Identical twins don’t always have identical DNA, study shows

The best twin films of all time

“Imagine you have identical twins raised separately,” DeCode Genetics founder and CEO, and study co-author, Kari Stefansson, told CNN. “If one of them developed autism, the classic interpretation is that this is due to environmental factors. But our work shows that, before concluding that it is caused by the environment, it is necessary to sequence the genome of the twins to know what could be responsible for the autism “. Stefansson said that this “mutation divergence” could be the cause of “devastating childhood illnesses”, such as epilepsy and metabolic disorders. She also said that a large percentage of these “horrible early childhood syndromes are due to mutations in the genome”.

Identical twins, who are also known as monozygotic twins because they come from a single fertilized egg, as noted by Science News, are often studied to determine the origin of specific characteristics, diseases or conditions, whether the result of genetics or the result of their environment . This particular study looked at 381 pairs of identical twins and determined that 38 of the pairs had identical genetics, but that most of the pairs had some differences in DNA that emerged very early in their development.

Thirty-nine of the pairs had more than 100 changes between the twins and the study suggests that these DNA differences occur when the embryo splits to form two at the beginning of development or shortly after splitting the embryo. This suggests that the embryo’s division is not as clean or organized as previously thought, resulting in the changes in DNA seen.

Some twins arise when a single cell or small group of cells separates from the embryo, Science News notes, and it is the number of cells from which a twin originates that can determine the genetic differences between him and his other twin. The more unequal divisions of the embryo occur, the greater the number of genetic differences between the twins.

“This is an extraordinary, exciting and insightful effort to identify the initial cellular mechanisms that explain the genetic differences between MZ (monozygotic) twins,” said Nancy Segal, professor of psychology at California State University, Fullerton, Nancy Segal. “It is well known that MZ co-twins are not perfectly similar and that some differences may reflect genetic differences. The present study offers new information regarding the origin of the differences between MZ co-twins.”

Segal said the study shows that “some twin models underestimate the genetic effects and require revision”.

For more twins, check out our list of the best twin films of all time, and if you’re looking for more DNA science, read this story about how a new study reveals that most Vikings were not blonde or blue-eyed.

Wesley LeBlanc is a freelance news writer and creator of guides for IGN. You can follow him on Twitter @LeBlancWes.