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Key Facts about Spinal Muscular Atrophy

Spinal Muscular Atrophy Support UK and Muscular Dystrophy UK, both certified members of The Information Standard, have worked alongside The SMA Trust to produce this information sheet. It is written for anyone wanting to know some basic facts about Spinal Muscular Atrophy (SMA).

What is Spinal Muscular Atrophy?

Spinal Muscular Atrophy (SMA) is a rare, genetically inherited neuromuscular condition, of which there are several distinct types. SMA causes progressive loss of movement and muscle weakness as a result of muscle wasting (atrophy). The condition may affect crawling and walking ability, arm, hand, head and neck movement, breathing and swallowing.

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

The four main types of SMA vary greatly in severity:

  • The symptoms of SMA Type 1 appear within the first few months of life, sometimes before birth. It is the most severe form of SMA. Children are never able to sit unaided and, without intervention, rarely survive their second birthday.
  • The symptoms of SMA Type 2 usually appear between the ages of 7 and 18 months. The condition is severely physically disabling, with children never able to stand unaided. Though this is a serious neuromuscular condition that may shorten life expectancy, improvements in care standards mean that the majority of people can live long, fulfilling and productive lives.
  • The symptoms of SMA Type 3 appear after 18 months of age. Children are able to stand and walk, though they will experience reduced walking ability over time. It is a less disabling condition than SMA Types 1 or 2. Life expectancy for children diagnosed with SMA Type 3 is normal and most people can live long productive lives. 
  • The symptoms of SMA Type 4 appear in adulthood. It is a type of Adult Onset SMA and is not life-threatening.

The effects of each type of SMA vary greatly between individuals. Life expectancy varies between and within the different types of SMA.

For more information about the different types of SMA, visit:

How many people are affected?

  • In the UK, approximately 100 children are born with SMA each year.
  • One in every 6,000 - 10,000 babies worldwide are born with the condition.
  • At any one time it is thought that there are between 2,000 – 2,500 children and adults in the UK living with SMA.

How do people get SMA?

  • SMA is an autosomal recessive inherited neuromuscular condition. This means that two faulty copies of the SMN1 gene, one from each parent, are needed for a person to have the condition.
  • When two SMA carriers have a child together, there is a 1 in 4 (25%) chance that the child will have inherited both faulty copies of the SMN1 gene and will develop SMA. These chances are the same for each pregnancy.
  • When two SMA carriers have a child together, there is a 1 in 2 (50%) chance that the child will be a carrier.
  • Approximately one in 40 – 60 people is an SMA carrier, which equates to around 1 to 1.5 million people in the UK.

Is there a treatment or cure?

Although there is currently no cure for SMA, this does not mean that nothing can be done. There are a range of options aimed at managing symptoms, reducing complications of muscle weakness and maintaining the best quality of life. These are outlined in the internationally agreed Standards of Care for SMA.

There is a considerable amount of research into SMA taking place around the world. This research will not only improve our understanding of the condition but will also help to develop effective treatments.

One area of extensive research is the genetics of SMA and the underlying mechanisms that lead to damage of the nerve cells. The UK is a significant contributor to this, with several UK centres involved in clinical trials and international collaborations. This has led to very encouraging breakthroughs in developing treatments that increase the production of SMN protein by addressing the genetic fault.

  • Nusinersen‚Äč

One of these treatments is nusinersen (brand name Spinraza) developed by pharmaceutical companies Ionis and Biogen which have run clinical trials with infants and children affected by SMA Types 1, 2 or 3.

  • Expanded Access Programme for eligible infants with SMA Type 1

These clinical trials produced interim results that were sufficiently positive for Biogen, in autumn 2016, to open a global ‘compassionate use’ or ‘Expanded Access Programme’ (EAP) for eligible infants with SMA Type 1 who had not been on the trial. Unfortunately, progress with delivering this programme in the UK has been slow, creating immense frustration and distress for families, clinicians and supporting charities.

Any family wanting to explore the possibility of treatment for their child with SMA Type 1 should talk to their medical team about how to do this.

SMA Support UK is working with Muscular Dystrophy UK, the SMA Trust and TreatSMA to progress access to the EAP. More information on this programme and any updates on what progress there has been is available here.

  • Longer Term Availability 

On June 1st 2017, nusinersen was approved by the European Commission for marketing as a treatment for those with 5qSMA. This is when there is a genetic confirmation of a fault on the SMN1 gene that is found on Chromosome 5. 5qSMA includes SMA Types 1, 2 and 3. It also includes SMA Type 4, a type of Adult Onset SMA. However, there have not yet been any clinical trials of nusinersen with anyone with SMA Type 4.

Nusinersen’s future availability in the UK depends on the National Institute for Health and Care Excellence (NICE), NHS England, the Scottish Medicines Consortium and other authorities in the devolved nations recommending that the NHS funds the drug in England, Scotland, Wales and Northern Ireland. At this stage, it is not known what SMA Types will be considered for possible funding. Availability may also finally depend on the treatment readiness of specialist centres. 

SMA Support UK is working with Muscular Dystrophy UK, the SMA Trust and TreatSMA to progress longer term UK access to all those affected by 5qSMA. To find out more about nusinersen and any updates on what progress there has been towards this, please click here.

  • Other developments in research

SMA Support UK’s website also notifies the SMA community about latest developments with other drug treatments, the science behind them and what clinical trials and other research is going on: We alert people to new postings via our social media and monthly E- news. You can sign up for mailings here:        

Version 2.3
Authors: Spinal Muscular Atrophy Support UK and Muscular Dystrophy UK in collaboration with the SMA Trust
First published: July 2014
                                               Updated: June 2017
                                               Full review due: July 2017

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Whilst every effort is made to ensure that the information in this document is complete, correct and up to date, this cannot be guaranteed and SMA Support UK shall not be liable whatsoever for any damages incurred as a result of its use. SMA Support UK does not necessarily endorse the services provided by the organisations listed in our information sheets.


Montes, J., Gordon, A.M., Pandya, S., De Vivo, D.C. and Kaufmann, P. (2009) ‘Clinical outcome measures in spinal muscular atrophy’, Journal of Child Neurology, 24(8), pp. 968-978.

Standards of Care for SMA: A Family Guide. Available at:

Wang, C.H., Finkel, R.S., Bertini, E.S., Schroth, M., Simonds, A., Wong, B., Aloysius, A., Morrison, L., Main, M., Crawford, T.O. and Trela, A. (2007) ‘Consensus statement for standard of care in spinal muscular atrophy’, Journal of Child Neurology, 22(8), pp. 1027-49. Available for free download at: