The two enzymes catalyzing cholesterol oxidation into 24-OH or into 27-OH, respectively, 24-cholesterol hydroxylase (CYP46) and 27-cholesterol hydroxylase (CYP27), showed an abnormal pattern in the AD brain, with increased expression of 24-cholesterol hydroxylase in the neighborhood of amyloid plaques (Brown et al., 2004). This evidence concerns the gene CYP46A1 and Alzheimer disease.