Patients who are interested in assisted reproduction techniques wish to have maximum control over the whole process. However, this is not always possible, but through the new technologies available in genetic laboratories, the risks of possible transmission of diseases to first-born children can be significantly minimized.
Although the most obvious would seem to be to study embryos to try to avoid a known familial disease, i.e. to study monogenic diseases (PGT-M), this study is the least common. It is only resorted to when one of the family members already has a previous study with specific determination of the disease-causing mutation. In addition, in some cases it is necessary to request authorization from the National Commission on Assisted Human Reproduction, the body under the Ministry of Health.
Selection of the viable embryo
The most common need, however, is the verification of the correct number of chromosomes of the embryo (23 pairs of chromosomes) and that it is balanced, since otherwise implantation will be difficult, the typical first trimester miscarriages or syndromic situations such as Down, Pateau, Edwards… (PGT-A or PGT-SR) will occur. The risk of producing aneuploid or unbalanced embryos increases in patients with “not completely normal” (not necessarily pathological) karyotypes and, above all, as the patient’s age increases.
For this purpose, PGT-M as well as PGT-A and PGT-SR are preimplantational studies that make it possible to anticipate the detection of genetic alterations, both chromosomal and genetic, in the embryos, thus facilitating the selection of viable embryos for transfer to the uterus.
This type of test is performed with a biopsy of the embryos obtained after the in vitro fertilization treatment, in the blastocyst stage, and requires their vitrification until the results are received.
But the study of the embryos is not the only genetic test that can be performed in an assisted reproduction center. In this sense, one of the most commonly performed tests is not performed on the embryos, but is a preconception test that is carried out by means of a simple blood test: the Genetic Compatibility Test (GCT).
In search of genetic compatibility
Many patients wonder what would happen if the donor has a disease and keep quiet about it. First of all, geneticists do not talk about diseases, because diseases imply symptoms and preliminary tests avoid that situation. So, in any case, we will talk about mutation.
Furthermore, this risk that we could have with a donor also occurs in the patients themselves. For this reason, the Spanish Fertility Society strongly recommends the use of GCT, especially in cycles in which it is necessary to resort to donated gametes, and the responsibility for their allocation falls on the bio-health team.
Likewise, it is common knowledge that nobody is perfect: we are all carriers of some mutation, which does not mean that we are all sick. Our mutations are recessive and need to join with another mutation that is the same to become manifest, so they can be transmitted from generation to generation without giving clues.
Our part of the commitment is to analyze the donors so that, when patients decide to be studied, by means of a blood draw it is easy and quick to compare the mutations of each one, avoiding that they share any, and thus reducing the risk of them joining together and manifesting symptoms.
Realistic risk minimization
In any case, both preimplantation tests (PGT-M, A or SR) and preconception tests (GCT) have some limitations: none of them will be able to provide 100% reliability.
Zero risk does not exist, since we will always be exposed to the appearance of mutations and de novo rearrangements, to research on new diseases -which obviously do not form part of the pre-established panels-, etc.
Even so, thanks to the technologies provided by the genetic laboratories with which assisted reproduction centers collaborate, it is now possible to provide each patient with a strategy that minimizes their risks, while being aware that limitations should never lead us to a sense of false security.