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Research offers insight into the cause of identical twins

An international group of researchers has made a discovery that could lead to new insights into how identical twins occur.

Their study, published in Nature Communications on Wednesday, September 29 AEST, was led by Dr Jenny van Dongen and Professor Dorret Boomsma of the Vrije Universiteit in Amsterdam, and involved scientists from QIMR Berghofer Medical Research Institute in Brisbane.

The researchers studied several large twin cohorts in The Netherlands, Australia, the United Kingdom and Finland to find identical twins – otherwise known as monozygotic twins – share a unique epigenetic profile.

The head of the Genetic Epidemiology Research Group at QIMR Berghofer, Professor Nick Martin, who led the Australian team, said it was an exciting breakthrough.

“Over the past 100 years, we’ve made huge advances on most of the big puzzles in biology but the origins of identical twins remain a mystery,” Professor Martin said.

“While nonidentical twins run strongly in families, identical twinning seems to be a random occurrence and we haven’t known what could possibly account for that.

“We still don’t have all the answers, but this research is a major step forward. Until now, there had been no advance in our understanding of the origins of monozygotic twinning for about a century.”

The researchers found evidence of identical twins having a unique epigenetic profile when they measured methylation in the DNA of thousands of identical twins and compared it to controls. DNA methylation is a process controlling gene expression – which genes are switched “on” and “off” in each cell of the body.

The study revealed there were 834 DNA locations where the methylation level was different in identical twins than in non-twins.

“These locations in the DNA are involved in functions in early embryonic development,” said Dr Jenny van Dongen, who led the study.

“In addition to insights into the fabrics of monozygotic twins, our results may lead to a better understanding of congenital abnormalities that occur more often in monozygotic twins in the future.”

Professor Martin said it was also interesting that greater methylation seemed to occur in protocadherin genes that determine how cells stick together.

“We know that splitting of the early stage embryo to form identical twins represents a failure of that ‘stickiness’, so this finding makes a lot of sense,” Professor Martin said.

Other institutions represented in the international study include The University of Queensland in Brisbane, Duke University and the Altius Institute for Biomedical Sciences in the United States, University of Helsinki in Finland and Leiden University Medical Center in The Netherlands.