02 Jun IVF: Preimplantation Genetic Screening Improved with Next Generation Sequencing
MedicalResearch: What are the main findings of the study?
Dr. Fiorentino: This study describes findings from first and second of a three-phase strategy to validate the use of next-generation sequencing (NGS) for comprehensive aneuploidy screening, as a preclinical step toward its routine use in the diagnosis of chromosomal aneuploidy on embryos. The first phase involved a large preclinical validation study on single cells, and demonstrated that the NGS-based 24-aneuploidy screening protocol was accurate and reliable. The results provided 100% consistency for aneuploid embryo call with array-CGH, the highly validated method of aneuploidy screening.
The second phase of the study, instead, focused on the clinical application of the NGS-based protocol for the detection of all chromosomes in embryos. A prospective trial involving analysis of human embryos at the blastocyst stage of development was designed for this purpose, in order to establish similar levels of chromosome-specific NGS copy number assignment concordance compared with 24sure array as those observed in the first phase of the study. Consistency of NGS-based aneuploidy detection was assessed matching the results obtained with array-CGH–based diagnoses,
Embryos obtained from 55 consecutive clinical PGS cycles, blindly assessed in parallel with both NGS and array-CGH techniques, displayed 100% concordance for aneuploid embryo call. Consistency obtained during this investigation was similar to those obtained in the first phase of the study that used NGS to examine single cell samples, demonstrating the reliability of the NGS-based method in detection of chromosome aneuploidy also in embryos at blastocyst stage derived from clinical preimplantation genetic screening (PGS) cycles. The clinical outcomes obtained in this study from preimplantation genetic screening cycles performed with the NGS approach were very encouraging, resulting in a clinical pregnancy rate per embryo transfer of 63.8% (mean age 38.5+2.1 years) and an ongoing implantation rate of 64.0%, values that are comparable with recent results from other comprehensive chromosome screening approaches.
In conclusion, the results achieved in this study demonstrate the reliability of the NGS-based protocol for detection of whole chromosome aneuploidies, mosaicism occurrences and segmental changes in embryos.
MedicalResearch: Were any of the findings unexpected?
Dr. Fiorentino: No, however, although clinical results have documented high pregnancy outcomes following transfer of screened embryos, further data and broad based clinical application are required to better define the role of NGS in PGS applications. The only effective way to demonstrate its clinical effectiveness is to perform a well designed and well executed prospective randomized controlled trial, showing actual improvements in clinical outcomes. Such a trial, that represents the third phase of our study and will complete the initial validation of comprehensive chromosome screening using NGS technology, is forthcoming and will be conducted involving participation of a limited number of leading PGS laboratories. The results of the study will be critical when considering the use of this new technology in a clinical setting and will help to outline the potential for routine clinical use of NGS-based preimplantation embryo assessment of aneuploidy.
MedicalResearch: What should clinicians and patients take away from your report?
Dr. Fiorentino: The NGS-based PGS approach has the potential to improve chromosomal diagnosis on embryos especially in terms of test performance, high-throughput, automation and sensitivity. NGS methods may ultimately lead to reduced costs per patient, allowing IVF couples a wider use of PGS for choosing the most competent embryo(s) for transfer. NGS-based PGS represents a valuable alternative to other currently available CCS techniques, ready to find a place in routine clinical use in IVF.
In addition, NGS technique has the advantage of screening not only for aneuploidies, but it may also allow for simultaneous evaluation of single-gene disorders, translocations and abnormalities of the mitochondrial genome, from the same biopsy without the need for multiple unique technological platforms. The additional sequence data obtained by using the NGS approach may also provide unprecedented amounts of genetic information from human embryos, useful for diagnostic and research purposes, with the potential to revolutionize preimplantation diagnosis.
MedicalResearch: What recommendations do you have for future research as a result of this study?
Dr. Fiorentino: We are hopeful that our findings will allow others to assess and reproduce our data and begin to assess the use of NGS for preimplantation genetic screening and perhaps other forms of preimplantation genetic testing methodologies.
Other our future plans, will include a trial aiming to assess accuracy and resolution limits of the NGS approach for detection of chromosomal mosaicism, which is a well described phenomenon in the preimplantation embryo, characterized by the presence a mixture of diploid and aneuploid cell lines. Chromosomal mosaicism is relatively common in human blastocysts. Now that trophectoderm biopsy is becoming the preferred stage for PGS, mosaicism may represent an issue in the analysis and interpretation of the results after comprehensive chromosome screening. Although its significance for implantation and the developmental potential of embryos is still unclear, it is reasonable to assume that this phenomenon is likely to influence IVF success rates.
The above trial, involving mixing experiments with different ratios of single cells, euploid and with known chromosomal aneuploidies, performed to mimic chromosomal mosaicims, is currently conducted by our lab. It will help to determine the minimum ratio of aneuploid to euploid cells that is needed to detect a chromosomal imbalance by NGS and thus to define the detection limits of mosaicism.
European Human Genetics Conference abstract:
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