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Hello all... So there's this UWorld question which asks - and I'm paraphrasing here after analyzing the question to get the diagnosis - what is the mechanism of the symptoms in Fragile X syndrome... So I, having done First Aid, argue - oh - many CGG repeats make the chromosome "fragile" and, as it says in FA 2010 (Associated with chromosome breakage - p87) I choose the "DNA damage" or whatever option there was similar to that. Wrong!!!! Apparently the answer is DNA Methylation. FA's comment on this on the same block is "X-linked defect affecting the methylation and expression of the FMR-1 gene" I wish I could extrapolate from that somehow that what FA meant was ohh - yeah if there are a lot of cysteine (from the extra CGG) residues then they get methylated and then this methylation inactivates the whole FMR gene so no transcription occurs so you get the symptoms. That my friends, is how Fragile X works... I am soo going to fail...
 
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