TREM2 and Onset: Genetic risks for sporadic, late-onset AD have been linked to Triggering Receptor Expressed on Myeloid Cells 2 (TREM2), which is expressed in microglia (Jin et al., 2014; Jonsson et al., 2013; Nguyen et al., 2020; Prokop et al., 2019; Ulrich et al., 2017).