Charcot-Marie-Tooth disease tends to affect peripheral nerves. These nerves are outside the brain and spinal cord (the central nervous system) and enervate the sensory organs and muscles in the arms and legs. CMT is caused by mutations in genes that produce proteins involved in the structure and function of either the peripheral nerve axon or the myelin sheath. In order to speed the transmission of messages and to prevent loss of electrical signals, Myelin surrounds the nerve axon like a jelly-roll cake. There are dozens of types of CMT. Some forms require only one copy of the mutated gene from one parent; some need a mutated gene from both parents; and some are linked to the X chromosome. Following are some resources for additional information.