TREM2 and Alzheimer disease: In the last 3 years, there has been growing evidence for the importance of genetic risk factors in AD pathogenesis with the discovery of 10 new loci from genome-wide association studies (GWAS) (Hollingworth et al., 2011; Naj et al., 2011), and, most recently, the identification of heterozygous rare variants in TREM2 as a cause of increased susceptibility to late-onset AD (Guerreiro et al., 2012; Jonsson et al., 2012).