Spinal muscular atrophy (SMA)

An inherited muscle-wasting condition, 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.

The four main types of SMA vary greatly in severity and the effects vary between individuals:

  • SMA Type 1. Symptoms appear within the first few months of life, sometimes before birth. Children are never able to sit unaided and rarely survive their second birthday.
  • SMA Type 2. Symptoms usually appear between 7-18 months of age. Children are never able to stand unaided. Although the condition may shorten life-expectancy, improvements in care standards mean that the majority of people can live long and fulfilling lives.
  • SMA Type 3. Symptoms appear after 18 months of age. Children are able to stand and walk, but will become less able to walk over time. Life-expectancy is normal and most people can live long independent lives.
  • SMA Type 4 (also known as Adult Onset SMA). Symptoms appear in adulthood. It is not a life-threatening condition.

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.


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