A blood test can predict Alzheimer's disease. A new discovery

The concentration of a specific protein in the blood can predict the development of Alzheimer's disease many years before symptoms appear. A test using this mechanism could identify people at risk in advance.

A team from Mass General Brigham (USA) reports that a blood test measuring plasma levels of phosphorylated tau protein 217 (pTau217), a known biomarker of Alzheimer's disease, can predict future cognitive decline in those older adults who remain cognitively healthy at the time of testing. It may also indicate the progression of changes visible in the most accurate PET (positron emission tomography computed tomography) scan to date.

These results may therefore help to move diagnosis to an earlier stage, enabling simpler and earlier prediction of the disease and identification of people at risk.

“We once believed that the detection of changes in a PET scan was the earliest signal of the progression of Alzheimer's disease and signaled the deposition of amyloid in the brain 10-20 years before symptoms appeared,” recalled Dr. Hyun-Sik Yang, author of the study published in Nature Communications. – “However, we now see that pTau217 can be detected even several years earlier, long before obvious abnormalities appear in amyloid PET studies.”

Researchers remind us that last year the FDA approved the first blood test for Alzheimer's disease. The new study provides important evidence of the predictive potential of this type of blood test.

It involved 317 cognitively healthy older adults participating in the Harvard Aging Brain Study (HABS) who were followed for an average of eight years. Volunteers aged 50 to 90 years underwent blood tests for pTau217, repeated amyloid and tau PET scans, and cognitive tests. Scientists checked whether the initial level of pTau217 and its changes over time predict future amyloid and tau protein deposition, i.e. the abnormal accumulation of misfolded proteins inside brain neurons, as well as cognitive decline.

They found that higher levels of pTau217 predicted a faster progression of Alzheimer's disease-related changes, even when initial brain imaging looked normal. An increase in pTau217 levels was often observed before amyloid PET scans became positive.

Importantly, participants with low pTau217 levels at baseline were very unlikely to have significant amyloid beta accumulation on PET scans, even over many years of follow-up.

“What particularly caught our attention was that even when amyloid scans look normal, the biomarker pTau217 can identify people who will later develop a positive amyloid result,” says Dr. Yang. – “It also shows that people with low pTau217 levels are likely to remain amyloid negative for several years.”

As the scientists emphasize, it is still too early to recommend pTau217 testing in routine practice. However, they hope that the results of their study will serve as a scalable screening tool for clinical trials aimed at preventing Alzheimer's disease and will help identify people at higher risk.

According to researchers, biomarker blood tests could ultimately be used in routine health prevention and constitute a more affordable alternative to PET tests. “Because this field is developing so rapidly, we are excited to see scientific discoveries rapidly being translated into clinical applications,” says Dr. Jasmeer Chhatwal, a neuroscientist at Mass General Brigham Neuroscience Institute and co-author of the paper. – “By trying to predict who will become amyloid positive in the future, we are trying to push back the moment the disease was detected to enable earlier prediction of Alzheimer's disease.”

Marek Matacz (PAP)

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