TREM2 and Nasu-Hakola disease: Because TREM2 and DAP12 are predominantly expressed by microglia (Bakker et al., 2000b; Paloneva et al., 2001; Schmid et al., 2002), microglial dysfunction caused by TREM2/DAP12 impairment was assumed to be involved in the pathogenesis of Nasu-Hakola disease (Paloneva et al., 2000, 2001; Schmid et al., 2002).