A protein found in the brain, known as Rest, could be the key to determining why certain people develop Alzheimer's disease.
Scientists at Harvard University believe that the protein, which is usually present in developing foetus brains, protects neurons from dementia symptoms in old age.
Research showed individuals who do have Alzheimer's, or other neurodegenerative diseases, had a distinct lack of Rest in certain parts of the brain.
Bruce Yankner, Harvard Medical School professor of genetics and leader of the study, said: "Our work raises the possibility that the abnormal protein aggregates associated with Alzheimer's and other neurodegenerative diseases may not be sufficient to cause dementia; you may also need a failure of the brain's stress response system."
He added that this could open up the potential for new treatment opportunities for dementia patients.
This study marks a change in the way Alzheimer's is looked at by medical professionals, as the focus is normally on what causes the disease.
However, now researchers may look at certain brain defences that are failing to protect it from degeneration, as this study suggests that high Rest levels can prevent dementia.
Mr Yanker said: "If we could activate this stress-resistance gene network with drugs, it might be possible to intervene in the disease quite early."
He suggested lithium as a potential treatment due to its safety and its apparent ability to stimulate the protein.
However, Mr Yanker also stated that the study didn't determine whether the decline in the presence of Rest was the cause or effect of brain conditions.
Li-Huei Tsai, director of the Picower Institute for Learning and Memory at the Massachusetts Institute of Technology, said that this was a crucial study in the fight against Alzheimer's disease.
In the UK, around 800,000 people have been diagnosed with dementia, while that figure is expected to reach the one million mark by 2021.
Globally, some studies estimate that approximately 70 million people will have the disease by 2030.
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