The aim of the study is to evaluate the role of cholesterol in the pathogenesis of neurodegenerative dementias. Hypercholesterolemia is a known risk factor for Alzheimer disease (AD) and oxysterols, the principal cholesterol metabolites, are involved in neuroinflammation, amyloid aggregation and tau accumulation. Oxysterols will be measured in different biological samples (post-mortem brain tissue, CSF and plasma) in patients with different neurodegenerative dementias, AD, frontotemporal dementia (FTD) and primary tauopathies. This will allow establishing whether their modifications correlate primarily with Aß deposition, tauopathy or neuronal loss with the aim of finding a correlation with the severity and progression of the disease. Since preliminary results suggest that the levels of most oxysterols in the brain significantly increase in parallel with the levels of the enzyme PCSK9, we will explore the role of cholesterol metabolism and PCSK9 in AD and other dementias to evaluate if cholesterol dysregulation represents a common alteration in these neurodegenerative disorders or is specific for AD.