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Madrid (pte027/05.07.2005/13:08) - A group of researchers from the Spanish National Cancer Center in Madrid http://www.cnio.es/ing/cursos/practicasverano.htm led by Dr Manel Esteller have discovered that the older identical twins get and the longer they live apart the more likely it is that their physiognomy will change.
Although identical twins possess exactly the same set of genes, differences in their epigenome will emerge.
The term epigenome refers to natural chemical modifications that occur in a person's genome shortly after conception. They act on a gene like a gas pedal or a brake, marking it for higher or lower activity.
Changes in identical twins can include a change in appearance, developing different diseases or sliding into different personalities. Identical women twins may differ in their fertility or in the age at which they reach menopause.
Dr. Nancy Segal, a psychologist who studies twins at California State University at Fullerton, is about to publish "Indivisible by Two," a book on twins. She is fascintated by Esteller's study. "This is one of the most fascinating things I have read," she said. "By giving us a handle on something specific, it opens up many new avenues of inquiry as to why twins are different."
Two possible explanations exist for Esteller's findings: the first is the known fact that epigenetic marks get lost as people age. The other is that personal experiences and environmental elements, such as the toxic agents of tobacco smoke, will interact with the pattern of epigenetic marks.
According to Esteller, both play a role. Sets of twins who had lived apart the longest, for example, showed the greatest difference in their epigenome, noted Esteller. "This is a way for the genome to be responsive to the environment," he said.
The study shows that the epigenome may play a role in how various diseases affect twins differently, for example schizophrenia, bipolar disorder and cancer.
Dr. Peter A. Jones, president of the American Association for Cancer Research and a professor at the University of Southern California, said: "We think that epigenetic changes are very common in cancer."
He added that Dr. Esteller's finding "is exceptionally interesting in that it underlines the importance of epigenetic changes in human development and disease."
Dr Esteller's study will be published in today's issue of The Proceedings of the National Academy of Sciences http://www.pnas.org/.
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