Intriguingly, a series of evidence demonstrated that in the brain of hereditary AD animals and patients, there are susceptible genes and gene polymorphism in the molecules responsible for the transport, uptake, and intracellular trafficking of cholesterol, including apolipoprotein E, ATP binding cassette transporters, low density lipoprotein receptor family, and Niemann-Pick Type C 1/2 (NPC1 and NPC2). The gene discussed is APOE; the disease is Alzheimer disease.