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This page is for families, friends and healthcare professionals who want to know more about SMA Type 4.

SMA Type 4 is form of 5q SMA. Please see our guide What is 5q SMA? for information about causes, diagnosis, inheritance and how many people are affected.

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 usually progresses 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
  • does not affect intelligence, and life expectancy is not affected¹.

SMA Type 4 affects the lower motor neurons. This is different from Motor Neurone Disease (MND), also known as Amyotrophic Lateral Sclerosis (ALS) which affects both the upper and lower motor neurons. Though SMA is also classed as a ‘motor neuron disease’, it is not MND. Whereas MND is almost always life-limiting, SMA Type 4 is not.

Access to treatments for those clinically diagnosed with SMA Type 4 varies between countries. This may depend on the decision made by the regulatory authorities – for example, in some countries access is approved for all who have 5q SMA. It may also depend on how distinct the ‘onset of symptoms’ age boundary is considered to be between Type 3b and Type 4.

In the UK, access to drug treatment (NHS-funded) is now only possible for those who have a clinical diagnosis of SMA Type 1, 2 or 3 and who meet the eligibility criteria. No drug treatments are currently available in the UK for people who have been given the clinical classification / diagnosis SMA Type 4. Discussions leading to this diagnosis should include a careful review of the history of the person’s onset of symptoms.

In 2024, the National Institute of Health and Care Excellence (NICE) is reviewing whether the NHS in England will continue to fund the two drug treatments, nusinersen and risdiplam, that may be prescribed for people who have SMA Type 1, 2 or 3 SMA. You can read more about this review, why SMA UK is advocating for adults diagnosed with SMA Type 4 to have access to drug treatment and how you can get involved on this page.

Support and advice can help manage the symptoms and effects. Nationally and internationally expert clinicians, researchers and people living with SMA are working together to review and update guidelines for best supportive care and management of symptoms.

1. Lunn MR & Wang CH (2008) Spinal muscular atrophy. Lancet, 371: 2120-2133

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Author: SMA UK Information Production Team
Last updated: February 2024
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.

For more detail about how we produce our information, please see these pages.

If you have any feedback about this information, please do let us know at: information@smauk.org.uk