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Start free with EleplanCongenital myasthenic syndrome
ORPHA:590Disease
Also called CMS
What it is
A rare genetic neuromuscular disease characterized by impaired transmission at the neuromuscular junction, typically presenting in infancy or childhood, although later onset is possible. The hallmark symptom is muscle fatigability, frequently accompanied by ocular manifestations (ptosis, ophthalmoparesis), bulbar involvement (dysphagia), a generalized weakness, which can lead to potentially life-threatening respiratory insufficiency.
Key facts
- Prevalence
- 1-9 / 1 000 000 (Europe)
- Age of onset
- Infancy, Neonatal
- Inheritance
- Autosomal dominant, Autosomal recessive
- Classified as
- Disease
Prevalence figures describe populations, not individuals, and are often estimates from a single study. Where the figure is an incidence or a birth prevalence, it says so.
Signs and symptoms
Very common80–99%
10Common30–79%
20- Apneic episodes precipitated by illness, fatigue, stress
- Arthrogryposis multiplex congenita
- Ataxia
- Bulbar palsy
- Central sleep apnea
- Choking episodes
- Cyanosis
- Decreased fetal movement
- Easy fatigability
- EMG: impaired neuromuscular transmission
- Episodic respiratory distress
- Gait disturbance
- Generalized muscle weakness
- Hypernasal speech
- Intellectual disability
- Muscle fiber atrophy
- Nasal regurgitation
- Ophthalmoplegia
- Recurrent respiratory infections
- Spinal deformities
Sometimes5–29%
20- Areflexia
- Distal amyotrophy
- Distal lower limb muscle weakness
- Dysphonia
- EMG: myopathic abnormalities
- High palate
- Hypotonia
- Kyphoscoliosis
and 12 more in this range
These ranges are how often a sign appears across everyone diagnosed, not a prediction for one person — most people have some of these and not others. Orphanet also records findings that are specifically absent in this disease; those are in the data but not listed here.
Genes reported in subtypes
Orphanet records these genes on 1 more specific entry under this disorder, not on this entry itself:
A well-studied disease is usually split into subtypes, and the gene is curated on whichever one the evidence belongs to. Open a subtype to see which gene goes with it.
ICD-10 codes
ICD-10 has no distinct code for most rare diseases, so many are filed under the nearest available one. A shared code identifies the group, not this disease — the ORPHAcode above is what identifies it.
Related health topics
Reached through the ICD-10 categories this disease is filed under, so these describe the broader group rather than this disease specifically.
Cross-references
Orphadata Science: Free access data from Orphanet. © INSERM 1999. Data version 2026-06-23. Available under CC BY 4.0. This is a reference, not medical advice.
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