MTHFR and ischemic stroke: MTHFR methylation profiles at CpG A were associated with serum folate and vitamin B12 levels and also with higher risks of ischemic stroke when compared to CpG B. Computational biology analyses have indicated that low density lysine 4 histone H3 trimethylation and incomplete RNA polymerase II in CpG B [10] may affect the transcriptional activity of MTHFR.