Pre-implantation genetic diagnosis PGD or PIGD is the genetic profiling of embryos prior to implantation as a form of embryo profiling , [1] and sometimes even of oocytes prior to fertilization. PGD is considered in a similar fashion to prenatal diagnosis. When used to screen for a specific genetic disease , its main advantage is that it avoids selective abortion , as the method makes it highly likely that the baby will be free of the disease under consideration. PGD thus is an adjunct to assisted reproductive technology , and requires in vitro fertilization IVF to obtain oocytes or embryos for evaluation. Embryos are generally obtained through blastomere or blastocyst biopsy. The latter technique has proved to be less deleterious for the embryo, therefore it is advisable to perform the biopsy around day 5 or 6 of development.

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Manuel J. Correspondence: jalvaram uc. The purpose of preimplantation genetic diagnosis by embryonary biopsy is to identify genetic alterations prior to the implantation of embryos produced by in vitro fertilization. The most important aim is the selection of genetically healthy embryos due to their genetic indemnity, but it can also be used to select the sex or, eventually, other detectable traits accrding to the wishes of the parents.

This procedure has been the subject of scientific debates, in relation to the harm that it can cause to healthy embryos that are going to be implanted, and in relation to the interpretation of the genetic tests made. Ethical debates have also focused on the production of and respect for the life and the integrity of developing human beings. In this work, it is argued that most of the uses of PGD are morally reprehensible, because they are done with disregard to the dignity that should be granted to embryos as human persons.

PGD can be used to detect genetic diseases in embryos and if its use were extended, it could allow for determining if an embryo has certain features desired by the parents, even though these may be related to diseases that require treatment.

PGD may have limited use in detecting and treating pathologies, but has in fact been used as a source of information for eliminating defective embryos. On the other hand, children that do not have favorable characteristics will end up frozen and then dead 7. It is obvious that the development of these technical possibilities requires reflection on their implications. What is in question is what children represent for their parents.

Are they a product or a gift? And if they have a genetic flaw, do they lack dignity and deserve to be condemned to die? Do parents have the right to decide what characteristics their children will have? There are important reasons to maintain that children cannot be disposable objects like consumer products 8 - 10 1. These ethical questions are presented in a global context of significant differences in the treatment of embryos under distinct jurisdictions.

Far from being a guide in relation to shared moral intuitions, legislation has been a source of confusion. In effect, although biology has shown beyond any doubt that the development of a new human being begins with fertilization, legislation in several countries questions whether the life of an embryo prior to implantation is that of a human being and whether an embryo deserves respect under these conditions For example, in the European Economic Community it is considered that the human nature of the embryo is acquired after fourteen days of development, given that it is at this point that the embryonic nervous system becomes evident.

This also coincides with the process of gastrulation, when conjoined twins can be generated. Law It establishes the respect deserving human beings from conception and explicitly prohibits the manipulation of embryos. Debates continue in other countries about regulating PGD 12 , In what follows we will first explain what the PGD technique consists of and discuss the risks that it implies or could imply for the development of the embryo. Secondly, we will argue that the embryo should be treated morally as a person and thirdly we discuss the implication of this on ethical reflections about PGD.

The fertilization of an oocyte egg by a spermatozoid occurs naturally in the Fallopian tubes and results in the formation of a zygote that represents the first stage in the development of a new human being.

The egg nucleus pronucleus contains the 23 maternal chromosomes and the spermatozoid contains the 23 paternal chromosomes. Both sets of chromosomes have genetic changes in DNA structure and epigenetic changes in gene expression that are complementary and required to biologically generate human beings. The maternal mitochondria contribute her DNA to complete the genome of the zygote. By successive divisions and differentiation the zygote forms all the cell types present in human beings.

There is no doubt that the zygote has a new genetic structure. With this the first stage in the development of a new human organism begins. It is an ongoing and predictable development that ends with the complete development of the organism 14 , The zygote contains a new genome, the fundamental structure of which is maintained throughout its development and identifies the unicellular embryo as biologically human and specifies its individuality The zygote is a totipotential cell capable of generating the entire organism.

After the membrane of the spermatozoid fuses with the egg, a series of biological events begin that lead to the development of the embryo 16 , The genome begins to express itself within a few hours of fertilization The first division of the zygote occurs around 30 hours after fertilization, resulting in the first two cells, which are termed blastomeres, each of which has 46 chromosomes.

The two blastomeres then divide in two and the embryonic genome begins to be expressed more massively, that is, an epigenome is configured At three days post-fertilization the embryo is full of cells blastomeres and a morula is formed. By the fourth or fifth day the embryo grows and produces a cavity, generating a blastocyst.

Cellular territories appear in the blastocyst with specific functions. Stem cells appear that are responsible for producing the distinct cellular tissue of the body By day 7 post-fertilization the embryo reaches and lodges in the uterus, where hormone production begins, the detection of which in laboratory tests provides the clinical identification of pregnancy.

This supports the definition of pregnancy of the World Health Organization. It is important to note that the mother hosts the embryo in her body unknowingly seven days prior to implantation. There is currently no reliable test to confirm that fertilization has occurred. The implanted blastocyst subsequently continues developing and gastrulation begin by day 14 to 16 post-fertilization, which gives rise to the fetal organs. Thus the central nervous system begins to develop on day 14 and up to day 14 or 16 it is possible that the embryo divides and generates conjoined twins Preimplantation genetic diagnosis PGD 22 - 26 was first described by Handyside et al.

