In healthy white matter, this movement is influenced by the organization of axons and myelin. “PSMD focuses on white matter tracts and provides an overall value for each individual. In the study, particularly among people with Down syndrome, PSMD identified abnormalities in cases where white matter hyperintensities were not yet present. PSMD was also associated with cerebral microbleeds and white matter hyperintensities, two radiological markers linked to vascular damage and cerebral small vessel disease. Taken together, these findings suggest that white matter damage in Alzheimer’s disease does not depend on a single mechanism but instead results from a combination of neurodegenerative, vascular, and inflammatory processes.