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A. Feizpour, V. Doré, J.D. Doecke, Z.S. Saad, G. Triana-Baltzer, R. Slemmon, P. Maruff, N. Krishnadas, P. Bourgeat, K. Huang, C. Fowler, S.R. Rainey-Smith, A.I. Bush, L. Ward, J. Robertson, R.N. Martins, C.L. Masters, V.L. Villemagne, J. Fripp, H.C. Kolb, C.C. Rowe

J Prev Alz Dis 2023;4(10):828-836

Background: Plasma p217+tau has shown high concordance with cerebrospinal fluid (CSF) and positron emission tomography (PET) measures of amyloid-β (Aβ) and tau in Alzheimer’s Disease (AD). However, its association with longitudinal cognition and comparative performance to PET Aβ and tau in predicting cognitive decline are unknown. Objectives: To evaluate whether p217+tau can predict the rate of cognitive decline observed over two-year average follow-up and compare this to prediction based on Aβ (18F-NAV4694) and tau (18F-MK6240) PET. We also explored the sample size required to detect a 30% slowing in cognitive decline in a 2-year trial and selection test cost using p217+tau (pT+) as compared to PET Aβ (A+) and tau (T+) with and without p217+tau pre-screening. Design: A prospective observational cohort study. Setting: Participants of the Australian Imaging, Biomarker & Lifestyle Flagship Study of Ageing (AIBL) and Australian Dementia Network (ADNeT). Participants: 153 cognitively unimpaired (CU) and 50 cognitively impaired (CI) individuals. Measurements: Baseline p217+tau Simoa® assay, 18F-MK6240 tau-PET and 18F-NAV4694 Aβ-PET with neuropsychological follow-up (MMSE, CDR-SB, AIBL-PACC) over 2.4 ± 0.8 years. Results: In CI, p217+tau was a significant predictor of change in MMSE (β = -0.55, p < 0.001) and CDR-SB (β =0.61, p < 0.001) with an effect size similar to Aβ Centiloid (MMSE β = -0.48, p = 0.002; CDR-SB β = 0.43, p = 0.004) and meta-temporal (MetaT) tau SUVR (MMSE: β = -0.62, p < 0.001; CDR-SB: β = 0.65, p < 0.001). In CU, only MetaT tau SUVR was significantly associated with change in AIBL-PACC (β = -0.22, p = 0.008). Screening pT+ CI participants into a trial could lead to 24% reduction in sample size compared to screening with PET for A+ and 6-13% compared to screening with PET for T+ (different regions). This would translate to an 81-83% biomarker test cost-saving assuming the p217+tau test cost one-fifth of a PET scan. In a trial requiring PET A+ or T+, p217+tau pre-screening followed by PET in those who were pT+ would cost more in the CI group, compared to 26-38% biomarker test cost-saving in the CU. Conclusions: Substantial cost reduction can be achieved using p217+tau alone to select participants with MCI or mild dementia for a clinical trial designed to slow cognitive decline over two years, compared to participant selection by PET. In pre-clinical AD trials, p217+tau provides significant cost-saving if used as a pre-screening measure for PET A+ or T+ but in MCI/mild dementia trials this may add to cost both in testing and in the increased number of participants needed for testing.

A. Feizpour ; V. Doré ; J.D. Doecke ; Z.S. Saad ; G. Triana-Baltzer ; R. Slemmon ; P. Maruff ; N. Krishnadas ; P. Bourgeat ; K. Huang ; C. Fowler ; S.R. Rainey-Smith ; A.I. Bush ; L. Ward ; J. Robertson ; R.N. Martins ; C.L. Masters ; V.L. Villemagne ; J. Fripp ; H.C. Kolb ; C.C. Rowe (2023): Two-Year Prognostic Utility of Plasma p217+tau across the Alzheimer’s Continuum. The Journal of Prevention of Alzheimer’s Disease (JPAD).


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