Learn about the FMR1/Fragile X premutation, commonly referred to as "carrier".

Fragile X is a group of conditions associated with alterations in the FMR1 gene on the X chromosome. These changes can result in a “full-mutation,” which causes Fragile X syndrome (FXS), or a “premutation,” which can sometimes lead to disorders like Fragile X-associated tremor/ataxia syndrome (FXTAS) or Fragile X-associated primary ovarian insufficiency (FXPOI).

Typically, a “carrier” of a genetic mutation is defined as a person who inherits an altered form of a gene but shows no effects of that mutation. A carrier has an altered form of a gene that can lead to having a child or grandchild with a genetic disorder. We are all carriers of gene mutations, many of which are “silent” (which means we can pass the gene on but suffer no ill effects from it ourselves). However, this is not the case with Fragile X. Carriers of the Fragile X premutation are also at risk to develop Fragile X-associated conditions including Fragile X-associated tremor/ataxia syndrome (FXTAS) and Fragile X-associated primary ovarian insufficiency (FXPOI).

An individual with the Fragile X premutation is a male or female who has between 55-200 CGG repeats in the FMR1 gene. The full mutation (Fragile X syndrome) is defined as over 200 CGG repeats. (A typical FMR1 gene has 6-54 CGG repeats- individuals with CGG repeats in this range do not have Fragile X.)

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