While extensive studies in the field have been focused on using TREM2 KO or loss-of-function variant mouse models to understand its functional roles in AD, there were TREM2 Tg mouse models developed to determine the effects of TREM2 over-expression under genomic regulation through a bacterial artificial chromosome (BAC) transgenic approach [149, 150]. The gene discussed is TREM2; the disease is Alzheimer disease.