Autism
Neurodevelopmental Disorders & Learning Differences
Authored by: The DrSensory Editorial Team
Reviewed by: 🛡️ DrSensory Clinical Review Board
Last updated: June 2026
Key Takeaways
- Fragile X Syndrome is a genetic condition that causes intellectual disabilities, behavioral challenges, and developmental delays, and it is the most common inherited cause of intellectual disability.
- Fragile X is caused by a mutation in the FMR1 gene on the X chromosome, which prevents the body from making enough FMRP, a protein essential for brain development.
- Up to 60% of individuals with Fragile X also meet the diagnostic criteria for Autism Spectrum Disorder, making Fragile X a known genetic contributor to autism.
- Girls with Fragile X tend to have milder symptoms because they have a second, unaffected X chromosome.
- Fragile X is diagnosed through genetic testing, specifically a DNA blood test that identifies the FMR1 gene mutation.
Frequently Asked Questions
What causes Fragile X Syndrome?
Fragile X Syndrome is caused by a mutation in the FMR1 gene on the X chromosome, which prevents the body from producing enough FMRP, a protein essential for brain development. The mutation is often passed from parent to child.
What are the symptoms of Fragile X Syndrome in children?
Symptoms often include delayed speech and language development, intellectual disability ranging from mild to severe, social anxiety and attention problems, hyperactivity or impulsive behavior, and sensory sensitivities to things like sound or touch. Physical features such as a long face, prominent ears, or flat feet may also be present and are more noticeable in males.
Is Fragile X Syndrome related to autism?
Yes, there is a strong genetic link between the two, and up to 60% of individuals with Fragile X also meet the diagnostic criteria for Autism Spectrum Disorder. Shared traits may include repetitive behaviors, social communication challenges, and sensory processing difficulties, though not all individuals with Fragile X have autism.
Why do girls with Fragile X tend to have milder symptoms than boys?
Girls with Fragile X tend to have milder symptoms because they have a second, unaffected X chromosome.
How is Fragile X Syndrome diagnosed?
Fragile X is diagnosed through genetic testing, specifically a DNA blood test that identifies the FMR1 gene mutation. Genetic testing is often recommended if a child shows signs of both intellectual disability and autism-like behaviors.
