Fragile X Fragile X
Centers for Disease Control and Prevention

Fragile X is a group of genetic disorders that can affect individuals and their families in many ways because they are all caused by changes in the same gene, the FMR1 gene. The group of Fragile X conditions include:

Fragile X syndrome Fragile X-associated tremor/ataxia syndrome (FXTAS) Fragile X-associated premature ovarian failure (POF) Problems with learning and behavior

What is Fragile X Syndrome?
Fragile X syndrome (FXS) is the most common known cause of intellectual disability, also known as mental retardation, and developmental disability that can be inherited (passed from one generation to the next).

Signs that a child has FXS include not sitting, walking, or talking as early as other children. This is known as having developmental delays. Often, there are other physical and behavioral signs, but features of FXS vary and signs can be subtle and easy to miss. Children often have a typical facial appearance that gets more noticeable with age. These features include a large head, long face, and prominent ears, chin, and forehead. Children who have FXS might also have learning disabilities, speech and language delays, and behavioral problems such as attention-deficit/hyperactivity disorder (ADHD). Males who have FXS usually have some degree of intellectual disability that can range from mild to severe. Females with FXS can have normal intelligence or some degree of intellectual disability with or without learning disabilities. Autism spectrum disorders (ASDs) also occur more frequently in children with FXS.

How Many People Have Fragile X Syndrome?
The exact number of people who have FXS is unknown, but it is estimated that about 1 in 4,000 males and 1 in 6,000 to 8,000 females have the disorder. Although FXS occurs in both males and females, females usually have milder symptoms.

What Causes Fragile X Syndrome?
FXS is caused by a change (mutation) in a gene on the X chromosome. Genes contain codes, or recipes, for proteins. Proteins are very important biological components (parts) in all forms of life. The gene on the X chromosome that causes FXS is called the Fragile X Mental Retardation 1 (FMR1) gene. The FMR1 gene makes a protein that is needed for normal brain development. This protein is not made in individuals who have FXS.

How is Fragile X Syndrome Diagnosed?
FXS can be diagnosed by testing a person’s DNA from a blood sample. A physician or genetic counselor must order the test. Testing can also be done to detect fragile X carriers.

What Conditions Can Occur in Fragile X Carriers?
Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurological condition that occurs in some older male gene carriers. It can cause tremors and problems with walking, balance, and memory. Fragile X-associated premature ovarian failure (POF) is a condition that affects some female gene carriers by reducing their ovarian function which can lead to infertility and early menopause. Some fragile X carriers may be at higher risk for mood disorders, learning disabilities, and behavioral issues.