Charcot-Marie-Tooth Disease, or CMT, is a group of inherited disorders that affect the peripheral nerves, which are the nerves outside the brain and spinal cord. There are more than 70 kinds of CMT. Each kind is caused by a different kind of mutation, and more causes are being discovered every year.
CMT is just one kind of neuropathy (also called peripheral neuropathy), meaning simply that the peripheral nerves are damaged. There are many other causes of neuropathy, including the most common cause—diabetes.
CMT affects about 2.8 million people worldwide, of all races and ethnic groups.
Where Did the Name CMT Come From?
Charcot-Marie-Tooth is named after the three physicians who were the first to describe it in 1886: Jean-Martin Charcot, Pierre Marie and Howard Henry Tooth.
CMT is inherited. It is not contagious, nor is it caused by anything in the environment. The most common forms of CMT are passed down from one generation to the next, meaning that it is dominantly inherited.
Some forms of CMT are recessively inherited—a person may be affected even though his or her parents do not have CMT. In this case, each of the parents harbors a mutation in one of their two copies of a CMT gene. If a child inherits one mutated CMT gene from each of their parents (the chance of this happening is one out of four), the child will develop CMT.
Sometimes the mutation that causes CMT happens spontaneously during the process that produces the eggs or sperm. In these rare cases, a child will have CMT even though neither parent has CMT. If a child has such a spontaneous mutation, he/she may pass that mutation down to his/her offspring.
Some types of CMT cause damage to the covering (myelin sheaths) that surrounds nerve fibers. Other kinds of CMT directly damage the nerves fibers themselves. In both cases, the damaged nerve fibers result in neuropathy. The nerves in the legs and arms, which are the longest, are affected first. Nerve fibers that create movement (called motor fibers) and nerve fibers that transmit sensations (called sensory fibers) are both affected. CMT causes weakness and numbness, usually starting in the feet.
In the most common kinds of CMT, symptoms usually begin before the age of 20 years. They may include:
- Foot deformity (very high arched feet);
- Foot drop (inability to hold foot horizontal);
- “Slapping" gait (feet slap on the floor when walking because of foot drop);
- Loss of muscle in the lower legs, leading to skinny calves;
- Numbness in the feet;
- Difficulty with balance;
- Later, similar symptoms also may appear in the arms and hands.
CMT almost never affects brain function.
A diagnosis of CMT is established through a thorough neurological evaluation by an expert in neuropathy, including a complete family history, physical exam, and nerve conduction tests, and appropriate genetic testing.
A physical exam may show:
- Difficulty lifting up the foot while walking;
- Difficulty with dorsiflexion of the toes and ankles (upward movement, away from the ground) and other foot movements;
- Reduced or absent deep tendon reflexes (like the knee-jerk reflex);
- Loss of muscle control and atrophy (shrinking of the muscles) in the feet and lower legs (and later the hands).
Genetic testing can provide the exact cause for most people who have CMT.
CMT usually gets worse, slowly, with age; rapid progression is rare, and should motivate a prompt re-evaluation. The problems with weakness, numbness, difficulty with balance, and orthopedic problems can progress to the point of causing disability. Pain can be an issue, either as a direct result of the neuropathy (neuropathic pain) or as consequence of orthopedic problems. Other potential complications include the following:
- Progressive inability to walk from weakness, balance problems, and/or orthopedic problems;
- Progressive inability to use hands effectively;
- Injury to areas of the body that have decreased sensation.
There are no known treatments that will stop or slow down the progression of CMT, but the CMTA is funding research to find these treatments.
Physical therapy, occupational therapy, and physical activity may help maintain muscle strength and improve independent functioning.
Orthopedic equipment (such as braces, inserts, or orthopedic shoes) may make it easier to walk.
Orthopedic surgery on the feet can often maintain or even restore function to enable walking.
Most patients can obtain an exact genetic diagnosis. Genetic counseling can inform patients of the chance that they will pass CMT on to their children.
The CMTA wants to help you better understand CMT by offering advice from professionals. Click here to find answers to the most frequently asked questions and post questions and concerns that have not yet been addressed—we’ll get you in touch with the right professional.