Fragile X -- breaks? FA vs. UW

[WashMe]

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P. 87 of FA 2011 says Fragile X syndrome IS associated with chromosomal breakage. UW question 1421 [344578] explanation says that there is NOT chromosomal breakage, but the increased CGG allows hypermethylation and gene inactivation...

Thoughts?

 

[kstreet]

The break is in vitro, not in vivo.

 

[SirGecko]

Yeah I don't know. The "fragile" part of fragile X isn't exactly referring to the chromosome actually breaking, it just looks that way because there is a stretch that doesn't stain. Then again a pubmed search on fragile sites indicates that people do think they are associated with chromosomal breaking. Robbins doesn't really say anything either way. (beyond saying what a fragile site looks like and that fragile X has it)

How was the question worded? Maybe they were making the point that the actual disease isn't caused by chromosomal breaking?

edit: the guy above expresses the opinion I had before doing a pubmed search. (that the breaking was just in vitro) Pub med only muddled the issue for me though.

 

[dude1344]

I was confused also. 😕

 

[WashMe]

Yeah I don't know. The "fragile" part of fragile X isn't exactly referring to the chromosome actually breaking, it just looks that way because there is a stretch that doesn't stain. Then again a pubmed search on fragile sites indicates that people do think they are associated with chromosomal breaking. Robbins doesn't really say anything either way. (beyond saying what a fragile site looks like and that fragile X has it)

How was the question worded? Maybe they were making the point that the actual disease isn't caused by chromosomal breaking?

The question was basically: "in a young man with >200 CGG repeats in a stretch of DNA, what is the most likely genetic occurrence responsible for causing disease?"

I picked chromosomal breakage, the answer was gene inactivation.

 

[SirGecko]

The question was basically: "in a young man with >200 CGG repeats in a stretch of DNA, what is the most likely genetic occurrence responsible for causing disease?"

I picked chromosomal breakage, the answer was gene inactivation.

Ahh there you go. The breaking (if it does occur in vivo, still not sure about that considering I think my path class said it doesn't and pubmed says it might) wouldn't be the cause the manifestations of fragile x.

 

[dude1344]

The question was basically: "in a young man with >200 CGG repeats in a stretch of DNA, what is the most likely genetic occurrence responsible for causing disease?"

I picked chromosomal breakage, the answer was gene inactivation.

I got that wrong also, but I thought about it afterwards and gene inactivation by methylation of the FMR-1 leads to the phenotype. The chromosomal breakage that occurs is just happenstance I think... though UW emphatically stated that chromosomal breakage was not found in the disease.

 

[kstreet]

Just to reiterate, they call it fragile X b/c when when they stained for the chromosome it appeared "broken". This doen't mean it happens in vivo and it's not the pathogenic cause of fragile X.

 

[WashMe]

Cool, thanks for the replies everyone!