Interestingly, genome wide association study (GWAS) analyses of sporadic AD cases have shown that variants of highly expressed microglial transcripts (including: membrane-spanning 4-domains sub family A member 6A (Ms4a6a), Cd33 and Trem2, are associated with an increased risk of AD, thus suggesting that microglia play an important role not only in the development but also in the onset of the disease (Heneka et al., 2014; Karch and Goate, 2015). This evidence concerns the gene TREM2 and Alzheimer disease.