Maria Vincenza Catania (Catania, Italy) briefly synthesized the state of the art research supporting the notion that dysfunctions of group-I metabotropic glutamate receptor 5 (mGlu5) are implicated in the pathophysiology of fragile X syndrome (FXS), the most common form of inherited intellectual disability and an important monogenic cause of autism. This evidence concerns the gene GRM5 and fragile X syndrome.