It is currently unknown which imprinted genes are responsible for the HM phenotype, but aberrant expression from the maternal allele of these placenta-specific genes is likely to play an important role, since they include the essential epigenetic gene DNMT1 and the micro-RNA processor LIN28B. In addition there are several strong candidates for influencing trophoblast development, including the cytochrome P450 (CYP) subfamily member CYP2J2 that has previously been shown to be up-regulated in preeclampsia and THSD7A, a placental and endothelial protein that mediates cellular migration [26, 27]. This evidence concerns the gene PPIG and preeclampsia.