CD33 and Alzheimer disease: Other rare variants previously described include 29 risk loci implicating 215 immunity processes and microglial activation (i.e., CD33, TREM2, and INPP5D) [8], lipid metabolism [9], tau binding proteins, APP metabolism [10], and four novel loci showing sex-specific association with AD risk (GRID1, RIOK3, MCPH1, ZBTB7C) [11].