FMR1 and fragile X syndrome: The X-linked Fragile X Mental Retardation 1 (FMR1) gene can also be abnormally expanded to over 200 CGG triplet repeats (versus about 30 repeats in normal individuals) in its 5′-UTR, which is almost the exclusive pathological cause of Fragile X Syndrome (FXS), a neurodevelopmental disease characterized by intellectual disability, hyperactivity and anxiety of the affected individuals.