Kennedy disease is a rare, X-linked slowly progressive neuromuscular disorder. Kennedy disease is typically an adult-onset disease, where symptoms occur mainly between the ages of 20 and 50. The disease is characterised by symptoms such as muscle weakness and cramps in the arms, legs, and facial area, enlarged breasts, and difficulty with speaking and swallowing (dysphagia).
Causes of Kennedy disease
Kennedy disease is an X-linked genetic disorder that occurs primarily in males. Very rarely, female carriers of the abnormal gene may show symptoms. It is caused by a mutation in a gene that encodes for a protein known as the androgen receptor (AR) and was mapped to band Xq11-q12 on the X chromosome. The instructions within every gene consist of different arrangements of four basic chemicals (nucleotide bases) called adenine (A), cytosine (C), guanine (G), and thymine (T). Individuals with the disease have an abnormal section in the AR gene, which is due to an excessive number of CAG trinucleotide repetitions in the DNA sequence. An unaffected individual has 10-35 CAG repeats in the AR gene while a person with Kennedy disease has more than 36 CAG repeats in the gene.
Symptoms
Affected individuals begin to develop neurological symptoms between 20 to 50 years of age. These early symptoms include:
The disease affects the lower motor neurons that are responsible for the movement of many muscles in the legs, arms, mouth, and throat. Affected individuals will show signs of twitching, often in the tongue or hand, followed by
muscle weakness and problems with facial muscles.
Diagnosis of Kennedy disease
Since Kennedy's disease is rare, it can be misdiagnosed. It is sometimes mistaken for the more common motor neurone disease (amyotrophic lateral sclerosis), a progressive nervous system disease characterised by the breaking down of
neurones in the spinal cord and brain.
Kennedy disease can be diagnosed using a number of tests including:
- Blood test to check for elevated serum creatine kinase (CPK): People with Kennedy disease usually have a greater than average amount of this particular enzyme circulating in their blood.
- Genetic tests using a blood sample: This test can check whether the Kennedy disease gene is present, even if the person is asymptomatic or a carrier. Genetic counselling is important.
Treatment
There is no cure for Kennedy disease, because medical science doesn't know how to regenerate muscle neurones. Treatment aims to ease some of the symptoms and can include:
- Medications to reduce muscle cramps and tremors
- Plenty of rest and avoidance of exhaustion
- Healthy, balanced diet
- Gentle and regular aerobic exercise
- Regular stretching to help reduce muscle cramping
- Pain management
- Speech therapy
- Occupational therapy
- Physiotherapy
