SMA Type 3 Information
The information on this page gives a general overview of SMA Type 3, 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 3?
- SMA Type 3a: symptoms usually begin between 18 months and 3 years of age. Children can stand and walk, though this will become more difficult with age and they will need more support over time.
- SMA Type 3b: symptoms usually begin after 3 years. Difficulties with standing and walking usually occur later than they do for children with SMA Type 3a.
Depending upon the individual impact of their condition, children and adults with SMA Type 3 may be described as ‘sitters’ or ‘walkers’. Very few people with SMA Type 3 have breathing problems and their life expectancy isn’t usually affected1. Most can live long, fulfilling lives.
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:
- 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 3
- Looking after your child who has SMA Type 3 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’.
- The Genetics of 5q SMA tells you more about the inheritance patterns, what it means for future pregnancies and for other family members