Fragile X syndrome is the leading
hereditary cause of developmental disabilities
in all populations. The absence of a functional
fragile X gene shuts off production of a special
protein in the brain needed for normal cognitive
development. Without this protein, children with
the syndrome will never learn normally, despite
hours of therapy and rehabilitation. Visit the
links at right to learn more about this common
genetic condition online.
What is Fragile X
In 1991, scientists
discovered the gene (called FMR1) that causes
Fragile X. In individuals with Fragile X Syndrome,
a defect in FMR1 (a full mutation) shuts the gene
down. Like a defective factory, the FMR1 gene
cannot manufacture the protein that it normally
makes. Some individuals are fragile X carriers;
they have a small defect in the FMR1 gene (called
a premutation) but do not show symptoms of Fragile
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Fragile X is inherited.
Carrier men (transmitting males) pass the premutation
to all their daughters but none of their sons.
Each child of a carrier woman has a 50% chance
of inheriting the gene. The Fragile X premutation
can be passed silently down through generations
in a family before a child is affected by the
syndrome. A DNA blood test identifies both carriers
and affected individuals. While the exact prevalence
of Fragile X is unknown, recent studies indicate
the statistics below:
in 2000 boys and 1 in 4000 girls are estimated
to be affected.
1 in 260 women are carriers.
|1.The FMR-1 gene is located
on the X chromosome. This gene is responsible
for instructing the cell to make FMRP, a protein
assumed to be essential for normal brain functioning.
|2.The genetic code for
the FMR-1 gene usually contains a limited
repetition of CGG sequences.
The normal range is 5-50 repeats.
|3. Some people have an
expanded number of CGG repeats. When the number
of CGG repeats is between 50 and 200 the individual
is a premutation carrier of fragile X syndrome.
Carriers are not usually affected by fragile
X syndrome, but they are at risk of having
|4. If the number of repeats
exceeds 200, usually this disrupts the code
and prevents the production of the FMR protein.
These individuals have the full mutation and
usually are affected by fragile X syndrome.
The Effects Of Fragile X
Fragile X is the leading form of
autism of known cause: 90 % of Fragile X patients
have autistic features, 50% of pre-school Fragile
X children meet autism diagnostic criteria, and
6% of all autistic individuals turn out to have
fragile X. Fragile X also gives rise to anxiety
disorders, attention deficit hyperactivity disorder,
psychosis, obsessive-compulsive disorder, and
many other problems.
Is There a Cure for Fragile X Syndrome?
There is currently no cure for
Fragile X Syndrome, although appropriate education
and medications can help maximize the potential
of each child. However, most boys and many girls
remain significantly affected throughout their
lives. The cost to society for treatment, special
education, and lost income is staggering. The
need for research aimed at treatment is urgent.
Recent significant progress has been made in understanding
mechanisms and developing potential treatments
for inherited diseases that are caused by a single
gene, such as Fragile X. Current medical research
focuses on: Gene Therapy - studying the gene that
causes Fragile X in order to determine whether
a healthy gene may be inserted into the cells
of affected individuals, thereby replacing the
mutated, ineffective gene. Protein Replacement
Therapy - studying the protein product that is
lacking due to the mutation, in hopes that the
protein may be supplemented from an external source.
Psychopharmacology - treating the symptoms of
the disorder with medications.
Many researchers believe
that medical treatment, when it becomes available,
will be able to help Fragile X individuals of
all ages. Experts think that the missing FMR protein
has a regulatory function in the brain, rather
than a structural function, and that this protein
is needed throughout a person's life.