Interestingly, a recent study has demonstrated that compounds activating 5-HT2B receptors or inhibiting 5-HT2A receptors could enhance phosphoinositide 3-kinase (PI3K) signaling transduction and AMPA GluR1 dependent synaptic plasticity, and restore learning in Fmr1 knockout mice, further linking 5-HT receptors to fragile X syndrome (Lim et al., 2014). This evidence concerns the gene FMR1 and fragile X syndrome.