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Kennedy Disease

Inherited Neurological Disorder


Updated March 16, 2012

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Kennedy disease, also known as spinal bulbar muscular atrophy or SBMA, is an inherited neurological disorder. Kennedy disease affects the lower motor neurons, which are responsible for movement of many muscles of the arms and legs. It also affects the nerves that control bulbar muscles, which control breathing, swallowing, and talking. Kennedy disease can also lead to "androgen insensitivity," which causes enlarged breasts in men, decreased fertility, and testicular atrophy.

Kennedy disease is caused by a genetic defect on the X (female) chromosome. Since males have only one X chromsome, they are most severely affected by the disorder. Females, who have two X chromsomes, may carry the defective gene on one X chromsome, but the other normal X chromsome lessens or hides the symptoms of the disorder. Kennedy disease is estimated to occur in 1 in 40,000 individuals worldwide.

On average, symptoms begin in individuals aged 40-60 years. Symptoms come on slowly, and may include:

  • Weakness and muscle cramps in the arms and legs
  • Weakness of the face, mouth, and tongue muscles. The chin may twitch or quiver, and the voice may become more nasal.
  • Twitching of small muscles that can be seen under the skin.
  • Tremors or trembling with certain positions. The hands may tremble when trying to pick up or hold something.
  • Numbness or loss of sensation over certain areas of the body.
Kennedy disease may have other effects on the body, including:
  • Gynecomastia, meaning enlargement of breast tissue in males

There are a number of neuromuscular disorders with symptoms similar to Kennedy disease, so misdiagnosis or underdiagnosis is common. Often, individuals with Kennedy disease are mistakenly thought to have amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease). However, ALS, as well as the other similar disorders, does not include endocrine disorders or loss of sensation. A genetic test can confirm if the Kennedy disease defect is present on the X chromosome. If genetic testing is positive, no other tests need to be done.

Kennedy disease does not affect life expectancy, so treatment is focused on maintaining the individual's optimum muscle function throughout his life. Physical therapy, occupational therapy, and speech therapy are important for maintaining an individual's abilities and for adapting to the progression of the disease. Adaptive equipment can help maintain mobility and independence.

Genetic counseling
Kennedy disease is linked to the X (female) chromosome, so if a woman is a carrier of the defective gene, her sons have a 50% chance of have the disorder and her daughters have a 50% chance of being a carrier. Fathers cannot pass Kennedy disease on to their sons. Their daughters, however, will be carriers of the defective gene.


Barkhaus, P. E. (2003). Kennedy disease. http://emedicine.medscape.com/article/1172604-overview

Kennedy's Disease Association. "What Is Kennedy's Disease?"

Medically reviewed on 3/16/2012

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