Down syndrome: trisomy 21 chromosome turned off

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Breakthrough in research: geneticists inactivate chromosome in laboratory tests

Scientists from the USA have made immense progress in the treatment of the so-called “down syndrome” because they were able to switch off the chromosome that triggers the disease. But until the new findings could actually be implemented within the treatment, the researchers would still need a few years of research.

Disease is caused by genome mutation As the team of experts from the "University of Massachusetts Medical School" in Worcester reports in the Wednesday issue of the specialist journal "Nature", laboratory tests have succeeded in finding the additional chromosome, which "down Syndrome ”causes the patient to shut down because the entire 21st chromosome or parts of it are triple due to a genome mutation, which is why the disease is usually referred to as“ trisomy 21 ”. With this result, according to the research team, "the essential first step in the direction of the possible development of a 'chromosome therapy' has been overcome."

Scientists are guided by a concept from nature In their article, the researchers led by Jeanne Lawrence from the University of Massachusetts describe how it was possible to switch off the third copy of chromosome 21 in human cells - the central idea behind the project was, “The concept to test that it assumes that an additional chromosome can actually correct a genetic imbalance by manipulating a single gene, ”the scientists said in their article.

The female genome also contains a decommissioned chromosome. With this approach, the researchers followed a method that is already well known from nature, because since the female genome contains two copies of the so-called "X chromosome", one of them is also decommissioned. Therefore, there are two X chromosomes in the female cells, each with a very different level of activity: While one takes on all the important functions in cell metabolism, the other X chromosome is inactive - but does not prevent its "sister chromosome" from working.

Inactivation by a single gene Only one gene is responsible for inactivating the X chromosome - more precisely, the so-called "X inactivation gene" ("XIST"), which, according to the researchers, has now shown in the current study that this not only switch off the sex chromosome, but also an excess chromosome 21. The researchers are now hoping that the newly acquired “basic evidence shows exciting ways to re-examine Down syndrome,” as the cell and developmental biologist and lead author of the study, Jeanne Lawrence, writes. However, years of research are still required, because since the immobilization of the chromosome has so far only worked in the laboratory, use on humans is still a long way off.

Trisomy 21 occurs in very different forms. In addition, in view of the new findings, an application in the womb, in which the down syndrome would be “switched off”, so to speak, would not be up for discussion - because that would not only be risky, but would also be Ethical considerations represent a serious problem, because trisomy 21 occurs in very different forms: For example, some children show only minor intellectual losses and basically develop "normally", while in other cases the disease leads to serious organ damage (especially from the heart and intestines) There is also an increased risk of early form of dementia. Because of the serious damage that trisomy 21 causes in many cases, according to the US researchers, "the cell and development pathology of human Down syndrome must first be better understood in order to be able to develop successful treatments."

Cause of trisomy 21 in most cases an unusual division of the nucleus. The cause of the so-called "down syndrome" lies in the vast majority of cases in an unusual "meiosis" or division of the nucleus, in which either the homologous chromosomes in the first division of maturity or the chromatids in the 2nd maturity division of meiosis are not separated. It is not yet known what causes this non-separation - however, one thesis is that the influence of ionizing radiation supports this process. Since the likelihood of giving birth to a child suffering from trisomy 21 increases with increasing age of the mothers, it is also suggested that damage to the egg cells in general - whether due to radiation or the natural aging process - increases the risk of unusual meiosis increase. (No)

Image: Gabi Schoenemann /

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