FMR1 and Intellectual disability: Since its cloning in 1991 (Verkerk et al., 1991), the official name of the gene mutated in Fragile X Syndrome (FXS) has been Fragile X Mental Retardation 1 (official gene symbol FMR1), as it was the first of a long series of X-linked genes associated with intellectual deficiency, termed at that time mental retardation.