O-273 A transcriptomic approach for embryo selection after preimplantation genetic diagnosis for aneuploidy
Authors: Ortega Jaén D , Mifsud A , Pardiñas M  L , Martín A , Gil J , Tejera A , De los Santos M  J 
Published: July 2024

Abstract

Study question
Is it possible to predict an euploid chromosomal constitution from RNA-Seq data and identify a transcriptomic profile compatible with extended embryonic development?

Summary answer
It has been possible to obtain a karyotype comparable to PGT-A, in addition to acquiring a transcriptomic signature of embryos 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. Preimplantation genetic testing (PGT) has improved pregnancy rates, but problems persist when high-quality euploid embryos do not reach term. In fact, around 50 to 60% implant, of which 10% miscarry. Comprehensive approaches, including RNA-Seq, offer potential to discover molecular markers of reproductive competence. Extended-embryo culture platforms up to day 14 can be utilized as a proxy to study embryo development at post-implantation stages

Study design, size, duration
Prospective pilot cohort study conducted from March 2023 to August 2023. A total of 30 vitrified human blastocysts with previous PGT-A diagnosis on day 5 (D5) or day 6 (D6) of development were analysed: n = 15 euploid and n = 15 aneuploid embryos. Finally, 21 embryo samples were included in the study (n = 10 euploid and n = 11 aneuploid), the rest (n = 9) were excluded due to poor quality after sequencing. All embryos were donated for research purposes

Participants/materials, setting, methods
Following warming and re-expansion, embryos underwent a second trophectoderm biopsy. The remaining embryo was cultured until day 11 to assess its development. After biopsy analysis by RNA-Seq, karyotypes were studied, as well as differential expression gene (DEG) of the comparison: unattached embryos (n = 12) vs embryos attached (n = 9) to the plate (padj&lt;0.05 and FC &gt; 1). In addition, we obtained a transcriptomic signature specific to embryos with a “theoretical” capacity for sustained implantation (raw p-value&lt;0.05 and shrunk LFC&gt;1.1)

Main results and the role of chance
Digital karyotype concordance was obtained with a sensitivity of 81%, a specificity of 83%, a Kappa index of 65.5% and an area under the ROC curve of 90%.
At the gene level, 76 DEGs (56 upregulated and 20 downregulated) were found in the comparison of embryos unattached to the plate in extended culture versus those that were attached. To address the functional implications of these differences, significantly deregulated pathways according to GO and KEGG categories were identified. The mural trophectoderm of the analysed blastocysts showed 63 significantly deregulated terms (30 GO-Biological Process, 13 GO-Cellular Component, 12 GO-Molecular Function and 8 KEGG pathways), displaying upregulation of autophagy, apoptosis, protein kinase and ubiquitin-like protein ligase activity, and downregulation of ribosome, spliceosome, kinetochore, segregation, and chromosome condensation processes.
The first described transcriptomic signature specific to embryos with theoretical enhanced implantation capacity consists of 501 genes, including: EMP2, AURKB, FOLR1, NOTCH3, LRP2, FZD5, MDH1, APOD, GPX8, COLEC12, HSPA1A, CMTM7, BEX3, which are related to implantation and embryonic development.
These findings indicate that it would be possible to identify euploid embryos with a greater capacity for implantation and development, excluding those embryos that, although they could be implanted and viable, present chromosomal alterations

Limitations, reasons for caution
This study included a small sample size and a remarkable variability between samples. Structural chromosomal abnormalities were not included. It is not possible to diagnose mosaic embryos. Trophectoderm biopsy does not assure the chromosomal status of the whole embryo. Maximum number of days for in vitro development was 11

Wider implications of the findings
Gene expression profiles of embryos with theoretical increased implantation capacity have been obtained. Clinical implementation of this technique, which assesses chromosomal content and transcriptomic profile, could be used to significantly increase clinical outcomes in assisted reproduction, allowing informed decisions to be made about future treatments and the prospects of success

Trial registration number
Not applicable