Understanding Fragile X
Educational information about the most common inherited cause of intellectual disability and autism
What is Fragile X?
Fragile X syndrome is a genetic condition that causes intellectual disability, behavioral and learning challenges, and various physical characteristics. It's caused by changes in the FMR1 gene on the X chromosome.
How Common is Fragile X?
In the United States:
- Approximately 1 million people carry the Fragile X premutation
- About 100,000 people have Fragile X syndrome
Worldwide:
- An estimated 1.4 million people have Fragile X syndrome
- Millions more carry the premutation
Prevalence rates:
- Fragile X syndrome: 1 in 7,000 males and 1 in 11,000 females globally
- Premutation carriers: 1 in 150-300 females and 1 in 400-850 males
Most Common Inherited Cause
Fragile X syndrome is the most common inherited cause of intellectual disability and the most common known genetic cause of autism.
Affects Both Genders
While Fragile X affects both males and females, males are typically more severely affected due to having only one X chromosome.
Spectrum of Effects
The effects range from mild learning disabilities to more severe intellectual disability. Each person with Fragile X is unique.
Fragile X-Associated Conditions
The FMR1 gene changes can cause different conditions depending on the number of CGG repeats:
Fragile X Syndrome (FXS)
Full Mutation (>200 CGG repeats)
Causes intellectual disability, behavioral challenges, and physical features. Most common in males.
Learn More →Fragile X Premutation
55-200 CGG repeats
Carriers may have no symptoms or mild issues. Can lead to FXTAS or FXPOI later in life.
Learn More →FXTAS
Fragile X-Associated Tremor/Ataxia Syndrome
Affects some premutation carriers, usually after age 50. Causes tremor, balance, and memory issues.
Learn More →FXPOI
Fragile X-Associated Primary Ovarian Insufficiency
Affects some female carriers. Can cause irregular periods, early menopause, and fertility issues.
Learn More →Important Information
Diagnosis
Fragile X can be diagnosed with a blood test that measures the number of CGG repeats in the FMR1 gene. Testing is recommended for:
- Individuals with intellectual disability or autism
- Family members of someone with Fragile X
- Women with fertility issues or early menopause
Inheritance
Fragile X is inherited in an X-linked pattern. Key points:
- Mothers pass the mutation to children
- Fathers pass only to daughters
- The mutation can expand through generations
Management
While there's no cure, many interventions can help:
- Educational support and therapies
- Behavioral interventions
- Medications for specific symptoms
- Ongoing medical monitoring
Learn More
For comprehensive information and support, visit these trusted organizations:
Learn More About Fragile X
Visit trusted government health websites for comprehensive information about Fragile X conditions.
View Resources →NIH Resources
Research information and clinical trial listings from the National Institutes of Health.
Visit NIH →