Inheritance of imbalances in recurrent chromosomal translocation t(11;22): clarification by PGT-SR and sperm-FISH analysis.

Research Question: To analyse why unbalanced viable offspring are derived mainly from the 3:1 segregation mode in t(11;22)(q23;q11.2) reciprocal translocation.

Design: Retrospective analysis of 24 pre-implantation genetic testing for chromosomal structural re-arrangements (PGT-SR) cycles was performed on seven male and five female carriers of t(11;22) translocation. Sperm analysis was performed on each male carrier. These patients were directed to the study centre after several years of miscarriages and/or abortions, primary infertility for male carriers or birth of an affected child.

Results: Twenty-four PGT-SR cycles were performed to exclude imbalances in both male and female carriers. The unbalanced embryos derived from the adjacent-1 segregation mode were the most represented in both male and female carriers (68.4% and 50%, respectively). These results were positively related with meiotic segregation analysis of reciprocal translocation in spermatozoa. A thorough analysis of the unbalanced embryo karyotypes determined that the expected viable +der22 karyotype resulting from 3:1 malsegregation was less represented at 5.3%.

Conclusions: These findings highlight the divergence that may exist between meiotic segregation and post-zygotic selection. Post-zygotic selection would be responsible for the elimination of unbalanced embryos derived from the adjacent-1 segregation mode. The combined action of several factors occurs at the beginning of post-zygotic selection. Genetic counselling must consider the risk of a birth related to the adjacent-1 segregation mode, irrespective of the sex of the translocation carrier. These results will allow deeper understanding of the PGT results of t(11;22) carriers, which often include a high number of aneuploid embryos.