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Start free with EleplanProximal spinal muscular atrophy type 2
ORPHA:83418Clinical subtype
Also called Intermediate spinal muscular atrophy · SMA type 2 · SMA type II · SMA-II · SMA2
What it is
A rare genetic motor neuron disorder characterized by degeneration of alpha motor neurons in the spinal cord and lower brainstem manifesting between 6 and 18 months of age with progressive, predominantly proximal muscle weakness. Classically, before the introduction of disease-modifying therapies, patients with proximal spinal muscular atrophy (SMA) type 2 learned to sit, but never achieved independent ambulation.
Key facts
- Prevalence
- 1-9 / 100 000
- Age of onset
- Infancy
- Inheritance
- Autosomal recessive
- Classified as
- Clinical subtype
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.
Genes
2 modifying genes — variants that can change how the disease behaves, not cause 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.
Benefit programs to look at
Programs whose eligibility touches the same ICD-10 categories. Eligibility is decided by the administering agency, never by this page.
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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