A simple blood test that measures levels of a protein called phosphorylated tau 217 (p-tau217) may predict the risk of developing dementia up to 10 years before symptoms appear, according to findings presented at the Alzheimer's Association International Conference in London.
P-tau217 is a known biomarker for Alzheimer's disease. The study found that elevated levels of this protein in the blood were consistently linked to an increased likelihood of cognitive impairment in older adults who were cognitively healthy at the study's outset.
The research pooled data from 2,684 cognitively healthy older adults with an average age of 69, across six studies in North America, Japan, and Australia. Participants were followed for up to 13.5 years, during which 478 individuals developed cognitive impairment.
Individuals with very high p-tau217 levels had a nearly 40 percent chance of developing cognitive impairment within five years, compared to a 12 percent chance for those with low levels. Over a ten-year period, the risk for those with very high levels rose to nearly 80 percent.
Understanding the Biomarker
In Alzheimer's disease, two primary proteins are involved: amyloid-beta, which forms plaques between brain cells, and tau, which normally supports neuron structure. In Alzheimer's, tau becomes abnormally phosphorylated, detaching from internal structures and forming tangles within neurons, disrupting function and leading to cell death. P-tau217 is a specific form of this abnormal tau, noted for being one of the earliest detectable changes related to Alzheimer's, reflecting both amyloid buildup and the initial stages of tau tangle formation.
Studies indicate that p-tau217 in blood is more effective than other markers, such as p-tau181, in identifying early biological changes associated with Alzheimer's. Elevated p-tau217 levels in blood have been shown to predict amyloid buildup on brain scans with over 90 percent accuracy and closely correlate with both amyloid and tau accumulation.
Potential for Early Intervention
Researchers suggest that if further trials confirm that early intervention can delay cognitive decline, this blood test could identify individuals who might benefit most from emerging treatments targeting brain proteins or from lifestyle modifications, years before symptoms manifest.
Dr. Reisa Sperling, a senior author of the study and neurologist at Mass General Brigham Hospital, stated that while disease-modifying treatments for those identified as high-risk are not yet available, p-tau217 can currently help identify individuals for participation in prevention trials. As these trials progress, individualized risk estimates, including the prognostic value of this biomarker, could guide earlier treatment and monitoring decisions.
While the test is not yet ready for routine clinical use, experts view these findings as a significant advancement toward a future where a simple blood draw could aid in predicting and potentially mitigating the progression of dementia. The study authors cautioned that the estimates are based on selected research cohorts, not the general population, and that 10-year projections are less reliable due to the limited number of participants followed for that duration.