EMBRYONIC SELECTION: WHAT IT IS AND HOW THIS ASSISTED REPRODUCTION TECHNIQUE IS PERFORMED

In these times, there are many couples with problems to conceive. These can come from different reasons: gametes (reproductive cells, such as ovules and sperm), the medium where fertilization occurs, embryo implantation or even viability.

To ensure maximum safety in case of problems, reproduction specialists can resort to a fertilization technique in vitro consisting of fertilizing the eggs artificially and incubating them until they are ready to return to the uterus In this process, doctors choose the most suitable embryos according to their genetic characteristics. But is this legal? How are they selected? What do you do with the rest? Today we explain how it works.

What is the embryonic selection

Summarized in a single sentence, the embryonic selection consists of choose the best genetically gifted embryos to implant in the womb. The process works as follows: at the time when the couple has no possibility of conceiving by natural procedures, the specialist can offer the possibility of fertilization in vitro.

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This type of fertilization, as the name implies, occurs "in glass", specifically in a special plate where it is placed to the ovule. With a microscope a single sperm is injected into the egg. This procedure is called ICSI, or Intracithoplasmic Injection, and we have seen it hundreds of times in images that show a microneedle penetrating the ovum. In this case it is necessary to extract the ovule by means of a follicular puncture, which consists of extracting with another special needle, and by the guidance of an ultrasound, the oocytes of the follicle vaginally.

Sperm can come from ejaculation or be extracted by puncture, too. It is not always necessary to fertilize by ICSI, a procedure that could be dangerous for the egg, but it is the most normal in these cases. Therefore several are fertilized. After this time, the egg (plus the sperm) becomes an embryo that begins to divide, creating more cells.

Several ovules are fertilized to maximize the possibility of pregnancy success

The process is very studied in embryology and has very defined phases: morula, blastula, gastric ... That correspond to the number of cells that contains the growing embryo, which at this time is just a bunch of cells. A biopsy is performed from this cell mass, that is, a few are extracted (between one and six, more or less) to analyze them. This is done at the right time (between day two and six of the development), and not before, to avoid damage to the possible embryo.

These cells undergo a series of tests that look for certain genetic markers. The tests are known as preimplantation genetic diagnosis, or DGP. As we know, all cells contain the same DNA, so if one of these genetic signals appears, doctors will discard the embryo. These markers indicate the presence of congenital diseases, low viability and other special factors..

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Among all embryos, those that are unviable or do not exceed the expected quality will be discarded. From the rest, at least two will be selected and implanted. In Spain, due to technical capacity, two are normally implanted to ensure pregnancy. Only 20% of moms can be implanted with a single embryo with sufficient security.

How do you choose an embryo?

As we said, from the biopsy the genetic material of the embryo is obtained. This material is used to search for a series of signals known as genetic markers. This is usually done through DGP, although there are other techniques as well. For example, panchromosomal screening analyzes aneuploidies, that is, the excess or lack of genetic material in the embryo.

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Another example is the PGS, or preimplantational genetic screening, which is a systematic technique used when it is known that there is a problem in embryos. In general, All techniques use a series of specially designed molecules that will bind to the genetic material we are looking for. The first thing is to copy the genetic material, as if it were a photocopier, to have many copies to experiment with. This is done by a technique called PCR.

The copies are subjected to a battery of tests with these molecules we were talking about (this technique is known as fluorescent hybridization on-site, or FISH). If there is a presence of these genetic markers that indicate embryo disease or infeasibility, the sample will glow with a fluorescent green color when viewed under a microscope. Each DGP test looks for a different marker.

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The final result is an "embryonic profile" or genetic that shows whether it has tested positive or negative for each of the tests. These profiles are used to select or discard embryos at the discretion of the specialist. This procedure may vary due to its complexity but, gross mode, it works like that.

But is that legal?

Recently we explained the stir formed around Nana and Lulu, the two genetically modified twins. In his case, He Jiankui, the author of this research, took a specific gene, called CCR5, cut it and exchanged it for the same mutated gene. This he did with all the cells of the embryo thanks to a technique called CRISPR Cas9. Then he took these embryos and implanted them in the mother. This is illegal in China, where the experiment was conducted, and in hundreds of countries.

However, as we can see, it has nothing to do with the embryonic selection. In this assisted reproduction technique embryos are not genetically modified, but are selected according to your profile. This is legal in Spain and in many other countries. Of course, there are some legal issues that must be met.

In Spain, for example, according to the "Law of February 16, 2006 on assisted reproduction techniques", it is essential that the embryo can contain an early onset disease, that the disease is not curable at present and that the disease is life threatening to be able to discard an embryo. If these three aspects are not met, a bioethics committee will review the specific case. If this committee approves the selection, then it will be given. If not, embryos cannot be selected.

The idea is that the embryonic selection serves to prevent the suffering of families and children. However, that has not reduced ethical questioning. For example, this technique has been performed to help cure the illness of a family member (usually the brother) on more than one occasion.

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The debate in the bioethical committees, however, does not make it clear whether it is correct to allow the baby to be chosen with the excuse of saving a relative, although at the moment it is legal. Another important issue is what is done with the rest of the embryos. Are they thrown in the trash? Do not. Discarded embryos freeze in the laboratory involved in assisted reproduction.

If the mother gives consent, they may be used in research or for other donations. If not, it will be 10 years after which, if the laboratory has no response, they will be able to use them to use them in research or destroy them legally. Embryos are, after all, potential humans, even if they are still an undifferentiated cell mass. In short, although legal and relatively clear, the embryonic selection continues to raise some suspicion (although far removed from the debate that exists with genetic modification), a manifestation, surely, of how young this technique is still.