Spinal Muscular Atrophy

Characterised by slowly progressive muscle weakness and atrophy of the limb muscles associated with motor neurone loss in the spinal cord

Aetiology

  • Genetic - autosomal recessive mutation of the SMN1 gene

Pathophysiology

  • Loss of anterior horn cells

Clinical presentation

Symptoms

  • Muscle weakness and wasting
    • Proximal skeletal muscles
    • Respiratory muscles

Signs

  • General clinical signs are that of lower motor neurone weakness - hypotonia, flaccid weakness, reduced/abscent tendon reflexes, normal/absent plantar reflexes, muscle fasciculation, muscle atrophy

Investigations

  • Creatine kinase - normal or slightly raised
  • Genetic testing
  • Electrophysiology testing shows diminished nerve signals
  • Muscle biopsy - muscle fibre atrophy

Management

  • Treatments have been developed that involve mRNA modification - correction of SM1 deficiency by altering splicing of SMN2 mRNA
    • Injection into spinal canal
    • Effective in preventing progression but do not reverse the loss of anterior horn cells - disability can be prevented by starting treatment at birth