Consistent with the discussions in Section 4.2, PARP1 mRNA expression is increased in hippocampus and entorhinal cortex (Figure 4) [154]; while APE1 mRNA is only reduced in entorhinal cortex, POLβ is significantly reduced in frontal cortex, hippocampus, and entorhinal cortex (Figure 4) [154], suggesting a possibility for alterations in more than one factor to impair BER during AD pathogenesis. Here, PARP1 is linked to Alzheimer disease.