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Charcot-Marie-Tooth Disease refers to a hereditary neurological disorder affecting primarily the legs, feet and hands. It is also known as Hereditary Motor-Sensory Neuropathy (HMSN) and Peroneal Muscle Atrophy. Charcot-Marie-Tooth (CMT) Disease is one of the more common hereditary diseases. One in 2,500 people is afflicted with some form of CMT.
CMT is a neurological disorder because it affects the peripheral nerves that supply the lower body. CMT is divided into two general types, Type I and Type II. Different forms of CMT fall under these two types. Type I affects the myelin sheath that surrounds the nerve fiber. Degeneration of the myelin sheath results in slowed conduction of the nerve signals to the muscles. Type II affects the nerve fibers itself. Conduction is generally normal, but abnormalities are evident in the nerve signals. Because of poor innervation, the muscles of the lower limbs start to weaken and waste away and atrophy. Early symptoms of CMT include high arch of the feet and flexed toes. Some varieties of CMT are associated with other disorders. These include CMT with Freidrich Ataxia, with Ptosis, and with Parkinsonism. Onset generally occurs either in childhood or adolescence. Symptoms vary in severity and progressively worsen. There is no cure for CMT, however, various treatments are widely available. They range from physical therapy, leg braces, shoe inserts and surgery to correct any severe abnormalities. Affected individuals are more vulnerable to injury.
At least six genetic defects have been traced to CMT. Generally, CMT is inherited in an autosomal dominant fashion but some forms of CMT have been found to be X-linked. Symptoms of X-linked forms of CMT are generally more pronounced in males than females. Once a patient is diagnosed with CMT, it is crucial to determine the form of CMT the patient has. A thorough genetic and pedigree analysis should be conducted to determine mode of inheritance of that particular form of CMT. A new test is now available to help couples with a family history of X-linked CMT. Pre-Implantation Genetic Diagnosis (PGD) examines an embryo prior to implantation and determines the sex of the baby. The transmission of diseases that are more prevalent in one gender can be greatly reduced through PGD. A thorough genetic analysis by a genetic counselor is needed to determine if PGD will be of benefit to couples.
Thus far, the following forms of CMT have been found to be X-linked,
CMT2B X-linked with Aplasia Cutis Congenita
CMT2B2 CMT combined with Friedrich Ataxia
CMT4A CMT with Ptosis and Parkinsonism
The forms listed above are not exclusively inherited in an X-linked pattern. PGD can only help in reducing the risk of having a child with CMT. However, PGD, is continuously being improved and hopefully, it will someday test for all the forms of CMT and many other genetic diseases.
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