TREM2 is exclusively expressed by microglia in the CNS (Colonna, 2003; Thrash et al., 2009) and missense variants have been recognized as a risk factor for ALS, FTD, Alzheimer’s and Parkinson’s disease (Rayaprolu et al., 2013; Cady et al., 2014; Harms et al., 2014). The gene discussed is TREM2; the disease is frontotemporal dementia.