SBMA belongs to a group of neurodegenerative disorders, called polyglutamine diseases, that includes Huntington's disease and spinocerebellar ataxias. Polyglutamine diseases are thought to arise because of a mutant protein that is misfolded and subsequently clumps together to form toxic aggregates that destroy cell function and cause disease. In SBMA, a mutated gene directs production of androgen receptors with an abnormal number of consecutive residues of the amino acid glutamine. Dr. Albert R. La Spada and colleagues from the University of Washington Medical Center in Seattle created transgenic mice containing the human androgen receptor carrying 100 glutamine repeats. The mice developed a gradually progressive limb weakness around mid-adulthood that was accompanied by motor neuron degeneration, strikingly similar to what is seen in human SBMA patients. The researchers determined that the abnormal androgen receptor interfered with production of a molecule called vascular endothelial growth factor (VEGF) that is important for the general health and survival of motor neurons. Interestingly, VEGF could rescue SBMA-like motor neurons grown in the laboratory.
The researchers conclude that VEGF may play a pivotal role in motor neuron degeneration. "Our findings in SBMA suggest that
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