In the same way, the body's methylation machinery can also silence genes that are introduced for therapeutic purposes. Finding ways of selectively inhibiting this process will go a long way in advancing gene therapy. Inhibitors of DNA methylation also have potential applications in the prevention and treatment of cancer, a disease in which methylation plays a major role. The discovery that methylation patterns are profoundly altered in tumours heralded a new line of inquiry in cancer research. Cancer begins when a cell acquires genetic mutations - changes in DNA base sequence that give it a growth advantage over its neighbours.
Mutations can affect genes that control the birth or death of cells.
The former can cause cells to divide rapidly, the latter act as brakes, inhibiting such events. Mutations can activate proto-oncogenes and silence tumour suppressor genes, and like a car whose brakes have failed, the cell runs out of control. The risk of a cell acquiring mutations is influenced by a variety of factors. An excess of reactive oxygen species produced by the body and present in environmental pollutants can damage DNA, increasing the likelihood of mutations. However, there is now considerable evidence that DNA methylation plays a major role in the cancer process.