Leukocyte DNA as Surrogate for the Evaluation of Imprinted Loci Methylation in Mammary Tissue DNA

There is growing interest in identifying surrogate tissues to identify epimutations in cancer patients since primary target tissues are often difficult to obtain. Methylation patterns at imprinted loci are established during gametogenesis and post fertilization and their alterations have been associated with elevated risk of cancer. Methylation at several imprinted differentially methylated regions (GRB10 ICR, H19 ICR, KvDMR, SNRPN/SNURF ICR, IGF2 DMR0, and IGF2 DMR2) were analyzed in DNA from leukocytes and mammary tissue (normal, benign diseases, or malignant tumors) from 87 women with and without breast cancer (average age of cancer patients: 53; range: 31–77). Correlations between genomic variants and DNA methylation at the studied loci could not be assessed, making it impossible to exclude such effects. Methylation levels observed in leukocyte and mammary tissue DNA were close to the 50% expected for monoallellic methylation. While no correlation was observed between leukocyte and mammary tissue DNA methylation for most of the analyzed imprinted genes, Spearman's correlations were statistically significant for IGF2 DMR0 and IGF2 DMR2, although absolute methylation levels differed. Leukocyte DNA methylation levels of selected imprinted genes may therefore serve as surrogate markers of DNA methylation in cancer tissue

Comparisons between blood and mammary tissue DNA methylation.

<p>Axes correspond to percent-methylation observed in blood and mammary tissue, respectively. Crosses correspond to non-cancerous cases, and circles to invasive cases.</p

Characteristics of the 87 women included in this study, drawn from the Clinical Breast Care Project.

1<p>Percentages may not add up to 100 due to missing values.</p

Average percent-methylation in leukocyte and mammary tissue DNA from women with benign breast disease and invasive breast cancer.

<p>N corresponds to the number of samples for which methylation values are available for both blood and mammary tissue. Values are means ± standard deviations. Spearman's ρ was calculated excluding pairs with unknown values.</p

Comparisons of methylation values between blood and matching mammary tissue in different subgroups of patients.

<p>Black circles correspond to the methylation value for an individual participant.</p