A high degree of mosaicism in preimplantation embryos from a carrier of a reciprocal translocation t(11;22)(q23;q11). E. Iwarsson¹, H. Malmgren¹, J. Inzunza², L. Ährlund-Richter², B. Rosenlund³, M. Fridström³, P. Sjöblom³, M. Nordenskjöld¹, E. Blennow¹. 1) Dept of Molecular Medicine, Karolinska Institutet, Stockholm, Sweden; 2) Department of Bioscience at Novum, Karolinska Institutet; 3) Department of Obstetrics and Gynaecology, Huddinge Hospital.

   Introduction: Carriers of reciprocal translocations are at risk of having unbalanced offspring. Therefore, preimplantation genetic diagnosis (PGD) was performed on a woman carrying a reciprocal translocation t(11;22)(q23;q11). It is known that normal developing human preimplantation embryos show a high degree of aneuploidy/mosaicism. This prompted us to analyze all cells from 26 biopsied embryos in three treatment cycles for presence of unbalance and mosaicism. Material and Methods: Using three color fluorescence in situ hybridization (FISH) with two probes from chromosome 22 (22q11.2 and 22q13) in combination with a centromere-specific probe from chromosome 11, we examined the majority of cells from each embryo. Results: Three PGD treatment cycles were performed and one balanced embryo was transferred in cycle two and three. However, no pregnancy was established. In total, 26 biopsied, normal developing embryos were analyzed and a successful FISH analysis was achieved in 189 of 230 nuclei (82%). Twenty-three out of 26 embryos (88%) were mosaic and only 3 out of 26 embryos (12%) were balanced. For the two balanced embryos that were transferred, only the two biopsied cells were analyzed and a possibility of mosaicism remains. In the third balanced embryo there was no mosaicism. There were different degrees of mosaicism in the embryos. Some showed only two cell types (regarding the chromosomal content) while others displayed a different chromosomal content in every cell (chaotic chromosomal content). No embryo with homogeneously unbalanced chromosomal content was found.Conclusion: Compared to our own results and others, the number of abnormal embryos was higher (88%) than earlier studies (up to 75%) on normal developing preimplantation embryos from IVF patients without known chromosomal abnormality. These findings ought to be considered in the clinical preimplantation genetic diagnosis situation.