A representative example of oxidative DNA damage, 8-hydroxy-2′-deoxyguanosine (8-OHdG), which is also increased in maternal serum in NTD cases [10], may suppress human DNA methyltransferase (DNMT) and murine Dnmt3a and inhibit DNA methylation by downregulating the methylation of nearby cytosine base [40, 41]. The gene discussed is DNMT1; the disease is neural tube defect.