Fragile X Syndrome
As a fourth year USU medical student, you are working
with a Pediatric Resident in clinic. A 27-year-old woman
presents to clinic with her 7 year-old-son. He was born
at term weighing 7 pounds and appeared normal. However,
as he grew older he was noted to have developmental delay,
and was noted to have several "dysmorphic features."
He was placed in "special education" classes
in school. On physical examination you noted that he had
a long face, large ears, lax joints and large testes.
His face was somewhat narrow with a prominent jaw. The
family history revealed normal parents and a normal
developing sister. Routine chromosomal analysis (450
bands) was noted to be normal.
Upon review of this data you conclude that this child
may have a form of X-linked mental retardation known
as the Fragile X syndrome. The fragile X marker was
recognized to depend on culture of cells in low folic
acid medium prior to karyotype. Subsequently, the fragile
site on the long arm of the X chromosome (Xq27) was
shown to be expanding triplet repeat mutation (the FMR-1
gene).
Go to OMIM:
- Search the OMIM database for: Fragile X
- Look up clinical synopsis, text, genetic defect
and treatment of FX gene.
- Review the diagnostic criteria, and the cytogenetic
and molecular information about this condition.
- Search OMIM for the term trinucleotide repeat disorders
to learn what other diseases have this form of mutation.
To ascertain information about genetic testing for
Fragile X syndrome you choose an on-line resource (www.genetests.org).
Search OMIM
(www.ncbi.nlm.nih.gov/Omim)
for the term trinucleotide repeat disorders to learn
what other diseases have this form of mutation.
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