Chromosome testing strategies, such as preimplantation genetic testing for aneuploidy (PGT-A), improve initial IVF outcomes by avoiding unwitting transfer of aneuploid embryos in morphology-based selection practices. Newer technologies have revealed that some embryos may appear to have intermediate whole chromosome (or parts of a chromosome termed segmental) copy number results suggesting trophectoderm mosaicism. An embryo with a trophectoderm mosaic-range result may be the only option for transfer for some patients. Recent data suggest that such mosaic embryos can be transferred without added risk of abnormal birth outcomes but may be associated with increased implantation failure and miscarriage rates, with higher values of mosaicism appearing to be less favourable for producing good outcomes. In this Position Statement, we provide guidance to laboratories, clinics, clinicians and counsellors to assist in discussions on the utility and transfer of mosaic embryos.
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A pilot study of transcriptomic preimplantation genetic testing (PGT-T): towards a new step in embryo selection?
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IVIRMA Global Research Alliance, IVI Foundation, Health Research Institute La Fe, Valencia, Spain.
Study Question: Is it possible to predict an euploid chromosomal constitution and identify a transcriptomic profile compatible with extended embryonic development from RNA sequencing (RNA-Seq) data?
Summary Answer: It has been possible to obtain a karyotype comparable to preimplantation genetic testing for aneuploidy (PGT-A), in addition to a transcriptomic signature of embryos which might be suggestive of improved implantation capacity.
What Is Known Already: Conventional assessment of embryo competence, based on morphology and morphokinetic, lacks knowledge of molecular aspects and faces controversy in predicting ploidy status. Understanding the embryonic transcriptome is crucial, as gene expression influences development and implantation.
Approximate Bayesian computation supports a high incidence of chromosomal mosaicism in blastocyst-stage human embryos.
bioRxiv
December 2024
Department of Biology, Johns Hopkins University, Baltimore, MD, USA 21218.
Chromosome mis-segregation is common in human meiosis and mitosis, and the resulting aneuploidies are the leading cause of pregnancy loss. Preimplantation genetic testing for aneuploidy (PGT-A) seeks to prioritize chromosomally normal embryos for transfer based on genetic analysis of a biopsy of approximately five trophectoderm cells from blastocyst-stage fertilized (IVF) embryos. While modern PGT-A platforms classify these biopsies as aneuploid, euploid, or mosaic (possessing a mixture of normal and aneuploid cells), the underlying incidences of aneuploid, euploid, and mosaic embryos and the rates of meiotic and mitotic error that produced them remain largely unknown.
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Brussels Health Campus/Faculty of Medicine and Pharmacy, Research Group Genetics Reproduction and Development, Vrije Universiteit Brussel, Brussels, Belgium.
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Departamento de Antropologia Social, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Brazil.
Since the 1990s, preimplantation tests within in vitro fertilization have promised to enhance the selection of embryos for uterine implantation. However, alongside ethical controversies, these diagnostic techniques often identify a high rate of mosaic embryos-those containing a mix of cells deemed normal and abnormal-creating one of the largest technical challenges related to the testing. These cases raise dilemmas for professionals in assisted reproduction and, more intensely, create challenges for individuals whose embryos are identified as mosaic.
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Int J Mol Sci
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Institute of Farm Animal Genetics, Friedrich-Loeffler-Institut, 31535 Neustadt, Germany.
Article Synopsis
- - In xenotransplantation research, genetically modified pigs are crucial, with traditional methods like somatic cell nuclear transfer being lengthy and complex, prompting the need for more efficient gene editing techniques.
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