Identical Twins: Not as Identical as You Think

This article talks about how identical twins show differences in their gene expressions. In many aspects, identical twins seem, well, identical! However, there are dissimilarities and it is unclear how they have come about. A new report suggests that epigenetic differences, differences in how the genome is expressed, could be responsible. Mario F. Fraga, of the Spanish National Cancer Center, studied 160 identical twins, ranging in all different ages. Two external factors through the entire genome were analyzed for each set of twins. Both DNA methylation and histone acetylation govern gene expression and can magnify or reduce the effects of certain genes. The team's research showed that twins tended to be indistinguishable in their gene expression, earlier in life. As the twins got older, more differences in gene expression became evident. Also, twins who had spent more time apart and had more varying medical histories showed the greatest epigenetic differences.

This is a picture of methylation patterns of three-year-old twins (left) and 50-year-old twins (right). The differences have been highlighted in red.

Environmental factors, physical activity levels, and diet can influence epigenetic patterns and may help in understanding how the same genotype can be translated in different ways. Scientists suggest that specific mechanisms that cause this so-called epigenetic drift in identical twins should be studied in the future.