Using a blood test as a clock for Alzheimer’s: can a single test predict when symptoms may begin? What is p-tau217? p-tau217 is a modified form of the tau protein found in blood that reflects Alzheimer’s disease related brain changes that may involve amyloid plaques and tau tangles. Kellen Petersen and colleagues describe in a new paper in Nature Medicine how plasma p-tau217 clock models may estimate when individuals will develop symptomatic Alzheimer’s disease. Key Points: - Plasma p-tau217 levels followed consistent trajectories across individuals and could be modeled as biological clocks to estimate the timing of Alzheimer’s disease progression. - The estimated age at plasma p-tau217 positivity was associated w/ the age when Alzheimer’s symptoms began, allowing prediction of symptom onset using a blood test. - Models predicted the age of symptom onset w/ a median error of roughly 3 to 4 years, suggesting usefulness for selecting participants for enrollment in prevention trials. My take: Blood biomarkers are reshaping neurology. The ability to estimate not only risk but also timing of disease could transform prevention trials and one day clinical care. These results suggest that Alzheimer’s disease progression may follow a biological clock that can be measured from the bloodstream. We should remember that prediction models are not destiny and they should not yet be used by individuals to estimate their own future disease timeline. Here are 5 points that resonated w/ me: 1- A single blood biomarker may allow health care providers to estimate when Alzheimer’s symptoms might appear. 2- Plasma p-tau217 appears to reflect both amyloid and tau pathology occurring in the brain. 3- The timing from biomarker positivity to symptoms varies widely across individuals. 4- Older individuals appear to develop symptoms more quickly after biomarker positivity compared to younger individuals. 5- These biomarker clocks may help clinical trials enroll folks who are most likely to develop symptoms during the study period. nature.com/articles/s41591-0… @ParkinsonDotOrg #parkinson