Congenital myasthenic syndrome

Congenital myasthenic syndrome is characterized by a deficiency in the acetylcholine receptor, a neurotransmitter essential for the transmission of nerve impulses to the muscles that we voluntarily control.

Congenital myasthenic congenital syndrome (CMS) is a group of rare inherited disorders that affect neuromuscular transmission and result in a condition of muscle weakness that is accentuated by exertion. In most cases CMS begins in early childhood, but it is possible for it to begin in adulthood. It may be inherited autosomal recessively or dominantly.

Up to 35 genes are involved in this group of disorders, which are classified into 14 groups according to pathomechanical characteristics.

Symptoms

The main symptoms of CMS include muscle fatigue, muscle weakness, muscle hypoplasia, and minor facial abnormalities such as low-set ears and high-arched palate in some patients.

As mentioned, there are 14 types of congenital myasthenic congenital syndrome, each with a variety of structural abnormalities in the neuromuscular junction. The pattern of inheritance, clinical symptoms, electrophysiology, and response to therapy vary depending on the type. Some of the subtypes that may be encountered include: “familial myasthenia infantile” and “congenital absence of acetylcholinesterase” which usually presents in childhood or adolescence with generalized weakness and decreased muscle tone.

Disease management

Symptom management and drug treatment depends on the type of CMS. When the affected gene is RAPSN, drugs that can alleviate symptoms such as cholinesterase inhibitors are available.

Genes analyzed

RAPSN

Bibliography

Abicht A, Müller JS, Lochmüller H. Congenital Myasthenic Syndromes Overview. 2003 May 9 [updated 2021 Dec 23]. In: Adam MP, Mirzaa GM, Pagon RA, Wallace SE, Bean LJH, Gripp KW, Amemiya A, editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2023.

Milone M, Shen XM, Selcen D, et al. Myasthenic syndrome due to defects in rhapsyn: Clinical and molecular findings in 39 patients. Neurology. 2009 Jul 21;73(3):228-35.

Ohno K, Ohkawara B, Shen XM, et al. 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.

Ohno K, Engel AG. Lack of founder haplotype for the rhapsyn N88K mutation: N88K is an ancient founder mutation or arises from multiple founders. J Med Genet. 2004 Jan;41(1):e8.

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