TREM2 and Alzheimer disease: A growing body of evidence provides new insight into the multifaceted roles of TREM2 in regulating extracellular Aβ pathology (Wang et al., 2016; Lee et al., 2018), hyperphosphorylation and aggregation of tau (Bemiller et al., 2017; Leyns and Holtzman, 2017; Sayed et al., 2018), microgliosis and inflammation in AD (Zhong et al., 2015, 2017b; Zheng et al., 2016; Jay et al., 2017a; Ulrich et al., 2017).