Table 5

Methylation analysis of HERVK and LINE1 in the 16 discordant MZ twins (pair 1 excluded)

Element

CpG^a

Mean MI heavy co-twins

Mean MI light co-twins

Mean MI difference

P^b

HERVK

1

0.61 ± 0.05

0.63 ± 0.02

-0.02 ± 0.06

0.38

2

0.36 ± 0.01

0.36 ± 0.01

0.0008 ± 0.006

0.86

LINE1

1

0.58 ± 0.02

0.58 ± 0.02

-0.0007 ± 0.01

0.86

2

0.37 ± 0.02

0.38 ± 0.02

-0.004 ± 0.02

0.50

All procedures (including bisulfite treatment, PCR and single-nucleotide primer extension assays in combination with ion-pair reversed-phase high-performance liquid chromatography separation technique (SIRPH) assays) were performed in duplicate; the mean values were used for the statistical analysis. Data are expressed as mean MI ± standard deviation. MI, methylation index; MI difference, MI heavy co-twin - MI light co-twin. ^aCpG 1 and 2 corresponds to the CpG tagged by SNuPE primer 1 and 2, respectively. ^bHeavy versus light calculated using a Wilcoxon signed-rank test.

Souren et al. Genome Biology 2013 14:R44   doi:10.1186/gb-2013-14-5-r44