CD33 and Alzheimer disease: Additionally, recent studies have discovered other genes that might be peripherally involved in AD, including clusterin (CLU), complement receptor 1 (CR1), phosphatidylinositol binding clathrin assembly protein (PICALM), sortilin-related receptor (SORL1), complement factor H (CFH), the triggering receptor expressed on myeloid/microglial cells 2 (TREM2), and the cluster of differentiation 33 (CD33) gene loci; although not one single case of AD has yet been found to be associated with more than one of these aberrant genetic loci (11, 25).