Charcot-Marie-Tooth (CMT) disease is the most common form of inherited peripheral neuropathy, and these conditions have a prevalence of approximately 1 in 3000 individuals. Clinical symptoms include distal muscle weakness with atrophy, loss of deep tendon reflexes, high-arched feet, and loss of sensation. These conditions tend to be progressive, and while most families demonstrate autosomal dominant inheritance, autosomal recessive and X-linked inheritance also occurs. Symptoms and age of onset are variable, but early signs of the disorder include clumsiness, balance problems, and difficulty using the hands to grasp. Hearing loss occurs in some affected individuals, and eventually, some patients require the assistance of a wheelchair. Lifespan and intelligence are not typically affected.
Charcot-Marie-Tooth disease is comprised of several types and subtypes. CMT1 is responsible for almost half of all cases of CMT, with CMT2 and CMTX making up an additional 10-15% each. Within the CMT1 type, about 70-80% of cases are due to changes in the PMP22 most often associated with a duplication involving chromosome 17p12. Reciprocal deletions of this region are associated with hereditary neuropathy with liability to pressure palsies, HNPP.