Fragile X syndrome is the most common inherited form of mental retardation. It is caused by loss of FMR1 gene activity due to either lack of expression or expression of a mutant form of the protein. In mammals, FMR1 is a member of a small protein family that consists of FMR1, FXR1, and FXR2. All three members bind RNA and contain sequence motifs that are commonly found in RNA-binding proteins, including two KH domains and an RGG box.The Drosophila genome contains a single gene homologous to the FXR family. dFMR1 is subjected to transcriptional and posttranscriptional regulation during development and it homomerizes, like its human counterpart. dFMR1 profile of expression recapitulates that of the human FXR protein family: it is highly enriched in muscles, in central nervous system and in gonads. In the larval brain, anti-dFMR1 also recognizes mushroom bodies, a centre that mediates learning and memory. These features make the fly an ideal system to analyse the role of the FXR family and to identify genes in the FMRP pathway.