APOE and Alzheimer disease: Given that apoE genotype is by far the strongest genetic factor modulating Aβ deposition, and the risk of suffering AD associated with TREM2 variants is comparable to that of the apoE4 allele, an interaction between apoE and TREM2 connects these two key AD risk factors, which could have pivotal roles in the pathogenesis of AD (Engstrom et al., 2017; Jendresen et al., 2017; Pankiewicz et al., 2017).