Charcot-Marie-Tooth Disease

Charcot-Marie-Tooth disease (CMT) is a condition that affects the nerves that control muscle movements. There are six main types of CMT, all of which happen because of a genetic mutation you inherited from one or both parents.

CMT is the most common form of inherited peripheral neuropathy (neuropathy means “nerve disease”). Your peripheral nervous system includes any nerves that aren’t part of your spinal cord or brain. Its name comes from Greek and means “around” or “outside the center.”

Who does it affect?

CMT is possible in people of all races and ethnicities. It happens equally to men and people assigned male at birth and women and people assigned female at birth.

How common is this condition?

CMT is an uncommon condition overall. Research estimates put the number of people affected worldwide between 700,000 and 2 million.

How does this condition affect my body?

Charcot-Marie-Tooth disease is a disease that affects your peripheral nerves, causing problems with how signals travel through those nerves. To understand why, it helps to know a little more about neurons, which are a key type of cell that make up your nerves.

More about neurons

Neurons send and relay signals through your nervous system, using both electrical and chemical signals. Each neuron consists of the following:

• Cell body: This is the main part of the neuron.
• Axon: This long, arm-like section extends out from the cell body. The axon has several finger-like extensions at its end. These extensions are synapses, which convert electrical signals within the neuron into chemical signals. The synapses connect to other neurons nearby, passing chemical signals to them.
• Dendrites: These are small branch-like extensions (their name comes from Latin and means “tree-like”) on the cell body. Dendrites are the receiving point for chemical signals from the synapses of other nearby neurons.
• Myelin: This thin, fatty layer surrounds the axon of many neurons and acts as a protective coating. Neurons with a myelin-coated axon send and relay signals at different speeds than neurons without this axon coating.

CMT affects your neurons in two ways, and some conditions cause one of these more than the other.

• Myelin loss: CMT can affect the myelin coating on your axons, causing them to lose myelin entirely or to have too little of it in the first place. Either way, this affects the speed of the signals traveling through your neurons, slowing them down.
• Axon problems: When Charcot-Marie-Tooth disease causes the axons on your neurons to shrink or deteriorate, this weakens the signals sent or relayed through that neuron.

In some cases, some subtypes of CMT slow your nerve signals slightly. The effect is enough to cause symptoms but not enough for healthcare providers to determine whether the problem is due to myelin loss or axon problems. Experts call these “intermediate” subtypes.

The neurons in your body aren’t all the same length or size. The neurons that reach down your spine to your legs and feet are the longest. These longer neurons (which bundle together and form nerve fibers) are most likely to show the early effects of CMT. A similar effect is possible in your arms and hands, but this usually doesn’t happen early on in this disease.