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Possible Explanation for Late Onset of Huntington Disease

Researchers have identified a molecular pathway that may play a role in delaying the onset of symptoms in Huntington disease (HD). The findings could possibly lead to the development of effective treatments for HD. The new data indicate that group I mGluR-mediated signaling pathways are altered in HD and that these cell signaling adaptations could be important for the survival of striatal neurons, neurons that are lost in the course of HD. The researchers used a genetically-modified mouse model of HD to look at the effects of the causative mutated huntingtin protein (mutant Htt) on the brain. "We found there was some kind of compensation going on early in the life of these mice that was helping to protect them from the development of the disease," said Dr. Stephen Ferguson, senior author of the paper and director of the Molecular Brain Research Group at the Robarts Research Institute at The University of Western Ontario in Canada, and also a professor in the Department of Physiology & Pharmacology at Western’s Schulich School of Medicine and Dentistry. "As they age, they lose this compensation and the associated protective effects, which could explain the late onset of the disease.” Dr. Ferguson added that the metabotropic glutamate receptors (mGluRs), which are responsible for communication between brain cells, play an important role in these protective effects. By interacting with the mutant Htt protein, mGluRs change the way the brain signals in the early stages of HD in an attempt to offset the disease, and save the brain from cell death. As a result, mGluRs could offer a drug target for HD treatment. HD is a dominant hereditary condition that leads to severe physical and mental deterioration, psychiatric problems, and eventually, death. Currently, there are no treatments to slow down or stop the disease.

HD sufferers are born with the disease, although they do not show symptoms until later in life. The symptoms of Huntington's disease are caused by cell death in specific regions of the brain. Patients who have HD are born with a mutated Htt, which is thought to cause these toxic effects.

While researchers know HD results from this single, mutated protein, no one seems to know exactly what it does, why it does not cause symptoms until later in life, or why it kills a specific set of brain cells, even though Htt is found in every single cell in the human body.

Hopefully, this new research will shed light on at least one of these questions and perhaps pave the way toward the development of treatments for this dread disease.

This new work was published in the January 6, 2010 issue of the Journal of Neuroscience. [Press release] [Journal of Neuroscience article]