Dados do Trabalho

Title

Extensive chromosomal genetic analysis in a baby born after mosaic monosomy chromosome 5 embryo transfer

Objective

According to recent publications, mosaic embryo transfer is now considered a possible option for women undergoing in vitro fertilization (IVF) with Preimplantation genetic testing for aneuploidy (PGT-A), since older women produce few euploid embryos. However, there are few articles reporting babies born following the transfers. With this report, we aim to describe the first Brazilian case of a healthy pregnancy of a 42-year-old woman after the transfer of an embryo with mosaic monosomy 5. The baby was evaluated by all chromosomal methods available.

Methods

Retrospective case report. The patients informed consent to the anonymous use of their clinical data in scientific studies before the procedure. The couple underwent the IVF treatment at Art Fértil, an assisted reproduction clinic in Recife, capital of Pernambuco state, northeastern Brazil, in 2020. They had a miscarriage in 2019 and due to the maternal age, the physician advised them to perform a chromosomal analysis of the embryos generated during the treatment. In the first IVF treatment with PGT-A, the female age at egg retrieval was 42 years old and her male partner was 33 years old. She had 21 metaphase II (MII) oocytes, of which 15 fertilized normally and 5 embryos made it to the blastocyst stage. All of them had the quality to perform the trophectoderm biopsy procedure on day 05 of development (D5). The embryos’ 5-10 trophectoderm cells were biopsied and samples were sent to DASA Genômica to perform the PGT-A. The steps of PGT-A included obtaining DNA from embryonic cells through whole genome amplification (WGA); next-generation sequencing (NGS) on the Ion GeneStudio S5 Prime System equipment with the Ion ReproSeq PGS kit (Thermo Fisher, USA) with an average coverage of order 0.01X; analysis with Ion Reporter software (Thermo Fisher Scientific, USA) with ReproSeq PGS w1.1 workflow. Normalization was carried out with a bioinformatic baseline generated from multiple normal samples. Readings were aligned against the human reference genome version GRCh37/hg19. The analysis could identify duplicated or deleted genome regions with a size equal to or greater than 10 Megabases (Mb). The threshold for aneuploidy detection was set at > 71% and the mosaic interval was set from >30 to 70%. Samples with copy number values < 30% were designated as euploid.

Results

The PGT-A analysis revealed aneuploidies in 4/5 of the embryos tested. Since there were no euploid embryos for transfer, the clinician had to counsel the couple to transfer the mosaic embryo grading 5AA. At the Art Fértil clinic. Routine obstetric ultrasound exams were performed by local practitioners. Invasive procedures to collect fetal material to confirm/discard chromosomal abnormalities were not performed, however, after the healthy male baby was born. Only after his birth, the couple opted to perform genetic tests. The results of G-banding Karyotype, SNP array 850K, and FISH reported that there was no abnormality of the specified chromosome. However, pediatric follow-up and developmental milestones are necessary.

Conclusion

Considering the mechanisms of mosaicism, one should remember the possible discrepancies between the chromosomal status of the embryo and prenatal or postnatal chromosomal evaluations. Also, the publication of successful cases helps physicians to guide couples toward making a safe decision when considering the transfer of low-grade mosaic embryos, especially when no euploid blastocyst is available for transfer.

Keywords

mosaic embryo transfer; PGT-A; PGS; genetic counselling; laboratory

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