Many proteins were found to be modified by protein carbonylation in AD and MCI brains, which supports the observation of altered energy metabolism, structural changes, tau hyperphosphorylation, altered Aβ production, mitochondrial dysfunction, pH alterations, etc. Protein oxidative modification (i.e., nitration, carbonylation, the subjects of this current review) almost always alters protein functionality [109,116]. The gene discussed is MAPT; the disease is Alzheimer disease.