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Key Findings: Prevalence of Fragile X Premutation Prevalence of CGG Expansions of the FMR1 Gene in a US Population-Based Sample

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The gene for fragile X-associated disorders and fragile X syndrome was identified in 1991, yet little is known about people with these conditions. Each new research study helps scientists and health care providers more fully understand these two conditions and develop the most beneficial programs and services to help individuals and families. These findings have the potential to impact many lives. This research is an important step in the study of fragile X-associated disorders.

About Fragile X-Associated Disorders

Fragile X syndrome and fragile X-associated disorders are genetic disorders. A genetic disorder means that there are changes to a person’s genes. These two conditions are caused by changes to the FMR1 gene. The FMR1 gene is important for normal brain development. People with a premutation in the FMR1 gene do not have fragile X syndrome, but they are at risk for fragile X-associated disorders. Women with a premutation are at increased risk of having a child with fragile X syndrome and all people with the premutation are at risk for other symptoms.

About the Study

Researchers from the University of Wisconsin-Madison’s Waisman Center, together with researchers from the Centers for Disease Control and Prevention (CDC), have published a new study describing the number of people who have a premutation in their FMR1 gene. You can read the abstract of the article here. This study is the first to report the frequency of the fragile X premutation among a group of people in the United States. This study on older adults reports data about symptoms often associated with fragile X-associated disorders.

Main Findings from This Study

This study showed a higher number of people having a premutation in the FMR1 gene than was found in previous research. This study also suggested that people with a fragile X premutation are more likely to report symptoms associated with fragile X-associated disorders. Having a fragile X premutation can pose challenges at all ages.

  • As reported in this paper, the frequency of fragile X premutation was as follows:
    • 1 in 151 females, or about 1 million women in the United States.
    • 1 in 468 males, or about 320,000 men in the United States.
  • These statistics are important because both men and women are at risk for having symptoms linked to fragile X-associated disorders.
    • Women with a premutation reported their last menstrual cycle at an earlier age than women without a premutation (48 vs. 51 years).
    • Men and women with a premutation were more than four times as likely to report dizziness or fainting as people without a premutation (18% vs. 4%). Men and women with a premutation were more than twice as likely to report numbness as people without a premutation (29% vs. 13%).
  • Twenty-three percent of people with a premutation had a child with a disability.
  • Twelve percent of people without a premutation had a child with a disability.

Diagnosis of Fragile X Syndrome

Changes in the FMR1 gene can be identified using a blood test. A doctor or genetic counselor can order the test. The results of a DNA test can affect other family members and can raise many other issues. Read more about a diagnosis of Fragile X Syndrome.

This study of 6,747 older adults in Wisconsin found 30 people with a change in the FMR1 gene. Based on this relatively small number of people, the results should be interpreted with caution. These findings may not reflect all people in the United States with an FMR1 premutation.

Next Steps

CDC has studied fragile X syndrome and fragile X-associated disorders since 2005. CDC’s goal is to conduct research to learn more about these conditions, and use this research to improve the health and well-being of people with fragile X syndrome and fragile X-associated disorders. Read more about this work.

More Information

Reference for Key Findings Summary

  • Prevalence of CGG expansions of the FMR1 gene in a US population-based sample.
    American Journal of Medical Genetics Part B Neuropsychiatric Genetics; 2012 Jul;159B(5):589-97. Epub ahead of print 2012 May 22.
    Seltzer, M, et al.
    [Read article]
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