Researchers at Washington University School of Medicine built models using plasma p‑tau217 to estimate the likely age of symptomatic Alzheimer’s disease onset, with average uncertainty of three to four years. The Nature Medicine study analyzed data from over 600 older adults across two cohorts and found p‑tau217 levels correlate with PET measures of amyloid and tau accumulation. Lead author Kellen Petersen likened amyloid and tau accumulation to tree rings: patterns that reveal timing. The models showed that older individuals typically had shorter intervals from biomarker elevation to symptom emergence than younger participants, suggesting age‑dependent resilience differences. Investigators caution that while promising for population‑level stratification and trial recruitment, plasma p‑tau217 clocks are not yet recommended for routine clinical screening in cognitively normal individuals outside research settings.