Single Cell Cytogenetics

Aneuploidy contributes significantly to pregnancy losses and implantation failures. Preimplantation Genetic Diagnosis (PGD) of single cells for selection of diploid embryos has been shown to increase implantation and reduce spontaneous abortion rates. A major challenge in blastomere analysis is the fact that most cells are in interphase. We screened 12 chromosomes on interphase cells (X,Y,8,13,14,15,16,17,18,21,22) for PGD and allowed us to detect ~63% of the aneuploidies in spontaneous abortions. To complement FISH karyotyping of single cells, we developed comparative genome hybridization (CGH) on polar bodies and blastocysts. Results from 60 cases of polar body and 28 cases of blastocyst analysis showed 34% and 57% of normal cells, respectively. The most common aneuploidy seen via CGH involved chromosomes 22, 21, 15, 16, 20, 13, 9, X and Y. Preliminary clinical results showed that PGD combined with CGH leads to a significantly higher implantation rate than controls (61% vs. 28%, p<0.005). PGD is routinely followed by amniocentesis and CVS. We found that aneuploidy plays an important role at the fetal‐maternal interface, and results from interphase FISH studies need to be interpreted with caution; human cytotrophoblasts gain extra copies of chromosomes 2, 3, 5, 7, 13, 14, 15, 19, 21, 22, and X as they differentiate along the invasive pathway. Research support: HD45736 and UC Discovery.