Cholesterol and 24S-hydroxycholesterol, which is formed from cholesterol via the Cytochrome P450 46A1(CYP46-A1) enzyme [13,14], are involved in the neuropathology of Alzheimer’s disease, and the primary genetic risk factor for Alzheimer’s disease is apolipoprotein E-ε4 [6]. The gene discussed is CYP46A1; the disease is Alzheimer disease.