CMT Association of Australia

What is Charcot-Marie-Tooth

What is its medical name

How common is CMT

Who can get CMT

What are the symptoms of CMT

• In the legs and feet
  • High arches of the foot
  • Hammer toes
  • High stepping gait - cause by foot drop
  • Wasting of the leg muscles resulting in poor balance and circulation
  
  
• In the arms and hands
  • Weakness of the hands generally
  • Weakness of the thumb muscle
  • Inability to manage fine coordination
  • Loss of sensation, resulting in cuts and burns

The condition is not life threatening and the symptoms can be alleviated by physiotherapy, orthotics and sometimes surgery.

CMT Type 1

Type 1 is comprised of Types a, b, and c (demyelinating CMT, with slow nerve conduction).

In autosomal dominant CMT Type 1a, the genetic defect occurs in a duplication region on chromosome 17 in about 60-80% of cases and the other CMT families do not have a microduplication; instead they have an abnormal base pair substitution in the gene that produces the myelin protein PMP-22. The gene (PMP-22) is known to lie within the microduplication as well. About 95% of Type 1 people are located on chromosome 17.

The gene responsible for type CMT 1b has been found on the long arm of chromosome 1. This type is caused by a genetic defect in another protein, myelin protein zero (MPZ).

In CMT Type 1c there are few families with this type and the chromosomal location is not known but the gene defects are not found on either chromosomes 17 or 1.

CMT Type 2

X-Linked CMT

The defect in X-linked CMT has been identified as Connexin 32, a gap junction protein. X-linked CMT patients show a slow nerve conduction velocity.

Autosomal Recessive CMT Type 4A

The gene for one of these forms, CMT4A is located on chromosome 8 and it is probable that two other genes can cause Types 4B and 4C although the location of these types is not known. The genetic defect in CMT4A is not yet known.