Aβ_42/40 and p-tau 181 as disease biomarkers in atypical Alzheimer's disease

Background: Studies suggest that plasma Alzheimer's disease (AD) biomarkers may aid in the overall diagnosis of AD, but their utility among patients with atypical clinical presentations of AD are unknown. Objective: The main objective of this study was to determine the relationship between amyloid-β (Aβ) and tau plasma biomarkers and PET measures of both Aβ and tau in atypical AD. The secondary objective was to determine if plasma biomarkers could differentiate patients with different atypical AD phenotypes and whether they were related to measures of disease severity. Methods: We assessed whether plasma p-tau 181 and Aβ_42/40 were associated with Aβ and tau PET uptake, clinical phenotype and severity in 77 patients with PET biomarker-confirmed atypical AD. Results: Plasma Aβ_42/40 ratio showed positive associations with tau PET uptake, with higher (more normal) Aβ_42/40 ratio associated with higher tau uptake; the ratio was not associated with Aβ PET. No associations were noted with plasma p-tau 181. Plasma Aβ_42/40 ratio and p-tau 181 concentrations were not associated with AD phenotype or cognitive severity. Conclusion: Plasma Aβ_42/40 ratio and p-tau 181 concentrations are not associated with amyloid or tau PET or with clinical severity among individuals presenting with atypical AD.