CYP27A1 and Alzheimer disease: Acknowledging the fact that CYP27A1 expression is considerable in neurons, its expression, and consequently 27-OHC levels, might decrease due to neuronal death; however, 27-OHC levels rise markedly over the course of AD because CYP27A1 is also expressed in astrocytes and microglia, potentially leading to in situ generation of the oxysterol [131].