SMA Type 1 Information

SMA Type 1 is a complex condition; there is a lot of information to take in, and every child with SMA is different.

The information on this page gives a general overview of SMA Type 1, the International Standards of Care for SMA and how they relate to children who have SMA, and signposts to the other most relevant areas of the website for families of children with this clinical diagnosis.

What is SMA Type 1?

SMA Type 1 is the most severe form of SMA with symptoms usually beginning between 0 and 6 months. 

Generally speaking, the earlier the onset of symptoms the more severe the condition. Babies are unable to sit without support and may be described as ‘non-sitters’. It‘s not possible to predict life expectancy accurately but for most children, without intervention for breathing difficulties, this has previously been estimated as less than two years1. Evidence suggests that since the International Standards of Care for SMA (see below) introduced more proactive managements in 2007, children have been living longer2

It’s important to remember that there are no distinct lines that distinguish the Types of 5qSMA from each other and that the impact varies greatly between individuals. Additionally, now that some are receiving drug treatments, there may be even greater variation in the impact of the SMA. 


When a clinical diagnosis is made, this is usually given as a Type of SMA. In general, this is based on the age at which symptoms first appear and the physical milestones reached:

SMA Type Usual age of symptoms onset Impact of muscle weakness on sitting / walking 
Type 1 Younger than 6 months Unable to sit or roll independently
Type 2 7 months – 18 months Able to sit but not walk independently
Type 3a 18 months – 36 months  Able to walk, though may lose this ability over time
Type 3b 3 years – 18 years Able to walk, though may lose this ability over time
Type 4 Over 18 years Mild walking (motor) difficulties

Clinical classification for SMA (adapted from RS Finkel et al, 2017, p.597)

When discussing best care and management, it’s therefore important to think not only about ‘clinical classification’, but also what physical milestones a child, young person or adult has reached. For simplicity these terms are used:

  • non-sitters - those who are unable to sit 
  • sitters - those who are able to sit but not walk 
  • walkers - those who are able to walk 

Signposting to other relevant information:

Please bear all the above information in mind when you’re  looking at these guides:
You may also find the section of our website Living with SMA helpful. This is being expanded from 1st August to include much more information, such as: equipment; transport; housing; leisure and holidays; financial, education, employment and social support, with information sorted separately for adults, teenagers, and parents of children.
1. Wang CH, Finkel RS, Bertini ES, Schroth M, Simonds A, Wong B, Aloysius A, Morrison L, Main M, Crawford TO, Trela A; Participants of the International Conference on SMA Standard of Care (2007) Consensus statement for standard of care in spinal muscular atrophy. J Child Neurol 22: 1027-1049. Available at: 
(Accessed: 29 August 2018)
2. Mercuri E, Finkel RS, Muntoni F, Wirth B, Montes J, Main M, Mazzone ES, Vitale M, Snyder B, Quijano-Roy S, Bertini E, Davis RH, Meyer OH, Simonds AK, Schroth MK, Graham RJ, Kirschner J, Iannaccone ST, Crawford TO, Woods S, Qian Y, Sejersen T; SMA Care Group. Diagnosis and management of spinal muscular atrophy: Part 1: recommendations for diagnosis, rehabilitation, orthopedic and nutritional care. Neuromuscul Disord. 2018 Feb;28(2):103-115. doi:10.1016/j.nmd.2017.11.005. Epub 2017 Nov 23. (Accessed 29 August 2018)