FMR1 and fragile X syndrome: Fragile X syndrome (FXS) is the leading cause of intellectual disability, affecting one in every 2500–4000 males and one in every 7000–8000 females.47 Affected individuals are also at risk of developing a wide array of psychiatric and behavioural comorbidities such as ASD, anxiety, hyperactivity, hyperarousal and attention deficit.48 FXS is caused by the absence of expression of the Fragile X messenger ribonucleoprotein (FMRP), resulting from the silencing of the FMR1 gene.