A major breakthrough was made by researchers from Melbourne in diagnosing Alzheimer's 15 years before symptoms strike, offering hope of avoiding dementia.
The discovery gives drug companies a target to aim for as they search for a cure to Alzheimer's.
A team from the Austin Hospital has tracked the build up of a waste protein called amyloid, discovering levels that can be detected accumulating in the brains of those who will go on to suffer dementia 15 years before they suffer extensive memory loss, the Herald Sun reported.
Speaking from an international gathering of Alzheimer's disease experts in Florence, lead researcher Prof Christopher Rowe said that the breakthrough meant doctors and researchers now knew who to target with emerging anti-dementia drugs.
"If somebody was going to get Alzheimer's disease at 70 years old, our study shows that process would actually start when they were 40, and by the age of 55 we would be able to pick it up on our amyloid PET scans, which show it building up in the brain," Prof Rowe said.
"The hope is that if we get in early and get people on these drugs it will stop the build up and stop them experiencing dementia," he added.
Amyloid is a waste product left over when brain membranes are replaced which are cleared by most people, but which can gradually build up in others later in life, causing dementia after 30 years.
While the high cost of PET scans makes them unsuitable as a routine Alzheimer's screening test, Prof Rowe said that blood tests were now being worked on to measure accumulating levels of amyloid.
The findings are published in the journal The Lancet Neurology.