Homozygous mutations in TREM2 or its intracellular signaling partner DAP12 are causal for Nasu-Hakola disease (NHD), which is associated with bone cysts and an early-onset dementia (Paloneva et al., 2000, Paloneva et al., 2002), while a frontotemporal dementia (FTD)-like syndrome without bone dysfunction has also been described in patients carrying certain TREM2 mutations (Chouery et al., 2008, Giraldo et al., 2013, Guerreiro et al., 2013b). Here, TREM2 is linked to frontotemporal dementia.