Identical twins share the exact same DNA, yet at times, one twin may develop different characteristics or diseased than the other. Epigenetics makes this phenomenon possible as the DNA sequences remain the same but are modified in a number of different ways. DNA methylation is an example in which a methyl group is added to a site on the DNA causing the gene to be turned off. The activity affects whether the gene is expressed or not and determines the corresponding phenotype of the individual. Modification of DNA occurs differently in each person, whether they have the same sequence of DNA or not. Dr. Esteller used this understanding of epigenetics and gene expression to compare the levels of DNA methylation between twins with and without breast cancer (IDIBELL-Bellvitge Biomedical Research Institute 2012). He found that women who developed breast cancer also had a higher level of DNA methylation in the DOK7 gene than their healthy twin (IDIBELL-Bellvitge Biomedical Research Institute 2012).
The goal of Heyn et al.'s (2013) study was to look for a marker in the blood of an individual that would allow them to determine whether the person was going to develop breast cancer. By comparing the blood of identical twins the researchers could detect different levels of epigenetics and determine what functions it had within the gene (Heyn et al. 2013). A cause of cancer is the hypermethylation of promoters of tumor-suppressor genes (Heyn et al. 2013). This process would turn off the suppressors, allowing the development and continued growth of tumors. The discovery of a difference in amount of methylation occurring between twins could provide a marker to predict the onset of cancer as well as create a target for scientists to develop preventative care and treatment for cancer.
Heyn et al. (2013) discovered that hypermethylation of the DOK7 gene took place in the blood of twins that developed cancer at different times, in breast tumors, and in breast cancer cell lines. The fact that DOK7 was methylated in varying amounts before and after the development of cancer allowed scientists to study the gene further and use it as a marker to detect breast cancer (Heyn et al. 2013). The difference in the amount of methylation of the gene was very small which made it difficult for Heyn et al. (2013) to determine exactly how much methylation causes breast cancer. Genes that have already been determined to influence breast cancer as well as new genes, like DOK7, were found to display differences in levels of DNA methylation between the pairs of twins (Heyn et al. 2013). From the results of their study, Heyn et al. (2013) proposed that increased methylation of DOK7 prevented transcription factors from binding and resulted in abnormal regulation of the gene. There is a possibility that this could alter the expression of the gene and result in the development of tumors and breast cancer (Heyn et al. 2013). More research is needed to determine the exact effects of the varying levels of methylation of DOK7, but this gene could become a marker to predict breast cancer in individuals (Heyn et al. 2013).
This is an interesting post. What makes it so interesting is what appears to be overlooked. The researchers found (very interestingly) that this particular gene is hyper-methylated, but what doesn’t appear to be looked at is why one twin shows higher methylation of this gene than the other? What makes the twins different? This, I think, is a fascinating question which definitely requires an answer!
ReplyDeleteYeah, I agree! I'm not sure if the differences in methylation levels persist throughout the twins lives or if this is just occurs when one twin expresses the cancer and the other doesn't. The twins generally showed onset of cancer at different times which is where the differences in methylation were discovered. Even with that, it is also interesting how twins are able to contract the same disease at different times.
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