> CMT Disease

• Alternative Names
• Symptoms & Characteristics
• Treatment
• How Common Is It?
• Genetics & Inheritance
• Genetic Testing
• Support & More Information

Alternative Names

Charcot-Marie-Tooth hereditary neuropathy; Charcot-Marie-Tooth syndrome; CMT; hereditary motor and sensory neuropathy; HMSN; Peroneal Muscular Atrophy; PMA; CMT disease

Symptoms & Characteristics

Charcot-Marie-Tooth disease (commonly called CMT disease) is a group of progressive conditions that affect the peripheral nerves. Peripheral nerves carry movement and sensation signals (i.e. touch, pain, heat and sound) between the brain and spinal cord and the rest of the body.

Symptoms usually begin in a person's teens. Foot problems, like high arches or hammertoes can be early symptoms. As symptoms worsen, the lower legs and hands may also become weak. The symptoms may be mild or severe enough to cause significant weakness. Many people with CMT lead active lives and have a normal life span.

Different types of CMT can be distinguished by the abnormality that disrupts proper nerve function as well as by their genetic cause.

• Type 1 CMT is characterized by abnormalities in myelin, which is the substance that covers and protects nerve cells.

• Type 2 CMT is characterized by abnormalities in the nerve axon, which is responsible for transmitting the nerve pulses from the nerve cell.

• Intermediate forms of CMT are characterized by abnormalities in axons and myelin.

• Type 4 CMT also affects either axons or myelin.

Types 1, 2, 4, and intermediate forms are further categorized into subtypes that are characterized by the specific gene involved.

• An addition type, type X CMT is caused by mutations in a gene on the X chromosome, one of the two sex chromosomes (X and Y).

No universal system is used to define the different types of CMT. Sometimes other names are used to categorize the different types, which can be confusing.

Treatment

There is currently no cure for CMT. However, early diagnosis, routine surveillance and treatment can help to manage some of the symptoms and sometimes prevent related problems.

How Common Is It?

About 1 in 2,500 to 1 in 3,300 people are affected with CMT worldwide. More than 50% of affected people have type 1 CMT.

Genetics & Inheritance

Charcot-Marie-Tooth disease is caused by mutations in one of several different genes that are essential to the proper function of peripheral nerves in the feet, legs, and hands.

• Type 1, most cases of type 2, and intermediate forms of Charcot-Marie-Tooth disease have autosomal dominant inheritance, which means that having a mutation in a single gene copy is sufficient to cause disease. An affected person has a 50% chance with each pregnancy to have an affected child.

• Type 4 and subtypes 2B1 and 2K have autosomal recessive inheritance, which means that two mutations are necessary to cause disease, one inherited from each parent. Both parents of an affected person are always both obligate carriers (each have only one mutation). Two carriers have a 25% chance with each pregnancy to have an affected child, but do not have symptoms themselves.

• Type X has X-linked dominant inheritance. X-linked means the mutated gene is located on the X chromosome. While both males and females are affected, females tend to have milder symptoms as they have two X chromosomes. Males have one X and one Y chromosome.

There are other genetic and non-genetic conditions that have symptoms that overlap with CMT disease.

A genetic consultation with a trained genetic professional is important for a complete evaluation, accurate diagnosis, as well as discussion of the benefits and limitations of testing and recurrence risk.

Genetic Testing

Clinical genetic testing for CMT disease can be broken down into two categories: diagnostic testing and carrier testing.

• Diagnostic testing may be used to confirm or rule out a diagnosis in a person suspected to have the disorder.

• Carrier testing for autosomal recessive CMT disease is typically offered after a clinical diagnosis and/or mutations have already been identified in an affected family member(s).

Clinical genetic testing for some types of CMT disease is available through an in person genetic consultation for people who are considered at risk. Clinical genetic testing for intermediate forms of CMT may be available on a research basis only. Use our find a genetic professional directory to locate a trained genetic professional in your area.

• A medical geneticist can also be found at the American College of Medical Genetics website.

• A genetic counselor can also be found at the National Society of Genetic Counselors website.

Support & More Information

More information can be found at:

• Genetics Home Reference
• MedlinePlus

Support can be found at:

• Charcot-Marie-Tooth Association
• The Hereditary Neuropathy Foundation