To know all the diseases in advance, to grow the intellectual abilities of the child - this is what people dream aboutparents
How is such a procedure carried out?
First, a human embryo created through in vitro fertilization (IVF) is extractedThen it is checked for genetic disorders.
There are companies all over the world thatoffer future parents to conduct a comprehensive genetic testing of embryos before IVF. For example, in Russia these are Atlas, Genotek and Genetico. This trend worries geneticists and bioethicists alike. The companies claim they can predict whether a child will be prone to most common diseases. Including those that are influenced by dozens or even hundreds of genes. Further, people who undergo IVF are given the opportunity to choose an embryo with a likely low risk of developing diseases.
Why are geneticists and bioethicists against such a procedure?
Because embryo selection based on these predictions is a procedure that has not been scientifically proven.Moreover, the social implications of using sophisticated genetic tests for embryo selection have not yet been fully explored.Others acknowledge that as more data accumulates, it is possible to draw valid conclusions, but all agree that this procedure should be carefully regulated.
A study was published in Nature Medicine at the end of March 2022 that explains some methods for determining polygenic risk scores.This caught the attention of scientists, but did not allay their fears.
The polygenic risk score is a genetic risk score, or genome-wide score. It reflects how much a person is genetically predisposed to a particular trait.
How are such procedures regulated today?
Some health authorities around the worldregulate the use of simple genetic testing along with IVF. But this is not a common practice. The purpose of these tests is to reduce the chance that a parent will pass on a hereditary disease to their unborn child. In Russia, there are no specific regulatory acts for genetic tests, which are very different in many procedures from simple biochemical ones. As a result, some genetic tests are banned, while others have virtually prohibitive barriers to the creation of laboratories.
Testing is usually needed if the patient hasrare mutations in a single gene that lead to devastating health consequences. For example, in the UK, the Office of Human Fertilization and Embryology has approved testing for more than 600 hereditary diseases. In particular, they are aimed at searching for Tay-Sachs disease and breast cancer caused by mutations in the BRCA1 and BRCA2 genes.
But the most common diseases such aslike type 2 diabetes, are associated with mutations not in one gene, but in many - potentially even thousands. To understand how to genetically predict such diseases, scientists analyze DNA sequences from thousands of sick people and compare them with DNA from people who are healthy. This information is then converted into an overall risk score that can be used to understand what the risk of developing this disorder is.
The goal is to continue togenetic studies on a wider and deeper sample. This will make polygenic risk indicators more accurate and eventually be used to guide treatment and prevention strategies. But there is a consensus that the preliminary results cannot yet be used outside of scientific research.
What have we learned about polygenic risk from the latest scientific work?
In the latest study, the authors, most of whom work for IVF or genetic testing companies, tried to figure out how to technically predict the exact sequence of the genome based on a small amount of DNA.For example, from one or two embryonic cells.
The authors constructed genetic sequences for more than 100 embryos: they analyzed hundreds of thousands of sites in the embryonic genomes.To do this, they used a technique called genotyping, which requires less DNA than whole-genome sequencing.
They then combined this data with the sequence of the parents' entire genome to fill in the rest of the gaps in the DNA.Next, they compared the reconstructed genome of the embryo with the actual genome sequence taken from the newborn child.
They have identified the correct genome sequence at sites that are responsible for diabetes, certain types of heart disease, several forms of cancer and autoimmune disorders. The accuracy was 97–99%.
If such methods might work, then why do geneticists bother?
One is that the estimates for embryo testing are based on genome-wide studies: they used large DNA samples from people of European ancestry only.Now they are trying to diversify this data, but still this information is based on an insufficiently diverse subset of people.Even among white Europeans, polygenic risk scores are not always relevant.Perhaps because the interactions between genes are stillare not fully understood.
In addition, scientists do not yet fully understand howselecting embryos with a lower risk of developing one disease can affect susceptibility to other diseases. Genetic variation can have a number of consequences, a phenomenon known as pleiotropy. It means that a DNA sequence associated with a beneficial characteristic can also increase the risk of a harmful one.
Many of these polygenic scores predict the risk of developing disorders that occurBut they don't take into account potential changes in the environment that couldoccur during this time, as well as the latest treatments that are emerging.
In addition, such procedures can lead to the unnecessary destruction of viable embryos: the woman will have to undergo additional cycles of ovarian stimulation in order to collect more eggs.
While the scientific community is exploring potentialproblems and possibilities of such a procedure. Due to their complexity, polygenic risk assessments can also help to learn not only about potential health risks, but also about height or intelligence. But now there is not enough information to develop a relevant test that will help future parents select embryos.
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