Variation in placenta-specific genomic imprinting is associated with intrauterine growth restriction.

The placenta has a critical role in fetal growth, with many key functions regulated by genomic imprinting. With the recent description of polymorphic placenta-specific imprinting, the molecular mechanisms leading to this curious epigenetic phenomenon are unknown, as is their involvement in pregnancies complications. Profiling ubiquitous and placenta-specific imprinted differentially methylated regions (DMRs) exposed isolated aberrant methylation at ubiquitous DMRs as well as abundant hypomethylation at placenta-specific DMRs. Analysis of underlying chromatin at polymorphic placenta-specific imprinted DMRs revealed biallelic enrichment of histone H3K4 methylation, a modification normally mutually exclusive with DNA methylation. Furthermore, characterisation of expression in intrauterine growth restricted samples (IUGRs) uncovered coordinated deregulation of the GPR1AS1-ZDBF2-ADAM23 locus. Our results emphasize that methylation is less stable at placenta-specific imprints compared to their ubiquitous counterparts and that further work is required to determine if these differences are the IUGR cause or reflect unique adaption of the placenta epigenome to developmental stresses. Bisulphite converted DNA from 13 IUGR human placenta samples together with 9 control (no-IUGR) ones were hybridised to the Illumina HumanMethylation450 BeadChip v1.2