Charcot Marie Tooth
Charcot-Marie-Tooth disease or CMT is named after the three neurologists who first described the condition in 1886. It 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.
CMT is not in fact a single disorder but a group of conditions that have some similarities. Neuropathy means a disease of the peripheral nerves. These are the nerves that connect the spinal cord to the muscles, joints and skin and carry messages in both directions, and in CMT they do not function normally. The group of conditions known as CMT cause weakness and wasting of the muscles below the knees and often those of the hands as well. Many affected individuals also have loss of feeling in the hands and feet. Disease onset usually occurs during the first decades of life and gets worse slowly. Severity is highly variable even within families, but the condition only rarely leads to severe disability.
The genetics of CMT is complicated. 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.
Because there are many different types of CMT, it is important to determine exactly which type someone has. 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. This means that nerve conduction studies (electrical tests on the nerves) are still often used to help make the diagnosis. A DNA test for the most common form of CMT (type 1A) might be performed first if there is a clear family history of autosomal dominant inheritance of the condition.
The links and downloads on this page provide more information about CMT for patients and professionals.