Epigenetics and disease

Epigenetic changes are part of normal development and health but they can also be responsible for certain diseases. Altering any of the epigenetic processes can cause abnormal activation or silencing Of genes. Such alterations have been associated with a number of diseases including cancer. In some cases the activation of a normally inactive gene can cause cancer, in other cases it is the inactivation of a tormally active gene that gives rise to the disease. In 1983, researchers found that diseased tissue taken from patients With colorectal cancer had less DNA methylation than normal tissue from the same patients. As we saw earler, increased DNA methylation normally inhibits transcription (switches off genes). This means that these patients with less DNA methylation would have higher than normal gene activity - more genes were turned on. It is known that there are specific sections of DNA (ones near regions called promoter regions) that have no methylation in normal cells. However, in cancer cells these regions become highly methylated causing genes that should be active to switch oft. This abnormality happens early in the development of cancer. We have seen that epigenetic changes do not alter the sequence of bases in DNA. They can, however, increase the incidence of mutations. Some active genes normally help repair DNA and so prevent cancers. In people with various types of inherited cancer, it is found that increased methylation of these genes has led to these protective genes being switched off. As a result, damaged base sequences in DNA are not repaired and so can lead to cancer.