What can epigenetics tell us about twin development?

Published: Tuesday 20 April 2021

As you would expect, 11-year-old identical twins, Marcos and Gabriel have a great deal in common. They love playing outside, riding on their bikes and playing board games.

But some differences started to emerge earlier in their lives. Gabriel suffered from asthma, hives on his skin and a heart murmur while Marcos didn’t.

It is these similarities and difference between twins that are helping researchers, like Professor Jeff Craig, to discover what role genes and environment play in our health.

Jeff is studying epigenetic differences within twin pairs. Epigenetics is the study of how changes to our DNA can turn genes ‘on’ or ‘off’. He is especially interested in how the environment in the womb may affect the genes of babies and their later health.

Ground-breaking research by the team has shown that the environment experienced in the womb may have a greater effect on our future health than previously thought - and more of an effect than our DNA, and the health and lifestyle of mothers while pregnant.

By comparing the level of epigenetic differences in identical twins versus non-identical twins, researchers were able to estimate the contributions of both genes and environment in the womb to the newborn.

"This study demonstrated that the unique environment in the womb impacts each twin differently. This must be due to events that happened to one twin and not the other whilst in the womb and shows that the experiences in the womb are important in defining the epigenetic profile we are born with," Jeff said.

Researchers say these ideas are further supported by their finding that birth weight differences within pairs of twins are related to epigenetic differences, especially in genes that may be linked with predisposition to diseases previously associated with low birth weight.

Marcos and Gabriel have been part of the research since it started in 2007 and are one of 250 participating pairs recruited over two and half years. The researchers hope to follow the health of the twins well into their teenage and adult lives.

The next step in the study is to analyse data to answer the question of whether biological differences within twin pairs seen in early life predict differences in brain structure and function at age 11.

For Marcos and Gabriel’s mother, Zaina Nehme, it came as a surprise that there were so many differences between her two boys.

“In their first couple of years these differences were a surprise to me. I was under the impression that because identical twins have the same genetic composition it is a given that both would suffer from the same health conditions,” she said.

“However, as my knowledge increases about twins and more research is done in the area, I get less surprised. Nevertheless, I keep on asking myself - if genes can account for their similarities, what accounts for their differences? And it seems epigenetics has a lot of the answers.”