Fragile X Syndrome and Autism Spectrum Disorder
July 18, 2023

Fragile X Syndrome and Autism Spectrum Disorder

Fragile X Syndrome (FXS) is a genetic disorder that causes developmental problems, including intellectual disabilities, learning disabilities, and cognitive impairment. FXS affects both boys and girls; boys, however, have a higher occurrence rate and present more severe symptoms. Around 1 in 3600-4000 males is affected while approximately 1 in 4000-6000 girls is affected.

What does Fragile X Syndrome Look Like?

Fragile X Syndrome causes behavioral, intellectual, and physical symptoms.

Behavioral characteristics include Attention Deficit (Hyperactivity) Disorder (ADD or ADHD), increased aggression, social anxiety, and autism or autistic behaviors.

Intellectual characteristics range from the presence of one or more learning disabilities to severe intellectual impairment. Most males with FXS will have significant intellectual problems. For example, while the average Intelligence Quotient (IQ) for the general population is 100, boys with FXS have an average IQ of around 55.

Physical features of FXS include having oversized ears, a prominent forehead and jawline, a long and narrow face, connective tissue problems like hyper flexibility, flat feet, and double-jointed fingers. Males may exhibit enlarged testicles, called macroorchidism.

Fragile X Syndrome is caused by mutations in the FMR1 gene, which creates an absence or reduction of a protein called FMRP. A deficiency of FMRP disrupts nervous system functions, which then leads to the symptoms of FXS. Scientists identified this gene in the 1990s, and now the FMR1 DNA test has replaced chromosomal testing and become the standard test for detecting FXS.

Fragile X Syndrome and Autism

There are some overlaps between Autism Spectrum Disorder (ASD) and FXS, which can often lead to confusion.

Individuals with FXS can have ASD or display ASD symptoms. It is estimated that FXS accounts for around 2-3% of all ASD cases. Unlike FXS, autism cannot be diagnosed through DNA analysis. Rather, ASD is diagnosed by examining and analyzing a person’s behavior, known as a behavior-defined diagnosis.

There are other proteins with similar functions as FMRP, the protein lacking in individuals with FXS. In addition, these other proteins, which either mimic or interact with FMRP, have a correlation with ASD, which is why FXS and ASD produce similar behavioral signs and symptoms. Simply, a deficiency of FMRP can affect other proteins that are associated with ASD, which accounts for the prevalence of ASD and autistic symptoms in those with FXS.

For those with both FXS and ASD, each disorder needs to be taken into account even though some of the treatments may overlap. This leads to a highly individualized treatment approach that will involve parents, caregivers, teachers, and health professionals. Early interventions that address communication and social skills will be one of the first, crucial steps; however, some behavioral treatments used for ASD, like forcing eye contact, would be inappropriate for someone with FXS. Most children with FXS, ASD, or both will qualify for Special Education.


  • Data & Statistics on Fragile X Syndrome

  • Fragile X Syndrome and Autism Spectrum Disorder: Similarities and Differences:

  • Fragile X Syndrome | FXS


This article is examined by Clinical Child Psychologist and Ph. D. Researcher Kevser Çakmak, and produced by Otsimo Editorial Team.

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This post does not provide medical advice. See Additional Information.