A new blood test could detect Alzheimer's disease even before symptoms appear, studies suggest.
Scientists on Tuesday reported results of multiple studies on advances in blood tests for a specific form of protein - p-tau217 - which spikes in people carrying the illness.
Changes in brain proteins amyloid and tau, and their formation into clumps known as plaques and tangles respectively, are defining physical features of Alzheimer’s disease in the brain.
Presenting the findings at the Alzheimer’s Association International Conference 2020, researchers studying three different cohorts of more than 1,400 cases said that blood p-tau217 could help distinguish Alzheimer’s from other neurodegenerative disorders with diagnostic accuracy between 89-98 per cent.
The researchers were led by Dr Oskar Hansson, from Lund University in Sweden, who said the test "opens the possibility of early diagnosis of Alzheimer’s before the dementia stage".
The team estimated the test may be able to detect changes in the brain 20 years before dementia symptoms occur.
Currently, scans and tests of spinal fluid are the only ways to detect the brain changes that occur before Alzheimer’s symptoms appear. But these methods are expensive and invasive.
Early diagnosis is important because it could translate into more opportunities to treat the disease and help determine whether a drug can hold it off before it does too much damage to the brain.
Alzheimer's causes memory loss and damages other cognitive abilities by destroying connections between nerve cells in the brain when proteins build up in the brain and cause these cells to die.
Another research team at Washington University School of Medicine meanwhile found that looking at p-tau217 in the blood gave as good a picture of a patient's condition as a brain (PET) scan.
The scientists were able to observe elevated levels of the p-tau217 protein in as little as 4ml of blood.
The researchers had suspected that p-tau217 might also be present in the blood of Alzheimer’s patients, albeit at very low levels that would make it difficult to detect.
Randall Bateman, professor of neurology at Washington University School of Medicine in St Louis, said: “We therefore wanted to quantify the levels of different tau proteins, especially p-tau217, in the blood and compare them with amyloid pathology and onset of dementia to assess their potential as blood-based Alzheimer’s disease biomarkers.”
Dr Bateman, Nicolas Barthelemy and colleagues found that p-tau217 accumulates in the cerebrospinal fluid of Alzheimer’s patients before the onset of cognitive symptoms.
It increases with disease progression, and can accurately predict the formation of amyloid plaques, according to the study published in the Journal of Experimental Medicine.
Dr Bateman said: “Our findings support the idea that tau isoforms in the blood are potentially useful for detecting and diagnosing Alzheimer’s disease pathology.
“Moreover, our assay for measuring plasma tau levels could be used as a highly sensitive screening tool to identify tau changes associated with amyloid plaque formation in normal subjects, replacing costly PET imaging.”
Commenting on the developments, Dr Amanda Heslegrave, a senior research fellow at the UK Dementia Research Institute at University College London, told the BBC the findings were great news for research.
But she added but added that "while these are exciting results, you could not say that they indicate a definitive test for potential Alzheimer's disease is available right now".