CD33 and Alzheimer disease: With the advent of genome-wide association studies (GWAS), a novel set of AD risk genes associated with microglial function have been identified, including Apolipoprotein E (APOE), Complement receptor 1 (CR1), TREM2, CD33, Membrane-spanning 4-domain subfamily A (MS4A), ATP-binding cassette (ABC) transporter A7 (ABCA7), and Inositol polyphosphate-5-phosphatase (INPP5D)/Src homology 2-containing inositol-5’-phosphatase 1 (SHIP1; Malik et al., 2015; Efthymiou and Goate, 2017; McQuade and Blurton-Jones, 2019; Nguyen et al., 2020).