FMR1 and fragile X syndrome: Our current hypothesis is that activation of 5-HT7 receptors, by correcting mGluR-mediated mechanisms in Fmr1 KO mice, besides reversing abnormal mGluR-LTD can also rescue other typical phenotypes of FXS, particularly abnormal dendrite morphology, cognitive impairment and autistic behavior (Osterweil et al., 2012; Ciranna and Catania, 2014).