Clusters of "memory-robbing" proteins could be one of the earliest signs of degenerative brain disorder Alzheimer's, scientists have suggested.
Being able to detect the protein early could warn of Alzheimer's
People at high risk of the disease show subtle signs years before the onset of more serious clinical symptoms.
This US study suggests that an early form of the plaque-forming protein seen in Alzheimer's affects memory.
Experts said the finding, published in Nature, could lead to a test to detect early signs of the disease.
Alzheimer's disease is thought to be caused by the build up of deposits of amyloid proteins in the brain.
One of the key mysteries scientists have been trying to solve is how the protein causes memory problems before such plaques develop.
The team from the University of Minnesota VA Medical Center and Johns Hopkins University genetically manipulated mice so they developed memory problems in the same way as people do before the earliest signs of Alzheimer's actually appear.
They discovered a form of the amyloid-beta protein, different to that seen in Alzheimer's plaques, which accumulates outside cells and affects memory.
The researchers extracted the protein complex from the mice and injected it into healthy animals.
They too showed signs of cognitive impairment and memory loss.
The authors suggest these protein complexes impair memory independently of plaques or nerve cell death, and could trigger a series of events leading to Alzheimer's disease.
They will now carry out further work to try and understand how this happens.
'Innovative and exciting'
Professor Karen Ashe, of the University of Minnesota, who led the research, said: "Finding the cause of memory loss and cognitive decline gives scientists a protein complex to target.
"Now we can begin work on how that protein leads to the disease and what we can do to prevent it harming the brain."
This finding could potentially be used to detect, and perhaps prevent, the disease long before more serious signs of memory loss arise - and distinguish them from those experiencing age-related memory loss. .
Professor Clive Ballard, director of information and research at the Alzheimer's Society, said the study was innovative and exciting study.
He added: "The study is an extremely important finding which will spur the development of new treatments and provide possible opportunities for the early identification of people at risk of developing Alzheimer's disease."