Until now, physical and behavioural differences between identical (monozygotic) twins have been usually attributed to environmental factors. However, a study published in Nature Genetics reveals the importance of early developmental mutations in shaping genomic differences between monozygotic twins.
For their analysis, the researchers sequenced the genomes of 387 identical twins and their parents, spouses and children to track mutation divergence and identify pre-twinning mutations. These early developmental mutations allowed them to characterise what happened to the mutated cells and their descendants.
The results show that, on average, twins differ by 5.2 early developmental mutations. Furthermore, approximately 15 per cent of monozygotic twins have a substantial number of these early developmental mutations which are specific to one of them.
These findings challenge the notion that environmental factors contribute to the differences between monozygotic twins, and suggests that the mutational component is underestimated in most heritability models. This is especially illustrated in some diseases, such as autism and other developmental disorders, where a substantial component is due to de novo mutations, which might affect only one twin in a pair.
This study uncovers the genomic differences between monozygotic twins and helps to re-evaluate their role in genetics research, the authors say.