Congenital myasthenic syndromes
Last updated 13 Feb 2026
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Congenital myasthenic syndromes are a group of conditions that are characterised by weak muscles that tire easily (myasthenia). In people with these conditions, myasthenia typically begins shortly after birth or during early childhood. The most commonly affected muscles are the muscles in the head and neck (bulbar muscles) that control chewing and swallowing, speech, and facial expressions; the muscles that move the eyes and eyelids; and the muscles in the arms and legs. However, any of the muscles used for movement (skeletal muscles) can be affected.
Description
Congenital myasthenic syndromes are a group of conditions that are characterised by weak muscles that tire easily (myasthenia). In people with these conditions, myasthenia typically begins shortly after birth or during early childhood. The most commonly affected muscles are the muscles in the head and neck (bulbar muscles) that control chewing and swallowing, speech, and facial expressions; the muscles that move the eyes and eyelids; and the muscles in the arms and legs. However, any of the muscles used for movement (skeletal muscles) can be affected.
In individuals with congenital myasthenic syndromes, episodes of severe weakness or breathing problems may be triggered by fevers, infection, or tiring physical activity. The severity of the myasthenia varies greatly, from minor muscle weakness to severe weakness that may require wheelchair assistance.
Babies with congenital myasthenic syndromes may have feeding difficulties. Some affected babies may also experience short pauses in breathing (apnea) that can lead to a bluish appearance of the skin or lips (cyanosis). In severe instances, a lack of movement before birth can lead to joint deformities (contractures) that cause joint stiffness (arthrogryposis) and impair movement.
Children with congenital myasthenic syndromes may have speech problems (dysarthria) or swallowing difficulties (dysphagia). The development of motor skills, such as crawling or walking, may be delayed in these children.
Inheritance patterns
The source lists the following possible inheritance patterns: Autosomal recessive; Autosomal dominant. More than one pattern can apply in different cases.
Related genes
Other names
CMS
Congenital myasthenia
Congenital myasthenic syndrome
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Further reading and references
- Congenital myasthenic syndromes; MedlinePlus, National Library of Medicine.
- Abicht A, Muller JS, Lochmuller H. Congenital Myasthenic Syndromes Overview. 2003 May 9 [updated 2021 Dec 23]. In: Adam MP, Bick S, Mirzaa GM, Wallace SE, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2026. Available from http://www.ncbi.nlm.nih.gov/books/NBK1168/
- Estephan EP, Zambon AA, Thompson R, Polavarapu K, Jomaa D, Topf A, Helito PVP, Heise CO, Moreno CAM, Silva AMS, Kouyoumdjian JA, Morita MDP, Reed UC, Lochmuller H, Zanoteli E. Congenital myasthenic syndrome: Correlation between clinical features and molecular diagnosis. Eur J Neurol. 2022 Mar;29(3):833-842. doi: 10.1111/ene.15173. Epub 2021 Nov 17.
- Finsterer J. Congenital myasthenic syndromes. Orphanet J Rare Dis. 2019 Feb 26;14(1):57. doi: 10.1186/s13023-019-1025-5.
- Ohno K, Ito M, Ohkawara B. Review of 40 genes causing congenital myasthenic syndromes. J Hum Genet. 2025 Jun 18. doi: 10.1038/s10038-025-01355-9. Online ahead of print.
- Ohno K, Ohkawara B, Shen XM, Selcen D, Engel AG. Clinical and Pathologic Features of Congenital Myasthenic Syndromes Caused by 35 Genes-A Comprehensive Review. Int J Mol Sci. 2023 Feb 13;24(4):3730. doi: 10.3390/ijms24043730.
- Prior DE, Ghosh PS. Congenital Myasthenic Syndrome From a Single Center: Phenotypic and Genotypic features. J Child Neurol. 2021 Jul;36(8):610-617. doi: 10.1177/0883073820987755. Epub 2021 Jan 20.
- Ramdas S, Beeson D, Dong YY. Congenital myasthenic syndromes: increasingly complex. Curr Opin Neurol. 2024 Oct 1;37(5):493-501. doi: 10.1097/WCO.0000000000001300. Epub 2024 Jul 25.
- Spendiff S, Lochmuller H, Maselli RA. Congenital myasthenic syndromes. Int Rev Neurobiol. 2025;182:253-274. doi: 10.1016/bs.irn.2025.04.025. Epub 2025 May 16.
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