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Fragile X syndrome (FXS), Martin–Bell syndrome, or Escalante's syndrome, is a genetic syndrome that is the most widespread single-gene cause of autism and inherited cause of mental retardation among boys.
It results in a spectrum of intellectual disabilities ranging from mild to severe as well as physical characteristics such as an elongated face, large or protruding ears, and large testes (macroorchidism), and behavioral characteristics such as stereotypic movements (e.g. hand-flapping), and social anxiety.
Fragile X syndrome is associated with the expansion of the CGG trinucleotide repeat affecting the Fragile X mental retardation 1 (FMR1) gene on the X chromosome, resulting in a failure to express the fragile X mental retardation protein (FMRP), which is required for normal neural development. A definitive diagnosis of fragile X syndrome is made through genetic testing to determine the number of CGG repeats. Testing for premutation carriers can also be carried out to allow for genetic counseling.
There is currently no drug treatment that has shown benefit specifically for fragile X syndrome. However, medications are commonly used to treat symptoms of attention deficit and hyperactivity, anxiety, and aggression.
Supportive management is important in optimizing functioning in individuals with fragile X syndrome, and may involve speech therapy, occupational therapy, and individualized educational and behavioral programs.
Autism and fragile X syndrome
Fragile X syndrome is the leading known genetic cause of autism, accounting for about 5% of cases. This finding has resulted in screening for FMR1 mutation to be considered mandatory in children diagnosed with autism. Of those with fragile X syndrome, prevalence of concurrent autism spectrum disorder (ASD) has been estimated to be between 15 and 60%, with the variation due to differences in diagnostic methods and the high frequency of autistic features in individuals with fragile X syndrome not meeting the DSM criteria for an ASD.
Although individuals with FXS have difficulties in forming friendships, those with FXS and ASD characteristically also have difficulties with reciprocal conversation with their peers. Social withdrawal behaviors, including avoidance and indifference, appear to be the best predictors of ASD in FXS, with avoidance appearing to be correlated more with social anxiety while indifference was more strongly correlated to severe ASD.
When both autism and FXS are present, a greater language deficit and lower IQ is observed as compared to children with only FXS.