Identical twins are alike, not perfectly similar: Study

A new study, published in the journal Nature Genetics, has revealed that genetic differences between identical twinscan begin in very early stages in embryonic development.

Identical twins, also known asmonozygotic, originally come from asingle fertilised egg and then get split into two. Scientists believe identical twins haveminimal genetic differences, meaning the majority of behavioural differences emerge due toenvironmental factors.

Scientists explained through this study that while "the classic model has been to use identical twins to help you to separate the influence of genetics versus environment in analysis of diseases", there is a possibility that a disease was caused in one of the siblings due to an early genetic mutation in the affected twin.

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"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," explainedKari Stefansson, co-author of the paper and the head of Iceland’s deCODE genetics, a subsidiary of the US pharmaceutical company Amgen. "But that is an extraordinarily dangerous conclusion."

To track genetic mutations, the scientistssequenced the genomes of 387 pairs of identical twins and their parents, spouses and children. In the process, they measuredembryonic growth and concluded that identical twins differed by an average of 5.2 early developmental mutations, with nearly 15 per cent twins having higher number of diverging mutations.

In one of the twins, used for study, one sibling had all cells, whereas the other one did not have any of them. This helped scientists understand thatit likely happened very early in development.

Stafansson explained out of the initial mass, which would form the individuals later, "one of the twins is made out of the descendants of the cell where the mutation took place and nothing else", but the other one had none.

"These mutations are interesting because they allow you to begin to explore the way in which twinning happens," he explained.

He also urged people to describe these twins as 'monozygotic' rather than 'identical'. "I am more inclined to call them monozygotic twins today than identical," he said.

This study has come years after few scientists discoveredgenetic differences between identical twins, concluding that twins are alike but not perfectly similar.