Identical twins not a true copy

Source: University of Alabama, Uppsala University

An international team of researchers have reported that differences between discordant monozygotic twins - where one twin has a genetic disorder and the other does not - are probably due to copy number variations.

The researchers studied 19 pairs of monozygotic twins and found differences in copy number variations in DNA. Copy number variations (CNVs) occur when a set of coding letters in DNA are missing, or when extra copies of segments of DNA are produced.

The researchers, from the University of Alabama at Birmingham, Uppsala University and the Karolinska Institutet in Sweden, Leiden University Medical Center and VU University in The Netherlands, reported their findings online in the February 14 issue of the American Journal of Human Genetics.

"Even though the genome is virtually identical in identical twins, our results show that there in fact are tiny differences and that they are relatively common," Dr Jan Dumanski from the UAB Department of Genetics, who led the study with colleague Dr Carl Bruder said.

"This could have a major impact on our understanding of genetically determined disorders."

"By uncovering these small genetic differences in identical twins where one of them is sick, we have a way of tying specific genetic changes to the genesis of common diseases," Bruder said.

Discordant twins are an interesting area of study as one twin might develop a particular disease such as Parkinson's while the other does not. Previously, it was thought that environmental factors were the likely culprits, not genetics.

Bruder and Dumanski think their findings indicate that CNVs may play a critical role and this can be efficiently studied in identical twins.

"More importantly, changes in CNV may tell us if a missing gene, or multiple copies of a gene, are implicated in the onset of disease," Bruder said.

"If twin A develops Parkinson's and twin B does not, the region of their genome where they show differences is a target for further investigation to discover the basic genetic underpinnings of the disease."