Type 1 SMA (young babies)
Children with type 1 SMA show symptoms in the first 6 months of life.
Babies with the condition:
- have very weak and floppy arms and legs (hypotonia)
- have problems moving, eating, breathing, and swallowing
- are unable to raise their head or sit without support
Most babies with type 1 SMA die during the first few years of life, usually as a result of serious breathing difficulties.
Spinal Muscular Atrophy UK has more information about type 1 SMA.
Type 2 SMA (older babies and toddlers)
Children with type 2 SMA usually show symptoms when they're 7-18 months old. The symptoms are less severe than type 1.
Children with the condition may:
- be able to sit up without help, but not stand or walk
- have weak arms or legs
- have shaking (tremors) in their fingers and hands
- later develop problems with their joints, such as an unusually curved spine (scoliosis)
- have weak breathing muscles and difficulty coughing – this can put them at risk of chest infections
Type 2 SMA can shorten life expectancy, but most children with it survive into adulthood and can have long, fulfilling lives.
Spinal Muscular Atrophy UK has more information about type 2 SMA.
Type 3 SMA (children and young adults)
People with type 3 SMA usually develop symptoms after 18 months of age, but this is very variable and sometimes it may not appear until late childhood or early adulthood.
People with the condition:
- are able to stand and walk without help, although they may find walking or getting up from a sitting position difficult
- may have balance problems, difficulty running or climbing steps, and a slight shaking in their fingers
- may find walking gets gradually harder over time, and they may eventually lose the ability to walk when they're older
Type 3 SMA doesn't usually affect life expectancy.
Spinal Muscular Atrophy UK has more information about type 3 SMA.
Type 4 SMA (adults)
Type 4 SMA, also called adult-onset SMA, usually begins in early adulthood.
Someone with the condition may have:
- weakness in the hands and feet
- difficulty walking
- shaking and twitching muscles
Type 4 SMA gets slowly worse over time, but doesn't normally cause problems with breathing or swallowing. It doesn't affect life expectancy.
Spinal Muscular Atrophy UK has more information about type 4 SMA.
Other types of SMA
There are several other types of SMA, including:
- spinal muscular atrophy with respiratory distress (SMARD) – a type of SMA that's usually diagnosed during a baby's first year of life and can cause serious breathing problems
- Kennedy's disease, or spinobulbar muscular atrophy (SBMA) – a rare type of SMA that only affects men and usually starts in middle age; it doesn't usually affect life expectancy
- distal spinal muscular atrophy (DSMA) – a type of SMA that mainly affects the hands, feet, lower arms, and lower legs