There are several different types of spinal muscular atrophy (SMA), which start at different ages.
They can all cause weakness and difficulty moving, but how bad these problems are varies.
Intelligence and learning ability aren't affected by any type of SMA.
Children with type 1 SMA show symptoms in the first 6 months of life.
Babies with the condition:
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.
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:
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.
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:
Type 3 SMA doesn't usually affect life expectancy.
Spinal Muscular Atrophy UK has more information about type 3 SMA.
Type 4 SMA, also called adult-onset SMA, usually begins in early adulthood.
Someone with the condition may have:
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.
There are several other types of SMA, including: