APOE and Alzheimer disease: Through genome-wide association studies and other methods, it was found that many genes related to lipid metabolism, immune response and endocytosis were correlated with the occurrence of sporadic AD, including APOE, TREM2, PICALM, and CLU, et al. Among them, apolipoprotein E4 (ApoE4), which is mainly expressed by astrocyte, is the most relative genotype to AD [52].