TREM2 and Nasu-Hakola disease: TREM−/− mice have an osteopenic phenotype similar to Nasu-Hakola disease. In vitro, lack of TREM2 impairs proliferation osteoclast precursors and affects the rate of osteoclastogenesis by accelerating differentiation into mature osteoclasts [93] suggesting different effects of knocking out TREM2 in vivo and in vitro.