TREM2 and Alzheimer disease: Whereas heterozygous variants in TREM2 are associated with AD (Guerreiro et al., 2013a, Jonsson et al., 2013), homozygous variants in TREM2 or its binding partner DAP12/TYROBP cause polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy (PLOSL), also known as Nasu-Hakola disease (NHD).