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Gene changes explain why identical twins differ

6 July 2005
By BioNews
Appeared in BioNews 316

Changes to gene 'on-off switches' caused by environmental and lifestyle influences could help explain why identical twins are often not identical, especially as they get older. An international team of scientists has looked at 'epigenetic' differences - changes that affect gene activity - in identical twins. The researchers found that young twins had almost identical 'epigenetic profiles', but with age, their profiles began to differ. The study, published in the Proceedings of the National Academy of Sciences, highlights the increasingly-recognised role of epigenetic changes in health and disease.

Although nearly all a person's body cells have an identical set of around 25,000 genes, different genes are active in different cell types at different times, depending on what proteins they need to make. These differences in gene activity are controlled by a series of chemical modifications to the cell's DNA. In the latest study, Mario Fraga of the Spanish National Cancer Centre in Madrid and colleagues wanted to see if environmental influences are linked to changes in these modifications, particularly one called methylation.

The researchers studied DNA samples from 40 pairs of identical twins aged between 3-74 years old. They found that DNA methylation patterns varied significantly between twins in a third of the pairs overall. But crucially, the epigenetic variation increased with age - 60 per cent of twins aged over 28 had significantly different DNA methylation patterns. Twins reared apart showed more differences than those reared together, providing evidence for the role of environmental and lifestyle factors in epigenetic changes. And the occurrence of a serious illness in just one twin of a pair was linked to greater variation between their epigenetic profiles, say the scientists.

The study shows for the first time that differences in gene activity are linked to lifestyle factors such as smoking, diet and exercise, according to the researchers. These changes could help explain the onset of diseases such as cancer, diabetes, heart disease and schizophrenia, which can often affect one identical twin and not the other. Team member Manel Esteller said: 'Both nature and nurture are acting on these twins', adding 'epigenetics is the bridge or gap between them'.

SOURCES & REFERENCES
Identical Twins Not So Identical
Science Now |  5 July 2005
Twin Data Highlight Genetic Changes
The Washington Post |  5 July 2005
Twins grow apart as they age
Nature News |  4 July 2005
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