‘Identical twins not so identical after all’

PARIS: Genetic differences between identical twins can begin very early in embryonic development, according to a study on Thursday that researchers said has implications for how these siblings help scientists tease out the effects of nature versus nurture.

Identical -- or monozygotic -- twins come from a single fertilised egg that splits in two. They are important research subjects because they are thought to have minimal genetic differences. But the new research, published in the journal Nature Genetics, suggests that the role of genetic factors in shaping these differences has been underestimated.

"The classic model has been to use identical twins to help you to separate the influence of genetics versus environment in analysis of diseases," said Kari Stefansson, head of Iceland’s deCODE genetics, a subsidiary of US pharma firm Amgen. "So if you take identical twins raised apart and one of them developed autism, the classic interpretation has been that that is caused by the environment."