DRD2 and Menkes disease: However, the expression of DNMT1 and 3 alpha (DNMT3A) and the methylated CpG levels in the promoter region of the DRD2 gene were not significantly altered in the MD group compared to the control group.120 Functional differences may have occurred in other sites at the DRD2 genes not included in the study, and/or other epigenetic modifications were associated with DRD2 mRNA expression.