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Congenital myasthenic syndrome 3B(CMS3B)

MedGen UID:
909404
Concept ID:
C4225371
Disease or Syndrome
Synonyms: CHRND-Related Congenital Myasthenic Syndrome; CMS3B; Myasthenic syndrome, congenital, 3B, fast-channel
 
Gene (location): CHRND (2q37.1)
 
Monarch Initiative: MONDO:0014584
OMIM®: 616322

Definition

Fast-channel congenital myasthenic syndrome (FCCMS) is a disorder of the postsynaptic neuromuscular junction (NMJ) characterized by early-onset progressive muscle weakness. The disorder results from kinetic abnormalities of the acetylcholine receptor channel, specifically from abnormally brief opening and activity of the channel, with a rapid decay in endplate current and a failure to reach the threshold for depolarization. Treatment with pyridostigmine or amifampridine may be helpful; quinine, quinidine, and fluoxetine should be avoided (summary by Sine et al., 2003 and 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.
Fatigable weakness
MedGen UID:
451076
Concept ID:
C0947912
Disease or Syndrome
A type of weakness that occurs after a muscle group is used and lessens if the muscle group has some rest. That is, there is diminution of strength with repetitive muscle actions.
Easy fatigability
MedGen UID:
373253
Concept ID:
C1837098
Finding
Increased susceptibility to fatigue.
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.
Muscle weakness
MedGen UID:
57735
Concept ID:
C0151786
Finding
Reduced strength of muscles.
Neck muscle weakness
MedGen UID:
66808
Concept ID:
C0240479
Finding
Decreased strength of the neck musculature.
Facial palsy
MedGen UID:
87660
Concept ID:
C0376175
Disease or Syndrome
Facial nerve palsy is a dysfunction of cranial nerve VII (the facial nerve) that results in inability to control facial muscles on the affected side with weakness of the muscles of facial expression and eye closure. This can either be present in unilateral or bilateral form.
Neonatal hypotonia
MedGen UID:
412209
Concept ID:
C2267233
Disease or Syndrome
Muscular hypotonia (abnormally low muscle tone) manifesting in the neonatal period.
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.
Weak cry
MedGen UID:
65892
Concept ID:
C0234860
Finding
High palate
MedGen UID:
66814
Concept ID:
C0240635
Congenital Abnormality
Height of the palate more than 2 SD above the mean (objective) or palatal height at the level of the first permanent molar more than twice the height of the teeth (subjective).
Decreased fetal movement
MedGen UID:
68618
Concept ID:
C0235659
Finding
An abnormal reduction in quantity or strength of fetal movements.
Ptosis
MedGen UID:
2287
Concept ID:
C0005745
Disease or Syndrome
The upper eyelid margin is positioned 3 mm or more lower than usual and covers the superior portion of the iris (objective); or, the upper lid margin obscures at least part of the pupil (subjective).
Ophthalmoplegia
MedGen UID:
45205
Concept ID:
C0029089
Sign or Symptom
Paralysis of one or more extraocular muscles that are responsible for eye movements.

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