What is CMS?

Congenital Myasthenic Syndrome (CMS) is really a large number of different conditions which affect transmission of signals from the nerves to the muscles at the neuro-muscular junction. Approximately 50 different genetic defects (mutations) are known which can cause malfunction of the transmission process. This causes some degree of perceived muscle weakness. The severity of the weakness, and the way it presents in the patient, depends to a very large extent on which particular mutation is involved. In most cases the problem appears near to, or at, birth, but in rarer cases it may not become apparent until later in childhood - or even adulthood .

Many patients with CMS can be helped by medication prescribed by expert physicians and can have a reasonable quality of life, but there is no cure. Diagnosis is often facilitated by reference to the NHS-funded national screening service which operates at Oxford. If the mutation involved can be identified, this can sometimes guide the treatment. In some cases there is no known effective treatment, and the patient may need extended palliative care. In the most severe cases, where breathing or other essential bodily functions are affected, CMS can be can be life-threatening or even fatal.

Most of the mutations associated with CMS are recessive, this means that both parents must carry the defective gene for any of their children to suffer from CMS. In a few rare cases, the mutation is dominant, which means that only one parent has to carry the defective gene for all their children to be affected. Genetic screening and counselling services are available to help families affected by these problems.

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