MAPK3 and Alzheimer disease: That is also shown by the observations (1) that cognitive impairment may frequently reverse and become normal in MCI where the level of TGF-β is normal but (2) that does not happen in AD where the level of TGF-β is reduced, and (3) as compared with controls, the levels of ERK1/2 were +77% in the CSF of patients with AD but only +22% in the CSF of patients with MCI [48].