Plasma and neurostructural biomarkers in the clinical-biological characterization of early stages of the Alzheimer's disease continuum: findings from the Compostela Aging Study.

Recent technical advances in peripheral blood analysis have enabled precise quantification of Alzheimer´s Disease (AD) biomarkers in the early stages of the AD continuum, in an economical, non-invasive and safe manner. The main objective of this study was to contribute to the clinical-biological characterization of the initial stages of cognitive impairment by measurement of blood and neurostructural AD biomarkers in groups of participants classified according to their cognitive clinical phenotype. Plasma concentrations of p-tau217, p-tau181, total tau, neurofilament light chain and amyloid-β 42/40 ratio biomarkers were measured along with APOE gene variants, hippocampal volume and cortical thickness of the AD signature regions. The cohort of 329 participants included Cognitively Unimpaired (CU), Subjective Cognitive Decline (SCD), single-domain amnestic Mild Cognitive Impairment (sd-aMCI), multidomain aMCI (md-aMCI), and single-domain non-amnestic MCI (sd-naMCI) groups. P-tau217 concentrations were significantly higher in the md-aMCI and sd-aMCI groups than in the CU, SCD and sd-naMCI groups. P-tau181 concentrations were significantly higher in md-aMCI group than in CU, SCD and sd-naMCI groups. Hippocampal volume and AD signature cortical thickness were significantly lower in the md-aMCI group than in the CU, SCD and sd-naMCI groups. No across group differences were found in the distribution of carriers/non-carriers of APOE-ε4. Mediation analysis revealed that hippocampal volume and AD signature cortical thickness mediated the relationship between p-tau217 and p-tau181 levels and cognitive performance. Sd-aMCI and md-aMCI represent two distinct and sequential clinical-biological stages of the AD continuum. Conversely, sd-naMCI does not appear to be associated with AD pathology. Finally, the SCD group does not seem to display a higher risk of progression along the AD continuum than the CU group.