Adult monozygotic twins discordant for intra-uterine growth have indistinguishable genome-wide DNA methylation profiles

Abstract

BackgroundLow birth weight is associated with an increased adult metabolic disease risk. It is widely discussed that poor intra-uterine conditions could induce long-lasting epigenetic modifications, leading to systemic changes in regulation of metabolic genes. To address this, we acquire genome-wide DNA methylation profiles from saliva DNA in a unique cohort of 17 monozygotic monochorionic female twins very discordant for birth weight. We examine if adverse prenatal growth conditions experienced by the smaller co-twins lead to long-lasting DNA methylation changes.ResultsOverall, co-twins show very similar genome-wide DNA methylation profiles. Since observed differences are almost exclusively caused by variable cellular composition, an original marker-based adjustment strategy was developed to eliminate such variation at affected CpGs. Among adjusted and unchanged CpGs 3,153 are differentially methylated between the heavy and light co-twins at nominal significance, of which 45 show sensible absolute mean β-value differences. Deep bisulfite sequencing of eight such loci reveals that differences remain in the range of technical variation, arguing against a reproducible biological effect. Analysis of methylation in repetitive elements using methylation-dependent primer extension assays also indicates no significant intra-pair differences.ConclusionsSevere intra-uterine growth differences observed within these monozygotic twins are not associated with long-lasting DNA methylation differences in cells composing saliva, detectable with up-to-date technologies. Additionally, our results indicate that uneven cell type composition can lead to spurious results and should be addressed in epigenomic studies.

Twin methodology in epigenetic studies

“…The observed epigenetic patterns in the discordant twins will be linked to metabolic phenotypes to look for epigenetic modification induced by birth weight discordance and its association with changes in metabolic profiles. Our results will also serve as reliable replicates to the findings of Souren et al (Souren et al, 2013).…”

“…In this regard, identical twins discordant for birth weight are ideal subjects for studying the impact of very early life adverse environment on epigenetic regulation of health at adult ages as the genetic part of epigenetic control is cancelled out, enabling pure association between environmental exposure and epigenetic status. Using a small sample of 17 pairs of MZ twins discordant for birth weight, Souren et al (Souren et al, 2013) reported no significant intra-pair differential DNA methylation pattern in a genome-wide analysis. We are currently working on whole-genome DNA methylation data on a relatively large sample of 150 pairs of identical twins discordant for birth weight.…”

Novel DNA methylation profiles associated with key gene regulation and transcription pathways in blood and placenta of growth-restricted neonates

“…12 However, these findings have not been reproduced in prospectively collected umbilical cord blood, or placental samples from babies born with growth restriction, or across a range of birth weights investigated in later life. [13][14][15] Furthermore, gestational age at delivery has a powerful effect on fetal and placental methylation status, 16,17 which has not always been considered in earlier studies of FGR offspring.…”

DNA Methylation Changes in theIGF1RGene in Birth Weight Discordant Adult Monozygotic Twins

“…The effects appeared to be specific to human umbilical vascular endothelial cells, and significant changes were not observed in placental tissue or cord blood mononuclear cells. The second study used Infinium 450K to compare the methylation levels in buccal samples from 17 monochorionic MZ adult twins (Souren et al, 2013). By comparing the methylation differences between the heavy and light co-twins and adjusting the methylation levels with leukocyte subtypes, the authors identified 3,153 birth weight differential methylation sites at p < .01 and 45 of these showed absolute methylation differences greater than 5%, but none of these changes reached genome-wide significance.…”

“…Several studies in twins have explored epigenetic and gene expression profiles in relation to birth weight or maternal factors strongly associated with birth weight (Gordon et al, 2011Loke et al, 2013;Ollikainen et al, 2010;Souren et al, 2013;Tan et al, 2014). To date, three EWAS have focused on MZ twins discordant for birth weight.…”