64. CAN FISH PROBE STRATEGIES INFLUENCE MOSAIC EMBRYO RATES IN ROBERTSONIAN TRANSLOCATION PGD?

Abstract

Introduction Robertsonian translocation (RT) results from centric fusion of two acrocentric chromosomes. RT carriers are phenotypically normal, but they are known to be at increased risk of repeated miscarriages or of pregnancies resulting in the birth of a child with congenital anomalies, mental retardation. Preimplantation Genetic Diagnosis (PGD) is therefore a solution for RT carriers. A suitable probe strategy on cleavage stage allows us to differentiate balanced embryos, unbalanced embryos, mosaic and chaotic embryos. According to ESHRE recommendations, only balanced embryos are considered for transfer. However, transfer of some mosaic embryos has resulted in live births. We performed the first comparative analysis between a two or a three probes FISH strategies, in order to enhance the safety and security of embryos transferred and to establish the best reliable and low-cost strategy for RT PGD management. Material and methods Retrospective analysis of 253 preimplantation genetic diagnosis (PGD) cycles were performed on 91 men and 42 women carriers of different Robertsonian translocations t(13;14), t(14;21), t(14;15), t(15;21), t(13;15), t(13;21), t(14;22), t(15;22), t(21;22), t(13;13). The first strategy involved two relevant probes use. Each probe is located within the terminal long arm. The second strategy required a third probe addition on one of the two translocated chromosomes. The additional probe is located close to centromeric regions. Result(s) Regardless of probe strategies, 253 PGD cycles were performed in the aim to exclude imbalances in both carriers. On a total of 1,549 biopsied cells, 1,458 were successfully analyzed. Among these, 232 were transferred. Clinical pregnancy was achieved in 108 patients, and 85 healthy babies were delivered. No significant difference was observed in the balanced embryo rates (40.5% and 40.4% in a two probes and a three probe strategies respectively). Among these balanced embryos, diagnostic established on single or two mononucleate cells, wasn't affected by the probe strategies. However, a significant difference (p Conclusion(s) According to the present findings, concerning balanced embryo rates, the two probes strategy seems more suitable for Robertsonian translocation PGD analysis, firstly because it led to similar results as the three probes strategy. Secondly, this study also highlighted an increase mosaic embryo rate observed with the two probes strategy. Recent data indicated that mosaic embryos may represent a second category to transfer after balanced embryos. Obviously, balanced embryos must be transferred in priority. However in absence of balanced embryos, transfer of a mosaic embryo should be considered. In this case, genetic counseling about risks and potential benefits is of utmost importance to ensure informed decision-making by patients.