To answer this question, we must first know what we mean by "disease" and what types there are.
Disease is defined by the WHO as an alteration or deviation from the physiological state in one or more parts of the body, due to generally known causes, manifested by characteristic symptoms and signs, and whose evolution is more or less foreseeable.
In reproductive medicine we have a diagnostic tool that allows us to identify alterations of genetic or chromosomal origin in embryos, PGT (Preimplantational Genetic Test) or PGD (Preimplantational Genetic Diagnosis). Depending on the type of alterations, there are three types of PGT:
- PGT-A: it provides information on the number of chromosomes of the embryos (chromosomal endowment) and, therefore, identifies embryos with a correct (euploid) and incorrect (aneuploid) endowment. By diagnosing aneuploidies we will largely avoid implantation failures, miscarriages or children with diseases related to alterations in the number of chromosomes.
- PGT-M: reports the existence in the embryos of mutations, already known in their progenitors (or family), which may give rise to genetic diseases. For this technique to be carried out, two requirements must be met. Firstly, we must be able to identify the mutation that generates the disease, as the technique will search for this signal in the embryo's genes. Secondly, the disease we want to prevent must meet certain requirements in order to be legally approved in our country. It must be a disease that occurs early in life, lacks effective treatment and leads to a serious or fatal disease.
- PGT-SR: it is performed in couples in which one of the members is a carrier of an alteration in the structure of one or more of their chromosomes, not in their number. In these cases, PGT looks for alterations in the structure of the chromosomes of the embryo that may cause the genes located in the affected areas of the chromosomes not to be expressed correctly and give rise to serious diseases in the children born from these embryos.
In summary, embryo biopsy allows us to know the chromosomal endowment or the presence of certain mutations (alterations in the genes), allowing us to diagnose chromosome-based diseases early, and some genetic-based diseases (those known and legally approved).
Therefore, in conclusion, PGT is a technique that allows us to exclude embryos that would otherwise be transferred and would result in the non-completion of the pregnancy, miscarriages or children with serious diseases. However, it cannot diagnose all diseases, so it is very important to carry out a correct perinatal control of the gestation and of the children born in order to diagnose other types of diseases at an early stage.
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