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Kennedy disease

Other Names for this Disease
  • Bulbospinal muscular atrophy
  • SBMA
  • Spinal and bulbar muscular atrophy
  • Spinobulbar muscular atrophy
  • X-linked bulbospinal amyotrophy
More Names
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What is Kennedy disease?

How is Kennedy disease inherited?

What is Kennedy disease?

Kennedy disease is a gradually progressive neuromuscular disorder chiefly characterized by wasting of the proximal muscles (those closer to the trunk) and bulbar muscles (those of the face and throat).[1][2] The condition mainly affects males, with onset between the ages of 30 and 60.[1][2] Early signs and symptoms may include tremor, muscle cramps and muscle twitching, followed by progressive muscle weakness and wasting which may manifest in a variety of ways.[1][2] Affected individuals may also have gynecomastia, testicular atrophy (reduction in size or function), and reduced fertility.[2] It is caused by a mutation in the androgen receptor (AR) gene, in which a DNA segment known as a CAG triplet repeat is abnormally expanded.[3] It is inherited in an X-linked recessive manner. Treatment may include physiotherapy and rehabilitation, medications for tremor and muscle cramps, and hormone therapy or surgical treatment of gynecomastia.[1]
Last updated: 9/28/2012

How is Kennedy disease inherited?

Kennedy disease is inherited in an X-linked recessive manner. A condition is considered X-linked if the mutated gene that causes the condition is located on the X chromosome (one of the two sex chromosomes). Males have one X chromosome and one Y chromosome, while females have two X chromosomes. In males, one mutated copy of a disease-causing gene on the X chromosome is sufficient to cause the condition. In females, a mutation typically must be present in both copies of the gene (one on each X chromosome) to cause the disorder to fully manifest.[3]

A characteristic of X-linked inheritance is that affected males cannot pass X-linked traits to their sons because they only pass their Y chromosome to their sons.[3] However, all daughters of an affected male will be carriers of the condition. A female carrier of an X-linked recessive condition has a 50% risk to pass the mutated gene on to each daughter (i.e. there is a 50% risk each daughter will also be a carrier) and a 50% risk to pass the mutated gene on to each son (i.e. there is a 50% risk that each son will be affected).
Last updated: 9/28/2012

  1. Josef Finsterer. Kennedy disease. Orphanet. July 2011; Accessed 9/28/2012.
  2. Albert La Spada. Spinal and Bulbar Muscular Atrophy. GeneReviews. October 13, 2011; Accessed 9/28/2012.
  3. Spinal and bulbar muscular atrophy. Genetics Home Reference. May 2006; Accessed 9/28/2012.