In RTT models, where these pathways are down-regulated, IGF1 induces an increase in the relative markers of neuronal function (Tropea et al., 2009; Castro et al., 2014), whilst in FXS models, where they are up-regulated, an (1-3)IGF1 analog induces a decrease in the cellular pathways (Deacon et al., 2015). This evidence concerns the gene IGF1 and fragile X syndrome.