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Single Gene Disorders and Disability (SGDD) |
People with premutation FMR1 genes do not have FXS. However,
sometimes they have other symptoms, such as the following nervous
system disorders, infertility, and problems with learning and
behavior.
- Fragile X-Associated Tremor / Ataxia Syndrome (FXTAS)
FXTAS is a disorder of the nervous system that leads to tremors,
problems with walking and balance (called ataxia), memory loss, and
mood disorders. Studies have shown that at least 30% of men with the
premutation who are older than 50 years of age develop FXTAS. Women
who have a premutation are less likely to be affected by FXTAS, but
if they develop FXTAS, it happens at a later age than in men.
- Premature Ovarian Failure (POF)
Normally, women will stop having menstrual cycles and experience
menopause around 51 years of age. Women with premature ovarian
failure (POF) stop having menstrual cycles and have symptoms of
menopause before 40 years of age. POF occurs in about 1% to 4% of
women in the general population; however, it occurs in about 22% of
women who have a premutation for FXS. Therefore, women who carry a
premutation are at risk for fertility problems in addition to the
risk of having children who have FXS. Women who have a full mutation
for FXS have the same risk for POF as women in the general
population.
- Problems with learning and behavior
The effects on learning and behavior in men and women with the FMR1
premutation are unclear. Women with the premutation might be more
likely to have mood disorders and learning disabilities. Behavioral
issues such as attention-deficit/hyperactivity disorder (ADHD) and
autism spectrum disorders (ASDs) might also be more common than in
the general population. However, more studies need to be done to
look at the relationship between the premutation and learning and
behavioral effects.
Why do people with premutations have symptoms that are different
than those in FXS?
In people who have FXS, the FMR1 gene has a very large number of CGG
repeats, which causes the gene to be turned off. As a result, there
is no protein made. FXS is the result of the lack of a specific
protein.
People with premutations do not have FXS because they still make
some of the protein from the FMR1 gene. However, the premutation can
affect how the gene works. Genes contain the recipes for proteins.
Before the protein is made, a temporary copy of the gene is created.
This temporary copy is made of RNA, a chemical very similar to DNA.
In FMR1 genes with a premutation repeat, the gene makes extra RNA.
The extra RNA affects how some cells work, which causes the symptoms
described previously. Scientists do not yet understand exactly how
the extra RNA causes these health problems.
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Date: August 28, 2006
Content source: National Center on Birth Defects and Developmental
Disabilities
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