MAPT and Mental deterioration: In MCI higher NfL levels (β<sub>main</sub> = -0.690, p<sub>FDR</sub> = 0.025) were associated with faster cognitive decline independent of tau-PET signal.<h4>Conclusions</h4>Biomarkers of co-existing pathological processes, in particular vascular pathology and axonal degeneration, interact with levels of tau pathology on its association with the downstream effects of AD pathology (i.e. brain atrophy and cognitive decline).