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Genetics Home Reference: your guide to understanding genetic conditions
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Spinal and bulbar muscular atrophy

Reviewed May 2006

What is spinal and bulbar muscular atrophy?

Spinal and bulbar muscular atrophy is a disorder of specialized nerve cells that control muscle movement (motor neurons). This condition, which mainly affects males, is characterized by muscle weakness and wasting (atrophy) that usually begins in adulthood and worsens slowly over time. Muscle wasting in the arms and legs results in cramping, difficulty walking, and a tendency to fall. Certain muscles in the face and throat (bulbar muscles) are also affected, which causes progressive problems with swallowing and speech. Additionally, muscle twitches (fasciculations) are common. Some men with the disorder experience unusual breast development (gynecomastia) and may be unable to father a child (infertile).

How common is spinal and bulbar muscular atrophy?

This condition affects fewer than 1 in 50,000 males and is very rare in females.

What genes are related to spinal and bulbar muscular atrophy?

Mutations in the AR gene cause spinal and bulbar muscular atrophy.

This disorder is caused by a mutation in which a DNA segment, known as a CAG triplet repeat, is abnormally expanded within the androgen receptor (AR) gene. Normally, this DNA segment is repeated up to about 36 times. In people with spinal and bulbar muscular atrophy, the CAG segment is repeated at least 38 times, and may be two or three times its usual length. The abnormally expanded CAG triplet repeat changes the structure of the protein made by the AR gene, disrupting the normal function of motor neurons in the brain and spinal cord. These nerve cells gradually die, leading to the muscle weakness and wasting seen in this condition. People with a higher number of CAG repeats tend to develop signs and symptoms of spinal and bulbar muscular atrophy at an earlier age.

Related Gene(s)

Changes in this gene are associated with spinal and bulbar muscular atrophy.

  • AR

How do people inherit spinal and bulbar muscular atrophy?

This condition is inherited in an X-linked recessive pattern. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), a mutation must be present in both copies of the gene to cause the disorder. Males are affected by X-linked recessive disorders much more frequently than females. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

Some females with one altered copy of the AR gene have mild signs and symptoms related to the condition, including muscle cramps and occasional tremors.

Where can I find information about diagnosis or management of spinal and bulbar muscular atrophy?

These resources address the diagnosis or management of spinal and bulbar muscular atrophy and may include treatment providers.

  • Gene Review: Spinal and Bulbar Muscular Atrophy (http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=kennedy)
  • Gene Tests: Spinal and Bulbar Muscular Atrophy (http://www.ncbi.nlm.nih.gov/sites/GeneTests/lab/clinical_disease_id/2388)
  • MedlinePlus Encyclopedia: Muscle Atrophy (http://www.nlm.nih.gov/medlineplus/ency/article/003188.htm)

You might also find information on the diagnosis or management of spinal and bulbar muscular atrophy in Educational resources (http://ghr.nlm.nih.gov/condition/spinal-and-bulbar-muscular-atrophy/show/Educational+resources) and Patient support (http://ghr.nlm.nih.gov/condition/spinal-and-bulbar-muscular-atrophy/show/Patient+support).

To locate a healthcare provider, see How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.

Where can I find additional information about spinal and bulbar muscular atrophy?

You may find the following resources about spinal and bulbar muscular atrophy helpful. These materials are written for the general public.

  • MedlinePlus - Health information

    • Encyclopedia: Muscle Atrophy (http://www.nlm.nih.gov/medlineplus/ency/article/003188.htm)
    • Health Topic: Spinal Muscular Atrophy (http://www.nlm.nih.gov/medlineplus/spinalmuscularatrophy.html)
  • Additional NIH Resources - National Institutes of Health
    National Institute of Neurological Disorders and Stroke (http://www.ninds.nih.gov/disorders/kennedys/kennedys.htm)

  • Educational resources - Information pages

    • Orphanet (http://www.orpha.net/consor/cgi-bin/OC_Exp.php?Lng=EN&Expert=481)
    • Swedish Information Center for Rare Diseases (http://www.socialstyrelsen.se/rarediseases/kennedydisease)

  • Patient support - For patients and families

    • Families of Spinal Muscular Atrophy (http://www.fsma.org/)
    • Kennedy's Disease Association (http://www.kennedysdisease.org/)
    • Muscular Dystrophy Association (http://www.mda.org/disease/sbma.html)
    • National Organization for Rare Disorders (http://www.rarediseases.org/rare-disease-information/rare-diseases/byID/986/viewAbstract)
    • Resource list from the University of Kansas Medical Center (http://www.kumc.edu/gec/support/spinal_m.html)

