CR1 and Onset: Furthermore, Genome‐Wide Association Studies (GWAS) have also determined many gene mutations related to an elevated risk of late‐onset AD (LOAD) and most are expressed abundantly in microglia, such as triggering receptor expressed on myeloid cells 2 protein (TREM2), complement receptor type 1 (CR1) and CD33 (Karch & Goate, 2015).