Kennedy Disease

Inherited neurological disorder

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 the arms. It also affects the nerves which supply the bulbar muscles, which control breathing, swallowing, and talking. Kennedy disease can also affect the endocrine system and the regulation of fats (lipids) in the blood.

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.

Symptoms
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 which 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
• Disorders of fats (lipids) in the blood
• Diabetes mellitus (blood sugar problems).

Diagnosis
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 [link url=http://rarediseases.about.com/cs/als/a/090701.htm]amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease)[/link]. However, ALS, as well as the other similar disorder, 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.

Treatmnet
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.

Last updated 12/23/05

Information for this article was taken from
- Barkhaus, P. E. (2003). Kennedy disease. eMedicine, accessed at http://www.emedicine.com/neuro/topic421.htm
- Kennedy's Disease Association. [link url=http://www.kennedysdisease.org/about.html]What is Kennedy's Disease?[/link]