CD33 and early-onset autosomal dominant Alzheimer disease: Recent studies have identified other genes which increase the risk of developing Alzheimer’s disease, including TREM2 (Guerreiro et al., 2012), CD33 (Hollingworth et al., 2011), SORL1 (Scherzer et al., 2004), CLU (Harold et al., 2009), ABCA7 (Hollingworth et al., 2011), PINX1 and BIN1 (Harold et al., 2009), etc. TREM2 and CD33 are expressed on microglia of the CNS and play important roles in neuroinflammation, which we will elaborate later.