What Is Fragile X Syndrome?

Have you ever heard about Fragile X Syndrome? If you're looking for some in-depth information about this Syndrome, you've found the right article. Keep on reading to find out more about this complex condition.

Fragile X syndrome is a genetic condition that causes intellectual disability and behavioural and learning challenges. It is caused by a mutation in the FMR1 gene located on the X chromosome, which leads to brain abnormalities and the development of symptoms associated with the condition. The severity of these symptoms can vary greatly among individuals with the condition.

There is much more to learn about Fragile X Syndrome, for example, how fragile X syndrome is diagnosed and the interventions and treatments that are currently available to help individuals with the condition. So, if you want to learn more about Fragile X Syndrome, be sure to read on! 


Fragile X Syndrome (FXS) is a genetic condition caused by mutations in the fragile X messenger ribonucleoprotein 1 (FMR1) gene. This gene is responsible for producing a protein called FMRP, which is critical for brain development. Individuals with FXS do not produce this protein, while those with fragile X-associated disorders produce small amounts of abnormal variants of FMRP. . Both people assigned male at birth (AMAB) and people assigned female at birth (AFAB) can be affected by FXS, with people AFABoften displaying milder symptoms compared to people AMAB. FXS impacts an individual's developmental progress, particularly their behaviour and learning abilities. Additionally, it can also affect their communication abilities, physical features and sensitivity to stimuli such as noise, light, and other sensory information. Fragile X syndrome is the most frequently encountered heritable disability that impedes both intellectual and developmental abilities.1

Causes of fragile X syndrome

FXS is monogenic, which means that a mutation in the FMR1 gene is enough to cause the condition. The FMR1 gene is responsible for producing FMRP, which is crucial and plays a fundamental role in the formation and maintenance of neural connections in the brain and the nervous system. Mutations in the FMR1 gene can cause  FMRP to be absent or to be present in small quantities in individuals with FXS, leading to the aberrant formation of neuronal connections in the brain.2

Signs and symptoms of fragile X syndrome

Individuals with Fragile X may exhibit symptoms that vary in severity, while some may not even display any symptoms at all. The extent of the symptoms depends on different factors, such as the size of the mutation in the FMR1 gene, the number of cells affected and the person's sex. If the mutation is smaller, the body may still be able to produce some FMRP, resulting in milder symptoms. Additionally, a phenomenon called mosaicism can occur; this is when some cells in the body have the mutation while others do not. Furthermore, females have two X chromosomes. Hence, if the FMR1 gene on one X chromosome is mutated while the gene on the other X chromosome remains unaffected, this can cause milder symptoms.3

Symptoms of FXS can start to present in infancy, with most children being diagnosed before they reach the age of three. Some of the signs and symptoms that can be observed in a child with FXS include:

  • Delays in development: they may not reach milestones, such as sitting, walking and speaking, as early as others who are of the same age
  • Learning difficulties: they may struggle to acquire new skills
  • Behavioural and social issues: they may display antisocial traits, such as avoidance of eye contact, repetitive hand movements, anxiety, inattentiveness, impulsive behavior, and excessive activity levels
  • Health problems: they may experience a number of health problems, such as eye problems, orthopedic problems, heart problems or skin problems 
  • Characteristic physical features: FXS patients may display a number of characteristic features, such as a large head, a long face, a prominent forehead and chin, and protruding ears. Males may also have loose joints and large testes after puberty
  • Sensory issues: some patients with fragile X syndrome can experience sensory issues. This entails discomfort or irritation from certain stimuli, such as bright light, loud noises, or particular textures3

Management and treatment of fragile X syndrome

Unfortunately, there is no cure for FXS. However, various treatment options can help individuals with FXS to reach developmental milestones. This can include:

  • Therapy: there are a number of therapies available that can improve the communication skills, physical movements, and social interactivity of FXS patients. Professionals that can provide these therapies are speech-language therapists, occupational therapists, physical therapists and behavioural therapists
  • Drug Treatment: no drugs are currently approved by the food and drug administration (FDA) that are intended for the treatment of fragile X syndrome or its symptoms. However, drugs can be used to manage some behavioural abnormalities  
  • Educational Interventions: the majority of children diagnosed with fragile X syndrome can benefit from specialized educational services that are customized to their individual strengths and limitations. These educational interventions should take into account the unique symptoms experienced by the child in order to create an optimal learning environment

Early intervention services can offer support to children with FXS between birth and the age of three to develop critical skills. To ensure the best outcome for the individual affected by FXS,  parents, healthcare providers, teachers, therapists and family members need to play an active role in planning their treatment. 


