GTR Home > Conditions/Phenotypes > Myasthenic syndrome, congenital, fast-channel

Summary

Congenital myasthenic syndromes are genetic disorders of the neuromuscular junction that can be classified by the site of the transmission defect: presynaptic, synaptic, and postsynaptic. FCCMS is an autosomal recessive form of postsynaptic CMS. For a discussion of genetic heterogeneity of CMS, see 608931. In most cases, FCCMS is caused by recessive gain-of-function mutations that decrease activity of the AChR by slowing the rate of opening of the receptor channel, speeding the rate of closure of the channel, or decreasing the number of openings of the channel during ACh occupancy. The result is failure to achieve threshold depolarization of the endplate and consequent failure to fire an action potential. FCCMS is the physiologic opposite of slow-channel CMS (SCCMS; 601462), but the 2 disorders cause similar phenotypes. Sine et al. (2003) provided a detailed analysis of the mechanistic diversity underlying fast-channel congenital CMS. Autosomal dominant inheritance has rarely been described. [from OMIM]

Associated genes

  • Also known as: ACHRA, ACHRD, CHRNA, CMS2A, FCCMS, SCCMS, CHRNA1
    Summary: cholinergic receptor, nicotinic, alpha 1 (muscle)

  • Also known as: ACHRD, CMS2A, FCCMS, SCCMS, CHRND
    Summary: cholinergic receptor, nicotinic, delta (muscle)

  • Also known as: ACHRE, CMS1D, CMS1E, CMS2A, FCCMS, SCCMS, CHRNE
    Summary: cholinergic receptor, nicotinic, epsilon (muscle)

Clinical features

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  • Gowers sign
  • Weak cry
  • Respiratory insufficiency due to muscle weakness
  • Easy fatigability
  • Bulbar palsy
  • Poor suck
  • Dysarthria
  • Arthrogryposis multiplex congenita
  • Generalized muscle weakness
  • Dysphagia
  • Decreased miniature endplate potentials
  • Macrotia
  • Type 2 muscle fiber atrophy
  • Micrognathia
  • Ophthalmoparesis
  • High palate
  • Ptosis
  • Muscular hypotonia
  • Motor delay
  • Scoliosis
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