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Hereditary motor and sensory neuropathies (HMSN) are a group of neuropathies which are characterized by their impact upon both afferent and efferent neural communication. HMSN are characterized by non typical neural development, and degradation of neural tissue. The two common forms of HMSN are either hypertrophic demyelinated nerves or complete atrophy of neural tissue. Hypertrophic condition causes neural stiffness and a demyelination of nerves in the peripheral nervous system, and atrophy causes the breakdown of axons and neural cell bodies. Hereditary motor and sensory neuropathies are disorders in which one or more components of the peripheral autonomic or cranial/spinal system is damaged. In these disorders a patient experiences progressive muscular atrophy and sensory neuropathy of the extremities. These disorders are inherited; if a parent has the disease the offspring have a 50% chance of also having the disease.〔American Association of Neuromuscular & Electrodiagnostic Medicine. (2013). Hereditary Motor Sensory Neuropathy. http://www.aanem.org/Education/Patient-Resources/Disorders/Hereditary-Motor-Sensory-Neuropathy.aspx Accessed on 11/10/13.〕 In these disorders numbness and weakness is usually more pronounced in the legs than in the arms. These disorders are also known as Charcot-Marie-Tooth (CMT) disease, which is divided into seven distinct subtypes. See table below. The weakness and numbness is caused by parts of the nerves in the extremities deteriorating and no longer receiving messages from the brain nor are sensory axons transmitting messages to the brain. This then causes muscles in the extremities to become very weak because they are not being used.〔 They are more common than hereditary sensory and autonomic neuropathies. ==History== CMT was first described in 1886 by Charcot, Marie, and independently Tooth.〔 In the 1950s further classification occurred and separated patients into two distinct groups. Group one was characterized by slow nerve conduction velocities and demyelinating neuropathy. Group two was characterized by mostly normal nerve conduction velocities and degeneration of axons. In 1975, the disease was again classified further by Dyck into seven distinct diseases: *HMSN types 1A and 1B (dominantly inherited hypertrophic demyelinating neuropathies) * *Individuals experience weakness and atrophy in the lower legs in adolescence, and later develop weakness in the hands. Most common type of CMT. *HMSN type 2 (dominantly inherited neuronal neuropathies) * *Onset in Adolescence, symptoms similar to type1. *HMSN type 3 (hypertrophic neuropathy of infancy ()) * *Onset in infancy and results in delayed motor skills, much more severe than types 1 & 2. *HMSN type 4 (hypertrophic neuropathy () associated with phytanic acid excess) * *Muscle weakness and atrophy as in other types of CMT, but set apart by being autosomal recessive inheritance. *HMSN type 5 (associated with spastic paraplegia) * *Onset between ages 5–12. Lower legs are affected first by muscle weakness and atrophy followed by the upper extremities. Type 5 is also associated with visual and hearing loss. *HMSN type 6 (with optic atrophy) * *Early onset muscular weakness and atrophy followed by optic atrophy resulting in vision loss and possibly blindness. *HMSN type 7 (with retinitis pigmentosa) 〔 * *Later onset with muscular weakness and atrophy mostly in the lower extremities. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hereditary motor and sensory neuropathy」の詳細全文を読む スポンサード リンク
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