Kennedy's Disease (Bulbospinal Muscular Atrophy, X-Linked Spinal and Bulbar Muscular Atrophy)
Kennedy’s disease is a rare genetic condition also known as Kennedy’s syndrome, Spinal bulbar muscular atrophy or SBMA. Symptoms tend to develop most commonly in middle age, but it is possible for them to become apparent earlier. There is currently no cure for Kennedy’s disease.
What causes Kennedy’s disease?
Kennedy’s disease is classed as an X-linked condition, which is caused by a genetic mutation in a gene responsible for producing the protein known as AR (androgen receptor). X-linked disorders are related to the X chromosome. Normally, a person has 10 sequences of CAG in their DNA on the AR gene (this relates to cytosine, adenine and guarine), but in people with Kennedy’s disease, there are more than 36 sequences.
The androgen receptor is responsible for reacting to signals from androgens, which are male hormones. The receptors are found in the cell cytoplasm in many different types of cell around the body. Normally, the androgen receptor binds to androgen, but in people with Kennedy’s syndrome, this process is unable to take place normally. It is not really understood why.
In female carriers, no symptoms are usually present because the defective androgen receptors are not activated. As a result of this, only males are affected by Kennedy’s disease, even when females carry the defective gene.
Females have two X chromosomes, while males have one X and one Y chromosome. A male will inherit Kennedy’s disease if they inherit the defective X chromosome. Males can only pass their Y chromosome onto their sons, so it will not be passed down through the male side of the family. All daughters, however, will be carriers. If the daughters then have sons, there is a 50 percent chance that they would inherit the gene and develop Kennedy’s syndrome and a 50 percent chance that any daughters would be carriers.
Who is affected?
Kennedy’s disease is rare and it is estimated to affect 1 in 150,000 males. In most cases, symptoms develop between the ages of 30 and 50. However, it is possible for signs to appear earlier.
Kennedy’s disease diagnosis
Kennedy’s disease can usually be diagnosed based on symptoms, but genetic testing may be ordered in order to confirm a diagnosis. In some cases, the symptoms are similar to other syndromes and the test can help to determine which syndrome is present. Other conditions often confused with Kennedy’ disease include ALD (adrenoleukodystrophy), motor neurone disease, Guillain-Barre syndrome and myasthenia gravis.
Symptoms of Kennedy’s disease
Symptoms of Kennedy’s disease include:
- Shakes and tremors
- Dysphagia (difficulty swallowing)
- Weakness in the muscles, including the facial muscles
- Loss of sensation and numbness
- Reduced size of the testicles
- Enlarged breasts
Symptoms are associated with the effects of the syndrome on the motor neurons, which control movement in the lower limbs, face and arms. The defective motor neurons eventually die and this prevents effective muscle contraction, leading to weakness and a restricted range of movement. Patients may also experience muscle pain and cramps and one side of the body may be more severely affected than the other.
The bulbar muscles are also affected. These muscles are responsible for controlling the actions of swallowing and speaking, making these movements more difficult for people with the syndrome.
The syndrome can also affect the role of androgen in the body and patients may experience erectile dysfunction, breast enlargement and infertility.
Treating Kennedy’s disease
There is currently no cure for Kennedy’s disease. However, treatments can help to reduce symptoms and encourage greater independence. Physiotherapy, occupational therapy and speech and language therapy can all be beneficial. Mobility aids are also commonly used and surgery can be carried out to treat breast enlargement.
The prognosis for Kennedy’s disease is fairly positive. In most cases, life expectancy is normal. However, around 1 in 10 people die in their 60s or 70s as a result of complications related to difficulty swallowing, choking and pneumonia.
Research into possible treatments is ongoing.