Comparative cytogenetics of embryoblast, trophectoderm and blastocoele fluid of human blastocyst

Relevance. A comparison of the molecular karyotypes of the cell-free DNA from the blastocoele fluid of the blastocyst, the embryoblast and trophectoderm cells provides new possibilities for studying of the cytogenetic mechanisms of the formation of numerical chromosomal abnormalities at the preimplantation stage of human development. In addition, such analysis allows us to evaluate the diagnostic yield of cell-free DNA as an additional source of information about the embryo karyotype for preimplantation genetic diagnosis. Aim. Comparative molecular cytogenetic karyotyping of embryoblast, trophectoderm and the cell-free DNA from the blastocoele fluid of the blastocyst. Materials and methods. Twenty-nine human blastocysts of the 5th day of development were analyzed by metaphase and array comparative genomic hybridization. Results. Cell-free DNA was successfully amplified in 86.2% (25/29) of the samples. Blastocysts were euploid in 31%, 36% and 28% of cases according to the results of analysis of trophectoderm, embryoblast and сell-free DNA, respectively. Only 3 out of 29 (10.3%) blastocysts had a normal karyotype according to the analysis of all three samples. A total of 175 aneuploidies were detected. Trisomies, monosomies, partial tri- and monosomies were observed at a frequency of 47.4%, 46.9%, 5.1%, and 0.5%, respectively. The prevalence of trisomy was noticed in the embryoblast, which is not available for preimplantation genetic screening. Chromosomal mosaicism was detected in 14 examined blastocysts (48.2%). The reciprocal aneuploidies presented by combination of trisomy and monosomy with one pair of homologous chromosomes were described in 44.8% of blastocysts. A total of 25 reciprocal aneuploidies were observed with involvement of 50 from 175 (28.5%) detected aneuploidies. Conclusions. The cell-free DNA can be successfully amplified and analyzed by current molecular cytogenetic techniques. The results of comparative molecular karyotyping of cell-free DNA, embryoblast and trophectoderm cells indicate an underestimation of the frequency of aneuploid and mosaic blastocysts. It was found that in 72.4% of cases the molecular karyotypes of the embryoblast and trophectoderm are not identical. This finding provides evidence for impossibility of a direct extrapolation of the results of preimplantation genetic screening of trophectoderm cells to the inner cell mass. Accordingly, the cell-free DNA from the blastocoele fluid can be considered as an important additional source of information about the embryo karyotype in preimplantation genetic diagnosis.

внеклеточная ДНК, внутриполостная жидкость бластоцисты, эмбриобласт, трофэктодерма, хромосомный мозаицизм, реципрокные анеуплоидии, cell-free DNA, blastocoele fluid, embryoblast, trophectoderm, chromosomal mosaicism, reciprocal aneuploidy

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