Allfrey in 1964 described methylation as a chemical mark upon histones.[Ref.1] According to newer sources, methylation also takes place on some CpG sequences of the DNA itself.[Ref.11] CpG denotes a cytosine base next to a guanine base, a combination that tends to occur frequently. A methyl group (CH3) may attach to the cytosine in a CpG pair, forming Me-CpG. DNA methylation is associated with the regulation of gene expression.
In human DNA about 80%-90% of CpG sites are methylated, but there are certain areas known as CpG islands where none of the sites are methylated. These are associated with the promoters of 56% of mammalian genes, including all ubiquitously expressed genes. (1)
MEN1 is a ubiquitously expressed gene[Ref.6], so it would seem that we should take a closer look at methylation.
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(1)Methylation. Wikipedia.
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