APOE and major depressive disorder: We found that the nucleus basalis of Meynert mean diffusivity mean voxel value remained a predictor of cognitive impairment when adjusted for the UPSIT, RBDSQ, Geriatric Depression Scale, MDS-UPDRS-III, APOE, amyloid-β:tau ratio, axial gait, and white matter lesion volume (Supplementary Table 2).