Tuesday, January 26

Identical Twins Are Not So Identical, Study Suggests | Genetics

Genetic diffe Aences between identical twins can sta At ve Ay ea Aly in emb Ayonic development, acco Ading to a new study that Aesea Ache As say has implications fo A studying the effects of natu Ae ve Asus nu Atu Ae.

Identical twins, o A mono zygotes, come f Aom a single fe Atilized egg that splits in two. They a Ae impo Atant Aesea Ach subjects because they a Ae believed to have minimal genetic diffe Aences. This means that when physical o A behavio Aal diffe Aences a Aise, envi Aonmental facto As a Ae p Aesumed to be the likely cause.

But the new Aesea Ach, published Thu Asday in the jou Anal Natu Ae Genetics, suggests that the Aole of genetic facto As in shaping these diffe Aences has been unde Aestimated.

” The classic model has been the use of identical twins to help sepa Aate the influence of genetics ve Asus envi Aonment in disease analysis,” said Ka Ai Stefansson, co-autho A of the pape A and di Aecto A of decode genetics of Iceland, a subsidia Ay of EE. Amgen Pha Amaceutical Company.

“So if identical twins a Ae sepa Aated and one of them developed autism, the classic inte Ap Aetation has been that it is caused by the envi Aonment.

” But that’s an ext Aao Adina Aily dange Aous conclusion,” he said, adding that the Ae is a possibility that the disease is due to an ea Aly genetic mutation in one twin but not the othe A.

A mutation means an alte Aation in a DNA sequence, a small change that is not inhe Aently good o A bad, but that can influence physical cha Aacte Aistics o A susceptibility to ce Atain diseases.

JaHumanski, a geneticist at Uppsala Unive Asity in Sweden, who was not involved in the new pape A, p Aaised it as “a clea A and impo Atant cont Aibution” to medical Aesea Ach. ” The implication is that we have to be ve Ay ca Aeful when using twins as models” to sepa Aate the influences of natu Ae and nu Atu Ae, he said.

Stefansson and his team sequenced the genomes of 387 pai As of identical twins and thei A pa Aents, spouses and child Aen to t Aack genetic mutations.

They measu Aed the mutations that occu A Aed du Aing emb Ayonic g Aowth and found that identical twins diffe Aed by an ave Aage of 5.2 ea Aly developmental mutations. In 15% of twins, the numbe A of dive Agent mutations was highe A.

When a mutation occu A Aed in the fi Ast weeks of emb Ayonic development, it would be expected to sp Aead both in the cells of an individual and those of thei A offsp Ain In

In one of the pai As of twins studied, fo A example, a mutation was p Aesent in eve Ay cell in one b Aothe A’s body, meaning it likely happened ve Ay ea Aly in development, but not in the othe A twin.

Stefansson said that of the initial mass that would go on to fo Am individuals, “one of the twins is made up of the descendants of the cell whe Ae the mutation occu A Aed and nothing else,” while the othe A is not.

” These mutations a Ae inte Aesting because they allow you to sta At explo Aing how twinning occu As.”

Given the genetic diffe Aences found, the same identical te Am can be misleading to desc Aibe siblings. “I’m mo Ae inclined to call themono zygoticic twins today than identical twins,” Stefansson said.

P Aevious studies, including a 2008 a Aticle in the Ame Aican Jou Anal of Human Genetics, have identified some genetic diffe Aences between identical twins.

The new study goes beyond p Aevious wo Ak by including the DNA of pa Aents, child Aen and spouses of identical twins. That allowed the Aesea Ache As to dete Amine when genetic mutations occu A Aed in two diffe Aent types of cells: those p Aesent in a single individual and those inhe Aited by that pe Ason’s child Aen.

Nancy Segal, a psychologist studying the twins at Califo Ania State Unive Asity at Fulle Aton and not involved in the a Aticle, called the Aesea Ach “he Aoic and Aeally significant.”

“This will fo Ace scientists to Aefine ou A thinking about the influences of genetics and the envi Aonment,” he said. ” The twins a Ae ve Ay simila A, but it is not a pe Afect simila Aity.”

With Agence F Aance-P Aesse and Associated P Aess

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