Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a rare autosomal recessive condition that causes a progressive loss of motor neurones, leading to progressive muscular weakness.

Spinal muscular atrophy affects the lower motor neurones in the spinal cord. This means there will be lower motor neurone signs, such as fasciculations, reduced muscle bulk, reduced tone, reduced power and reduced or absent reflexes.



There are four categories of spinal muscular atrophy that are numbered from most to least severe. SMA type 2 is the most common type.

SMA type 1 has an onset in the first few months of life, usually progressing to death within 2 years.

SMA type 2 has an onset within the first 18 months. Most never walk, but survive into adulthood.

SMA type 3 has an onset after the first year of life. Most walk without support, but subsequently loose that ability. Respiratory muscles are less affected and life expectancy is close to normal.

SMA type 4 has an onset in the 20s. Most will retain the ability to walk short distances but require a wheelchair for mobility. Everyday tasks can lead to significant fatigue. Respiratory muscles and life expectancy are not affected.



There is no cure for spinal muscular atrophy. Management is supportive and involves the multi-disciplinary team.

Physiotherapy can be helpful in maximising strength in the muscles and retaining respiratory function. Splints, braces and wheelchairs can be used to maximise function.

Respiratory support with non-invasive ventilation may be required to prevent hypoventilation and respiratory failure, particularly during sleep. Children with SMA type 1 may require a tracheostomy with mechanical ventilation, which can dramatically extend life by supporting failing respiratory muscles.

Percutaneous endoscopic gastrostomy (PEG) feeding may be required when a weak swallow makes swallowing unsafe.


Last updated January 2020
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