Charcot-Marie-Tooth disease (CMT) is one of the most common inherited neurological disorders, affecting approximately 1 in 2,500 people in the United States and about 2.8 million people world wide. The disease is named for the three physicians who first identified it in 1886 – Jean-Martin Charcot and Pierre Marie in Paris, France, and Howard Henry Tooth in Cambridge, England. CMT, also known as hereditary motor and sensory neuropathy (HMSN) or peroneal muscular atrophy, comprises a group of disorders that affect peripheral nerves. The peripheral nerves lie outside the brain and spinal cord and supply the muscles and sensory organs in the limbs. Disorders that affect the peripheral nerves are called peripheral neuropathies.
CMT is inherited. 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 the 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 the child inherits the one mutated CMT gene from each of their parents (the chance of this happening is 1 out of 4), then 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. Thus, 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 because of foot drop);
- Loss of muscle in the lower legs, leading to skinny calves;
- Numbness in the feet;
- Difficulty with balance;
- ‘Claw hand’ when muscles in the hand tighten and curl inward;
- CMT almost never affects brain function.
There is no cure for CMT, but physical therapy, occupational therapy, braces and other orthopedic devices, and even orthopedic surgery can help individuals cope with the disabling symptoms of the disease. In addition, pain-killing drugs can be prescribed for individuals who have severe pain.