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Congenital myasthenic syndrome 2C(CMS2C)

MedGen UID:
903254
Concept ID:
C4225373
Disease or Syndrome
Synonym: Myasthenic syndrome, congenital, 2c, associated with acetylcholine receptor deficiency
 
Gene (location): CHRNB1 (17p13.1)
 
Monarch Initiative: MONDO:0014582
OMIM®: 616314

Definition

Congenital myasthenic syndrome associated with AChR deficiency is a disorder of the postsynaptic neuromuscular junction (NMJ) characterized clinically by early-onset muscle weakness with variable severity. Electrophysiologic studies show low amplitude of the miniature endplate potential (MEPP) and current (MEPC) resulting from deficiency of AChR at the endplate. Treatment with cholinesterase inhibitors or amifampridine may be helpful (summary by Engel et al., 2015). For a discussion of genetic heterogeneity of CMS, see CMS1A (601462). [from OMIM]

Clinical features

From HPO
Feeding difficulties
MedGen UID:
65429
Concept ID:
C0232466
Finding
Impaired ability to eat related to problems gathering food and getting ready to suck, chew, or swallow it.
Hypotonia
MedGen UID:
10133
Concept ID:
C0026827
Finding
Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist.
Myopathy
MedGen UID:
10135
Concept ID:
C0026848
Disease or Syndrome
A disorder of muscle unrelated to impairment of innervation or neuromuscular junction.
Muscle weakness
MedGen UID:
57735
Concept ID:
C0151786
Finding
Reduced strength of muscles.
Neonatal hypotonia
MedGen UID:
412209
Concept ID:
C2267233
Disease or Syndrome
Muscular hypotonia (abnormally low muscle tone) manifesting in the neonatal period.
EMG: decremental response of compound muscle action potential to repetitive nerve stimulation
MedGen UID:
892749
Concept ID:
C4021728
Finding
A compound muscle action potential (CMAP) is a type of electromyography (EMG). CMAP refers to a group of almost simultaneous action potentials from several muscle fibers in the same area evoked by stimulation of the supplying motor nerve and are recorded as one multipeaked summated action potential. This abnormality refers to a greater than normal decrease in the amplitude during the course of the investigation.
Respiratory insufficiency
MedGen UID:
11197
Concept ID:
C0035229
Pathologic Function
Impairment of gas exchange within the lungs secondary to a disease process, neoplasm, or trauma, possibly resulting in hypoxia, hypercarbia, or both, but not requiring intubation or mechanical ventilation. Patients are normally managed with pharmaceutical therapy, supplemental oxygen, or both.
Anti-acetylcholine receptor antibody positivity
MedGen UID:
868186
Concept ID:
C4022578
Finding
The presence of autoantibodies (immunoglobulins) in the blood circulation that react against neuromuscular junction acetylcholine receptors.

Recent clinical studies

Etiology

Navarro C, Teijeira S
Acta Myol 2003 May;22(1):11-4. PMID: 12966699

Diagnosis

Lehnhardt A, Lama A, Amann K, Matejas V, Zenker M, Kemper MJ
Pediatr Nephrol 2012 May;27(5):865-8. Epub 2012 Jan 8 doi: 10.1007/s00467-011-2088-2. PMID: 22228401

Therapy

Lehnhardt A, Lama A, Amann K, Matejas V, Zenker M, Kemper MJ
Pediatr Nephrol 2012 May;27(5):865-8. Epub 2012 Jan 8 doi: 10.1007/s00467-011-2088-2. PMID: 22228401

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