Fragile X Syndrome (FXS), the most common inherited cause of intellectual disabilities, is an X-linked
dominant disorder caused by the amplification of a CGG repeat in the 5' untranslated region of the fragile X mental
retardation gene 1 (FMR1). Prevalence estimates of the disorder are approximately 1/3600. Psychiatric manifestations of
the disorder include anxiety, attention deficit hyperactivity disorder, autism, mood instability and aggression. In this
article we review the above psychiatric manifestations and challenges to accurate assessment. We also discuss how the
neurobiological underpinnings of these symptoms are beginning to be understood and can help guide treatment.