Plasma Phosphorylated Tau 217 and Aβ42/40 to Predict Early Brain Aβ Accumulation in People Without Cognitive Impairment

Abstract

Importance: Phase 3 trials of successful antiamyloid therapies in Alzheimer disease (AD) have demonstrated improved clinical efficacy in people with less severe disease. Plasma biomarkers will be essential for efficient screening of participants in future primary prevention clinical trials testing antiamyloid therapies in cognitively unimpaired (CU) individuals with initially low brain β-amyloid (Aβ) levels who are at high risk of accumulating Aβ. Objective: To investigate if combining plasma biomarkers could be useful in predicting subsequent development of Aβ pathology in CU individuals with subthreshold brain Aβ levels (defined as Aβ levels <40 Centiloids) at baseline. Design, Setting, and Participants: This was a longitudinal study including Swedish BioFINDER-2 (enrollment 2017-2022) and replication in 2 independent cohorts, the Knight Alzheimer Disease Research Center (Knight ADRC; enrollment 1988 and 2019) and Swedish BioFINDER-1 (enrollment 2009-2015). Included for analysis was a convenience sample of CU individuals with baseline plasma phosphorylated tau 217 (p-tau217) and Aβ42/40 assessments and Aβ assessments with positron emission tomography (Aβ-PET) or cerebrospinal fluid (CSF) Aβ42/40. Data were analyzed between April 2023 and May 2024. Exposures: Baseline plasma levels of Aβ42/40, p-tau217, the ratio of p-tau217 to nonphosphorylated tau (%p-tau217), p-tau231, and glial fibrillary acidic protein (GFAP). Main Outcomes and Measures: Cross-sectional and longitudinal PET and CSF measures of brain Aβ pathology. Results: This study included 495 (BioFINDER-2), 283 (Knight ADRC), and 205 (BioFINDER-1) CU participants. In BioFINDER-2, the mean (SD) age was 65.7 (14.4) with 261 females (52.7%). When detecting abnormal CSF Aβ-status, a combination of plasma %p-tau217 and Aβ42/40 showed better performance (area under the curve =0.949; 95% CI, 0.929-0.970; P