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Preimplantation genetic diagnosis: concepts and applications

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Author(s): Fabiana Viana Ramos

Journal: Acta Obstetrica e Ginecologia Portuguesa
ISSN 1646-5830


ABSTRACT
Preimplantation genetic diagnosis (PGD) has been developed over the last ten years and used by couples known to be at a high risk of transmitting specific inherited monogenic disorders or unbalanced chromosomal rearrangements to their offspring. Currently, more than 200 different genetic conditions have constituted an indication for this procedure, including some conditions for which traditional prenatal diagnosis has not been used. PGD involves a complex procedure requiring ample experience in sampling of genetic material from oocytes or from embryos after intracytoplasmic sperm injection. Polymerase chain reaction or fluorescence in situ hybridization allow the identifation and transfer of embryos that are free from the familial disease. This constitutes an attractive alternative to traditional prenatal testing and termination of pregnancy for fertile couples, and has also become useful for infertile couples carrying chromosomal rearrangements. PGD has recently been extended to screening of aneuploidies at advanced maternal ages, implantation failure and repeated unexplained miscarriages, an area that is still controversial and as yet inconclusive. Misdiagnosis may occur, specially due to mosaicism in embryos at the stage of cleavage and allele drop out in polymerase chain reaction, conditions that can be diminuished by the use of two or more blastomeres and polymorphic markers. Recent advances in genetic technology, such as array-comparative genomic hybridization can allow an improved genetic screening of most chromosomal abnormalities, and may expand the indications for PGD.

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