Fragile X mental retardation protein (FMRP) is a widely expressed protein coded by the FMR1 gene that binds to G-quadruplex secondary structures in neurons and is involved in synaptic plasticity. FMRP acts as a negative regulator of translation, and its binding stabilizes G-quadruplex structures in mRNA transcripts, inhibiting ribosome elongation of mRNA in the neuron's dendrite and controlling the timing of the transcript's expression. Mutations of this gene can cause the development of Fragile X Syndrome, autism, and other neurological disorders. Specifically, Fragile X Syndrome is caused by an increase from 50 to over 200 CGG repeats within exon 13 of the FMR1 gene. This repeat expansion promotes DNA methylation and other epigenetic heterochromatin modifications of FMR1 that prevent the transcription of the gene, leading to pathological low levels of FMRP.