Charcot-Marie-Tooth disease is an inherited nervous system disorder that causes progressive degeneration of the nerves that supply the muscles of the limbs, resulting in gradually increasing muscle weakness.
Named for the three physicians who discovered the disorder in 1886, Charcot-Marie-Tooth disease is the most common inherited nervous system (neurological * ) disorder. About 2.6 million people have the condition. The disease causes progressive degeneration of the nerves that supply the muscles of the limbs, resulting in gradually increasing muscle weakness.
Charcot-Marie-Tooth disease runs in families and is caused by a genetic defect. Genes (JEENS) are chemical structures composed of deoxyribonucleic acid (DNA) that help determine a person's body structure and physical characteristics. Inherited from a person's parents, genes are contained in the chromosomes * found in the body's cells. Under normal circumstances, long nerve fibers (called axons) that carry signals from the brain and spinal cord to the muscles are covered with a special sheath called myelin. Myelin allows the electrical signal to travel quickly and efficiently along the nerve, and it also provides some nutrition for the continued health of the nerve. In Charcot-Marie-Tooth disease, defective genes do not produce the appropriate proteins necessary for the normal composition of the axons or of the myelin sheath. Abnormal axons result in weaker than normal transmission of electrical signals; abnormal myelin results in slower than normal transmission of electrical signals. This genetic disease causes weakness in limbs, generally beginning in the legs and then affecting the arms.
Most forms of Charcot-Marie-Tooth disease are inherited in an autosomal dominant fashion. This means that an individual only has to have one parent with the disorder in order to inherit the disease. A couple in which only one member has the disorder has a 50 percent chance of passing it on to their offspring. A few forms of Charcot-Marie-Tooth disease are inherited in an autosomal recessive fashion, meaning that an affected individual has to receive a copy of the defective gene from each parent. Type 1X is x-linked, which means that it is passed by the mother to the son on the X chromosome, and only males will display symptoms of the disorder. In some cases, Charcot-Marie-Tooth disease can occur as a spontaneous mutation, in which case neither parent of the affected individual had the disorder, but offspring of the affected individual are at risk of inheriting the defective gene.
About 10 to 20 percent of all people with Charcot-Marie-Tooth disease do not develop any symptoms of the disorder at all. The other 80 to 90 percent experience gradually increasing muscle weakness. Muscles grow smaller, walking becomes difficult, and balance is affected. There may be decreased sensation or painful numbness and tingling (paresthesias) in the feet, lower legs, hands, and forearms. If the muscles become abnormally tight, joints may become stiff. In some cases, people with Charcot-Marie-Tooth disease develop a curved spine (scoliosis) or foot sores (ulcers) that do not heal. Although most people with Charcot-Marie-Tooth disease live a normal lifespan, the disease can be associated with significant disability, particularly by the time afflicted individuals reach their 60s or 70s.
The diagnosis of Charcot-Marie-Tooth disease is straightforward among people who already know the disorder runs in their family. Others are examined by a neurologist * who takes a detailed family history and does a thorough examination (such as observing walking and testing reflexes). Electrodiagnostic testing may be performed, including an electromyogram * (EMG) to test how strong the electrical signals are in the muscles, and a nerve conduction velocity test to see how quickly and strongly the electrical signal travels along nerves. Some forms of Charcot-Marie-Tooth disease can also be diagnosed through genetic testing.
As of 2015, there was no known cure for Charcot-Marie-Tooth disease. Treatment in the early 2000s addressed the weakness and deformity that may be caused by the disease. Braces and appropriate footwear may improve mobility, and physical therapy and an appropriate exercise program may help optimize muscle strength and flexibility. Occupational therapy can also help people learn how to function better, despite their impairment. In some cases, an orthopedic surgeon may recommend surgery to help improve tight heel cords, lower the arch of the foot, fuse the ankle joint, or straighten toes that have been deformed by the condition. Pain medications or consultation with a pain specialist may be helpful for people with paresthesias.
Charcot-Marie-Tooth disease cannot be prevented, but genetic counseling can help affected individuals understand the risk of passing the defective gene on to their children.
Krupin, Paul J. Charcot Marie Tooth (CMT). Kennewick, WA: Direct Contact, 2014.
Muscular Dystrophy Association. “Charcot-Marie-Tooth Disease (CMT).” MDA.org . https://www.mda.org/disease/charcot-marietooth/signs-and-symptoms (accessed November 27, 2015).
Charcot-Marie-Tooth Association. 2700 Chester St., Philadelphia, PA 19013. Toll-free: 800-606-2682. Website: http://www.cmtausa.org (accessed November 27, 2015).
* neurological (nur-a-LAH-je-kal) refers to the nervous system, which includes the brain, spinal cord, and the nerves that control the senses, movement, and organ functions throughout the body.
* chromosomes (KRO-mo- somz) are threadlike chemical structures inside cells on which the genes are located. There are 46 (23 pairs) chromosomes in normal human cells. Genes on the X and Y chromosomes (known as the sex chromosomes) help determine whether a person is male or female. Females have two X chromosomes; males have one X and one Y chromosome.
* neurologist (new-RHAL-eh-jist) is a physician who specializes in diagnosing and treating diseases of the nervous system.
* electromyogram (ee-lek-tro- MY-eh-gram) (EMG) is a visual record made by an electromyograph, which measures the electrical activity associated with functioning muscle.