Spinal muscular atrophy type II

SMA type 2

• spinal muscular atrophy type II is a progressive condition, with onset later than type I, but equally relentless and ultimately fatal
  
  
• presentation is between three and twelve months old with muscle wasting, hypotonia, scoliosis and contracture, and is usually fatal by ten years old
  • children with type 2 SMA are able to sit unassisted at some point during their development, however they are never able to walk independently
  • form of SMA tends to manifest as progressive proximal leg weakness that is greater than weakness in the arms
    • there is hypotonia and areflexia on examination. Many of the comorbidities in this patient population are related to the orthopedic complications of bone and joint development in the setting of muscular weakness and progressive scoliosis, joint contractures and ankylosis of the mandible may develop
    • combination of scoliosis and intercostal muscle weakness can also result in significant restrictive lung disease
    • in these children, cognition is normal
      
      
• is autosomal recessive

Nusinersen improves motor function in SMA type II, based on moderate-certainty evidence (3).

Notes:

• term spinal muscular atrophy (SMA) refers to a group of genetic disorders all characterized by degeneration of anterior horn cells and resultant muscle atrophy and weakness
  • most common SMA, accounting for over 95% of cases, is an autosomal recessive disorder that results from a homozygous deletion or mutation in the 5q13 survival of motor neuron (SMN1) gene
• clinical severity of SMA correlates inversely with SMN2 gene copy number and varies from an extreme weakness and paraplegia of infancy to a mild proximal weakness of adulthood

Reference;

• Sugarman EA, et al. Pan-ethnic carrier screening and prenatal diagnosis for spinal muscular atrophy: clinical laboratory analysis of >72,400 specimens. Eur J Hum Genet. 2012; 20(1):27–32.
• Kolb JS, Tissel SpinalJT. Muscular Atrophy. Neurol Clin. 2015 November ; 33(4): 831–846.
• Walden RI et al. Drug treatment for spinal muscular atrophy types II and III . Cochrane Systematic Rev. January 2020.