More than four million Americans currently suffer from Alzheimer's disease and the number is expected to balloon as the population ages. The results of a new mouse study offer fresh hope that the damage inflicted by the disease could be at least partially reversible.

Karen SantaCruz of the University of Minnesota and her colleagues genetically engineered mice to experience symptoms similar to those seen in humans with Alzheimer's disease--notably brain atrophy and associated memory loss that worsened over time. The mutant gene responsible for the brain damage, called tau, was modified such that it could be deactivated in the animals using medication. To gauge the effects of the disease over time, the researchers trained the animals to locate a submerged platform in a tank of water.

When placed in the pool, the animals would swim to its location, even after it had been removed. But as their dementia progressed the animals forgot where they expected the platform to be and began paddling aimlessly around the water instead. The scientists hypothesized that when the effects of the overactive tau gene were removed, the animals' memory loss would stop. In fact, when the dementia-causing gene was deactivated, not only did their memories no longer degrade, but they began to improve. The mice once again began to concentrate their searches in the correct area of the pool, suggesting they had recovered memories of their training sessions.
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