"Identical twins" not always identical, Dutch study says

Identical twins can still have subtle differences in their DNA sequences, according to a Dutch study. These variations determine behavioral characteristics like attention disorders, and the findings could lead to a future breakthrough in early diagnosis of disorders like ADHD, scientists say.

Abdel Abdellaoui, researcher fro, the VU, "free university" in Amsterdam as well as the Dutch Twin Registry, and Erik Ehli from the Avera Institute looked at the so-called DNA-copy number variations (CNVs). The team looked at a total 50 pairs of monozygotic twins.

At what exactly? Well, the study paper explained that CNVs are pieces of DNA that can be present on a chromosome, and that can influence the functioning of different genes. With their functioning, they offer an important contribution to genetic variation. If all sounds like a foreign language to you, you're not the only one. But, the essence is that small genetic variations actually have a huge impact on a person's psychological well-being.

What the researchers wanted to know if CNVs were present in people with attention disorders more frequently, and if they differed from one twin to another in cases where one sibling has an attention disorder and they other didn't. Analyses the researchers conducted showed that there were differences on chromosomes four and 17 between monozygotic twins.

This study shows that CNVs are important and give a lot of information about behavior and about psychiatric disorders. The study's lead researcher said that a lot more time was still needed to figure out exactly how these CNVs influence ADHD, and how often these differences turn up in identical twins. The study was published in the European Journal of Human Genetics.