Is fragile X syndrome hereditary?

Fragile X syndrome is an inherited disorder, as the gene responsible for it is located on the X chromosome. Both males (XY) and females (XX) have at least one X chromosome, which means that both can potentially pass on the mutated gene to their children.

How is fragile X syndrome diagnosed?

FXS can be diagnosed through a blood test that analyses a person's DNA, which is ordered by a genetic counsellor or a doctor. The test can also reveal changes in the FMR1 gene that are associated with fragile X-associated disorders.

Can fragile X syndrome be prevented?

It is not possible to prevent Fragile X syndrome as it is a hereditary condition caused by a mutation in the X chromosome. This mutation is usually passed down from one or both parents and is influenced by any known environmental factors. Nevertheless, genetic counseling and testing can assist families in understanding the risk of having children with this condition, allowing them to make informed decisions about starting a family.4

Who is at risk of developing fragile X syndrome?

Anyone can develop fragile X syndrome as it is a genetic condition that can affect individuals of all races and ethnicities. However, the risk of having a child with fragile X syndrome is higher for families with a history of the condition (presence of other affected family members) or for women who are carriers of the mutated FMR1 gene.5

How common is fragile X syndrome?

The exact prevalence of FXS is unclear but estimates suggest that it affects around 1 in 7,000 males and 1 in 11,000 females.

When to see a doctor?

In cases when you have concerns about your child's development, it is recommended to discuss abnormalities or delays in development with your child's doctor. In addition, if your child displays a developmental or intellectual disability for which the cause is unknown, you may ask your doctor to conduct a  "FMR1 DNA Test for Fragile X" to test for fragile X syndrome.


Fragile X Syndrome (FXS) is a genetic disorder caused by mutations in the fragile X messenger ribonucleoprotein 1 (FMR1) gene located on the X chromosome. The mutation leads to limited or no production of the FMRP protein, which is crucial for brain development, and results in intellectual disabilities, behavioural abnormalities and learning challenges. Both sexes can be affected, but people AFAB usually display milder symptoms. The severity of symptoms varies, depending the size of the mutation, the number of cells affected, and sex. FXS patients may exhibit delays in development, learning difficulties, behavioural and social issues, health problems, characteristic physical features, and sensory issues. Although there is no cure, therapies, medications, and educational interventions can help an affected child develop critical skills. FXS is diagnosed through blood tests or genetic testing, which can detect the mutation in the FMR1 gene. FXS is an inherited disorder, and parents with the mutated gene may pass it on to their children. 


  1. Salcedo-Arellano MJ, Dufour B, McLennan Y, Martinez-Cerdeno V, Hagerman R. Fragile X syndrome and associated disorders: Clinical aspects and pathology. Neurobiology of Disease [Internet]. 2020 Mar 1 [cited 2020 Mar 10];136:104740. Available from: https://www.sciencedirect.com/science/article/pii/S0969996120300152 
  2. Bagni C, Tassone F, Neri G, Hagerman R. Fragile X syndrome: causes, diagnosis, mechanisms, and therapeutics. Journal of Clinical Investigation. 2012 Dec 3;122(12):4314–22 https://pubmed.ncbi.nlm.nih.gov/23202739/ 
  3. Protic DD, Aishworiya R, Salcedo-Arellano MJ, Tang SJ, Milisavljevic J, Mitrovic F, et al. Fragile X Syndrome: From Molecular Aspect to Clinical Treatment. International Journal of Molecular Sciences [Internet]. 2022 Feb 9;23(4):1935. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8875233/
  4. Niu M, Han Y, Dy ABC, Du J, Jin H, Qin J, et al. Fragile x syndrome: prevalence, treatment, and prevention in china. Frontiers in Neurology [Internet]. 2017 [citado 16 de fevereiro de 2023];8. Disponível em: https://www.frontiersin.org/articles/10.3389/fneur.2017.00254 
  5. Science Update: Fragile X carriers may be at higher risk for several health conditions, NIH-funded study suggests [Internet]. https://www.nichd.nih.gov/. 2019 [citado 16 de fevereiro de 2023]. Disponível em: https://www.nichd.nih.gov/newsroom/news/082919-FMR1-premutation 
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Joana Carneiro

Masters of Public Health - Escola Nacional de Saúde Pública, Lisboa

Joana is a recent graduate, who has a Degree in Biomedical Sciences and a Master's Degree in Public Health. She has more than two years of experience working as a healthcare professional in both private and public settings and more than 4 years of experience working as a volunteer in a non-profit organization, helping disadvantaged communities. Joana is passionate about public health, specifically about everything related to health education, health communication and health equity.

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