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Review
. 2014 Mar;37(1 Suppl):271-84.
doi: 10.1590/s1415-47572014000200013.

Reprogenetics: Preimplantational genetics diagnosis

Roberto Coco  1
Affiliations
Review

Reprogenetics: Preimplantational genetics diagnosis

Roberto Coco. Genet Mol Biol. 2014 Mar.

Abstract

Preimplantational Genetics Diagnosis (PGD) is requested by geneticists and reproductive specialists. Usually geneticists ask for PGD because one or both members of the couple have an increased genetic risk for having an affected offspring. On the other hand, reproductive specialists ask for embryo aneuploidy screening (PGS) to assures an euploid embryo transfer, with the purpose to achieve an ongoing pregnancy, although the couple have normal karyotypes. As embryonic aneuploidies are responsible for pre and post implantation abortions, it is logical to considerer that the screening of the embryonic aneuploidies prior to embryo transfer could improve the efficiency of the in vitro fertilization procedures. Nevertheless, it is still premature to affirm this until well-designed clinical trials were done, especially in women of advanced age where the rate of embryos with aneuploidies is much greater. Although the indications of PGD are similar to conventional prenatal diagnosis (PND), PGD has less ethical objections than the PND. As with the PGD/PGS results only unaffected embryos are transferred, both methods can avoid the decision to interrupt the pregnancy due to a genetic problem; this makes an important difference when compared to conventional prenatal diagnosis.

Keywords: PGD; PGS; PGSS; embryo biopsy; trophectoderm biopsy.

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Figures

Figure 1
Figure 1
Possibilities of segregation during the second division from a normal oocyte. One of the three possibilities is normal (A).
Figure 2
Figure 2
Possibilities of segregation during second division from an abnormal oocyte by non-disjunction. One of the six possibilities is normal (B).
Figure 3
Figure 3
Possibilities of segregation during second division from an abnormal oocyte by early separation of sister chromatids. Two of the six possibilities are normal (B and C).
Figure 4
Figure 4
Segregation with and without cross-over. (A) Normal segregation without cross-over at the level of the mutated gene. The oocyte will always have the opposite chromosome constitution to that of polar body I. (B) Normal segregation with a cross-over at the level of the mutated gene. In contrast, when exchange occurs, the egg may or may not have the mutation.
See this image and copyright information in PMC

References

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