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Colorado Fragile X Consortium

The Fragile X Premutation


Background and Prevalence
The Fragile X premutation is another of the spectrum of disorders related to the fragile X mental retardation 1 (FMR1) gene. The premutation is quite common in the general population. It is estimated that approximately 1 in 250 females and 1 in 800 males carries the premutation.

Like fragile X syndrome, the fragile X premutation results from a mutation in the FMR1 gene, which resides on the X chromosome. The mutation involves an expansion of a specific pattern of molecules that make up the gene (i.e., cytosine, guanine, and guanine, or "CGG"). The number of repetitions of the pattern is referred to as "CGG repeats." Individuals with between 6 and 40 CGG repeats have a normal gene. Those with 55 to 200 CGG repeats have the fragile X premutation and are referred to as "carriers" of the mutated fragile X gene.

Individuals with the fragile X premutation experience less severe symptoms and disabilities than do individuals with fragile X syndrome. Generally, premutation carriers are of normal intelligence. A small percentage of males and females with the premutation show subtle problems with certain cognitive abilities, such as planning, organization, and behavioral self-regulation. Psychological problems, such as anxiety and depression, are relatively common among individuals with the premutation. Female carriers of the fragile X premutation often experience premature ovarian failure.

As with fragile X syndrome, there is no cure for the fragile X premutation. Given that the premutation often is accompanied by only mild symptoms or no discernible impairments, premutation carriers often receive no medical treatment. Most do not even know that they carry the premutation unless they have a child or other family member who has been diagnosed with an abnormal FMR1 gene. For those individuals who do experience cognitive, behavioral, or psychological problems associated with the premutation, a variety of treatments are available. Several web sites, including Online Mendelian Inheritance in Man (OMIM), GeneClinics, and the web site of the National Fragile X Foundation provide information about the treatment of disorders related to mutations of the FMR1 gene.