The origin and significance of additional aneuploidy events in couples undergoing PGD for translocations by aCGH

Diagnostic application of array-CGH in PGD for reciprocal and Robertsonian translocations has revealed 55-65% embryos with additional aneuploidies with or without translocation related imbalances. The occurrence of extra abnormalities with translocations reduces the number of embryos suitable for transfer. This study followed up 83 embryos on day 5-7 of development from 23 infertile or sub-fertile carriers for whole chromosome and segmental aneuploidies present in addition to the balanced or unbalanced translocations detected on aCGH diagnosis. Embryos were analysed by FISH (63) and aCGH (20). Meiotic aneuploidy affected 35% of embryos and 47% had mitotic events; 15% had both types. In total, meiotic and mitotic events were almost equal (60 versus 64), 97 affected whole chromosomes (58 meiotic, 39 mitotic) and 27 were segmental (2 meiotic, 25 mitotic). In 85.5% of embryos with whole chromosome additional aneuploidies, either the aneuploidy was present throughout or in more than 50% of cells. All embryos diagnosed as abnormal (translocation balanced or unbalanced) after aCGH diagnosis at cleavage stage would have remained unsuitable for transfer if tested at later stages of development. Additional aneuploidies, whether segmental or affecting whole chromosomes, are important findings and merit full consideration when considering the choice of embryos to transfer.