Until recently, researchers have largely assumed that identical twins are 100 percent genetically identical and that only environmental factors could cause any variations between them. But in recent years, research has shown that although identical twins may look the same, when it comes to the genetics there can be in fact tiny differences. In addition, a new ‘twin study’ has discovered that these subtle dissimilarities in DNA are associated with differences in psychopathologic traits such as Attention Problems (APs).
An international team of researchers analysed the so-called copy number variations (CNVs) in the DNA of 50 pairs of identical twins. CNV occurs when a set of coding letters in DNA are missing, or when extra copies of segments of DNA are produced. CNVs influence the functioning of different genes, and therefore variations in CNV could explain why one of the two can suffer from psychopathologic traits while the other remains healthy.
The researchers examined whether CNVs were more common in children with APs and whether CNVs differed between twin pairs in which one of the two children had APs, and the other child did not. The genetic analysis showed that within identical twins there were differences on chromosomes 4 and 17. Also, children with APs had significantly larger CNVs spread across the genome than unaffected children.
The researchers note that “this study suggests that the presence of larger CNVs may increase the risk for APs, because they are more likely to affect genes, and confirms that MZ [identical] twins are not always genetically identical.”
“Our study confirms that CNVs are worth our attention. It is noteworthy that there is strong evidence from other studies that the sites in the DNA where we found differences within twin pairs [chromosomes 4 and 17] are involved in psychiatric disorders. More research is needed to understand how CNVs increase the risk of Attention Problems and how often these genetic differences are present within identical twin pairs,” said researcher Abdel Abdellaoui of the Vrije Universiteit, Amsterdam.
According to researcher Erik Ehli of the Avera Institute, US, these findings will help to enable early detection of children at risk for Attention Problems in the future.
Human Genetics, by Noel Merino
Photo: zandwacht / Flickr
Ehli, E., Abdellaoui, A., Hu, Y., Hottenga, J., Kattenberg, M., van Beijsterveldt, T., Bartels, M., Althoff, R., Xiao, X., Scheet, P., de Geus, E., Hudziak, J., Boomsma, D., & Davies, G. (2012). De novo and inherited CNVs in MZ twin pairs selected for discordance and concordance on Attention Problems European Journal of Human Genetics DOI: 10.1038/ejhg.2012.49