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.
Diagnosis
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:
- What is SMA introduces the types of 5q SMA, what causes it, how it’s inherited and how many people are affected
- Symptoms, diagnosis and effects of 5q SMA includes SMA Type 1
- Looking after your child who has SMA Type 1 is for parents whose child has recently been given this clinical diagnosis
- Guide to the 2017 International Standards of Care for SMA is a user friendly summary. Each chapter discusses an aspect of care and management and clearly outlines what is appropriate for ‘non-sitters’, ‘sitters’ and ‘walkers’.
- Nusinersen treatment for infants with SMA Type 1 provides a summary for parents who want to know more about this possibility so that they can discuss this with their child’s medical team
- The Genetics of 5q SMA tells you more about the inheritance patterns, what it means for future pregnancies and for other family members
(Accessed: 29 August 2018)
