TREM2 and Alzheimer disease: This aim was motivated by recent findings of a close relationship between tau pathology and white matter diffusion alterations (Sydykova et al., 2007; Kantarci et al., 2017; Jacobs et al., 2018), as well as alterations of CSF levels of TREM2, a marker of microglia activity in Alzheimer’s disease (Kleinberger et al., 2014; Suarez-Calvet et al., 2016a, b).