FXS is an inherited disorder characterized by mental retardation, caused by silencing of the fmr1 gene, encoding the Fragile X mental retardation protein (FMRP) [86], an RNA-binding protein expressed mainly in neurons and astrocytes of the brain and associated with approximately 4% of transcripts, including those for mitochondrial proteins [87]. The gene discussed is FMR1; the disease is fragile X syndrome.