Identical twins don’t always have identical DNA, according to a new scientific study.
Identical twins differ by an average of 5.2 genetic changes, according to a new study Jan. 7 in Nature Genetics, as reported by Science News. This study goes against the belief that identical twins are genetically identical, which was often the basis for the idea that health differences between twins are the result of their environment. This new study shows that genetics may have more to do with it than previously believed.
“Imagine you have identical twins who are raised separately,” DeCode Genetics CEO and founder and study co-author Kari Stefansson told CNN. “If one of them developed autism, the classical interpretation is that it is due to environmental factors. But our work shows that before concluding that it is caused by the environment, you must sequence the genome of the twins to know what could explain autism” .
Stefansson said that this “divergence of mutations” could be the cause of “devastating childhood diseases” such as epilepsy and metabolic disorders. He also said that a large percentage of “these horrible early childhood syndromes are due to genome mutations.”
Identical twins, which are also known as monozygotic twins Because they come from a single fertilized egg, as Science News points out, they are often studied to determine the origin of specific traits, diseases or conditions, whether it is the result of genetics or the result of their environment. This particular study analyzed 381 pairs of identical twins and determined that only 38 of the pairs had identical genetics, but that most pairs had some differences in DNA that arose 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 divides to form two in early development or shortly after the embryo divides. It suggests that this division of the embryo is not as clean or orderly as previously thought, resulting in the observed changes in DNA.
Some twins arise when a single cell or a small group of cells detach 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 one twin and another. The more unequal divisions of the embryo that occur, the greater the number of genetic differences between twins.
“This is an extraordinary, exciting, and insightful effort to identify the early cellular mechanisms that explain genetic differences between monozygotic twins,” Nancy Segal, a professor of psychology at California State University, Fullerton, told CNN. “It is well known that monozygotic co-twins do not show perfect similarity and that some differences may reflect genetic differences. The present study offers new information on the source of the differences between monozygotic co-twins.”
Segal said the study shows that “some twin models underestimate genetic effects and require revision.”
For more DNA science, read this story about how a new study reveals that most Vikings weren’t blond or blue-eyed.