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Table 1 Studies of CpG methylation discordance in monozygotic (MZ) twins

From: Genetic, environmental and stochastic factors in monozygotic twin discordance with a focus on epigenetic differences

Study Type Method Tissue MZ pairs, n Conclusion
Fraga et al. [29] Cross-sectional, age-stratified High-performance capillary electrophoresis of total methyl-cytosine content Peripheral lymphocytes; buccal epithelial cells; muscle biopsy; adipose tissue 40 Young MZ twins are nearly identical epigenetically; discordance progresses with age, mediated by a combination of external and/or internal factors·
Kaminsky et al. [85] Cross-sectional Human 12 K CpG island microarrays White blood cells, buccal epithelial cells, rectal biopsy 571 Methylation discordance in MZ twins confirmed;· monochorionic MZ twins significantly more discordant than dichorionic MZ twins.. Epigenetic drift suggested as the main cause of discordance.
Saffery et al. [86] Cross-sectional, taken at birth Bis-seq (IGF2/H19) Cord blood, mononuclear cells, buccal epithelial cells, placental cells, umbilical vein cells, endothelial cells 56 CpG methylation discordance can arise in newborn twins by combination of environmental and/or stochastic factors acting in utero and varies depending on the type of the tissue.
Wong et al. [87] Longitudinal, with single 5-year interval High-throughput mass spectrometry (DRD4, SERT, MAOA) Buccal cells, epithelial cells 46 CpG methylation discordance is present in early childhood and susceptibility to epigenetic change is highly locus-specific.. Environmental influence is the main cause of discordance, with various loci having differential susceptibility to shared and non-shared exposures.
Talens et al. [88] Cross-sectional and longitudinal with single 10-year interval High-throughput mass spectrometry; global methylation and selected loci (IGF2, LEP, CRH, ABCA1, INS, KCNQ1OT1, GNASAS) Whole blood 230 Global and locus-specific methylation increases gradually with age, owing to unique environmental and stochastic factors.
  1. Abbreviations: MZ, monozygotic; Bis-seq, bisulfite sequencing
  2. 1Not all pairs were used for each estimate in the study