MAPT and Alzheimer disease: Key findings revealed three progressive patterns: (1) DTI-ALPS index significantly declined in AD versus HC/MCI (p < 0.001); (2) Hippocampal FA reduction plateaued at MCI stage while right MD showed continued progression to AD; (3) CSF biomarkers exhibited hierarchical amyloid depletion (Aβ42↓) and tau accumulation (t-tau↑).