Fragile X syndrome is the most common inherited form of mental impairment, affecting approximately 1 in 4000 males and 1 in 8000 females. In addition to intellectual disability, children with FXS exhibit behavioral problems, sensory hypersensitivity, language delay, and as many as 30% also have autism or autistic traits. The disease is caused by a CGG trinucleotide repeat expansion in the 5’ untranslated region of the FMR1 gene, which leads to its transcriptional silencing and loss of the Fragile X Mental Retardation Protein (FMRP). FMRP has important roles in translational control of a large number of messenger RNAs, many of which encode for synaptic proteins. The resultant dysregulated expression of many proteins involved in synaptic development causes major disruptions in synapse maturation and experience-dependent wiring of brain circuits.