MAPT and major depressive disorder: At this aim, in this study we studied elderly patients affected by dementia coupled with depression undergoing a complete diagnostic work-up, including 2-[18F]fluoro-2-deoxy-d-glucose positron emission tomography (18FFDG-PET) and lumbar puncture (LP) for CSF biomarkers analysis (tau proteins and β-amyloid42–Aβ42), and then followed for 2 years.