Alzheimer’s disease can be classified into three variants according to genetic backgrounds, environmental factors, and the burden of Aβ/tau pathology, neurodegeneration, and cognitive symptoms: autosomal dominant Alzheimer’s disease, APOE ε4-related sporadic Alzheimer’s disease and APOE ε4-unrelated sporadic Alzheimer’s disease [34]. This evidence concerns the gene APOE and Alzheimer disease.