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Charcot-Marie-Tooth Disease (CMT)


Causes of CMT


More than 30 genes have been implicated in CMT. In different types of CMT, peripheral nerve damage can be caused by defects in genes coding for proteins affecting axons, or by defects in genes coding for proteins affecting the insulating myelin coating around each axon — or both.



Inheritance patterns in CMT

Although CMT can look very similar to an acquired neuropathy — a type of nerve damage caused by diabetes, immunological abnormalities, or exposure to certain chemicals or drugs — it is not caused by anything a person does, and it is not contagious. It is hereditary, meaning that it can be passed down through a family from one generation to the next.

Because of these features, CMT is sometimes called hereditary motor and sensory neuropathy (HMSN). Some doctors also use the older name, peroneal muscular atrophy, which refers to atrophy of the peroneal muscle in the lower part of the leg.

CMT can run in a family, even when there is no obvious family history. In part, this is because CMT can be inherited in three different ways — X-linked, autosomal dominant, and autosomal recessive — that are not always easy to trace through a family tree.

X-linked inheritance means that the genetic defect (or mutation) is located on the X chromosome. In females, who have two X chromosomes, a normal copy of the gene on one chromosome can often compensate (at least partially) for the defective copy. Therefore, X-linked diseases usually affect males more severely than females, because males have only one X chromosome. X-linked diseases (like CMTX) cannot be passed from father to son.

Autosomal inheritance means the mutation occurs on a chromosome other than the X or Y. Therefore, autosomal diseases affect males and females equally. Autosomal recessive inheritance means that two copies of a defective gene are required for the disease to appear. One copy is inherited from each parent, neither of whom would normally have the disease.


When CMT is passed on in an autosomal dominant pattern, it can be easy to recognize in the family tree. In contrast, X-linked or autosomal recessive types of CMT might seem to occur “out of the blue.” In reality, the mother or both parents might be carriers who silently harbor a genetic mutation. Many parents have no idea they are carriers of a disease until they have a child with the disease.



A good way to find out more about this risk is to talk with your MDA Care Center physician, or a genetic counselor on your MDA care team. Also, see Facts About Genetics and Neuromuscular Diseases.

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