X-linked Spinal Muscular Atrophy

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

What is X-linked SMA?

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

There’s limited information about X-linked SMA because it’s 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.

Which gene is affected?

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.

The affected gene is:

  • UBA1 (X sex chromosome)1

Further information can be found here

Inheritance pattern

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

To find out more about this please see our information sheet ‘The inheritance patterns of some rarer forms of SMA’.

Support and resources

Phone: 01789 267520
Website: www.smauk.org.uk
Provides information and support for anyone in the UK affected by any form of SMA.

Phone: 0808 808 3555
Website: www.contact.org.uk           
Provides information and support for families with children with a disability.

Together for Short Lives
Phone:  0808 8088 100
Website: www.togetherforshortlives.org.uk
Provides information, support and services for families of children who are expected to have short lives.

Version: 1.1
Author: SMA UK Information Production Team
Published: August 2018
Last updated: March 2019
Next full review due August 2021


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.


We are grateful to the writers and reviewers who assist us in our information production. A list of who this includes may be viewed on our website: www.smauk.org.uk/our-writers-and-reviewers-panel or requested from supportservices@smauk.org.uk

Whilst every effort is made to ensure that the information in this publication is complete, correct and up to date, this cannot be guaranteed and Spinal Muscular Atrophy UK shall not be liable whatsoever for any damages incurred as a result of its use. SMA UK does not necessarily endorse the services provided by the organisations listed in our information sheets.

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