Spinal and Bulbar Muscular Atrophy (SBMA) – Kennedy’s Disease

This information is for if you have been recently diagnosed with SBMA - Kennedy's Disease.

What is SBMA-Kennedy’s Disease?

Kennedy’s Disease is a rare inherited neuromuscular condition. It’s also known as:

  • X-linked motor neuron disease  
  • X-linked recessive bulbospinal neuropathy or
  • X-linked spinal and bulbar atrophy

It’s an adult onset, form of SMA that mainly affects men. It’s estimated that 1 in 40,000 people have the genetic fault that causes it and, because it’s relatively rare, Kennedy’s Disease is often initially misdiagnosed or goes undiagnosed for years.


What are the symptoms and effects?

Kennedy’s Disease causes progressive weakening and wasting of the muscles, particularly in the arms and legs. This is due to the degeneration of lower motor neurons within the spinal cord and brainstem. It also causes hormonal changes. Symptoms and effects of Kennedy’s Disease are described in more detail in the information published by the MND Associations and Kennedy’s Disease UK (see below).


Which gene is affected?

Some of the genes that cause rare 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:

  • The Androgen receptor (AR) gene, on the X sex chromosome1.

Further information can be found here.


Inheritance pattern

Kennedy’s Disease 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

Kennedy’s Disease UK
Phone: 01604 250505
Website: www.kd-uk.com     

MND Association:
Website: www.mndassociation.org
(search for Kennedy’s Disease)

Version: 1.1
Author: SMA UK Information Production Team
Published: September 2018
Last updated: March 2019

Next full review date September 2021


1. La Spada et al. (1991) ‘Androgen receptor gene mutations in X-linked spinal and bulbar muscular atrophy’, Nature, 352, pp. 77–79.


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