There is a general assumption that the sequences of monozygotic twins are almost identical, but there are few studies on the subject. Now, a new study published in Nature Genetics, entitled Differences between germline genomes of monozygotic twins (January 7, 2021), appears to change this paradigm.

An article on the aforementioned paper published in Science News reports that “Researchers in Iceland deciphered the complete genetic makeup, or genome, of 381 pairs of identical twins. Of those, 38 pairs were genetic duplicates of each other, but most had some differences in DNA that probably arose very early in development, either just before one embryo split to form two or shortly after the split [emphasis added]. Some of the twins had many genetic differences, including 39 pairs who had more than 100 changes between the twins.”

ADN differences in identical tweens

The Icelandic authors of the study concluded that “Phenotypic discordance between monozygotic twins has generally been attributed to the environment. This assumes that the contribution of mutations that separate monozygotic twins are negligible; however, for some diseases such as autism and other developmental disorders, a substantial component is due to de novo mutations. Our analysis demonstrates that in 15% of monozygotic twins a substantial number of mutations are specific to one twin but not the other. This discordance suggests that in most heritability models the contribution of sequence variation to the pathogenesis of diseases with an appreciable mutational component is underestimated.”

ADN differences in identical tweens could change the results in many studies of certain hereditaries diseases

The biomedical relevance of this finding is that, until now, monozygotic twins — which develop come from a single fertilized egg — have been studied to determine whether different traits, conditions and diseases are a result of genetics or the environment. This new evidence entirely changes the paradigms in the study of hereditary diseases. The finding is also a valuable contribution to embryology, and particularly to the study of the very first step in the development of a new human being from fertilization. Further research is needed.






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