Furthermore, in other clinical studies, the decreased OGG1 activity reveals the early occurrence in the progression of AD, which is possibly mediated by 4-HNE inactivation and may contribute to the elevated 8-hydroxydeoxyguanosine (8-OHdG) in the brain associated with MCI and late-stage AD (Shao et al., 2008). Here, OGG1 is linked to Alzheimer disease.