One‐year Longitudinal Stability of Plasma Biomarkers Associated with Dementia in Normal Controls

Background Regular examinations to assess dementia play a role in its prevention and early diagnosis. Plasma biomarker assays are possibly the most appropriate for routine assessments or monitoring severity of dementia in the clinic. To accomplish this task, the natural changes in biomarker levels over time should be determined first. With this information, the abnormal changes in plasma biomarker levels in longitudinal clinical visits could be determined. However, such studies are very rare. Method In this study, 27 subjects with normal cognition were enrolled for a 1‐year longitudinal study. Two of the 27 subjects returned for a follow‐up visit 71 days and 195 days after the first visit. Fourteen subjects returned 112–139 days after the first visit. Four subjects returned 132 and 405 days after the first visit. Five subjects returned 190 days after the first visit. Four participants returned 299 and 344‐405 days after the first visit. Plasma biomarkers of total tau protein (T‐Tau), amyloid β 1‐42 (Aβ 1‐42 ), α‐synuclein and TAR DNA‐binding protein (TDP‐43) were assayed using immunomagnetic reduction (IMR). Result The occurrence percentages in the set of recovery rates were 0.8–1.2 and nearly higher than 85% for T‐Tau, Aβ 1‐42 and Aβ 1‐42 xT‐Tau but were 74.1% for α‐synuclein and 77.8% for TDP‐43. Plasma T‐Tau and Aβ 1‐42 showed a high degree of longitudinal stability, whereas plasma α‐synuclein showed poor stability over time. Conclusion Although there was a certain variation range for the plasma biomarker concentrations compared to baseline in the return visits, the concentration measurements of each biomarker for every normal subject at each visit were below the cutoff values to discriminate Alzheimer’s disease, Parkinson’s disease or frontotemporal dementia from normal controls. These results imply that the risk of misdiagnosis of dementia due to longitudinal instability using plasma biomarkers is low.