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This page is for families, friends and healthcare professionals who want to know more about SMA Type 2.

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.

SMA Type 2 is a form of 5q SMA. Please see our guide What is 5q SMA? for information about causes, diagnosis, inheritance and how many people are affected.

Before drug treatments became approved and available specifically for SMA, clinicians and researchers gathered information about the usual disease progression someone diagnosed with SMA Type 2 might expect. This is called the ‘natural history’.

Symptoms and effects

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.

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 child 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, the age at which any treatment was started and a child’s 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.

  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.

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Author: SMA UK Information Production Team
Last updated: July 2022
Next full review due: September 2024

Links last checked: June 2023

The information provided in this guide, on our website, and through links to other websites, is designed to complement not be a substitute for clinical and professional care and advice.

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