All fragile X-associated disorders are caused by changes in the same gene, the fragile X mental retardation 1 (FMR1) gene. The FMR1 gene usually makes a protein called fragile X mental retardation protein (FMRP). FMRP is needed for normal brain development. Fragile X-associated disorders include:
- Fragile X syndrome
- Fragile X-associated primary ovarian insufficiency
- Fragile X-associated tremor/ataxia syndrome
Fragile X Syndrome (Full Mutation)
Fragile X syndrome (FXS) is the most common known cause of inherited intellectual disability. People who have FXS do not make the protein FMRP. In these people, the FMR1 gene has been turned off. Fragile X syndrome often results from a full mutation of the FMR1 gene.
Other Fragile X-Associated Disorders (Premutation)
People who have other fragile X-associated disorders (not FXS) have changes in their FMR1 gene but usually make some FMRP. In these people, the FMR1 gene is not turned completely off, but the gene does not function normally. Fragile X-associated disorders can be caused by a premutation of the FMR1 gene. People with a premutation of the FMR1 gene do not have FXS but may have another fragile X-associated disorder. Some people with a premutation may have noticeable symptoms, and others may not.
Fragile X-Associated Primary Ovarian Insufficiency (FXPOI)
Fragile X-Associated Primary Ovarian Insufficiency (FXPOI) is a cause of infertility and early menopause among adult women. Women with a condition called primary ovarian insufficiency stop having menstrual cycles and have symptoms of menopause before 40 years of age. Women who have a premutation in their FMR1 gene are at higher risk for primary ovarian insufficiency and are at higher risk for having children who have FXS.
Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS) is a disorder of the nervous system that can cause tremors and problems with walking, balance (also called ataxia), memory, and mood disorders among older adults. FXTAS can be caused by a premutation in the FMR1 gene.
Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS)
- Centers for Disease Control and Prevention
National Center on Birth Defects and Developmental Disabilities
Division of Human Development and Disability
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Atlanta, GA 30333
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