Before drug treatments (also sometimes known as ‘disease-modifying’ treatments) started to be developed and tested for SMA, clinicians and researchers gathered information about what impact parents / carers might expect the condition to have on their child as they grew into adulthood, and what young people and adults with the condition may expect. This was called the ‘natural history’ of the condition and was different for each ‘Type’ of SMA.

In SMA Type 2, symptoms of muscle weakness usually begin between 6 and 18 months of age. Generally, the earlier the onset of symptoms, the more severe the condition.

In the natural history of SMA Type 2, each child is affected differently but, in general, infants have:

• muscle weakness on both sides of the body
• muscle weakness closest to the centre of the body; these are more severely affected than muscles furthest away
• difficulties moving arms, but hands and fingers less so
• difficulties lifting legs
• legs that are weaker than arms

Intellectual and sexual development¹ is not usually affected.

As they get older, the natural history of SMA would usually cause them to have:

• muscle weakness that may make it difficult to keep up with daily activities. For example, if someone had been able to crawl or roll, they may have lost this ability.
• weak breathing muscles, making it difficult to cough effectively and more vulnerable to chest infections.
• muscles supporting the spinal column that are weak; most children have developed sideways curvature of their spine² (scoliosis).
• reduced ability to move so that some joints may have become tight (contractures), further restricting their range of movement.

The natural history can also weaken chewing and swallowing muscles. For some this means their tongue and shoulder muscles may twitch and they may have a slight tremor in their hands³.

Bladder and bowel control is not usually affected.

Major growth spurts, such as puberty, often create greater demands on weak muscles. SMA Type 2 can also mean that children and adults may become weaker after infections.

Most children, young people and adults living with SMA Type 2 need powered wheelchairs to maintain independent mobility, and help with daily tasks like washing, getting onto and off the toilet, as well as dressing and undressing.

Serious complications (such as severe respiratory infections) are associated with reduced life expectancy⁴, but improvements in healthcare standards mean that the majority of people live long lives.

Global clinical trials and follow-up studies of possible drug treatments for those who have SMA Type 2 had tended to focus on their impact on motor milestones gained in childhood. There is more understanding now of the importance of respiratory outcomes, and the value of other outcomes that impact on quality of life for older children, young people and adults, such as fine motor skills and fatigue levels, which enable or maintain independence in daily living.

• Changing Outcomes

In the UK, most children now living with SMA Type 2 will have started ongoing Spinraza™ / Nusinersen treatment (from late 2019). For adults, this possibility came later. More recently, ongoing treatment with Evrysdi™ / Risdiplam also became a possibility for children and adults. Many children with SMA Type 2 have gained strength, movement and better health with treatment. Symptoms have stabilised for many adults, with some seeing improvements.

How SMA will impact the health and daily life of a treated person living with SMA Type 2 today – and how the natural history of their condition may change – is very individual. It will be influenced by factors including the age at which symptoms first appeared, the severity of symptoms, how early any treatment was started and their individual response to treatment.

Though they can alleviate some symptoms, none of the drug treatments are a cure and, for children and adults, must be combined with the best supportive care and management of symptoms to ensure the best possible outcomes for each individual.

• Drug Treatments for Children in England who have SMA >
• Looking after your child who has had a recent diagnosis of SMA Type 2 – for parents and carers >
• Living With SMA – information and ideas for daily living >
• International Standards of Care for SMA >
• What is 5q SMA? >
• The Genetics of 5q SMA >
• Treatments & Research >
• Drug Treatments for Adults in England who have SMA >

1. Montes J et al. (2009) Clinical outcome measures in spinal muscular atrophy, J Child Neurol 24: 968-978
2. Mercuri E, et al. (2012) Childhood spinal muscular atrophy: controversies and challenges. Lancet Neurol 11: 443-452.
3. Tsirikos AI & Baker ADL (2006) Spinal muscular atrophy: classification, aetiology, and treatment of spinal deformity in children and adolescents. Curr Orthop 20: 430-445.
4. Farrar MA et al. (2013) Pathophysiological insights derived by natural history and motor function of spinal muscular atrophy. J Pediatrics 162: 155-159.