These are the two most common forms of CMT, a genetic, neurological disorder that causes damage to the peripheral nerves — tracts of nerve cell fibers that connect the brain and spinal cord to muscles and sensory organs.
A subtype of CMT1, called CMT1A (caused by a defect in the PMP22 gene on chromosome 17) accounts for around 60 percent of all CMT cases.
CMT1 and CMT2 are characterized by muscle weakness and atrophy, and changes in sensation, mostly in the periphery of the body, particularly in the feet, lower legs, hands and forearms.
CMT2 also is sometimes associated with a treatable condition called restless leg syndrome, an irresistible urge to move the legs while sitting or lying down. For more, see Signs and Symptoms.
CMT is caused by defects in the genes for proteins that affect axons (fibers that carry electrical signals between the brain and spinal cord and the rest of the body) or in the genes for proteins that affect myelin (a coating on axons that insulates and nourishes them).
CMT1 is caused by demyelination (loss of the myelin coating), and CMT2 is caused by axonopathy (abnormalities in the axons), but both produce the classic symptoms of CMT.
CMT1 is inherited in an autosomal dominant pattern; CMT2 is inherited in an autosomal dominant or recessive pattern. For more, see Causes/Inheritance.
CMT1 and CMT2 typically begin in childhood or adolescence, and progression is generally slow. CMT usually isn't life-threatening, and it almost never affects the brain.
CMT research is focused on exploring the effects of defects in genes related to the peripheral nervous system and devising strategies to combat these effects.