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Genetic and Rare Diseases Information Center (GARD)

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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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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.[1]

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.[1] 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. Spinal and bulbar muscular atrophy. Genetics Home Reference. May 2006; Accessed 9/28/2012.