Hereditary motor neuropathies describe a group of diseases which include Charcot-Marie-Tooth disease (CMT). CMT is the most common inherited neuromuscular disorder, affecting approximately 1 in 2,500 individuals. The other term commonly used to describe the condition is hereditary motor and sensory neuropathy (HMSN). This name describes the two primary features of this condition: it is hereditary (passed on in the genes from parent to child) and it affects the motor and sensory peripheral nerves. The peripheral nerves connect the spinal cord to the muscles, joints and skin and carry messages in both directions. In CMT they do not function normally, causing weakness and wasting of the muscles below the knees and often those of the hands as well. Disease onset usually occurs during the first decades of life and gets worse slowly. Severity is highly variable even within families, but only rarely does the condition lead to severe disability.
Mutations in about 50 genes cause the various forms of CMT and the closely related conditions of hereditary motor neuropathy (HMN) and hereditary sensory and autonomic neuropathy (HSAN). Two further complicating factors are that different mutations in the same gene can cause different phenotypes (meaning that two patients with the same gene affected can have different symptoms), and that the same phenotype (same symptoms) can be caused by mutations in different genes.
Although in the last decade many genes responsible for CMT have been identified, not all of the genes that cause the condition have yet been found.
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