TREM2 and Alzheimer disease: These transcriptional changes are regulated by the triggering receptor expressed on myeloid cells 2 (TREM2) and apolipoprotein E (APOE), two main risk genes in human AD, and lead to decreased expression of homeostatic genes together with an upregulation of genes involved in lysosomal, phagocytosis, and lipid metabolism pathways [4, 5].