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Old 04-22-2011
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DNA Fragile X Syndrome Genetics Question

A 13 yr old caucasian male with moderate mental retardation and a dysmorphic face is found to have 226 trinucleotide repeats in a gene located on the X chromosome. Which of the following is the most likely cause of this condition?
A) Exon deletion
B) Chromosomal breaks
C) Gene methylation
D) Impaired intron splicing
E) Mismatch repair defect

I am putting up this question because the answer given in the qbank differs from what's put in FA ..so first let me know what ur answer is and I will put up the answer given in the qbank.
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Old 04-22-2011
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Is the answer C????
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Old 04-22-2011
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Check this out
Fragile X Syndrome
They discussed the same issue exactly!
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Old 04-22-2011
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Quote:
Originally Posted by Dr_Laura View Post
Is the answer C????
Gene Methylation defects are seen in Genomic Imprinting defects such as Angelman Syndrome and Prader Willi Syndrome...where you dont have a Barr Body from the maternal and paternal side, respectively.

I think this is an intron and exon defect. I would go with D) Impaired intron splicing. Is that the right answer ?
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Old 04-22-2011
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Yes Dr Laura, the answer given in the qbank is C. The explanation reads: The familial mental retardation gene 1 (FMR1) is located on the long arm of Chromosome X. An increased number of CGG trinucleotide repeats leads to hypermethylation of cysteine bases and gene inactivation.

..So I guess that's it.
Wikip says this>
Expansion of the CGG repeating codon to such a degree results in a methylation of that portion of the DNA, effectively silencing the expression of the FMR1 protein.

some examples I found on chromosomal breakages are : Fanconi anemia, Ataxia telangiectasia, Xeroderma pigmentosum.
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Old 04-22-2011
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I forgot to mention. I guess the answer does not differ from FA.. it's just a matter of interpretation.
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