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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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Your Question

My wife is showing many symptoms of this disease and is a confirmed carrier. Is it possible that she has it?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

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

Can female carriers of Kennedy disease have the condition?

Females who are carriers of an abnormal CAG expansion in the androgen receptor (AR) gene are usually unaffected, but some may have mild signs and symptoms including muscle cramps or occasional tremors.[2][1][3] No reported female carriers have had significant motor neuron disease. Females who are symptomatic may have an abnormal electromyogram or abnormal findings on muscle biopsy.[2][3]
Last updated: 9/28/2012