APOE and Alzheimer disease: Compared with the healthy control group, the levels of serum total cholesterol (TC), low‐density lipoprotein (LDL), Apo B100, and plasma Apo E ε3/ε4 were higher in the AD group, and serum high‐density lipoprotein (HDL) level was lower in the AD group (both p < 0.05).