One such gene is Triggering Receptor Expressed on Myeloid Cells 2 (TREM2) [11,12,13], which senses brain tissue damage due to aging or neurodegeneration by triggering a microglial response aimed at scavenging and clearing brain tissue debris [14,15,16,17]; genetic variants which impair this function also increase the risk of AD more than threefold [18,19]. The gene discussed is TREM2; the disease is Alzheimer disease.