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Infantile-onset X-linked spinal muscular atrophy

Disease definition

A rare form of spinal muscular atrophy characterized by the neonatal onset of severe hypotonia, areflexia, profound weakness, multiple congenital contractures, facial dysmorphic features (myopathic face with open, tent-shaped mouth), cryptorchidism, and mild skeletal abnormalities (i.e. kyphosis, scoliosis), that is often preceded by polyhydramnios and reduced fetal movements in utero and followed by bone fractures shortly after birth. Muscle weakness is progressive and chest muscle involvement eventually leads to ventilatory insufficiency and respiratory failure.


Classification level: Disorder
  • Synonym(s):
    • SMAX2
    • Spinal muscular atrophy with arthrogryposis
    • X-linked distal arthrogryposis multiplex congenita
    • X-linked spinal muscular atrophy type 2
  • Prevalence: <1 / 1 000 000
  • Inheritance: X-linked recessive 
  • Age of onset: Neonatal
  • ICD-10: G12.1
  • ICD-11: 8B61.Y
  • OMIM: 301830
  • UMLS: C1844934
  • MeSH: C535380
  • GARD: 8521
  • MedDRA: -

Detailed information


Disease review articles

Clinical Outcome Assessment (COA)

  • Patient-Centered Outcome Measures (PCOMs)
  • English (2023) - PROQOLIDTM
ERN produced/endorsed by ERN(s)   FSMR produced/endorsed by FSMR(s)
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