Studies: Why children of older mothers are born more often with Down syndrome

Studies: Why children of older mothers are born more often with Down syndrome

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Why especially older mothers are more likely to give birth to children with Down syndrome
As the mother ages, the risk that her child will have a chromosome defect, such as Down syndrome (trisomy 21), increases. Researchers from Austria have come a bit closer to the question of why this is so.

The average age of mothers is increasing more and more
The average age of mothers continues to rise. This poses some health risks. For example, the risk of miscarriage, gestational diabetes and the transmission of genetic defects increases. The risk of a chromosomal abnormality in the baby, such as that that causes Down syndrome (trisomy 21), increases with the age of the mother. The fear of trisomy is great, even if experts repeatedly point out that children with Down syndrome are not sick but only slower. It is helpful to learn more about the chromosome defects and how they are passed on. Austrian scientists have gained new knowledge here.

Only one chromosome is too much
Down syndrome is the most common genetic intellectual disability. Only one chromosome is too much in the genome of those affected. The mechanisms of Down syndrome were deciphered years ago. Researchers at the Institute for Molecular Biotechnology (IMBA) at the Austrian Academy of Sciences have now found out more about the connections. As the APA news agency reports, the Viennese scientists have discovered that the division of egg cells in mammals depends on a protein complex that surrounds the chromosomes before birth and may be lost over the years. This could explain why children from older mothers are more likely to suffer from Down syndrome.

Very long-lasting protein complex
Although this cohesin complex is remarkably long-lived, it may be irreversibly lost from the chromosomes over the years. The inability of the egg cells to renew the circular band that holds the chromosomes together is said to contribute to the age-related appearance of faulty chromosome division. A trisomy has a single chromosome in addition to the usual set of chromosomes. The most important risk factor for trisomies in children, such as Down syndrome, which has three copies of chromosome 21, is the mother's age, according to the APA report. The loss of cohesin could be a cause here. A few years ago it had been observed that cohesin became unstable in aging eggs.

First evidence in previous investigation
"My team and I want to find out how the chromosomes in the egg are held together by the cohesin complex from birth to ovulation," explained lead author Kikuë Tachibana-Konwalski of the study published in the journal "Current Biology". The study is based on Tachibana-Konwalski's work as a postdoc at the University of Oxford (UK). There, the scientist examined whether cohesin is renewed in egg cells during a period of two to three weeks before ovulation (ovulation) and found no evidence of this. According to the information, this brought the first proof that the cohesin is remarkably long-lived in egg cells.

Age-related loss likely to be irreversible
As a rule, proteins in most cells of the body are renewed within a few hours. However, the IMBA research team found that cohesin is maintained in adult mice for at least four months and does not renew itself. As reported in the APA report, this means on humans that cohesin may hold the chromosomes in the female egg cells together for decades without renewal. According to the scientists, the age-related loss of cohesin from the chromosomes is likely to be irreversible. The next step is to find out the molecular causes of this loss. (ad)

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