TREM2 and neurodegenerative disease: Heterozygous missense mutations in TREM2 also increase the risk for other neurodegenerative diseases (Borroni et al, 2013; Rayaprolu et al, 2013; Cuyvers et al, 2014), and homozygous loss‐of‐function mutations in TREM2 cause Nasu–Hakola disease (NHD) (Paloneva et al, 2002) and frontotemporal dementia (FTD)‐like syndrome (Guerreiro et al, 2013b), which are both early‐onset neurodegenerative diseases presenting as a frontal syndrome.