Project Summary Our objective is to develop a blood-based diagnostic for Pre-symptomatic detection of Alzheimer's disease (AD) based on a Multiparameter Profiling (PreAMP). Currently there are over 18 million cases of AD worldwide, with the number of cases expected to nearly double over the next 15 years. In the US alone, total economic costs are estimated at nearly $200 billion per year1. Diagnosis is complex, costly and time-consuming. In part because of the lack of diagnostic tools and because AD represents a continuum of neurodegenerative disorders that share overlapping symptoms and protein pathologies. For these reasons, ~58% of dementia is thought to be undiagnosed altogether, which result that many patients do not receive adequate, timely care or treatment2. Recent work has revealed that forms of the aggregated proteins commonly found in the brains of AD patients can also be detected in the blood, showing promise for the development of a blood-based diagnostic. So far, however, different studies have emphasized single markers over a multiparameter approach, with no consensus as to which marker is superior3-9. Therefore, a multiparameter biomarker assay may prove to be extremely valuable for early diagnosis of a diverse range of patients against a continuum of dementias. The vast majority of biomarker efforts have focused on detection of non-toxic variants rather than the actual toxic aggregated protein species involved in neurodegeneration. Recently, our project team has developed novel biopanning technologies that enabled us to generate single chain antibody variable domain antibodies (scFvs) that bind to disease-specific variants of four key neuronal proteins implicated in AD and Related Dementias (ADRD): tau, Aβ, TDP-43, and α-syn. Our scFvs react only to the variants found in brain and plasma samples from ADRD patients but not cognitively normal controls10-12. Levels of Aβ and TDP-43 oligomers recognized by four of our scFvs were significantly elevated years before an initial diagnosis of mild cognitive impairment (MCI)9. During disease progression, we found that biomarker profiles change, so our antibody-based diagnostic could also be used to stage progression of AD from pre-symptomatic through late stage, permitting clinical stratification of patients to support experimental therapy decision-making for ADRD9. Building from this work, this proposal is designed to develop a blood-based diagnostic for AD called PreAMP. The specific aims are to: 1) develop a low-volume, multiplex antibody assay for quantitation of plasma protein variants. 2) determine the optimal biomarker set for pre-symptomatic diagnosis of AD, 3) validate the assay performance in a blinded retrospective study of longitudinal AD patient samples.