body?
The symptoms vary in severity and age of onset from person to person and are different even in family members. The symptoms range from mild to severe; most people usually have a moderate disability. On very rare occasions, it can become life-threatening; however, in most instances, it does not affect the life expectancy of a person.
Charcot Marie Tooth disease causes muscle atrophy of the feet and foot deformities including pes cavus (high arched feet), pes planus (flat feet) or hammertoes (curled toes). It also leads to difficulty flexing the foot and walking on the heel of the foot, which results in steppage gait (high stepped gait). These abnormalities predispose a person to increased risk of fall, tripping and ankle injuries. With the worsening of the disease, muscle weakening and wasting of lower legs are pronounced; however, it rarely leads to wheelchair use.(1)
The people with Charcot Marie Tooth disease may also complain of weakness in hands that may lead to difficulty with daily tasks, such as writing, buttoning and turning doorknobs. They also have reduced sensitivity to heat, cold, touch in feet and lower legs; they can also have occasional pain or burning sensations. In very rare occasions, they may also develop vision loss or progressive hearing loss that may ultimately cause deafness.(1)
What Triggers Charcot Marie Tooth Disease?
Charcot Marie Tooth disease is mainly triggered by a genetic abnormality that can be inherited in an autosomal dominant, autosomal recessive or X-linked dominant pattern. The genetic transmission of the genes depends on the traits of chromosomes received from both the father and mother. Genetic disorders are either recessive or dominant. The recessive disorder is one in which two abnormal genes should be inherited from each parent for the disease to be apparent; whereas, dominantly inherited disorders require only one gene from either of the parents to show the symptoms of the disease. X-linked dominant genetic disorders are caused due to an abnormal gene on the X chromosome. Charcot Marie Tooth (CMT) hereditary neuropathy is divided into CMT-1, CMT-2, CMT-3, CMT-4 and CMT-X.(2)
CMT-1 is the most common type and is an autosomal dominant disorder that is associated with slowing of nerve conduction due to disruption of function and structure of myelin sheath. CMT-1 is further subdivided into CMT-1A, CMT-1B, CMT-1C, CMT-1D and CMT-1X depending on specific abnormalities in the gene. CMT-1A is the most common type of CMT-1 that is caused by an abnormality on the PMP22 gene located on chromosome 17 at 17p11.2.(2)
CMT-2 is an autosomal dominant disorder in which the nerve conduction velocity is normal or slightly slower than normal. It is caused by an abnormality in the structure and function of axons and is further subdivided into CMT-2A to CMT-2L. Dominant Intermediate CMT (DI-CMT) has an intermediate conduction velocity due to uncertainty related to whether it is axonal or demyelinating type. CMT-3, also known as Dejerine-Sottas disease, has a gene mutation in one of the genes of CMT-1A, CMT-1B, CMT-1D or CMT4. CMT-4 is an autosomal recessive and is further subdivided into CMT-4A, CMT-4B1, CMT-4B2, CMT-4C, CMT-4D, CMT-4E and CMT-4F. CMT-X is caused by X-linked autosomal dominant inheritance pattern and CMT-X1 accounts for about 90% of CMT-X. CMT-2 also has an autosomal recessive inheritance.(2)
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