Table 1

Studies of CpG methylation discordance in monozygotic (MZ) twins

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.


Abbreviations: MZ, monozygotic; Bis-seq, bisulfite sequencing

1Not all pairs were used for each estimate in the study

Czyz et al. BMC Medicine 2012 10:93   doi:10.1186/1741-7015-10-93

Open Data