A blood test has been developed that can predict the onset of Alzheimer's symptoms up to three years in advance.
According to the scientists responsible, it could mean that early diagnosis of dementia in older people is possible.
However, the test has raised some concerns with its 90 per cent accuracy - meaning that one in ten people could be wrongly diagnosed with Alzheimer's.
The researchers believe that this could be the first step towards finding an effective treatment for the disease, possibly a cure.
Alzheimer's is a mental illness that breaks down the membranes in certain brain cells.
This causes fatty chemicals that circulate the bloodstream known as lipids to change, which is what the scientists involved researched for this particular study.
Ten lipids in the blood were analysed by Dr Howard Federoff of Georgetown University Medical Centre in Washington and his team.
Dr Federoff said: "Our novel blood test offers the potential to identify people at risk for progressive cognitive decline and can change how patients, their families and treating physicians plan for and manage the disorder."
A total of 525 individuals were looked at for the study, all of whom were healthy and over the age of 70.
They were tested before the researchers monitored them over a period of five years to see whether they developed any signs of Alzheimer's or other dementia-related illnesses.
When a few did, the lipids in those subjects were identified and then used to predict whether the others would begin to display similar symptoms.
Doug Brown, director of research and development at the Alzheimer’s Society, was cautious about the opportunities this would provide.
He said: "Having such a test would be an interesting development, but it also throws up ethical considerations. If this does develop in the future, people must be given a choice about whether they would want to know."
Dr Federoff said that he was designing a clinical trial for patients with a high-risk of developing Alzheimer's disease.