Scientists are edging closer to developing a “game changing” blood test that could detect Alzheimer’s years before a patient shows symptoms.
The disease has no set diagnosis, with suspected patients being assessed and possibly undergoing a brain scan.
Alzheimer’s can come about when abnormal amounts of the protein tau accumulate inside nerve cells, forming tangles that block neurone communication.
Scientists from Lund University in Sweden found high levels of the protein p-tau217 in a person’s blood was linked to Alzheimer’s-like changes in the patient’s brain tissue after they died.
In those who were genetically at-risk of the disease, p-tau217 levels began to rise 20 years before they showed cognitive decline.
While Alzheimer’s is incurable, one expert said an effective treatment would “need to be started before symptoms develop”, which would require “mass screening”.
‘Urgent need for simple, inexpensive’ Alzheimer’s test
Alzheimer’s is the most common form of dementia, an umbrella term for a progressive loss in brain function, which affects around 850,000 people in the UK.
“There is an urgent need for simple, inexpensive, non-invasive and easily available diagnostic tools for Alzheimer’s,” said Dr Maria Carrillo from the Alzheimer’s Association.
“New testing technologies could also support drug development in many ways.
“For example, by helping identify the right people for clinical trials and by tracking the impact of therapies being tested.
“The possibility of early detection and being able to intervene with a treatment before significant damage to the brain from Alzheimer's disease would be game changing for individuals, families and our healthcare system.”
To uncover the potential of a blood test, the Lund scientists looked at more than 1,400 people, some of whom had Alzheimer’s.
After analysing different biomarkers in blood and spinal fluid, as well as positron-emission tomography (PET) scans, they found p-tau217 distinguished Alzheimer’s from other neurodegenerative disorders with up to 98% accuracy.
Brain changes that occur before Alzheimer’s symptoms appear can be reliably assessed via PET scans, which require injecting a patient with a mildly radioactive drug to highlight areas where cells are overly active.
Doctors can also measure amyloid and tau proteins in spinal fluid. All of these approaches are expensive and reasonably invasive.
In the Lund study, the scientists found testing for p-tau271 in the blood better detected Alzheimer’s than assessing other tau or amyloid proteins, or magnetic resonance imaging (MRI) scans.
Similar to tau, abnormal amyloid levels can clump together, forming plaques that collect between nerve cells and disrupt cell function.
The scientists also found p-tau217 in blood samples collected while a patient was alive could detect Alzheimer’s-related brain changes in tissue analysed post-mortem.
Further results – presented at the Alzheimer’s Association International Conference – revealed the test distinguished between people who had plaques and tangles from those without such brain changes with 89% accuracy.
This rose to 98% in those with plaques and “more extensive” tangles.
Overall, p-tau217 levels were around seven times higher in Alzheimer’s patients.
Levels became elevated around 20 years before cognitive impairment set in among those with a gene predisposing them to the disease.
“This test, once verified and confirmed, opens the possibility of early diagnosis of Alzheimer’s before the dementia stage, which is very important for clinical trials evaluating novel therapies that might stop or slow down the disease process,” said lead author Dr Oskar Hansson.
Professor David Curtis from University College London called the results “robust”, but added they throw up potential implications.
“Many researchers believe effective treatment for Alzheimer’s disease will need to be started before symptoms develop,” he said.
“This will entail mass-screening, just as is now done to detect people with high cholesterol.
“The potential implications of such predictive tests could raise some challenging issues for society.
“Do people want to know that they will develop Alzheimer’s disease, given that there is no treatment? There may well be some difficult ethical issues to think about.”
Another expert called the results “encouraging”, but added a blood test will not be available anytime soon.
“We remain a long way from a blood test to detect Alzheimer’s disease,” said Professor John Gallacher from the University of Oxford.
“Simply, the predictive value of a test is much lower in a general population than in the laboratory and the ethical concerns of getting it wrong much greater. The search continues.”