MS4A1 and Alzheimer disease: Recently, the role of inflammation in AD has been re-evaluated, as GWAS studies have reported several AD-associated genes beyond TREM2, including ABI3, CASS4, CD33, CR1, HLA-DRB1/5, IL1RAP, MEF2C, MS4A1, MS4A4E, PLCγ2, SHIP1, and PU.1 that are expressed selectively or preferentially in microglia (Heppner et al., 2015; dos Santos et al., 2017; Sims et al., 2017; Bis et al., 2018).