How Common Is Charcot Marie Tooth Or Is It A Rare Disease?
Charcot Marie Tooth (CMT) disease is the most common inherited muscular disorder. It is an inherited disorder that affects both motor and sensory nerves without any evidence of an underlying metabolic disorder. It is also known as hereditary motor and sensory neuropathies (HMSNs) and they are different from hereditary sensory neuropathies or hereditary motor neuropathies. The name of the disease is coined after the physicians Jean-Martin Charcot and Pierre Marie of France and Howard Henry Tooth of England in 1886. It can be further subdivided into CMT 1, CMT 2, CMT 3, CMT X and CMT 4.(1)
CMT is quite a common disease affecting about 1 person per 2500 population and about 125,000 individuals in the United States. The incidence of Charcot Marie Tooth 1 is about 15 persons per 100,000 populations out of which CMT 1A dominates, with an incidence of 10.5 persons per 100,000 populations. Charcot Marie Tooth 2 incidence is 7 cases per 100,000 populations; whereas CMT X accounts for about 10-20% of all Charcot Marie Tooth cases. In Spain it accounts for 28.2 cases per 100,000 populations, in Italy, it accounts for 17.5 cases per 100,000 populations, in Japan, 10.8 cases per 100,000 populations are reported. In Norwegians, it is reported to affect about 1 in 1214 individuals.(1)
Cause Of Charcot Marie Tooth Disease
A nerve is responsible for communicating information to a distant site by the transmission of electrical signals via axon of a nerve cell. An axon is insulated by a myelin sheath (made up of Schwann cells), which protects the nerve and prevents the loss of electrical signals. If the axons and myelin sheath are not intact or there is a disruption in any then the nerve conduction will be interrupted with disruption inactivation of target muscles and communication of sensory information from the muscles to the brain. Charcot Marie Tooth is caused when there is a mutation in genes that are responsible for the production of structural or functional proteins of the axons or the myelin sheath. There are different mutations in different forms of Charcot Marie Tooth, but all of these lead to abnormal function of the peripheral nerves. This consequently leads to motor nerve degeneration causing weakness of the muscle and ultimately atrophy of the involved extremity (hands, arms, feet, and legs) along with sensory nerve disruption resulting in decreased sensations toward hot, cold, and pain.(2)
The mutations in the genes are generally inherited, either in an autosomal dominant pattern or autosomal recessive pattern. Charcot Marie Tooth disorder may also be inherited in an X linked pattern. CMT disease may also result in a sporadic form, in which the mutation is not passed down by the family, but occurs in the individual on its own.(2)
Symptoms Of Charcot Marie Tooth Disease
Charcot Marie Tooth affects both motor and sensory nerves, so the functions related to both the types of nerves is affected. The disease usually occurs in the first two decades of life. Slow progressive muscle weakness of the extremity is noted, especially of the lower extremity; Charcot Marie Tooth 1A patients may be seen with proximal muscle wasting and weakness. The symptoms also include difficulty walking, frequent sprains and frequent tripping due to muscle weakness and with severe muscle weakness foot drop and steppage is noted. Foot deformities such as pes cavus (high arch foot) and hammertoes are commonly noted due to which calluses, ulcers, cellulitis, and lymphangitis may be noted. Spinal deformity, such as thoracic scoliosis may also be seen in some patients.(1)
The weakness of the hands may lead to poor control of fingers, poor handwriting, clumsiness, and difficulty with zipping and buttoning and other manipulations associated with the hands. The sensations are mostly lacking in Charcot Marie Tooth patients, so they do not complain of sensory symptoms, such as numbness, but sensations of vibration and proprioception are markedly reduced. Muscle cramping, neuropathic pain or musculoskeletal pain may be present. Usually, autonomic symptoms are not present, but some patients may complain of them.(1)
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