Understanding Fragile X Syndrome: Symptoms, Causes, and Genetic Testing

July 27, 2023

Fragile X syndrome is the most common inherited form of intellectual disability and a leading cause of autism spectrum disorder. It affects more males than females due to how it is inherited.


What causes fragile X syndrome? Fragile X syndrome is caused by changes in the FMR1 gene found on the X chromosome. Typically, this gene produces a protein which is essential for proper brain development. In Fragile X syndrome, a part of the FMR1 gene is repeated too many times, resulting in reduced protein production that disrupts the normal brain function and leads to the characteristic symptoms of Fragile X. The number of repeats within the FMR1 gene impacts the severity of the condition.


What are the symptoms of fragile X syndrome? The symptoms of fragile X can vary widely from person to person. Common features include intellectual disability, learning difficulty, language delay, social and communication challenges, attention deficit hyperactivity disorder (ADHD), anxiety, and hyperactivity. Some individuals with fragile X syndrome have certain physical features, such as a long and narrow face, large ears, and flexible joints.


What is the relationship between fragile X syndrome and autism? Fragile X syndrome is associated with autism spectrum disorder. While not all individuals with fragile X have autism, the presence of fragile X significantly increases the chance of developing autism. According to the CDC, a national parent survey found that 46% of males and 16% of females with fragile X syndrome have been diagnosed with or treated for autism. Fragile X is not the only cause of autism, and we can’t yet identify the cause of autism in many cases.

Is there a cure for fragile X? Currently, there is no known cure for fragile X syndrome. However, there are treatments available to manage some symptoms and improve the quality of life for affected individuals. Early intervention programs, educational support, speech and language therapy, occupational therapy, and behavioral interventions can all contribute to better outcomes for individuals with fragile X.

How does fragile X inheritance work? Fragile X syndrome follows an X-linked inheritance pattern. Since the FMR1 gene is found on the X chromosome, the condition is usually passed down from mothers who have extra repeats of a portion of the FMR1 gene to their children. Typically, females have two X chromosomes, while males have one X and one Y chromosome. If a female has extra fragile X repeats on one of her X chromosomes, she has a 50% chance of passing those on to each of her children, and the number of repeats can increase with each generation. Once the number of repeats gets high enough, the individual will be born with fragile X. If a male has extra fragile X repeats, he will pass those to all of his daughters, but not to his sons. The number of repeats tends not to increase when passed from a male to his daughters.

How common is fragile X? Fragile X syndrome affects approximately 1 in 4,000 males and 1 in 8,000 females worldwide.

When is genetic testing for fragile X recommended? Genetic testing for fragile X can be done for individuals with intellectual disabilities, developmental delays, or autism, especially if there is a family history of fragile X. For individuals who want to know if they have a chance to have a child with fragile X, carrier testing can be done prior to or during pregnancy. Carrier testing for fragile X and other inherited conditions allows for informed family planning decisions. JScreen is a national program that provides at-home access to carrier screening for fragile X and over 200 other conditions that could impact a couple’s future children.


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Headquartered in Atlanta at Emory University’s Department of Human Genetics, JScreen is a national non-profit offering at-home comprehensive and affordable genetic testing and counseling.

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