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Myasthenic syndrome, congenital, 7B, presynaptic, autosomal recessive(CMS7B)

MedGen UID:
1794157
Concept ID:
C5561947
Disease or Syndrome
Synonym: CMS7B
 
Gene (location): SYT2 (1q32.1)
 
Monarch Initiative: MONDO:0030341
OMIM®: 619461

Definition

Autosomal recessive presynaptic congenital myasthenic syndrome-7B (CMS7B) is characterized by severe generalized muscle weakness apparent from birth; decreased fetal movements may be apparent in utero. Affected infants have generalized hypotonia with poor cry and feeding, head lag, and facial muscle weakness with ptosis. Some patients may have respiratory involvement. Electrophysiologic studies show decreased compound muscle action potentials (CMAPs) and a decremental response to repetitive nerve stimulation. Treatment with 3,4-diaminopyridine and pyridostigmine may result in clinical improvement (summary by Bauche et al., 2020). [from OMIM]

Clinical features

From HPO
Knee flexion contracture
MedGen UID:
98042
Concept ID:
C0409355
Finding
A type of knee joint contracture in which the knee is in a fixed bent (flexed) configuration such that it cannot be straightened actively or passively.
Ankle flexion contracture
MedGen UID:
332440
Concept ID:
C1837407
Anatomical Abnormality
Mitral stenosis
MedGen UID:
44466
Concept ID:
C0026269
Disease or Syndrome
An abnormal narrowing of the orifice of the mitral valve.
Subvalvular aortic stenosis
MedGen UID:
90950
Concept ID:
C0340375
Disease or Syndrome
A fixed form of obstruction to blood flow across the left-ventricular outflow tract related to stenosis (narrowing) below the level of the aortic valve.
Failure to thrive
MedGen UID:
746019
Concept ID:
C2315100
Disease or Syndrome
Failure to thrive (FTT) refers to a child whose physical growth is substantially below the norm.
Dysphagia
MedGen UID:
41440
Concept ID:
C0011168
Disease or Syndrome
Difficulty in swallowing.
Congenital hypertrophic pyloric stenosis
MedGen UID:
196010
Concept ID:
C0700639
Congenital Abnormality
Pyloric stenosis, also known as infantile hypertrophic pyloric stenosis, is an uncommon condition in infants characterized by abnormal thickening of the pylorus muscles in the stomach leading to gastric outlet obstruction. Clinically infants are well at birth. Then, at 3 to 6 weeks of age, the infants present with projectile vomiting, potentially leading to dehydration and weight loss.
Dysarthria
MedGen UID:
8510
Concept ID:
C0013362
Mental or Behavioral Dysfunction
Dysarthric speech is a general description referring to a neurological speech disorder characterized by poor articulation. Depending on the involved neurological structures, dysarthria may be further classified as spastic, flaccid, ataxic, hyperkinetic and hypokinetic, or mixed.
Areflexia
MedGen UID:
115943
Concept ID:
C0234146
Finding
Absence of neurologic reflexes such as the knee-jerk reaction.
Cerebral atrophy
MedGen UID:
116012
Concept ID:
C0235946
Disease or Syndrome
Atrophy (wasting, decrease in size of cells or tissue) affecting the cerebrum.
High pitched voice
MedGen UID:
66836
Concept ID:
C0241703
Finding
An abnormal increase in the pitch (frequency) of the voice.
Easy fatigability
MedGen UID:
373253
Concept ID:
C1837098
Finding
Increased susceptibility to fatigue.
Cerebellar vermis hypoplasia
MedGen UID:
333548
Concept ID:
C1840379
Finding
Underdevelopment of the vermis of cerebellum.
Thin corpus callosum
MedGen UID:
1785336
Concept ID:
C5441562
Anatomical Abnormality
An abnormally thin corpus callous, due to atrophy, hypoplasia or agenesis. This term is intended to be used in situations where it is not known if thinning of the corpus callosum (for instance, as visualized by magnetic resonance tomography) is due to abnormal development (e.g. a leukodystrophy) or atrophy following normal development (e.g. neurodegeneration).
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.
Scoliosis
MedGen UID:
11348
Concept ID:
C0036439
Disease or Syndrome
The presence of an abnormal lateral curvature of the spine.
Elbow flexion contracture
MedGen UID:
98367
Concept ID:
C0409338
Acquired Abnormality
An elbow contracture that limits the ability of the elbow joint to be extended (straightened), meaning that the elbow is fixed in an flexed (bent) position.
Weakness of facial musculature
MedGen UID:
98103
Concept ID:
C0427055
Disease or Syndrome
Reduced strength of one or more muscles innervated by the facial nerve (the seventh cranial nerve).
Increased variability in muscle fiber diameter
MedGen UID:
336019
Concept ID:
C1843700
Finding
An abnormally high degree of muscle fiber size variation. This phenotypic feature can be observed upon muscle biopsy.
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.
Reduced forced vital capacity
MedGen UID:
337630
Concept ID:
C1846678
Finding
An abnormal reduction in the amount of air a person can expel following maximal inspiration.
Respiratory insufficiency due to muscle weakness
MedGen UID:
812797
Concept ID:
C3806467
Finding
Weak cry
MedGen UID:
65892
Concept ID:
C0234860
Finding
Weak voice
MedGen UID:
66033
Concept ID:
C0241700
Finding
Reduced intensity (volume) of speech.
Hypernasal speech
MedGen UID:
107884
Concept ID:
C0566620
Finding
A type of speech characterized by the presence of an abnormally increased nasal airflow during speech associated with structural abnormality of the nasal passages.
Tongue fasciculations
MedGen UID:
65987
Concept ID:
C0239548
Finding
Fasciculations or fibrillation affecting the tongue muscle.
Decreased fetal movement
MedGen UID:
68618
Concept ID:
C0235659
Finding
An abnormal reduction in quantity or strength of fetal movements.
Slow saccadic eye movements
MedGen UID:
232942
Concept ID:
C1321329
Finding
An abnormally slow velocity of the saccadic eye movements.
Limited extraocular movements
MedGen UID:
388060
Concept ID:
C1858427
Finding
Limited mobility of the eye within its socket.

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