Additionally, the concentration of PAR showed a significant positive correlation with TREM2 expression in the caudate of AD brains (Figure 2d, rs = −0.542, p = 0.020), which potentially explained the hypothesis that poly (ADP-ribose) polymerase-1 (PARP-1) modulate microglial phenotypes [37]. This evidence concerns the gene PARP1 and Alzheimer disease.