MAPT and Alzheimer disease: Alves et al. found that CSF p-tau181 levels in PD-MCI patients are significantly higher than in PD patients without cognitive impairment, but the increase is less pronounced compared to AD-MCI patients and lacks strong correlation with hippocampal atrophy, suggesting that Tau pathology in PD-MCI may be confined to subcortical regions (such as the brainstem and limbic system) (31).