However, other factors such as the abnormal aggregation of tau protein [16], expression of apolipoprotein E variant APOE4 [17], herpes virus and coronaviruses (including SARS-CoV2) infections [18–21], diabetes [22,23], brain inflammation [24], oxidative damage in cells [25–27], endoplasmic reticulum and ciliary dysplasia [28–31], myelin dysplasia [32,33], and retrotransposons activities [34–36] have also been reported to influence the onset and progression of AD. Here, APOE is linked to diabetes mellitus.