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Aurora magazine

Can mosaic embryos be used for IVF?

Not all embryos contain 46 perfect chromosomes. Some have fewer and others have more, which causes a number of genetic abnormalities. About 80% of human embryos present these anomalies, which prevent their implantation and subsequent development. Other embryos, however, present the anomaly only in part of the cells and are called mosaic embryos.

What happens if IVF (in vitro fertilization) only produces embryos of this type? Scientists usually discard mosaic embryos during IVF. However, some couples can only produce these embryos, which causes the cycle to almost fail.

Researchers at the Oregon National Primate Research Center examined the development of mosaic embryos in primates. In particular, they tried to understand if they were able to develop into healthy children. The team identified a relationship between mosaicism, cell fragmentation and exclusion of blastomeres. Blastomers are large cells formed by the division of the fertilized oocyte.

Sometimes they break into smaller pieces, called cell fragments. When this happens, blastomeres collect cells with genetic abnormalities and separate them from the rest of the embryo. As a result, the embryo may respond well to the plant and develop normally.


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Patau syndrome: causes and symptoms

Patau syndrome or Trisomy 13 is a genetic disorder based on a chromosomal abnormality. Those who suffer have an extra copy of chromosome 13 in some cells or all of them. In some cases, the child has even three copies of the chromosome.

This causes abnormalities in the development of the fetus, which often result in a miscarriage. For children with Patau syndrome the chances of survival are very limited. It is estimated that only 10% of children born with this syndrome exceeds the year of life. Many of them even die in the first week of life. The remaining percentage survives longer, but living with serious health problems such as: heart defects; microcephaly; brain and spinal abnormalities; blindness and deafness; intellectual disabilities.

The manifestation of the disease is completely random, therefore untied from genetic predispositions of the parents. From a statistical point of view, however, the more parents are adults the more likely they are to manifest anomalies. After age 35, there are many more risks that gametes will get damaged and cause malformations or genetic diseases. Non-invasive prenatal screening texts can identify the most at-risk pregnancies.

Thereafter, prenatal diagnosis tests confirm or deny the first result, usually very reliable. If the test is successful, there is no resolution therapy against Patau syndrome. All the treatments that exist today are symptomatic, aimed at minimizing the pain and discomfort of the child.


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Can embryos be obtained with fewer chromosomal abnormalities?

Researchers at the University of Montreal have reduced the chromosomal abnormalities of a sample of mouse embryos. This is an unprecedented discovery that could improve current in vitro fertilization techniques. In fact, the anomalies, even when they do not translate into real diseases, reduce the chances of success of IVF. About 50% of the embryos generated by in vitro fertilization contain chromosomal abnormalities.

The most widespread are aneuploidies, or cells with an abnormal number of chromosomes. This anomaly is thought to be the leading cause of infertility, but the mechanisms are not yet known. The study in question managed to explain at least part of it. Part of the aneuploidy could occur during the so-called "assembly of the mitotic spindle". By manipulating this mechanism with drugs, it is possible to reduce the likelihood of anomalies by 50%. To this end, the researchers administered a drug called proTAME to embryos.

Those treated in this way have developed far fewer cells with an abnormal number of embryos. The discovery opens up a new range of possibilities for human beings, despite being in the early stages. Nevertheless, before working on human embryos, further study and analysis of all possible implications must be carried out. We do not know what the long-term consequences could be and if, over time, treatment could give rise to new problems.


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Sequencing all human chromosomes uncovers rare disorders

Extending non-invasive prenatal screening to all 24 chromosomes would help and expose new genetic disorders. It could also explain cases of spontaneous abortion and anomalies during pregnancy. The National Institutes of Health (NIH) researchers say.

Typical genetic testing focuses on chromosomes 21, 18 and 13 to detect Down's syndrome and the most common trisomies. They rarely analyze all 24 human chromosomes. Yet doing so would increase the accuracy of the tests and explain why some of the very few false positives.

Dr. Diana W. Bianchi's team analyzed all the chromosomes of 90,000 maternal plasma samples. Of these 72,972 came from the United States and 16,885 from Australia. For each of them, researchers have calculated a normalized index of chromosome quality. The index measured the probability that the sample contained the two standard copies of each chromosome. Under the age of 50, the researchers proceeded with further analysis.

The team identified 328 US samples and 71 Australian abnormal samples, of which 60 were rare trisomies. Thanks to the full analysis, researchers found cases of trisomy 7, 15, 16 and 22. Some of these were related to difficulties in gestation and spontaneous abortion. In some cases, researchers also reported abnormal cellular placenta levels related to malformations.


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