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.