Intriguingly, whereas TREM2 (triggering receptor expressed on myeloid cells 2) and APOE (apolipoprotein E) are major AD risk genes [15–17], the expressions of TREM2 and APOE in microglia were found to be necessary for the induction of DAM/ARM/MGnD in both AD and ALS model mice [12–14]. Here, TREM2 is linked to Alzheimer disease.