Researchers are unsure exactly what causes Alzheimer's, a creeping brain degeneration that affects an estimated 4.5 million Americans and is on the rise as the population ages; however, tests on mice suggest the brain damage caused by the disease may be at least partially reversible.

In fact, the genetically engineered mice in the study regained the ability to navigate mazes after the genes that caused their dementia were de-activated, which suggests the brain damage caused by Alzheimer's is not permanent.

Understanding Alzheimer's

Visible symptoms of Alzheimer's begin with memory loss, which escalates to complete helplessness as brain cells are destroyed.

In the brain, neurons die as messy plaques and tangles of protein form. Research has shown that the mutant protein tau--an unhealthy form of a brain compound linked to Alzheimer's--is responsible for poisoning brain cells and that blocking its production may allow some of those sick neurons to recover.

With this in mind, researchers engineered the mice to develop the mutant tau protein to see if the tangles themselves are a cause or a symptom of Alzheimer's. As projected:

• The mice developed dementia and suffered from brain atrophy similar to human Alzheimer's.

• When the engineered gene was turned off, however, memory loss stopped and the mice improved.

More importantly, the results showed that the tangles of brain cells were not toxic to surrounding brain tissue, indicating it's not the tangles themselves responsible for killing brain cells, but rather the mutant tau.

While it is a long journey from treating a mouse to treating a human, researchers are not ruling out the possibility of successfully stopping the mutant proteins in humans.

Reuters July 14, 2005

Science July 15, 2005;309(5733):476-81