What is Charcot-Marie-Tooth disease?
Charcot-Marie-Tooth (CMT) disease is named after the three neurologists who first noted the condition around a century ago. CMT is an inherited neurological disease, which is characterized by the slow degeneration of muscles in the lower legs, feet, hand and forearms.
There are different types of CMT, each resulting in varying symptoms and levels of severity. Type 1, usually referred to as CMT1, affects the insulating covering surrounding the nerve fibers, and symptoms are usually first noticed during late childhood or adolescence.
Type 2, CMT2, affects the nerve fibers themselves and may start to become noticeable a little later in life.
CMT is sometimes called Hereditary Motor and Sensory Neuropathies (HMSN) or Peroneal Muscular Atrophy (PMA). Dejerine-Sottas Disease is also very similar to Charcot-Marie-Tooth disease and is sometimes referred as CMT3.
Symptoms of Charcot-Marie-Tooth disease
CMT commonly affects the lower legs, feet and hands, with a minority of patients reporting partial sight and hearing loss.
The disease weakens the muscles and people with CMT will usually experience some degree of atrophy (wasting of muscle tissue), loss of muscle bulk, and a mild loss of sensation in the affected areas.
This may result in physical abnormalities such as high arches on the feet, hammer toes and ‘claw’ fingers.
Many people with CMT experience some level of pain or discomfort associated with muscle wasting. The loss of muscle often puts additional stress on parts of the body such as joints and ligaments, and this can cause damage and discomfort.
Causes of Charcot-Marie-Tooth disease
Most commonly, CMT has an autosomal dominant inheritance pattern. This means that a child who has one parent (mother or father) who carries a single faulty gene, has a 50% chance of inheriting CMT.
The carrier does not necessarily show symptoms of CMT. Less commonly, CMT may be passed on through an autosomal recessive inheritance pattern. This means that the child must inherit two abnormal genes from the parents.
Most commonly, this will mean that both parents carry a single abnormal gene, but are often not affected themselves by it.
Through this inheritance pattern the child has a 25% chance of inheriting and being affected by CMT, and a 50% chance of becoming a carrier without any symptoms.
The third inheritance pattern is called x-linked recessive. This means that the abnormal gene is carried on the x chromosome and is passed from mother to son only.
Daughters cannot inherit the disease in this way but can become carriers and pass it down to their sons.
The son has a 50% chance of inheriting the disease from his mother. The daughter has a 50% chance of becoming a carrier. Often the mother has no symptoms of the disease at all.
Very rarely, CMT can occur spontaneously. In other words, without any inheritance pattern. This can only happen with Type 1 CMT. The disease then becomes autosomal dominant (see beginning of section)
Diagnosis of Charcot-Marie-Tooth disease
After examination of the physical symptoms, a doctor may suggest a Nerve Conduction Velocity (NCV) test. The NCV test measures the speed of the nerve impulses: In CMT1 the speed will be slower than usual, while CMT2 patients will show other abnormalities such as smaller or less nerve impulses.
Another test called an electromyogram (EMG) may also be carried out to record electrical activity of the muscle cells.
In families with a strong history of CMT1a, prenatal diagnosis may be available.
Charcot-Marie-Tooth disease treatment
Breathing problems from Phrenic nerve paralysis, when the nerve that controls the diaphragm becomes paralyzed, can very rarely occur as a result of CMT1, but this complication is more common with CMT2. Some patients with CMT2 have prominent nerve and vocal paralysis, which results in hoarseness and shortness of breath.
Some of the physical problems caused by CMT can be treated with surgery. For example, surgery is often carried out on feet to correct problems with ankles and toes.
People with CMT who experience pain or discomfort may be prescribed pain killing drugs or, in some cases, referred to a specialist pain clinic.
Staff at pain clinics can help people to develop coping strategies for dealing with long-term pain as well as helping people to find the most appropriate drug treatments.
People with CMT can also benefit from a range of special aids, equipment and home modifications depending on how they are affected by the disease. In some cases, financial assistance may be available for this through local council social services departments.