Congenital Myasthenic Syndrome, CHAT-Related

Gene : CHAT

What is Congenital Myasthenic Syndrome?

Congenital myasthenic syndrome (CMS) is a group of inherited disorders characterized by skeletal muscle weakness and fatigue, including facial muscles and muscles controlling swallowing and sucking. Onset is usually at birth, but disease symptoms can begin in childhood and, rarely, adulthood. Severity of the disorder is variable, but generally, the earlier the symptoms appear, the more pronounced the disease is likely to be. Affected infants may be delayed in learning to crawl or walk and later on display difficulty running or climbing stairs. They may also have joint deformities and breathing problems. There is no cure for CMS; however there are drugs available for some types of CMS that help to improve muscle strength and endurance. Also, medical surveillance and care may help to improve some symptoms and overall condition of life. CMS is caused by pathogenic variants in multiple genes, including RAPSN, CHAT, DOK7, and CHRNE, which accounts for the majority of CMS cases.

How is Congenital Myasthenic Syndrome inherited?

CMS is usually inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

What does it mean to be a carrier?

There are generally no signs or symptoms associated with being a carrier for CMS. However, the risk to have a child affected with CMS is increased. Testing of reproductive partners is recommended for carriers of CMS.

How common is Congenital Myasthenic Syndrome?

It is unknown exactly how often CMS occurs worldwide, although it is estimated to occur in 1 in 500,000 newborns in Europe.

Family References and Resources
Clinician References
What is Analyzed?
  • Full gene sequencing
Affected Systems


Carrier Rates
Detection Rate
Carrier Frequency
General Population > 99% 1 in 632

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