TREM2 and Alzheimer disease: Variants of the gene “triggering receptor expressed on myeloid cells 2” (TREM2) are major genetic risk factors for late-onset Alzheimer’s disease, frontotemporal lobar degeneration, and the Nasu–Hakola disease (Paloneva et al, 2002; Guerreiro et al, 2013; Guerreiro et al, 2013; Jonsson & Stefansson, 2013; Rayaprolu et al, 2013; Borroni et al, 2014; Cady et al, 2014; Cuyvers et al, 2014).