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

  • Gene Reviews - Clinical summary (http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=kennedy)
  • Gene Tests - DNA tests ordered by healthcare professionals (http://www.ncbi.nlm.nih.gov/sites/GeneTests/lab/clinical_disease_id/2388)
  • ClinicalTrials.gov - Linking patients to medical research (http://clinicaltrials.gov/ct2/results?cond=%22spinal%20and%20bulbar%20muscular%20atrophy%22%20OR%20%22Kennedy%20Syndrome%22)
  • PubMed - Recent literature (http://www.ncbi.nlm.nih.gov/pubmed?term=(Muscular%20Atrophy,%20Spinal%5BMAJR%5D)%20AND%20((spinal%20and%20bulbar%20muscular%20atrophy%5BTIAB%5D)%20OR%20(x-linked%20bulbospinal%20muscular%20atrophy%5BTIAB%5D)%20OR%20(x-linked%20bulbo%5BTIAB%5D%20AND%20spinal%20muscular%20atrophy%5BTIAB%5D)%20OR%20(kd%5BTIAB%5D)%20OR%20(kennedy%20disease%5BTIAB%5D)%20OR%20(kennedy%20spinal%20and%20bulbar%20muscular%20atrophy%5BTIAB%5D)%20OR%20(kennedy's%20disease%5BTIAB%5D)%20OR%20(sbma%5BTIAB%5D)%20OR%20(x-linked%20spinal%20and%20bulbar%20muscular%20atrophy%5BTIAB%5D))%20AND%20english%5Bla%5D%20AND%20human%5Bmh%5D%20AND%20%22last%201800%20days%22%5Bdp%5D)
  • OMIM - Genetic disorder catalog (http://omim.org/entry/313200)

What other names do people use for spinal and bulbar muscular atrophy?

  • Bulbospinal muscular atrophy, X-linked
  • KD
  • Kennedy disease
  • Kennedy's disease
  • Kennedy spinal and bulbar muscular atrophy
  • SBMA
  • X-linked spinal and bulbar muscular atrophy

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines (http://ghr.nlm.nih.gov/ConditionNameGuide) and How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.

What if I still have specific questions about spinal and bulbar muscular atrophy?

Ask the Genetic and Rare Diseases Information Center (http://rarediseases.info.nih.gov/GARD/).

What glossary definitions help with understanding spinal and bulbar muscular atrophy?

androgens ; atrophy ; cell ; chromosome ; DNA ; fasciculation ; gene ; gynecomastia ; infertile ; inheritance ; motor ; motor neuron ; mutation ; nerve cell ; neuron ; protein ; receptor ; recessive ; sex chromosomes ; sign ; symptom ; trait ; tremor ; wasting ; X-linked recessive

You may find definitions for these and many other terms in the Genetics Home Reference Glossary (http://ghr.nlm.nih.gov/glossary).

References

  • Atsuta N, Watanabe H, Ito M, Banno H, Suzuki K, Katsuno M, Tanaka F, Tamakoshi A, Sobue G. Natural history of spinal and bulbar muscular atrophy (SBMA): a study of 223 Japanese patients. Brain. 2006 Jun;129(Pt 6):1446-55. Epub 2006 Apr 18. (http://www.ncbi.nlm.nih.gov/pubmed/16621916?dopt=Abstract)
  • Gene Review: Spinal and Bulbar Muscular Atrophy (http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=kennedy)
  • Greenland KJ, Zajac JD. Kennedy's disease: pathogenesis and clinical approaches. Intern Med J. 2004 May;34(5):279-86. Review. (http://www.ncbi.nlm.nih.gov/pubmed/15151675?dopt=Abstract)
  • Poletti A, Negri-Cesi P, Martini L. Reflections on the diseases linked to mutations of the androgen receptor. Endocrine. 2005 Dec;28(3):243-62. Review. (http://www.ncbi.nlm.nih.gov/pubmed/16388114?dopt=Abstract)
  • Scriver, Charles R; The metabolic & molecular bases of inherited disease; 8th ed.; New York : McGraw-Hill, c2001. p4147-4157.
  • Sperfeld AD, Karitzky J, Brummer D, Schreiber H, Häussler J, Ludolph AC, Hanemann CO. X-linked bulbospinal neuronopathy: Kennedy disease. Arch Neurol. 2002 Dec;59(12):1921-6. (http://www.ncbi.nlm.nih.gov/pubmed/12470181?dopt=Abstract)

 

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.

 
Reviewed: May 2006
Published: May 21, 2012