Spinal Muscular Atrophy

Question 1

what is spinal muscular atrophy?

Answer 1

rare genetic condition that causes the loss of anterior horn cells (causing loss of motor neurones in spinal cord)

Question 2

what causes spinal muscle atrophy

Answer 2

Autosomal recessive disorder

SMN1 deficiency on chromosome 5 (this is needed for survival of anterior horn cells)

Question 3

symptoms of spinal muscle atrophy?

Answer 3

Muscle weakness and wasting:
-proximal skeletal muscles
-respiratory muscles

SIGNS:
affects lower motor neurones- will have lower motor neurone signs:
-fasciculations
-hypotonia (will feel resistance on passive movement)
-reduced muscle bulk
-reduced reflexes

Question 4

signs of spinal muscle atrophy?

Answer 4

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

Question 5

Investigations for spinal muscular atrophy?

Answer 5

Creatine kinase - normal or slightly raised
Genetic testing (autosomal recessive condition SMN1 deficiency on chromosome 5)

Electrophysiology testing shows diminished nerve signals
Muscle biopsy - muscle fibre atrophy

Question 6

Management- spinal muscle atrophy?

Answer 6

mRNA modification through spinal cord injection
-correction of SMN1 deficiency by altering splicing of SMN2 mRNA
-effective in preventing progression but does not reverse loss of anterior horn cells