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This information is for you if your child has been recently diagnosed with X-linked SMA.

This very rare form of SMA appears in infancy and causes severe muscle weakness and difficulty breathing. Children often have mis-shapen joints that make movement difficult. Babies who are severely affected may be born with broken bones.

There is only limited information about X-linked SMA because it is so rare, but your child’s medical team will be able to discuss how it will affect your child and how to manage symptoms for maximum comfort and quality of life.

The affected gene is:

  • UBA1 (X sex chromosome)¹‾²

Further information can be found here.

Some of the genes that cause rarer forms of SMA are associated with more than one condition, so please be aware that the website links suggested might provide information that is not just about SMA.

X-linked SMA has an X-linked Recessive inheritance pattern.

To find out more about this, please see our information guide The Inheritance Patterns of Some Rarer Forms of SMA

Little is known about the biology of X-Linked SMA. However, in 2023 Muscular Dystrophy UK awarded a grant to Professor Thomas Gillingwater and colleagues to characterise a newly generated mouse model. This is much needed to test new treatments for the condition.

Read more on their website >

Though not a substitute for professional medical advice, the US National Library of Medicine, Genetics Home Reference provides more information. Click here to read more.


Provides information and support foranyone in the UK affected by any form of SMA.


Provides information and support for families with children with a disability.

Children’s hospices
Located throughout the UK, these offer a wide range of services and support to eligible children and families; some also offer short breaks. Details of hospice services are available from Together for Short Lives and more information is available on their website.

1. Ramser et al. (2008) ‘Rare missense and synonymous variants in UBE1 are associated with X-linked infantile spinal muscular atrophy’, American Journal of Human Genetics, 82, pp. 188-193.

2. (accessed 25th August 2022)

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Author: SMA UK Information Production Team
Last updated: December 2023
Next full review due September 2024

Links last checked: September 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.

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