BIRMINGHAM, Ala. – In a scientific double-take, new research is challenging the long-held belief that identical twins have identical genetics.

Jan P. Dumanski and Carl Bruder of the University of Alabama at Birmingham’s Department of Genetics headed an international effort to analyze the genes of 19 sets of identical twins. Using cutting-edge technology, the researchers found genetic differences in every set of twins, according to the study published online Thursday in the American Journal of Human Genetics.

“We are showing this is a very common phenomenon,” Dumanski said.

Besides overturning a basic scientific premise, Dumanski and Bruder said the research is important because it may provide a shortcut for scientists trying to understand the genetic components for many conditions and diseases.

The study focused on monozygotic, or identical, twins. These twins are the product of a single egg being fertilized to form one zygote. The zygote then divides into two embryos, producing identical babies.

Identical twins, particularly when they are reared apart, have always provided scientists with a powerful research model. Studies of twins have helped scientists learn about human development and behavior, and helped them sort out whether something is caused by heredity or by environment.

This new knowledge about genetics will add more scientific depth to the practice of studying twins, Dumanski said. “It’s a wonderful model; it’s even more wonderful now because we have a tool to explore it.”

Already, the researchers are planning to study identical twins to determine why one developed a disease or condition while the other didn’t. Among other things, they hope to focus on obesity, Parkinson’s disease and asthma.

Scientists have always known there were differences between identical twins. Some of the differences were so slight that only a mother could spot them, while others were profound, such as one twin developing a fatal disease while the other remained healthy.

“So far it has been blamed on environmental factors,” Bruder said.

Dumanski and Bruder were recruited to UAB from Sweden two years ago. Bruder said they had already started their study, using an advanced system of genetic mapping that allowed them to compare two sets of DNA.

The core lab at UAB’s Howell and Elizabeth Heflin Center for Human Genetics has some of the most advanced genetic analysis equipment in the world.

Using blood collected from twins in Holland, the researchers compared DNA sequences and found copy number variation, or CNV. In other words, substantial chunks of DNA sequences were missing, doubled or reversed in one of the two twins.

Having chunks of DNA sequences shifted around or missing is a common genetic mutation.

When first discovered, scientists thought it was inconsequential. Often it is, but researchers are beginning to learn that sometimes CNV can be a major factor in developing a disease.

Bruder and Dumanski believe CNV could help explain why one identical twin develops a disease while the other remains healthy.

“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.”

Other researchers collaborating in the study were from Leiden University Medical Center and UV University, The Netherlands; and Uppsala and Karolinska Institutet, Sweden.

PH END PARKS

(Dave Parks is a staff writer for the Birmingham (Ala.) News. He can be contacted at dparks(at)bhamnews.com.)

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