<P> In recent years it has come to the attention of researchers that many types of cancer are caused largely due to epigenetic factors . Cancer can be caused in a variety of ways due to differential methylation of histones . Since the discovery of oncogenes as well as tumor suppressor genes it has been known that a large factor of causing and repressing cancer is within our own genome . If areas around oncogenes become unmethylated these cancer - causing genes have the potential to be transcribed at an alarming rate . Opposite of this is the methylation of tumor suppressor genes . In cases where the areas around these genes were highly methylated, the tumor suppressor gene was not active and therefore cancer was more likely to occur . These changes in methylation pattern are often due to mutations in methyltransferase and demethyltransferase . Other types of mutations in proteins such as isocitrate dehydrogenase 1 (IDH1) and isocitrate dehydrogenase 2 (IDH2) can cause the inactivation of histone demethyltransferase which in turn can lead to a variety of cancers, gliomas and leukemias, depending on in which cells the mutation occurs . </P> <P> In one - carbon metabolism, the amino acids glycine and serine are converted via the folate and methionine cycles to nucleotide precursors and SAM . Multiple nutrients fuel one - carbon metabolism, including glucose, serine, glycine, and threonine . High levels of the methyl donor SAM influence histone methylation, which may explain how high SAM levels prevent malignant transformation . </P>

Why histone methylation occurs over large areas of chromatin during differentiation