WASHINGTON, April 1 (Reuters) - Exercise delayed the symptoms of Huntington's disease in mice genetically engineered to develop the brain disease, and may offer some small hope to people who know they will develop it, researchers said on Tuesday.

They said the combination of exercise and other environmental stimulation may help slow the onset of the genetic disease, which has no cure and is always fatal.

And their findings, published in the journal BioMed Central Neuroscience, might offer ways to treat other brain diseases, such as Alzheimer's, they said.

Huntington's disease affects up to one person in every 10,000. Children of people with the disease have a 50 percent chance of inheriting the faulty gene that causes it, and if they get the gene, they will develop Huntington's.

About a third of patients have no family history of the disease, which progresses from mood swings and depression to complete disability.

Anthony Hannan of Britain's University of Oxford and Australia's University of Melbourne and colleagues tested young mice genetically engineered with the Huntington's genes.

"We have previously demonstrated that environmental enrichment delays the onset of disease in these Huntington's disease mice," they wrote.

Those allowed to run on an exercise wheel developed the symptoms of the disease later than other mice -- although when killed and dissected, their brains showed the same damage.

"This suggests the possibility that sensory stimulation, mental exercise and physical activity could all be employed in attempts to harness environmental enrichment for the benefit of human sufferers," the researchers wrote.

"These findings may have broader implications for other brain disorders. Mental and physical engagement with a stimulating environment is thought to have beneficial effects in delaying dementia in Alzheimer's disease," they added in the report, available on the Internet at http://www.biomedcentral.com/bmcneurosci/

(Reporting by Maggie Fox; Editing by Will Dunham)

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