HEALTH NOW -What is Charcot-Marie-Tooth (CMT) disease?
WHAT IS CHARCOT-MARIE-TOOTH (CMT) DISEASE?
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 90 types of CMT. Each type is caused by a different type of mutation, and more causes are discovered each year. CMT is just one type of neuropathy (also known as peripheral neuropathy). These names simply mean that the peripheral nerves are damaged. There are many other causes of neuropathy besides CMT, including the most common cause – diabetes. CMT affects all people, all races, and all ethnic groups throughout the world, affecting about 3 million people.
WHERE DOES THE NAME CMT COME FROM?
Charcot–Marie–Tooth is the name of three physicians who first described the disorder in 1886: Jean–Martin–Charcot, Pierre Marie, and Howard Henry Tooth.
Things in our environment do not cause CMT. CMT is not contagious. The CMT is inherited. The most common forms of CMT are passed from one generation to the next, which means that it is dominantly inherited. Some forms of CMT are inherited recessively – a person can be affected even though the parents do not have CMT. In these cases, each parent harbors a mutation in one of their two copies of a CMT gene. If the child inherits a mutated CMT gene from each of her parents (the chance of this happening is 1 in 4), then the child will develop CMT. Sometimes the mutation that causes CMT occurs 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 a spontaneous mutation,
Some types of CMT cause damage to the covering (myelin sheaths) that surrounds nerve fibers. Other types of CMT directly damage nerve fibers. In both cases, damaged nerve fibers result in neuropathy. The nerves to the legs and arms, which are the longest, are affected first. Nerve fibers that create movement (called motor fibers) and nerve fibers that transmit sensation (called sensory fibers) are also affected. Therefore, CMT causes weakness and numbness that usually starts in the feet.
- In the most common types of CMT, symptoms usually start before the age of 20. They may include:
- Foot deformity (bow feet);
- Foot drop (inability to keep foot horizontal);
- “Bumped” gait (feet hit the ground when walking due to foot drop);
- Loss of muscle in the legs, leading to very thin calves;
- numbness in the feet;
- Balance problems.
Later, similar symptoms can also appear on the arms and hands. CMT almost never affects brain function.
A careful neurological evaluation by an expert in neuropathy, including a complete family history, physical examination, and nerve conduction tests, with appropriate genetic testing, is the way to establish the diagnosis of CMT. A physical exam may show:
- Difficulty raising the foot when walking;
- Difficulty with dorsiflexion of the toes and ankles (movement up, away from the ground) and other movements of the feet;
- Reduced or absent deep tendon reflexes (such as the knee jerk);
- Loss of muscle control and atrophy (shrinking of muscles) in the feet and legs (and later the hands).
Genetic testing can provide the exact cause for most people with CMT.
CMT usually gets worse, slowly, with age; rapid progression is rare, and should prompt prompt re-evaluation. Problems with weakness, numbness, difficulty with balance, and orthopedic problems can progress to the point of disability. Pain can be a problem, both as a direct result of neuropathy (neuropathic pain) and as a consequence of orthopedic problems. Other potential complications include the following:
- Progressive inability to walk due to weakness, balance problems, and/or orthopedic problems;
- Decreasing to use hands effectively;
- Injuries to areas of the body that have decreased sensation.
There are no known treatments that stop or slow the progression of CMT, but the CMTA is funding research to find these treatments. Physical therapy, occupational therapy, and physical activity can help maintain muscle strength and improve independent functioning. Orthopedic equipment (such as orthopedic braces, shoe inserts, or orthotic shoes) can make it easier to walk. Orthopedic foot surgery can often maintain or even restore walking function.
Most patients can receive an exact genetic diagnosis if that is what they want. Genetic counseling can inform patients of the possibility of their CMT being passed on to their children.
The CMTA wants to help you better understand the CMT by offering advice from professionals. Click here to find answers to frequently asked questions and post questions and concerns that haven’t been addressed yet – we’ll connect you with the right professional.
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