The present study found that 27-OHC increased brain cholesterol levels and Aβ1-42 deposition in the cortical area and hippocampal CA1 area, confirming the hypothesis that high levels of 27-OHC could promote AD-like lesions by regulating Aβ1-42 in ApoE ε4 mice. The gene discussed is APOE; the disease is Alzheimer disease.