The technique involves extracting blastomeres by biopsy from embryos that are at the two-cell stage to the blastocyst stage to obtain DNA for genetic molecular analysis with microchips that simultaneously analyze the DNA in thousands of genes And now the same embryo can be re-biopsied The potential harm that biopsy can cause embryos in early stages of development has been assessed and it has been shown that biopsies of blastomeres at day 3 in the morula stage significantly reduces subsequent implantation and results in fewer live births The DNA from a single cell is sufficient to research thousands of genetic mutations responsible for many genetic disorders 31 , for example, alterations in just one gene, as in cystic fibrosis, in many genes, as in breast cancer, or in chromosomes, as in Down syndrome.

It is important to consider that finding genetic mutations in embryonic DNA does not necessarily mean that the disorder will emerge, given that genes do not have a predetermined role but rather a probabilistic one that requires interaction with many other genes and with the environment in which the embryo develops 8. In fact, there has been a debate recently about the significance of findings of genetic variants of clinical uncertainty The absence of any alteration in the genes examined by the technique does not ensure that the embryo will be healthy given that there may be alterations in other genes that were not tested.

In terms of the degree of risk involved in embryonic biopsy, it cannot be ensured that extracting cells does not have harmful consequences for the subsequent development of the embryo 33 , In this regard, samples have been taken from other parts of the embryo where biopsy would be potentially less harmful. Thus, biopsy of the trophectoderm structure that gives rise to embryonic appendages like the placenta in the blastocyst state appears to be a safer technique Biopsies of polar bodies have also been used to explore genetic alterations in embryos A technical problem that remains unresolved is the detection of numeric chromosome alterations aneuploidy in only one or two cells of an 8-cell embryo, while the rest are normal termed mosaicism and in particular the final result of a pregnancy 37 , PGD also presents limitations in relation to specific genetic diseases such as mitochondrial disorders When a genetic alteration is found in an embryo, it is not implanted and most often is eliminated.

In relation to the safety of the technique, effects on the growth and behavior of animals born after PGD have been shown Nevertheless, such effects on humans have not been observed in preliminary studies 22 , 41 - One variant of the PGD procedure is preimplantation genetic screening PGS , which emerged in with the introduction of the next-generation sequencing method, which was used to identify more than genes associated with recessive genetic disorders.

This technology is currently being used to detect changes in the number of chromosomes aneuploidy in embryos obtained from genetically normal parents by in vitro fertilization Ethical consideration of PGD not only requires careful attention to the specifics of the techniques that are used and their effect on the development of the embryo, but it is also critical clarity as to whether or not the embryo is a person.

There are important differences that turn on this question in evaluating the risks involved in PGD. A relevant fact for this question is that the human organism begins life with fertilization. There is no serious doubt that embryo is the same biological organism that later becomes a fetus, then a child and then an adult person.

The question posed by several philosophers, however, is whether or not we should identify a human person with a human organism. The central motivations to differentiate between a human being and a biological organism have arisen at least since John Locke 45 , II, cap. In the earlier philosophical tradition, well represented by Boecio, a person is an individual substance of rational nature rationalis naturae individua substantia ; ML 64, It continues over time and is the same at different moments.

Taking into consideration that this substance has a rational nature, it is argued that it has an intrinsic form of being that, if not impeded, tends to foster the rational activity of mature human.

A human being is typically capable of higher cognitive activity and of deliberate and conscious decision-making. This reflective capacity endows human beings with a special moral responsibility for their actions and makes them responsible for their moral character. However, in the philosophical tradition, the morally special character of persons is not related to the actual exercise of freedom and rationality.

One does not exercise these capacities when in a deep sleep, nor do small children or, of course, embryos. This does not prevent them from being persons as we are dealing with the same substance that because of its intrinsic nature has an internal dynamism destined to give rise to freedom and rationality provided this dynamism is not in some way impeded 2.

For Locke, the conditions of identity of a person arise from the continuity of psychological states, among which memory plays a crucial role 45 , II, cap. For the psychological view introduced by Locke, what makes a person P 1 at time t 1 the same as P 2 at t 2 is the fact that there is continuity between the psychological states of P 2 -at- t 2 and P 1 -at- t 1.

Psychological continuity has preeminence with respect to the continuity of the same biological organism. What supports such mental states is something secondary. The question then is whether only one with mental states of this type is a person. Only those are individuals that have a sense of continuing over time as a person. It can be appreciated then that there are motives of the philosophical tradition present in these ideas, but profoundly transformed.

For the philosophical tradition, a person is one that possesses a nature that tends to produce mental states of a rational character. The states should be localized in one human organism or another, if you will, but this localizing is ultimately accidental. During much of the last century the debate about personal identity was a continuation and refinement of the psychological Lockean conception 46 , Two philosophers that have taken up this point of view very notably are Michael Tooley and Peter Singer.

For them, only those who are conscious of themselves in different moments, have interests and are capable of planning for their lives in the long-term are persons 48 , For Singer, the fetus does not fall under this characterization of a person, while many animals do. However, very young children and persons with highly limited cognitive capacities also do not meet this characterization. The same reasons for excluding embryos from the condition of a person also serve to exclude many other human beings that are already born.

Many find this position excessive, although it seems more coherent if one has accepted the psychological conception of identity in any of its forms.


Revista Peruana de Ginecología y Obstetricia

ISSN: X. Descargar PDF. Rubio 1 , L. Rodrigo 1 , A. Mercader 1 , E. Mateu 1 , C.


Preimplantation genetic diagnosis

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Evaluación reproductiva: diagnóstico genético preimplantacional

Pathogenesis, developmental consequences, and clinical correlations of human embryo fragmentation. Fertil Steril. Multinucleation in cleavage stage embryos. Hum Reprod. Timing of the first zygotic cleavage as a marker of developmental potential of mammalian embryos.

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