CMT is a genetic condition that damages peripheral nerves. These nerves are responsible for passing on commands from the brain to the muscles (motor nerves) and for passing information to the brain about sensations, such as pain, heat, cold, touch, importantly for balance – where your joints are in space (sensory nerves). When these are damaged, people are said to have a neuropathy.
Because of this nerve damage, people with CMT may find that some of their muscles become slowly weaker over the years, particularly in their feet and hands. Some find that feeling becomes duller, or numb, in the same areas.
In the UK, around 25,000 people are thought to have CMT, making it the most common inherited neurological condition.
Other key points about CMT are that the condition:
- is hardly ever life-threatening, but often becomes slowly worse over the years
- comes in many forms, some of which are much more severe than others
- can affect people very differently, even in the same family
- can cause the muscles in the foot, lower leg, hand and forearm to become wasted and weak
- can cause foot drop gait, foot bone abnormalities (e.g. high arches and hammer toes), problems with hand function, balance problems, occasional lower leg and forearm muscle cramping, and loss of some normal reflexes
- may cause long-term pain and tiredness (fatigue)
- can be passed on from parent to child: the precise way it is passed on to subsequent generations depends on the genes involved
- affects all ethnic groups throughout the world
- is the focus of much research, bringing us close to answering the CMT enigma.
Explanation of names
CMT is an acronym for Charcot Marie Tooth, the surnames of the three doctors who first described CMT in the late 1800s: Frenchmen Jean-Martin Charcot and Pierre Marie; and Howard Henry Tooth from the UK.
CMT has many other names, the most common being:
Hereditary motor and sensory neuropathy (HMSN) – so called because it is passed on through families (hereditary) and affects both the motor and sensory nerves (neuropathy).
Peroneal muscular atrophy (PMA) – so called because one of the muscles that is often first affected, becoming weaker and wasted (atrophy), is called the peroneus muscle, found in the shin.