Nuclear transfer for full karyotyping and preimplantation diagnosis for translocations

Preimplantation genetic diagnosis (PGD) for chromosomal disorders is currently performed by interphase fluorescence in-situ hybridization (FISH) analysis. This technique is known to have limitations for detecting some translocations and complete karyotyping, so visualization of chromosomes in single cells is required to improve the PGD accuracy for chromosomal disorders. To achieve this, single blastomeres were fused with enucleated or intact mouse zygotes, followed by fixing the resulting heterokaryons at the metaphase of the first cleavage division, or treating them with okadaic acid to induce premature chromosome condensation. This method allowed a significant improvement in the accuracy of testing both maternally- and paternally-derived translocations. In all, 437 blastomeres were tested, achieving full karyotyping in as many as 383 (88%), making it possible to pre-select only normal embryos or those with balanced chromosomal complements for transfer. Overall, PGD for translocations was applied in 94 clinical cycles, resulting in 66 transfers and 20 (30.3%) clinical pregnancies, with healthy deliveries of 15 children. Fifty-two of these cycles were performed using a nuclear transfer (conversion) technique, which resulted in 38 transfers of balanced or normal embryos, demonstrating that the technique is accurate and reliable for karyotyping single blastomeres for PGD of translocations.