New research suggests that plasma phosphorylated tau 217 (pTau217) can detect Alzheimer’s disease pathology years before it appears on traditional PET scans. In longitudinal studies, elevated pTau217 levels accurately predicted future amyloid accumulation and cognitive decline in currently asymptomatic, healthy older adults. While not yet recommended for routine clinical screening, this biomarker offers a potential “clock” for estimating the onset of symptoms within a three to four year margin.
Participants who were amyloid-beta-negative and had very low pTau217 (below ~2.6% in this cohort) rarely became amyloid-beta-positive, suggesting this subgroup may be low risk and might not require amyloid-beta PET until pTau217 rises, the researchers said.
Higher baseline plasma %pTau217 also predicted tau accumulation in the brain — even when amyloid levels were still low, suggesting it captures very early disease processes.
In terms of cognition, across the full cohort, higher plasma pTau217 was associated with faster decline on a composite cognitive score. However, this relationship was largely driven by individuals who already had elevated amyloid; among amyloid-negative participants, pTau217 did not significantly predict cognitive decline over the follow-up period.