Bulbospinal muscular atrophy, also known as Kennedy Disease is a rare genetic disorder which primarily affects the lower motor neurons. It is a debilitating neurodegenerative disorder resulting in muscle weakness and cramps secondary to degenerative changes in the motor neurons of the brain stem and spinal cord. The symptoms of Bulbospinal muscular atrophy are usually asymmetrical and it may affect one side more than the other side. It is caused due to mutation of AR gene (androgen receptor gene). Like most of the genetic diseases, bulbospinal muscular atrophy does not have any cure at present.
Bulbospinal muscular atrophy or Kennedy disease was described by Dr. William R. Kennedy in 1966 and was named after him thereafter. Bulbospinal muscular atrophy is also known by other medical terminologies such as spinal and bulbar muscular atrophy (SBMA), spinobulbar muscular atrophy, x-linked bulbospinal neuropathy (XBSN), and x-linked spinal muscular atrophy type 1 (SMAX1). It may be associated with other neurodegenerative diseases such as Huntington's disease.
Causes and Pathophysiology of Bulbospinal Muscular Atrophy
Bulbospinal muscular atrophy is an X-chromosome linked disorder caused by mutation of the androgen receptor gene or the AR gene. It is caused due to the expansion of CAG repeat of AR gene in the first exon. This is called as trinucleotide repeats. This CAG repeats and then encodes a polyglutamine tract in the androgen receptor protein. The onset of disease depends on the extent of the expansion of the CAG repeat.
Symptoms of Bulbospinal Muscular Atrophy
The symptoms of bulbospinal muscle atrophy are grouped based on the system affected by it. The most common symptoms are listed as follows:
- Neurological Symptoms of Bulbospinal Muscular Atrophy
- The bulbar muscles are a group of muscles that predominantly control breathing, talking, swallowing and other functions of the throat. These muscles are supplied by motor neurons arising from the brain. Any abnormalities with above mentioned functions are called as bulbar signs.
- Difficulty swallowing.
- Tremors in upper extremities while carrying out physical activities.
- Normal Babinski reflex or plantar response i.e., the toes bend downward when the bottom of the foot in scraped.
- Weakness and wasting of muscles supplied by lower motor neurons.
- Numbness and loss of sensation over the affected areas.
- Absent or reduced deep tendon reflexes. Clinically, this sign is presented as lack of normal response when the knee is tapped by a hammer.
- Muscular Symptoms of Bulbospinal Muscular Atrophy
- Reproductive Symptoms of Bulbospinal Muscular Atrophy
Epidemiology of Bulbospinal Muscular Atrophy
In United States, studies have shown that the incidence rate of bulbospinal muscular atrophy is about 1 case in 40,000 male populations. World-wide, Bulbospinal muscular atrophy is more common in areas in Europe, Japan, Brazil, Australia and Finland. In terms of mortality and morbidity, Bulbospinal muscular atrophy usually lasts for 2 to 3 decades and does not compromise with the life expectancy of the affected individual. In certain cases, the Bulbospinal muscular atrophy patient may develop aspiration pneumonia in the long run. It is an X chromosome linked disease, and thus affects only males. Affected females do not express the symptoms and behave as carriers. Affected male does not pass on the genetic trait to their son, but passes on the trait to their daughters who in turn can pass on the trait to her children. Bulbospinal muscular atrophy typically affects between 40 to 60 years of age. In some cases, Bulbospinal muscular atrophy may present the symptoms as early as in mid 20s.
Diagnosis of Bulbospinal Muscular Atrophy
Diagnosis of bulbospinal muscular atrophy is usually done by an expertise panel of neurologist and genetic specialist. A detailed case history is obtained followed by physical examination and detailed neurological examination. Blood work usually reveals elevation of CPK enzymes. This can be confused with similar enzymes released during myocardial infarction. DNA tests are beneficial in the diagnosis of bulbospinal muscular atrophy. The gene responsible for bulbospinal muscular disease may be found in affected male and also in carrier female. Genetic testing helps in detection of CAG triplet expansion in the androgen receptor gene, a common finding in bulbospinal muscle atrophy. Video radiographic swallow study may be required for the evaluation of dysphagia.
Treatment of Bulbospinal Muscular Atrophy
Bulbospinal muscular atrophy does not have a specific treatment. Treatment modality involves symptomatic management of the condition. Physical therapy and rehabilitation is beneficial in providing symptomatic relief to Bulbospinal muscular atrophy patients. Aerobic exercises are often helpful in the management of muscular symptoms and for improving strength, mobility, balance and quality of life. Surgical intervention may be considered for correction of spinal disorder. Bulbospinal muscular atrophy patients with difficulty swallowing may need a gastrostomy tube. It is advised to the patient and his family to undergo a genetic testing for an in-depth analysis of genetic inheritance. Psychiatric counseling may be required in cases of patients affected with depression, anxiety and other emotional stress in view of the existing condition.
Prognosis of Bulbospinal Muscular Atrophy
Bulbospinal muscular atrophy being a genetic disease does not have a definite cure. It is a slow progressive disorder. Though the condition does not have any fatal consequences, there is a possibility of developing permanent disability due to Bulbospinal muscular atrophy. About 20% of the patients affected by Bulbospinal muscular atrophy may need a wheelchair and assistance with movement.
Complications of Bulbospinal Muscular Atrophy
Patients affected by bulbospinal muscular atrophy can develop permanent disability over a period of time. Bulbospinal muscular atrophy patients usually have difficulty with movements, which limits ability to carry out daily activities such as cooking, driving and movement. Some patients may develop aspiration pneumonia.
Prevention of Bulbospinal Muscular Atrophy
Bulbospinal muscular atrophy cannot be prevented. However, it is advised to undergo a genetic testing and consult a genetic counselor before planning a pregnancy. Genetic testing is comparatively more important in cases of known family history of genetic disorders.
Bulbospinal muscular disease or Kennedy disease is a rare genetic disorder that predominantly affects the male population. It is a neuromuscular disease secondary to X-chromosome linked recessive genetic mutation of the AR gene. Bulbospinal muscular atrophy affects the spinal and the bulbar neurons leading to muscle weakness and atrophy. This is more evident in the extremities, face and throat. Bulbospinal muscular disease is an adult onset condition and the onset is usually noted between the ages of 30 to 50 years. Being a rare disease, not much is known about this condition. A large number of studies and researches are being carried out to understand Bulbospinal muscular atrophy closely. The NINDS supports a broad spectrum of researches for understanding motor neuron diseases including bulbospinal muscular atrophy. The condition is incurable at present and may lead to permanent disabilities.