Relation of fluid neurodegeneration biomarkers with white matter integrity in Alzheimer's disease patients in Latin America

Background Alzheimer's disease (AD) is increasingly prevalent in Latin America. Neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP) are promising biomarkers of neurodegeneration, but their relationship with white matter (WM) integrity remains unclear. Objective To investigate associations between fluid neurodegeneration biomarkers and WM microstructure in a Brazilian cohort of individuals across the AD continuum and cognitively healthy controls. Methods Ninety-one participants were included: 27 cognitively healthy controls (mean age = 68.3 ± 5.2 years) and 64 amyloid-positive individuals with mild cognitive impairment or AD dementia (mean age = 70.6 ± 6.9 years). AD participants were characterized by low cerebrospinal fluid (CSF) Aβ 42 concentrations (<540 pg/mL) and altered Aβ 42 /p-Tau and Aβ 42 /t-Tau ratios. Serum and CSF concentrations of NfL and GFAP were measured using single-molecule array technology and examined in relation to diffusion tensor imaging metrics, including fractional anisotropy, mean diffusivity, radial diffusivity, and axial diffusivity (AxD). Results Within the clinical AD group, higher serum NfL levels were associated with lower AxD in the left cingulum tract (r = -0.372, p = 0.007). In cognitively healthy controls, serum NfL showed positive correlations with AxD and mean diffusivity in the right cingulum (r = 0.650, p = 0.001 and r = 0.607, p = 0.003, respectively). No significant associations were observed between serum or CSF GFAP concentrations and diffusion tensor imaging metrics. Conclusions Serum NfL was associated with anatomically specific WM microstructural changes, with differing patterns across clinical groups.