Considering that reduced antioxidant enzyme activity, specifically superoxide dismutase, glutathione peroxidase, and glutathione reductase, and increased levels of 8-isoprostane were found in the CSF, plasma, and urine of patients with mild cognitive impairment (MCI) [65], a condition commonly seen in pre-AD patients, it is likely that the failure of antioxidant therapy in the treatment of AD can be ameliorated through earlier intervention. This evidence concerns the gene GSR and Alzheimer disease.