Young adults, who carry a genetic variant that raises their risk of developing Alzheimer's Disease (AD), have different brain activity than normal adults, according to a study.
Led by scientists from the University of Oxford and Imperial College London, the brain imaging study has revealed that young carriers of APOE4 genetic variant show changes in their brain activity decades before any symptoms might arise.
The results clearly support the belief that the brain's memory function may gradually wear itself out in those who go on to develop Alzheimer's.
The study provides clues as to why certain people develop AD, paving the way towards a diagnostic test that identifies individuals at risk.
Not everyone who carries the APOE4 variant will go on to develop AD, but people who inherit one copy of the gene have up to four times the normal risk of developing the late-onset variety of the disease.
Those having two copies of the gene have around ten times the normal risk.
The study's researchers stress that most carriers of APOE4 will not go on to develop Alzheimer's and carriers should not be alarmed by the study's findings.
However, the study is the first to show hyperactivity in the hippocampus of healthy young carriers and also the first to show that APOE4 carriers'' brains behave differently even at ''rest''.
For the study, the researchers used functional Magnetic Resonance Imaging (fMRI) to compare activity inside the brains of 36 volunteers, with 18 carrying at least one copy of the APOE4 gene and 18 non-carriers acting as controls.
Looking at how the volunteers'' brains behaved while they were resting and also while they were performing a memory-related task, the researchers found that carriers and non-carriers each had distinct patterns of brain activity even when the APOE4 carriers were resting.
The fMRI scans showed visible differences in how the hippocampus was relating to the rest of the brain.
Now, the researchers will carry out a similar study of patients with mild cognitive impairment to explore how these differences in patterns of brain activity in young people may be associated with later changes.
Dr Clare Mackay, the lead author of the study, said: "We have shown that brain activity is different in people with this version of the gene decades before any memory problems might develop."
"We've also shown that this form of fMRI, where people just lie in the scanner doing nothing, is sensitive enough to pick up these changes. These are exciting first steps towards a tantalising prospect: a simple test that will be able to distinguish who will go on to develop Alzheimer's," Mackay added.
The study has been published in the journal Proceedings of the National Academy of Sciences.