Overview Congenital myasthenic syndrome (CMS)

Congenital myasthenic syndrome (CMS) is a group of inherited conditions that are present from birth or early childhood.

Many different genetic mutations in a series of different genes can cause CMS. These mutations cause problems with the way the messages are transmitted from the nerves to the muscles, causing weakness (myasthenia) and causing the muscles to tire easily (fatigue).

Muscle weakness varies depending on the type of genetic mutation, so impact on mobility ranges from mild to severe. In the less severe cases, the condition may cause drooping eyelids and fatigue, but only mildly interferes with daily life. In the more severe cases however, where breathing or other essential bodily functions are greatly affected, CMS can be life-threatening or even fatal.

Symptoms usually start in early childhood, although there are some adult onset cases. Symptoms are similar to those of myasthenia gravis but can’t be treated with the steroids and treatments, which are effective on myasthenia gravis.

Is Congenital myasthenic syndrome the same as myasthenia gravis?

No. When people talk about myasthenia, they usually mean myasthenia gravis – an autoimmune condition like rheumatoid arthritis, which can affect children and adults. Myasthenia gravis causes the body to produce proteins that block and destroy some of their receptors, making messaging from nerves to muscles less effective. Myasthenia gravis can be treated with steroids, immunosuppressive drugs and thymectomy (surgical removal of the thymus gland).