Fragile X

What is fragile X syndrome?

Fragile X syndrome is a common hereditary cause of mental retardation and learning disability. Both males and females can be affected by fragile X syndrome, although females often have milder effects. Males with fragile X syndrome usually have mental retardation, and may have some autistic-like behaviors. Females with fragile X syndrome may have mental retardation or learning disabilities, social difficulties, and anxiety.

What causes fragile X?

Fragile X is caused by mutations of a gene called the FMR1 gene. These gene mutations can affect the development of specific regions of the brain and make a person more susceptible to developing cognitive and behavioral difficulties. Individuals with the full mutation of the gene have fragile X syndrome, while individuals with the premutation of the gene usually are usually not affected. Individuals with the premutation, however, are at risk for having a child with the full mutation and fragile X syndrome.


The figure above shows the most common fragile X mutation- an expansion of extra DNA within a specific component of the FMR1 gene. In the premutation, the expansion is relatively small, however, in the full mutation the expansion is quite large and is usually accompanied by abnormal methylation. The presence of abnormal methylation leads to decreased production or absence of the FMR1 gene's protein product, called FMRP. The specific function of FMRP in the human brain is currently under study; current evidence suggests it may be involved in the regulation of proteins produced by other genes.

Fragile X Research

At CIBSR researchers are engaged in a wide range of projects designed to address several questions concerning the fragile X syndrome.

  • What is the typical course of behavioral and cognitive development in children with fragile X syndrome?
  • What are the genetic and environmental factors that influence the range of developmental and behavioral outcomes of children with fragile X syndrome?
  • How does the fragile X mutation cause problems in the nervous system and hormonal functioning of individuals with fragile X syndrome?
  • What are the effects, if any, of the fragile X permuation?
  • What is the role of the protein produced by the FMR1 gene in brain development and function?
  • What are the best behavioral and pharmacological treatments for fragile X ?

Links and Resources:

Participating in our current research projects

To learn more about fragile X, please visit the web site of the National Fragile X Foundation

For publications on this study click here.