Highly abnormal cleavage divisions in preimplantation embryos from translocation carriers

We have developed preimplantation genetic diagnosis (PGD) for carriers of c hromosomal abnormalities using fluorescent in situ hybridisation (FISH). He re we present the detailed analysis of 64 biopsied, normally developing emb ryos obtained from four Robertsonian and three reciprocal translocation car riers in 11 treatment cycles of which four resulted in normal pregnancies ( three simplex, one duplex). In order to investigate the degree of mosaicism and segregation mode in the embryos, the primary analysis of the biopsied cells was extended with the analysis of all cells from the non-transferred embryos. The analysis also included a second hybridisation with two additio nal probes, not involved in the translocation (chromosomes 1 and 9), in ord er to investigate the overall degree of mosaicism. Seventeen out of 64 anal ysed embryos were balanced for the chromosomes involved in the translocatio n and 14 of these were transferred. Forty-seven out of 64 embryos (73%) wer e mosaic regarding the chromosomes involved in the translocation and altern ate segregation mode was the most common mode of segregation. Moreover, we have found a higher degree of mosaicism for the chromosomes involved in tra nslocations as compared to control chromosomes. This difference was more pr onounced for the embryos from reciprocal translocation carriers. The result s, mechanisms significance and implications of our findings are discussed. Copyright (C) 2000 John Wiley & Sons, Ltd.