Charcot Marie Tooth Disease

Charcot-Marie-Tooth Disease (CMT), also named hereditary motor and sensory neuropathies, is a genetically varied group of disorders affecting the peripheral nervous system. They tend to cause weakness and wasting of the muscles below the knees and in the hands.

CMT can be divided into two types. Type 1 is caused by the insulating layer around the nerve fibres (the myelin sheath) being damaged, slowing down the transmission of nerve impulses. Type 2 is caused by damage to the nerve fibres themselves - this means that the speed of the impulse is normal but its strength is reduced.

CMT disease can be inherited in a variety of ways. Most common is by autosomal dominant inheritance where only one copy of the faulty gene is needed to cause the condition.

More unusual is autosomal recessive inheritance where one copy of the gene is inherited from each parent both of whom are carriers but do not themselves have the disease.

Finally, CMT can occasionally be a sex-linked condition where it is carried on the X chromosome only. Boys only have one X-chromosome (inherited from their mother). If it carries a gene for CMT, there is no 'normal' X-chromosome to override it and he will have the condition. This means that it is almost exclusively boys who are affected by this form of the disease.

More information is available on the Muscular Dystrophy Campaign website.