Diagnosis/Testing

The diagnosis of CMS is based on clinical findings, a decremental EMG response of the compound muscle action potential (CMAP) on low-frequency (2-3 Hz) stimulation, absence of anti-acetylcholine receptor (AChR) and anti-MuSK antibodies in the serum, and lack of improvement of clinical symptoms with immunosuppressive therapy. Mutations in one of multiple genes encoding proteins expressed at the NMJ are currently known to be associated with subtypes of CMS, including the genes encoding different subunits of the acetylcholine receptor:

  • • CHRNE (eAChR subunit)
  • • CHRNA1 (aAChR subunit)
  • • CHRNB1 (pAChR subunit)
  • • CHRND (5AChR subunit)
  • • AGRN encoding agrin
  • • CHAT encoding choline O-acetyltransferase
  • • COLQ encoding acetylcholinesterase collagenic tail peptide
  • • DOK7 encoding protein Dok-7
  • • GFPT1 encoding glucosamine-fructose-6-phosphate aminotransferase 1
  • • MUSK encoding muscle, skeletal receptor tyrosine protein kinase
  • • RAPSN encoding rapsyn (43-kd receptor-associated protein of the synapse)
  • • SCN4A encoding the sodium channel protein type 4 subunit alpha
 
Source
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