Kennedy Disease: Causes, Symptoms and Treatment

What is Kennedy Disease?

Kennedy disease, also known as spinal and bulbar muscular atrophy (SBMA), is a rare, slowly progressive neuromuscular disorder. It affects the motor neurons located in the spinal cord and brainstem (bulbar region), which are responsible for controlling voluntary muscle movements. Kennedy disease belongs to the group of motor neuron diseases and was first described in 1968 by American neurologist William R. Kennedy.

Causes

Kennedy disease is caused by a genetic mutation in the androgen receptor gene (AR gene) located on the X chromosome. It is classified as a trinucleotide repeat disorder: the CAG sequence within the gene is abnormally repeated. In healthy individuals, this sequence repeats approximately 9 to 36 times, while in affected individuals it repeats more than 38 times.

Because the mutated gene is located on the X chromosome, Kennedy disease almost exclusively affects men. Women can be carriers of the mutation and may pass it on to their sons, but typically do not develop significant symptoms themselves.

Symptoms

Symptoms usually begin in adulthood, most commonly between the ages of 30 and 50. The disease progresses slowly over many years or decades.

Neuromuscular Symptoms

• Muscle weakness and muscle atrophy (wasting), primarily in the arms and legs
• Muscle fasciculations (visible twitching of muscle groups, often in the face, tongue, or limbs)
• Tremor (shaking) of the hands
• Difficulty swallowing (dysphagia) and slurred speech due to bulbar muscle involvement
• Impaired mobility in advanced stages

Endocrine Symptoms

• Gynecomastia (enlargement of breast tissue in men)
• Testicular atrophy
• Reduced androgenic effects, which may lead to infertility

Diagnosis

The diagnosis of Kennedy disease is based on a combination of clinical evaluation, laboratory tests, and genetic testing:

• Neurological examination: Assessment of muscle strength, reflexes, and coordination
• Electromyography (EMG): Detection of characteristic changes in muscle electrical activity consistent with motor neuron disease
• Blood tests: Elevated creatine kinase (CK) levels indicating muscle damage; potentially elevated gonadotropins and reduced testosterone
• Genetic testing: Molecular confirmation of CAG repeat expansion in the AR gene – this is the gold standard for diagnosis
• Muscle biopsy: Occasionally performed to support the diagnosis

Treatment

Currently, there is no curative treatment for Kennedy disease. Management focuses on relieving symptoms and maintaining quality of life.

Physical and Occupational Therapy

Regular physiotherapy helps preserve muscle strength, prevent contractures, and maintain mobility for as long as possible. Occupational therapy supports patients in managing daily activities.

Speech and Swallowing Therapy

Speech-language therapy is important for patients with swallowing difficulties or speech impairments, helping to reduce the risk of aspiration (inhaling food or liquid into the lungs).

Medical Treatment

Symptoms such as tremor can be managed with medication. Hormonal changes such as gynecomastia may also be treated when clinically indicated. Research studies are investigating the potential benefit of androgen-suppressing therapies (e.g., leuprorelin), since the mutated androgen receptor protein is activated by male sex hormones.

Assistive Devices and Rehabilitation

As the disease advances, patients may require walking aids, orthopedic supports, or a wheelchair. A multidisciplinary care team including neurologists, pulmonologists, gastroenterologists, and social workers is recommended.

Prognosis

Kennedy disease progresses more slowly than other motor neuron diseases such as ALS (amyotrophic lateral sclerosis). Life expectancy is often only mildly reduced; however, the disease can lead to significant physical disability. Respiratory complications may become life-threatening in advanced stages.

References

1. Kennedy W.R., Alter M., Sung J.H. (1968): Progressive proximal spinal and bulbar muscular atrophy of late onset. A sex-linked recessive trait. Neurology, 18(7):671-680.
2. Fischbeck K.H. (1997): Kennedy disease. Journal of Inherited Metabolic Disease, 20(2):152-158. PubMed PMID: 9211189.
3. National Institute of Neurological Disorders and Stroke (NINDS): Spinal and Bulbar Muscular Atrophy Information Page. Available at: https://www.ninds.nih.gov (accessed 2024).