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.

由于癌症患者的原发靶组织通常难以获取，寻找可用于检测癌症患者表观突变的替代组织的研究日益受到关注。印记基因座的甲基化模式在配子发生及受精后阶段建立，其改变与癌症风险升高相关。本研究对87名伴或不伴乳腺癌的女性（癌症患者平均年龄53岁，年龄范围31~77岁）的白细胞及乳腺组织（正常组织、良性病变组织或恶性肿瘤组织）DNA中，多个印记差异甲基化区域（GRB10 ICR、H19 ICR、KvDMR、SNRPN/SNURF ICR、IGF2 DMR0及IGF2 DMR2）的甲基化水平进行了分析。由于无法评估基因组变异与研究位点DNA甲基化之间的相关性，因此无法排除此类效应的干扰。在白细胞与乳腺组织DNA中观测到的甲基化水平，接近单等位基因甲基化预期的50%水平。尽管多数分析的印记基因的白细胞与乳腺组织DNA甲基化水平未观测到相关性，但IGF2 DMR0与IGF2 DMR2的斯皮尔曼相关性具有统计学显著性，尽管二者的绝对甲基化水平存在差异。因此，所选印记基因的白细胞DNA甲基化水平可作为癌症组织DNA甲基化的替代标志物。