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This information is for you if you have been recently diagnosed with SBMA, which is also commonly referred to as Kennedy’s Disease.

SBMA is a rare inherited neuromuscular condition. It is also sometimes known as:

  • X-linked motor neuron disease
  • X-linked recessive bulbospinal neuropathy
  • X-linked SBMA

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

SBMA 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 SBMA are described in more detail in the information published by the MND Associations and Kennedy’s Disease UK (see below under Support and Resources).

The affected gene is:

  • The Androgen Receptor (AR) gene, on the X sex chromosome¹‾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 provided website links may give information about disorders additional to SMA.

SBMA 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.

Kennedy’s Disease UK

MND Association

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

2. (last accessed 16th August 2022)

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Author: SMA UK Information Production Team
Last updated: August 2022
Next full review date 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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