TREM2 and Alzheimer disease: However, genes in group 2 include DDR2 (regulates TREM2, microglia and neurotoxic proteins) (Hebron et al., 2017), IP6K3 (Inositol phosphate metabolism) (Crocco et al., 2016), and GJA1 (regulates known AD risk factor genes) (Kajiwara et al., 2018).