Spinal and bulbar muscular atrophy

A genetic disorder affecting motor neurons

Spinal and bulbar muscular atrophy (SBMA), also known as Kennedy's disease, is a rare, X-linked recessive genetic disorder characterized by the progressive degeneration of motor neurons in the spinal cord and brainstem. This condition primarily affects males, with onset typically occurring in adulthood.

Pathophysiology

SBMA is caused by a mutation in the androgen receptor (AR) gene located on the X chromosome. This mutation involves an expansion of a CAG trinucleotide repeat within the gene, leading to the production of an abnormal protein that accumulates in motor neurons, causing their dysfunction and eventual death. The disease is classified as a polyglutamine (polyQ) disorder, similar to Huntington's disease.

Clinical Features

The clinical manifestations of SBMA include progressive muscle weakness and atrophy, particularly affecting the proximal muscles. Patients often experience difficulty with activities such as climbing stairs, lifting objects, and swallowing. Bulbar symptoms, such as dysarthria and dysphagia, are common due to the involvement of the brainstem motor neurons.

Other symptoms may include:

• Gynecomastia
• Testicular atrophy
• Reduced fertility
• Hand tremors
• Muscle cramps

Diagnosis

Diagnosis of SBMA is confirmed through genetic testing, which identifies the expanded CAG repeat in the AR gene. Electromyography (EMG) and nerve conduction studies may also be used to assess the extent of motor neuron involvement.

Management

There is currently no cure for SBMA, and treatment is primarily supportive. Management strategies focus on alleviating symptoms and improving quality of life. These may include:

• Physical therapy to maintain muscle strength and mobility
• Speech therapy for bulbar symptoms
• Nutritional support to address swallowing difficulties
• Hormonal therapy to manage androgen-related symptoms

Prognosis

The progression of SBMA is typically slow, and life expectancy is not significantly reduced. However, the disease can lead to significant disability over time, impacting daily activities and quality of life.

Related pages

• Motor neuron disease
• Genetic disorders
• Neurodegenerative diseases