What Is Fragile X Syndrome?

Fragile X syndrome affects the X chromosome 

Fragile X syndrome (FXS) is a genetic disorder and one of the leading causes of inherited learning disabilities. FXS occurs when the single gene, fragile X messenger ribonucleoprotein 1 (FMR1) mutates on the X chromosome. FMR1 usually makes an essential protein necessary for brain development, FMRP, and people who have FXS do not make this protein. FXS is also referred to as Martin-Bell syndrome because, when the X chromosome is examined under a microscope, a portion of it appears broken or fragile, which led to the name (Cleveland Clinic, 2025).

Gender Differences in Risk 

Affected males typically experience moderate intellectual disability (ID), while affected females tend to have mild ID (National Organization for Rare Disorders, 2022). It was found that males are more severely affected by FXS as compared to females (1:7000 males and 1:11000 females). Males have 1 X chromosome (XY) while females have 2 X chromosomes (XX), thus reducing the effects of FXS gene mutation on the X chromosome. A damaged FMR1 gene for females can be compensated by the other healthy X chromosome, this is why males are more susceptible. Female carriers have a 50% chance of passing to each of her children while males will pass to only their daughters and none to their sons (Zolecki, 2022). 

Symptoms

FXS causes a wide range of physical abnormalities and developmental issues, such as delayed speech and hand-flapping. (Cleveland Clinic, 2025). FXS usually starts with delayed speech and language issues by age 2 with slow motor developmental milestones. Males may develop large testicles after puberty, and may have increased aggressive tendencies. Symptoms tend to be milder in girls. Girls with FXS may face issues of conceiving or go into menopausal state much earlier (Levine & Benisek, 2024). Children with FXS may suffer from anxiety and hyperactive behavior such as fidgeting or impulsive actions. They may have difficulty in maintaining attention and focus on specific tasks.

Certain features of FXS become more noticeable with age. These include a long and narrow face, large ears, prominent jaw and forehead, unusually flexible fingers and flat feet. For males, they may have enlarged testicles after puberty (National Human Genome Research Institute, 2019). 

Diagnosis and Treatment

FXS can be diagnosed through testing an individual's DNA through a blood test. It is done by finding changes in the FMR1 gene that leads to FXS. Mutation in the FMR1 gene affects the production of fragile X mental disability protein. If the body makes too little or no protein, the brain cannot develop normally (Centers for Disease Control and Prevention, 2024).

There is no cure for FXS but with medication and therapy, it can help manage symptoms. Therapy may focus on developing skills like speaking, walking, and socializing with others. Additionally, medication can be prescribed to manage certain challenges, such as behavioral issues. Using all these advantageous resources, the best treatment plan can be developed (Centers for Disease Control and Prevention, 2024). 

Written by: Keisha 

References

Canva. (n.d.). DNA helix [Icon]. https://www.canva.com/icons/MAFYm9x99AQ/

Centers for Disease Control and Prevention. (2024). About fragile X syndrome. Fragile X Syndrome (FXS). Retrieved from https://www.cdc.gov/fragile-x-syndrome/about/index.html 

Levine, H., & Benisek, A. (2016). Fragile X syndrome: What is it? WebMD. Retrieved from https://www.webmd.com/children/what-is-fragile-x-syndrome 

National Human Genome Research Institute. (2019). About fragile X syndrome. Genome.gov. Retrieved from https://www.genome.gov/Genetic-Disorders/Fragile-X-Syndrome 

National Organization for Rare Disorders. (2022). Fragile X syndrome. Retrieved from https://rarediseases.org/rare-diseases/fragile-x-syndrome/ 

Zolecki, M. (2022). What is Fragile X syndrome? National Fragile X Foundation. Retrieved from https://fragilex.org/understanding-fragile-x/fragile-x-101/