Fragile X Syndrome

(Martin-Bell Syndrome; FXS)


Fragile X syndrome (FXS) is a genetic problem that results in intellectual disability.

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FXS is inherited from parents. It is caused by problems with the FMR1 gene. These problems stop the fragile X mental retardation protein (FMRP) from developing. This protein is needed to make connections in the brain.

Risk Factors

The risk of this problem is higher in people who have a family history of the faulty FMR1 gene.


Problems are different from person to person. They happen less often and are mild in females. Problems may be:

  • Learning problems
  • Slowed development
  • Speech problems
  • Behavioral problems, such as:
    • Mood swings
    • Outbursts
    • Being very sensitive to loud noises or bright lights
    • Aggression
    • Extreme shyness, especially in girls
  • Physical problems, such as:
    • A long face with a jaw that sticks out
    • Large ears
    • Flat feet
    • Joints that bend past normal limits
    • A high-pitched voice and enlarged testes in males after puberty
    • Floppy muscles
    • Problems with motor skills like sitting and walking


The doctor will ask about your child's symptoms and health history. A physical exam will be done.

The diagnosis can be confirmed with a genetic test.


There is no cure for FXS. The goal is to manage symptoms. Choices are:

  • Medicines, such as:
    • Stimulants to treat attention and behavior problems
    • Medicine to control mental health problems
    • Antiseizure medicines
  • Speech, occupational, physical, or behavioral therapy
  • Special education services to help with learning


There are no known guidelines to prevent this health problem.


FRAXA Research Foundation
The National Fragile X Foundation


Fragile X Research Foundation of Canada
Sick Kids—The Hospital for Sick Children


Fragile X syndrome. EBSCO DynaMed website. Available at: Accessed November 4, 2020.
Fragile X syndrome overview. National Institute of Child Health and Human Development website. Available at:
...(Click grey area to select URL)
Accessed November 4, 2020.
Lozano R, Azarang A, et al. Fragile X syndrome: A review of clinical management. Intractable Rare Dis Res. 2016 Aug;5(3):145-157.
What is fragile X? FRAXA Research Foundation website. Available at:
...(Click grey area to select URL)
Accessed November 4, 2020.
Last reviewed September 2020 by EBSCO Medical Review Board Kari Kassir, MD
Last Updated: 5/11/2021

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