Kennedy’s disease is an inherited lower motor neuron disease, called X-linked spinal and bulbar muscular atrophy, or SBMA. It affects only males. It disrupts neuronal transmission between brain and spinal motor neurons, causing progressive paralysis. The usual onset of symptoms is between 20 to 40 years.
The first symptoms include tremor of outstretched hands, visible muscle twitching, and muscle cramping with strenuous activity. This is followed by the onset of weakness of the shoulder or hip musculature, and progresses down the limbs. Later still, facial weakness occurs, or tongue weakness. This results in slurred speech, swallowing difficulty, and inadvertent passage of food into the trachea, causing repeated bouts of aspiration pneumonia.
Complications include diabetes mellitus, gynecomastia, oligospermia and infertility, as a result of mild androgen insensitivity.
Mode of inheritance
Kennedy’s disease is X-linked recessive. Thus the patient’s mother has one defective gene copy, which was passed on to the son, and one normal one. The mother is asymptomatic and clinically disease-free, and is called a carrier. She has a 50% chance of passing the abnormal gene to any of her offspring. She may pass the defective gene to her daughters, in which case they will also be carriers. If they inherit their mother’s normal gene copy, they will be completely free of the disease.
Diagnosis and treatment
Diagnosis is by clinical signs and by genetic testing. The test looks for a sequence of more than 35 repeating CAG trinucleotide sequences, called a trinucleotide repeat, on the androgen receptor gene. Treatment is purely supportive, and may include physical therapy and rehabilitation measures to improve present muscle strength.
Braces and walkers may help to preserve ambulation. This is aimed at slowing the rate of deterioration and paralysis. The paralysis usually creeps, so that people with the disease can move about till a late stage, when they are forced to use wheelchairs. Their life expectancy is normal, however.
Surveillance is required for pulmonary function as well as muscular strength, to assess the progress of the disease.