Fragile X syndrome (FXS) is the most common known cause of intellectual disability (formerly referred to as mental retardation) that can be inherited, that is passed from parent to child. It is estimated that FXS affects about 1 in 4,000 boys and 1 in 6,000 to 8,000 girls. Both boys and girls can have FXS, but girls usually are more mildly affected. What causes FXS? The cause of FXS is genetic. FXS occurs when there is a change in a gene on the X chromosome called FMR1. The FMR1 gene makes a protein needed for normal brain development. In FXS, the FMR1 gene does not work properly. The protein is not made, and the brain does not develop as it should. The lack of this protein causes FXS.
The individual with fragile X will often have an unusual facial appearance characterised by large protruding ears, a long nose and a high forehead. Many may have flat feet and generally exhibit a ‘floppy’ gait owing to poor muscle tone. Learning needs can range from mild to severe, with girls usually less affected. The individual with fragile X is often described as impulsive, acting before thinking, wanting everything straight away, having impaired concentration and being dependent on following a consistent routine. They may appear uncooperative at times and exhibit oppositional type behaviours.
Other behavioural habits include hand-biting/flapping, rocking and gaze avoidance. However, those with fragile X are interested in others and enjoy social contact on their own terms in a ‘safe’ environment. Inappropriate behaviours are triggered by an inability to select and organise sensory information from the environment, which causes the individual to become overwhelmed by the mass of sensory input. Typically, more males are severely affected than females.
What conditions are common among children with FXS?
Children with FXS might have learning disabilities, speech and language delays, and behavioral problems such as attention deficit/hyperactivity disorder (ADHD) and anxiety. Some boys can develop aggressive behavior. Depression can also occur. Boys with FXS usually have a mild to severe intellectual disability. Many girls with FXS have normal intelligence. Others have some degree of intellectual disability, with or without learning disabilities. Autism spectrum disorder (ASD) occurs more often among children with FXS.