SMA Type 1
The symptoms and effects of SMA Type 1 usually begin from birth or within the first few weeks or months of life. Generally, the earlier the onset of symptoms, the more severe the condition.
Each child is affected differently, but in general, babies with early onset SMA are:
- bright, alert and responsive; their intelligence isn’t affected
- able to smile and frown as their facial muscles aren’t severely affected
- often described as ‘floppy’ babies due to their low muscle tone (hypotonia) and severe muscle weakness.
- unable to support or lift their head due to their weak neck muscles
- unable to sit unsupported and have difficulty rolling over
- able to move their hands and fingers but have difficulty lifting their arms and legs
They have:
- breathing muscle weakness, which can cause a weak cry and difficulties with breathing and coughing
- an increased chance of chest infections, which can be lifethreatening
- difficulty swallowing their saliva and other secretions, which may make them sound chesty or make them cough
- difficulties feeding and gaining weight
- an increased risk of fluids or food passing into their lungs (aspiration), which can cause choking and, sometimes, chest infections or pneumonia
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 years. Evidence suggests that since the International Standards of Care for SMA introduced more proactive managements in 2007, children have been living longer.
SMA Type 2
The symptoms and effects of SMA Type 2 usually begin between 6 and 18 months of age. Generally, the earlier the onset of symptoms, the more severe the condition.
Each child is affected differently, but in general, children with SMA Type 2 are usually bright and engaging. However, due to SMA, they are likely to experience:
- muscle weakness on both sides of their body
- muscle weakness closest to the centre of their body as these muscles are more severely affected than muscles furthest away
- difficulties moving their arms, but their hands and fingers less so
- difficulties lifting their legs - legs that are weaker than their arms
As they get older, their intellectual and sexual development isn’t affected but SMA usually causes them:
- muscle weakness that may make it difficult for them to keep up with their daily activities. For example, if they have been able to crawl or roll, they may lose this ability
- a tendency to become weaker after infections and at times of major growth spurts such as puberty
- weak breathing muscles, making it difficult for them to cough effectively and more vulnerable to chest infections
- muscles supporting the spinal column that are weak meaning that most children will develop a sideways curvature of their spine6 (scoliosis)
- reduced ability to move so that some joints may become tight (contractures) and further restrict their range of movement
Children and adults will need help with daily tasks like washing, dressing and undressing. Though their bladder and bowel control isn’t usually affected, they will need help transferring from their wheelchair to the toilet.
SMA Type 2 can weaken chewing and swallowing muscles. For some children, their tongue and shoulder muscles may twitch and they may have a slight tremor in their hands.
Though this is a serious condition that may shorten life expectancy, improvements in care standards mean that the majority of people can live long, fulfilling lives.
SMA Type 3
The symptoms and effects of SMA Type 3a usually begin between 18 months and 3 years.
The symptoms and effects of SMA Type 3b usually begin after 3 years, but before adulthood.
Each child is affected differently, but in general, children with SMA Type 3 are bright and engaging. However, their SMA causes:
- muscle weakness on both sides of their body
- muscle weakness closest to the centre of their body as these muscles are more severely affected than muscles furthest away
- legs that are weaker than arms
As they get older, their intellectual and sexual development isn’t affected, but their SMA usually causes them to have:
- difficulties with standing and walking. This usually happens later for children with SMA Type 3b than for children who develop the first symptoms at an earlier age
- difficulties keeping up with daily activities. For example, if they have been able to walk or climb stairs, they may lose this ability. Some children may fall more easily because of their muscle weakness. If they’re sitting on the floor they may need help to get up - muscles supporting the spinal column that are weakened. This means that some children develop a sideways curvature of their spine (scoliosis)
- a reduced ability to move due to some joints becoming tight (contractures), restricting their range of movement.
- a tendency to become weaker after infections and at times of major growth such as puberty.
Some children, young people and adults will need help with daily tasks like washing, dressing and undressing. Though their bladder and bowel control isn’t affected, some may need help getting to and sitting on the toilet.
Most people with SMA Type 3 don’t have breathing problems and their life expectancy isn’t affected9 . Most can live long, fulfilling lives.
SMA Type 4
The symptoms and effects of SMA Type 4 begin in adulthood.
Each person is affected differently, but in general, symptoms can include:
- tired, aching muscles
- a feeling of heaviness
- numbness
- cramp
- a slight shaking of the fingers and hands
- fatigue SMA Type 4 progresses steadily and slowly over time causing increased muscle weakness with age. This may impact on daily living activities such as walking, dressing and bathing.
SMA Type 4:
- rarely affects swallowing or breathing
- doesn’t affect intelligence, and life expectancy is normal.
It’s important not to confuse SMA Type 4, which affects the lower motor neurons, with Motor Neurone Disease (MND) - also known as Amyotrophic Lateral Sclerosis (ALS). MND affects both the upper and lower motor neurons. Though SMA is also classed as a motor neuron disease, it isn’t MND. Whereas MND is almost always life-threatening, SMA Type 4 isn’t.