It is pertinent to note that TREM2 expression was reduced in hippocampus from AD patients compared to controls (Zhao et al., 2013), although increased TREM2 expression has also been shown in AD-like mouse models and models of demyelinating disease (Piccio et al., 2007; Cantoni et al., 2015; Jay et al., 2015; Wang et al., 2015). This evidence concerns the gene TREM2 and Alzheimer disease.