MAPT and Cognitive impairment: Therefore, we performed an ELISA test for GDF15 on the CSF of 40 AD patients (AD), subdivided into two groups on the basis of the levels of total Tau (T-Tau, considered as a biomarker for the degree of neuronal damage), as compared with the CSF of 8 age-matched, non-demented subjects (non-AD) with mild cognitive impairment (MCI) stable over at least 3 years.