To clarify, transcription (rewriting) occurs when DNA is converted into RNA. Then RNA is translated into proteins (an entirely different language). I skipped over the RNA stuff in the above posts, to keep things simpler.
MTHFR production is part of methylation, but it sounds like methylation has an impact after translation, not before or during it. So basically after the amino acids are formed into a chain, a methyl group can get added to certain amino acids. And that alteration can result in the protein being expressed or repressed.
So methylation isn't really involved with transcription or translation, but is involved with gene expression (protein/enzyme function) following translation.
(I happened to come across this while searching on vitamin D issues discussed in nearby posts.)
I just wanted to quickly mention that there are many types of methylation reactions - I used to do lots of them every year as a medicinal chemist. Several different versions of these happen biochemically in hundreds of different reactions in the human body (using various enzymes and often S-adenosyl methionine, for example).
One type of methylation reaction involves directly methylating cytosine bases in the DNA using DNA methyltransferase (DNMT) enzymes (there are several genes for these, e.g., DNMT1, etc).
Thus, this type of methylation reaction occurs
pre-transcriptionally. This is what epigenetic methylation is, which is largely the process of silencing certain gene activity.
It's possible relevance to ME/CFS is noted on this thread:
http://forums.phoenixrising.me/inde...tion-modifications-associated-with-cfs.31960/
Of some importance is that epigenetic methylation is heritable.
And since it does not change the gene nucleotide sequence, it's not seen with the particular testing setup 23andMe uses, for example. Hopefully someday inexpensive commercial testing will be available, as obviously it might be very important.