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X-linked disorder characterized by degeneration of both sensory and lower motor neurons supplying the limb and bulbar musculature caused by a defect in the androgen receptor. Extraocular muscles are spared, possibly because of reduced numbers of androgen receptors in these muscles.

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Bulbospinal Neuronopathy; Kennedy Spinal and Bulbar Muscular Atrophy; X-Linked Bulbospinal Muscular Atrophy.

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Approximately 1:40-50,000 males are affected worldwide (seems consistently more frequent in western Finland).

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X-linked recessive (only males can express the full phenotype). Affects mainly Caucasians and Asians, but not Africans. The genetic defect is located at the DXYS1 marker on the proximal long arm of the X chromosome (Xq11-12). Females are carriers.

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Degeneration of sensory and motor neurons supplying the limb and bulbar musculature, sparing extraocular muscles (possibly because of reduced numbers of androgen receptors in these muscles). Caused by an expanded trinucleotide (cytosine-adenine-guanine [CAG]) repeat in the androgen receptor within the first exon of the gene. The disease mechanism likely involves toxicity of an expanded polyglutamine tract in the androgen receptor protein. Electromyography and muscle histology demonstrate neurogenic atrophy. Necropsy shows diffuse loss and atrophy of anterior horn cells in the spinal cord.

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Laboratory findings include elevated serum creatine kinase, pronounced involutional changes in Leydig cells, hypobetalipoproteinemia, and abnormalities in the androgen receptor gene.

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This is a slowly progressing muscle atrophy associated with mild androgen insensitivity that affects only males. Muscle atrophy is initially not obvious and usually starts between 20 and 50 years of age. Its onset is insidious and early signs may include difficulties with walking and a tendency to fall. Deep tendon reflexes are decreased and some patients complain about muscle cramps and/or intention tremor. The muscle weakness not only involves the extremities, but also the facial muscles (including facial fasciculations). Calf hypertrophy may occur. Over the following 10-20 years, most patients will start to experience difficulties with climbing stairs or other strenuous efforts, while about one third will even be wheelchair-bound. Most patients will also suffer from involvement of bulbar muscles with dysphagia, dysarthria (with a change in the voice character, e.g., a more nasal sound) and drooling. Bulbar palsy results in increased risk for aspiration and consecutive pneumonias, which can rarely be life-threatening. Lower motor and primary sensory neuropathy have been described and are due to degeneration of anterior horn cells and dorsal root ganglia, respectively. The disease may be symmetrical or asymmetrical.

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Gynecomastia is an almost constant finding and usually the first sign of androgen insensitivity, manifesting already in adolescence. Testicular atrophy, erectile dysfunction, oligospermia/azoospermia with decreased fertility or sterility, as well as diminished secondary sex characteristics are frequently found. Diabetes mellitus has been described in some patients. Life expectancy is usually not affected, except when complications from aspiration/pneumonia arise.

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Preoperative assessment should evaluate the degree of muscle weakness and assess the neurologic function. Lung function tests may be indicated. Check fasting ...

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