What is methylation in regard to Fragile X?

Having more than 200 CGG repeats sets in motion methylation of part of the FMR1 gene. The methylation stops the synthesis of FMRP and the absence of FMRP causes Fragile X syndrome. We do not know why having too many CGG repeats triggers methylation. Methylation inactivates that part of the chromosome. It’s as if we were to put glue on the edges of some of the books in the library; those pages would become unavailable to readers. 

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