Table of Contents

Congenital Myasthenic Syndromes (CMS)

What are congenital myasthenic syndromes?

Congenital myasthenic syndromes (CMS) are a group of conditions that are all characterized by muscle weakness that is exacerbated by physical activity. The facial muscles are typically impacted the most, but any of the skeletal muscles can be affected. 

What are the symptoms of congenital myasthenic syndromes?

The severity of symptoms varies greatly between individuals. Some are unable to walk, while others experience minor weakness. 

Weakness of the facial muscles can cause difficulty with chewing and swallowing, and it may also affect the muscles in the eyelids. This makes it hard to keep the eyes open. 

This condition often has a large impact in infancy, with babies having feeding difficulties, delays in the development of motor skills, and issues with crawling and walking. 

If one has a severe form of CMS, they can experience breathing issues that are triggered by a fever or infection. They can have episodes of apnea that lead to bluish skin and/or lips. 

What causes congenital myasthenic syndromes?

There are a number of genes that can mutate and result in CMS. The major one that accounts for half of cases is CHRNE, with others being DOK7, CHAT, RAPSN, and COLQ. All of these genes are responsible for the instructions for proteins that are needed for the neuromuscular junction to function properly. When they are mutated, the signaling between muscle cells and nerve cells is disrupted, leading to the characteristic symptoms. 

These genes are typically inherited in an autosomal recessive pattern. In very rare cases they are inherited in an autosomal dominant pattern or are the result of a new mutation. 

How are congenital myasthenic syndromes diagnosed?

Doctors will first perform a clinical examination and look for the characteristic symptoms. Tests that will be used include electrodiagnostic testing, geneting testing, EMGs, RNS tests, sleep studies, blood tests, muscle biopsies, and pulmonary function tests. 

What are the treatments for congenital myasthenic syndromes?

Treatment for this condition is symptomatic. Doctors may prescribe albuterol, potassium channel blockers, AChE inhibitors, ephedrine, and other medications. They also heavily suggest physical, occupational, and speech therapy. 

Where can I find out more about congenital myasthenic syndromes?

CMS Articles