Project description:Comparison between groups of monozygotic (MZ) and dizygotic (DZ) twins enables an estimation of the relative contribution of genetic, shared and non-shared environmental factors to phenotypic variability. Using DNA methylation profiling of ~20,000 CpG sites as a phenotype, we have examined discordance levels in multiple tissues in neonatal twins. MZ twins exhibit a wide range of within-pair differences at birth, but show discordance levels generally lower than DZ pairs. Within-pair methylation discordance was lowest in CpG islands in all twins and increased as a function of distance from islands. This was largely independent of distance from transcriptional start site in promoters without CpG islands. Variance component decomposition analysis of DNA methylation in MZ and DZ pairs revealed a low mean heritability across all tissues, although a wide range of heritabilities was detected for specific genomic CpG sites. The largest component of variation was attributed to the combined effects of non-shared intrauterine environment and stochastic factors. Regression analysis of methylation on birth weight revealed a general association between methylation of genes involved in metabolism and biosynthesis, providing further support for epigenetic change in the previously described link between low birth weight and increasing risk for cardiovascular, metabolic and other complex diseases. Finally, comparison of our data with that of several older twins, revealed little evidence for genome-wide epigenetic drift with increasing age. This is the first study to analyse DNA methylation on a genome scale in twins at birth, further highlighting the importance of the intrauterine environment on shaping the neonatal epigenome. Data from cord blood mononuclear cells (CBMCs), human umbilical vascular endothelial cells (HUVECs) and placenta from 22 MZ and 11 DZ pairs with one replicate sample
Project description:Inter-individual variability in DNA methylation has been hypothesized to contribute to complex phenotypes through epigenetic modulation of gene expression levels. Population epigenetic studies have been examining differences in DNA methylation in a variety of accessible tissues for association with specific diseases or exposures, but relatively little is known about how this inter-individual variation differs between tissues. This study presents an analysis of global DNA methylation differences between matched peripheral blood mononuclear cells and buccal epithelial cells; specifically it examines differential DNA methylation, probe-wise DNA methylation variance, and how methylation relates to a number of demographic factors across the two tissues. We found that peripheral blood mononuclear cells have overall higher DNA methylation than buccal epithelial cells, and regions of the genome that are differently methylated between the tissues tend to have low CpG density. We also discovered that although both tissues show extensive probe-wise variability, the specific regions and magnitude of variability differed between tissues. Finally, we observed that while both buccal epithelial and peripheral mononuclear blood cell DNA methylation was associated with gender, only methylation of the latter was associated with body mass index. The work presented here offers insight into variability of DNA methylation between individuals and across tissues and the suitability of buccal epithelial and peripheral mononuclear cells for the biological questions explored by epigenome-wide association studies in human populations.
Project description:Comparison between groups of monozygotic (MZ) and dizygotic (DZ) twins enables an estimation of the relative contribution of genetic, shared and non-shared environmental factors to phenotypic variability. Using DNA methylation profiling of ~20,000 CpG sites as a phenotype, we have examined discordance levels in multiple tissues in neonatal twins. MZ twins exhibit a wide range of within-pair differences at birth, but show discordance levels generally lower than DZ pairs. Within-pair methylation discordance was lowest in CpG islands in all twins and increased as a function of distance from islands. This was largely independent of distance from transcriptional start site in promoters without CpG islands. Variance component decomposition analysis of DNA methylation in MZ and DZ pairs revealed a low mean heritability across all tissues, although a wide range of heritabilities was detected for specific genomic CpG sites. The largest component of variation was attributed to the combined effects of non-shared intrauterine environment and stochastic factors. Regression analysis of methylation on birth weight revealed a general association between methylation of genes involved in metabolism and biosynthesis, providing further support for epigenetic change in the previously described link between low birth weight and increasing risk for cardiovascular, metabolic and other complex diseases. Finally, comparison of our data with that of several older twins, revealed little evidence for genome-wide epigenetic drift with increasing age. This is the first study to analyse DNA methylation on a genome scale in twins at birth, further highlighting the importance of the intrauterine environment on shaping the neonatal epigenome.
