In the brains of individuals with AD and preclinical AD (i.e., evidence of Aβ and tau deposition in the brain without any clinical manifestation of the disease), as well as patients with MCI (a mild clinical impairment with no proof of underlying pathology with biomarkers), many oxidative damage products are measured, and numerous investigations have pointed to OS as a key and early player in the pathogenesis of neurodegeneration and AD [18,19]. The gene discussed is MAPT; the disease is Alzheimer disease.