In the early stages of neurodegenerative diseases, anti-inflammatory cytokines such as transforming growth factor beta (TGF-β), glial cell-derived neurotrophic factor (GDNF) and some interleukines (IL-4, IL-10 and IL-13) guide microglia to a neuroprotective state (M2 microglia) leading to the release of diverse neuroprotective factors such as insulin-like growth factor (IGF-1) [121, 122]. This evidence concerns the gene GDNF and neurodegenerative disease.