Project description:Inter-individual variability in DNA methylation has been hypothesized to contribute to complex phenotypes through epigenetic modulation of gene expression levels. Population epigenetic studies have been examining differences in DNA methylation in a variety of accessible tissues for association with specific diseases or exposures, but relatively little is known about how this inter-individual variation differs between tissues. This study presents an analysis of global DNA methylation differences between matched peripheral blood mononuclear cells and buccal epithelial cells; specifically it examines differential DNA methylation, probe-wise DNA methylation variance, and how methylation relates to a number of demographic factors across the two tissues. We found that peripheral blood mononuclear cells have overall higher DNA methylation than buccal epithelial cells, and regions of the genome that are differently methylated between the tissues tend to have low CpG density. We also discovered that although both tissues show extensive probe-wise variability, the specific regions and magnitude of variability differed between tissues. Finally, we observed that while both buccal epithelial and peripheral mononuclear blood cell DNA methylation was associated with gender, only methylation of the latter was associated with body mass index. The work presented here offers insight into variability of DNA methylation between individuals and across tissues and the suitability of buccal epithelial and peripheral mononuclear cells for the biological questions explored by epigenome-wide association studies in human populations. This cohort consist of genomic DNA extracted from the peripheral blood mononuclear cells and buccal epithelial cells of 25 individuals, bisulphite converted and hybridized to the Illumina GoldenGate Methylation Cancer Panel for genome wide DNA methylation profiling
Project description:<p>Monozygotic (MZ) twins have been widely employed for dissection of the relative contributions of genetics and environment in disease. In multiple sclerosis (MS), an autoimmune demyelinating disease that commonly causes neurodegeneration and disability in young adults, disease discordance in MZ twins has been interpreted to indicate environmental importance in pathogenesis. However, genetic and epigenetic differences between MZ twins have been described, challenging the accepted experimental paradigm in disambiguating effects of nature and nurture. Here, we report the genome sequences of one MS-discordant MZ twin pair and messenger RNA (mRNA) transcriptome and epigenome sequences of CD4+ lymphocytes from three MS-discordant, MZ twin pairs. No reproducible differences were detected between co-twins among ~3.6 million single nucleotide polymorphisms (SNPs) or ~0.2 million insertion-deletion polymorphisms (indels). Nor were any reproducible differences observed between siblings of the three twin pairs in HLA haplotypes, confirmed MS-susceptibility SNPs, copy number variations, mRNA and genomic SNP and indel genotypes, or expression of ~19,000 genes in CD4+ T cells. Only two to 176 differences in methylation of ~2 million CpG sites were detected between siblings of the three twin pairs, in contrast to ~800 differences in methylation between T cells of unrelated individuals and several thousand differences between tissues or normal and cancerous tissues. In the first systematic effort to estimate sequence variation among MZ co-twins, we did not find evidence for genetic, epigenetic or transcriptome differences that explained disease discordance. These are the first female, twin and autoimmune disease genome sequences reported.</p>
Project description:Background: The widespread use of accessible peripheral tissues for epigenetic analyses has prompted increasing interest in the study of tissue-specific DNA methylation (DNAm) variation in human populations. To date, characterizations of inter-individual DNAm variability and DNAm concordance across tissues have been largely performed in adult tissues and therefore are limited in their relevance to DNAm profiles from pediatric samples. Given that DNAm patterns in early life undergo rapid changes and have been linked to a wide range of health outcomes and environmental exposures, direct investigations of tissue-specific DNAm variation in pediatric samples may help inform the design and interpretation of DNAm analyses from early life cohorts. In this study, we present a systematic comparison of genome-wide DNAm patterns between matched pediatric buccal epithelial cells (BECs) and peripheral blood mononuclear cells (PBMCs), two of the most widely used peripheral tissues in human epigenetic studies. Specifically, we assessed DNAm variability, cross-tissue DNAm concordance and genetic determinants of DNAm across two independent early life cohorts encompassing different ages. Results: BECs had greater inter-individual DNAm variability compared to PBMCs and highly variable CpGs were more likely to be positively correlated between the matched tissues compared to less variable CpGs. These sites were enriched for CpGs under genetic influence, suggesting that a substantial proportion of DNAm co-variation between tissues can be attributed to genetic variation. Finally, we demonstrated the relevance of our findings to human epigenetic studies by categorizing CpGs from published DNAm association studies of pediatric BECs and peripheral blood. Conclusions: Taken together, our results highlight a number of important considerations and practical implications in the design and interpretation of EWAS analyses performed in pediatric peripheral tissues.