This observation, together with the finding that proNGF levels are higher in AD versus FTD samples, suggests that a higher proNGF level is not always related to a higher NGF level, as might be expected, but depends on the disease, in a fine tuning of the relative concentrations and distribution of all the actors of the NGF system (proNGF, NGF, and receptors), whose unbalance with respect to the physiological conditions may generate distinct processing patterns and ensuing signaling dysmetabolism, resulting in different diseases. Here, NGF is linked to Alzheimer disease.