APOE and early-onset autosomal dominant Alzheimer disease: In humans, there are three different isoforms resulting from the three allelic variants ε2, ε3, and ε4. APOEε4 carriers show an increased risk of the development of Alzheimer’s disease (AD), which is why a major focus of APOE research is on the relationship between APOE and AD pathology, and most studies focus on the role of APOE in the brain or neuronal cells and astrocytes [1–3].