Charcot-Marie-Tooth disease is a group of progressive disorders that affect the peripheral nerves and result in problems with movement and sensation. Peripheral nerves connect the brain and spinal cord to muscles and to sensory cells that detect sensations such as touch, pain, heat, and sound.
Charcot-Marie-Tooth disease usually becomes apparent in adolescence or early adulthood, but onset may occur anytime from early childhood through late adulthood. Typically, the earliest symptoms involve muscle weakness in the feet, which can cause foot abnormalities such as high arches (pes cavus) or curled toes (hammer toes). It may become difficult to flex the foot or to walk on the heel of the foot. These difficulties may cause a higher than normal step (or gait) and can increase the chance of ankle injuries and tripping.
As the disease progresses, muscles in the lower legs usually weaken, but leg and foot problems rarely require the use of a wheelchair. Affected individuals may also develop muscle weakness in the hands, causing difficulty with daily activities such as writing, fastening buttons, and turning doorknobs. Because signals to sensory cells can be disrupted in Charcot-Marie-Tooth disease, people with this disorder may feel aching or burning sensations in the feet and lower legs, or they may experience a decreased sensitivity to touch, heat, and cold. In rare cases, sensory loss can include gradual hearing loss, deafness, or loss of vision.
Symptoms of Charcot-Marie-Tooth disease vary in severity, even among members of the same family. Some people never realize they have the disorder, but most have a moderate amount of physical disability. A small percentage of people experience severe weakness or other problems which, in rare cases, can be life-threatening. In most affected individuals, however, Charcot-Marie-Tooth disease does not affect life expectancy.
No universal system is used to classify types of Charcot-Marie-Tooth disease. Different types of Charcot-Marie-Tooth disease can be distinguished by the details of their signs and symptoms, the abnormality that disrupts nerve function, the genetic cause, and how the condition is inherited. Type 1 Charcot-Marie-Tooth disease is characterized by abnormalities in myelin, the protective substance that covers nerve cells. Type 2 Charcot-Marie-Tooth disease is characterized by abnormalities in the fiber, or axon, that extends from a nerve cell and transmits nerve impulses. Type 4 Charcot-Marie-Tooth disease affects either the axon or myelin and is distinguished by its pattern of inheritance. In intermediate forms of Charcot-Marie-Tooth disease, abnormalities occur in both axons and myelin. Type X Charcot-Marie-Tooth disease is caused by mutations in a gene on the X chromosome, one of the two sex chromosomes. Within the various types of Charcot-Marie-Tooth disease, subtypes (such as 1A, 2A, 4A, and X1) are distinguished by the specific gene that is altered.
Sometimes other, more historical names are used to describe this disorder. For example, Roussy-Levy syndrome is a form of type 1 Charcot-Marie-Tooth disease associated with rhythmic shaking (tremors). Dejerine-Sottas syndrome is a term sometimes used to describe a severe, early childhood form of Charcot-Marie-Tooth disease that has also been called type 3. Depending on the specific gene that is altered, this severe, early onset form of the disorder may also be classified as type 1 or type 4. Charcot-Marie-Tooth syndrome type X5 is also known as Rosenberg-Chutorian syndrome. Some researchers believe that this condition is not actually a form of Charcot-Marie-Tooth disease. Instead, they classify it as a separate disorder characterized by peripheral nerve problems, deafness and vision loss.
