Genetically, AD is divided into familial AD (fAD), which accounts for <5% of AD cases and is caused by the presence of pathogenic and deleterious mutations harbored in major genes (segregating in a mendelian way) such as APP, PSEN1, PSEN2 [9,16,17,18], ADAM10, AKAP9, PICALM, PLD3, TREM2, and UNC5C [19,20,21,22,23,24,25,26,27], and sporadic AD (sAD), without a clear mendelian pattern of segregation, which accounts for >90% of AD cases. Here, TREM2 is linked to Alzheimer disease.