Blood test offers earliest prediction of Alzheimer's disease

(CN) — Cognitively healthy adults may show signs of Alzheimer’s disease several years earlier than previously thought possible and with less invasive testing, scientists say in a new study from Mass General Brigham.

The scientists’ findings revealed that a new blood test used to detect Alzheimer’s can predict key indicators of the disease in older adults who are otherwise cognitively healthy and show no other evidence of the disease. The new research was published in the journal Nature Communications on Tuesday.

The scientists say this research may help enable earlier disease prediction and detect who might be at risk for cognitive decline several years earlier than brain imaging scans.

Alzheimer’s disease, the most common type of dementia, begins with the buildup of proteins in the brain that form amyloid plaque and neurofibrillary tangles that cause brain cells to die over time and the brain to shrink, according to the Mayo Clinic. Memory loss is the most common symptom associated with the disease.

The new study found that a key protein, known as phosphorylated tau 217, or pTau217, found in blood plasma tests, can predict the same brain changes that show up on positron emission tomography, or PET, scans. The presence of this protein is associated with the buildup of amyloid plaque in older adults who do not yet have symptoms of Alzheimer’s disease.

“We used to think that PET scan detection was the earliest sign of Alzheimer’s disease progression, revealing amyloid accumulation in the brain 10 to 20 years before symptoms appear,” said the study’s lead author, Dr. Hyun-Sik Yang, a neurologist with Mass General Brigham Neuroscience Institute. “But now we are seeing that pTau217 can be detected years earlier, well before clear abnormalities appear on amyloid PET scans.”

The U.S. Food and Drug Administration approved the first blood test for Alzheimer’s disease last year. Researchers say the test approval paves the way for more affordable and less invasive tests, like lumbar punctures and brain scans.

The study followed 317 cognitively healthy older adults, ranging between 50 and 90 years old, for an average of eight years each. The older adults, each from the Harvard Aging Brain Study, participated in blood tests, brain scans and long-term cognitive testing.

The researchers examined whether baseline and changing pTau217 protein levels could predict future amyloid plaque buildup and cognitive decline among their participants. They found higher levels of pTau217 predicted a faster buildup of the amyloid plaque in the study, even when brain imaging scans did not appear to show any changes. Increases in the protein regularly occurred among participants before any scans showed amyloid plaque buildup. Participants with low pTau217 levels at the start of the study were unlikely to show significant amyloid plaque buildup in their scans over many years of follow-up, the study found.

“What stood out in our study is that even when amyloid scans appear normal in the clinic, the pTau217 biomarker can identify individuals who later become amyloid-positive,” said Yang. “It also shows that those with low pTau217 levels are likely to stay amyloid-negative for several years.”

Although the researchers say it’s too early to recommend pTau217 testing for older adults, they hope the study results may serve as a screening tool for clinical trials for Alzheimer’s disease prevention and identify older adults at higher risk.

Researchers say the new study also adds important evidence to the potential for these kinds of blood tests, which, they add, could be used for routine health maintenance in the future.

More than 7 million people in the United States and 55 million worldwide live with Alzheimer’s disease, the researchers note in their study. Among those in the U.S., 74% are 75 and older, a report from the Alzheimer’s Association says. That number is expected to increase as the country’s aging population continues to grow disproportionately.

“As the field is evolving quickly, we’re excited to see discoveries on the research side being rapidly translated to clinical application,” said study co-author Dr. Jasmeer Chhatwal, also a neurologist with Mass General Brigham Neuroscience Institute. “By anticipating who’s going to turn amyloid-positive in the future, we are trying to push back the clock to enable earlier Alzheimer’s disease prediction.”