Fernandes, Gustavo Bruniera Peres

Introduction Blood-based biomarkers offer a promising, minimally invasive approach to Alzheimer’s disease (AD) diagnosis, yet validation in admixed populations remains limited. We investigated whether plasma biomarkers predict CSF-defined AD pathology in a Brazilian cohort. Methods Seventy-eight older adults [including individuals with mild cognitive impairment (MCI), subjective cognitive decline (SCD), and cognitively unimpaired controls] underwent cognitive testing, neuroimaging, and plasma biomarker assessment. CSF data were available for symptomatic participants (MCI and SCD; n = 61), and regression and ROC analyses were performed in the subset with both CSF and APOE genotyping data ( n = 53). Plasma Aβ42, p-Tau181, p-Tau217, t-Tau, and derived ratios were quantified. Multivariable logistic regression and ROC analyses evaluated prediction of abnormal CSF p-Tau181/Aβ42 and t-Tau/Aβ42, adjusting for age, sex, and APOE ε4 status. Results Approximately 25% of individuals with MCI exhibited abnormal CSF p-Tau181/Aβ42 and t-Tau/Aβ42 ratios. Moderate correlations were observed between plasma and CSF biomarkers (r > 0.4), particularly for Aβ42/p-Tau217 and p-Tau217. In adjusted models, plasma p-Tau217 and the Aβ42/p-Tau217 ratio independently predicted abnormal CSF pathology. Each one standard deviation increase in p-Tau217 was associated with 3.53–4.83-fold higher odds of abnormal CSF ( p ≤ 0.003). In contrast, higher Aβ42/p-Tau217 ratios were associated with substantially lower odds of pathology, with each one standard deviation increase corresponding to a 91%–93% reduction in risk ( p ≤ 0.002). The ratio showed stronger associations than p-Tau217 alone. ROC analyses demonstrated good discrimination. For CSF p-Tau181/Aβ42, Aβ42/p-Tau217 achieved an AUC of 0.88 (83% sensitivity, 85% specificity), compared with 0.83 for p-Tau217. For CSF t-Tau/Aβ42, both biomarkers yielded AUCs of 0.89. Discussion Plasma Aβ42/p-Tau217 and p-Tau217 effectively identify CSF-defined AD pathology in an admixed cohort. While higher p-Tau217 levels were associated with increased odds of pathology, higher Aβ42/p-Tau217 ratios were associated with lower pathological burden and demonstrated stronger effect sizes, supporting the added value of combining amyloid and tau biomarkers. These findings provide initial evidence for local validation of blood-based AD biomarkers in Brazil.

Abstract The diagnosis of predementia stages indicates an increased risk of progression to dementia. The Amyloid, Tau, and Neurodegeneration AT(N) classification considers measurements of altered proteins and the presence of neurodegeneration to classify the risk groups regarding the pathophysiology of Alzheimer's disease (AD). The cognitive and anatomical characteristics of the patients in the predementia stage according to the AT(N) classification are not fully understood. To investigate whether there are differences in the clinical and anatomical profiles among older adults in the predementia stage according to the ATN classification, and to investigate the associations involving cognition and cortical thickness and subcortical volume in the AT(N) groups. In total, 72 older adults with subjective cognitive decline and mild cognitive impairment were allocated to groups according to the AT(N) classification (AD continuum: n = 37; suspected non-AD pathophysiology: n = 8; normal biomarkers: n = 27). The participants were investigated through cognitive tests, magnetic resonance imaging scans, and cerebrospinal fluid analyses. We used multivariate and univariate analyses with post-hoc testing to verify differences among groups. In addition, linear regressions were performed to verify the interactions involving cognition and gray matter metrics. The suspected non-AD pathophysiology group showed worse performance in attention/executive function than the AD continuum and normal biomarkers groups (p = 0.04). However, the ATN classification groups did not differ in terms of cortical thickness (p > 0.05). In addition, in the AD continuum group, memory was associated with left fusiform gyrus thickness (p = 0.000 uncorrected; r = 0.238). Cognition, but not gray matter metrics, differs among AT(N) classification groups. Memory is associated with cortical thickness in patients with positive amyloid Beta (AD continuum).