Spinal muscular atrophy

Question 1

What is spinal muscular atrophy?

Answer 1

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

Question 2

Describe the genetics of spinal muscular atrophy

Answer 2

Autosomal recessive mutation of the SMN1 gene

Question 3

Describe the pathophysiology of spinal muscular atrophy

Answer 3

Loss of anterior horn cells

Question 4

What are some symptoms of spinal muscular atrophy?

Answer 4

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

Question 5

What are some clinical signs of spinal muscular atrophy?

Answer 5

Hypotonia
Flaccid weakness
Reduced/abscent tendon reflexes,
Normal/absent plantar reflexes
Muscle fasciculation
Muscle atrophy

Question 6

What are the 4 types of SMA dependant on history?

Answer 6

Type 1 - Never sits, median age of death or ventilation - 13.5 months

Type 2 - Never walks independently

Type 3 - Childhood onset

Type 4 - Adult onset

Question 7

What investigations are required in SMA?

Answer 7

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

Question 8

What new treatment has been developed for treatment of SMA?

Answer 8

Drugs that perform correction of SM1 deficiency by altering splicing of SMN2 mRNA

Effective in preventing progression but do not reverse the loss of anterior horn cells - disability can be prevented by starting treatment at birth