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Spinal muscular atrophy (SMA)

An inherited muscle-wasting condition, spinal muscular atrophy (SMA) may affect a person’s ability to crawl and walk, to move their arms, hands, head and neck, as well as their breathing and swallowing.

SMA is caused by a fault in a gene called Survival Motor Neuron 1 (SMN1). This gene carries the information required for the production of an important protein. When there is not enough of this protein, the nerve cells that help control the muscles for moving and breathing become damaged.

There are four main types of SMA:

  • SMA Type 1: Symptoms usually begin between 0 and 6 months.
  • SMA Type 2: Symptoms usually appear between 7 and 18 months of age.
  • SMA Type 3: There are two types of SMA Type 3:

– SMA Type 3a: Symptoms usually begin between 18 months and 3 years of age.

– SMA Type 3b: Symptoms will usually begin after 3 years of age.

  • SMA Type 4: Symptoms begin in adulthood.


You can find out more about SMA by reading these information factsheets.

About 100 children are born with this rare condition each year. There may be between 2,000 – 2,500 children and adults in the UK living with SMA.

A great amount of cutting edge research on SMA is taking place in the UK and worldwide. Improved understanding of the cause of the condition has already led to the development of potential treatments which are being tested in clinical trials. They mainly aim to restore the production of SMN protein in the nerve cells.

Find out more about SMA by watching our video on care and support available:


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