Abstract

BACKGROUND: Fluorescence in-situ hybridisation (FISH) is the most widely used method for detecting unbalanced chromosome rearrangements on preimplantation embryos. FISH is known to have several well-documented technical limitations which may lead to incorrect interpretation of the results and a potentially adverse outcome. The clinical application of a molecular-based assay, known as array comparative genomic hybridization (Array-CGH), used to simultaneously screen for unbalanced translocation derivatives as well as aneuploidy of all 24 chromosomes is described in this study. METHODS: This is a prospective longitudinal cohort study performed in order to evaluate the clinical efficiency of Array-CGH in a specific category of patients. Cell biopsy was carried out on cleavage stage embryos (day 3). Single cell were first lysed and DNA amplified by whole genome amplification (WGA). WGA products were then processed in 24 hours by Array-CGH using high density arrays 24sure+, BlueGnome. Balanced/normal euploid embryos were then selected for transfer on day 5 of the same cycle. The chromosomally abnormal embryos that developed to blastocyst stage were reanalyzed in order to confirm PGD results. RESULTS: Twenty-eight consecutive cycles of PGD were carried out for 23 couples carrying 18 different balanced translocations. Overall, 187/200 (93.5%) embryos were successfully diagnosed, 16% (30/187) were normal or balanced, 17.1% (32/187) were unbalanced for the translocation and normal for aneuploidy, 39.6% (74/187) had aneuploidy and were unbalanced, 27.3% (51/187) were normal or balanced but showed aneuploidy of chromosomes not involved in the translocation. The re-analysis at blastyocyst stage were concordant for all embryos followed-up. Despite high levels of mosaicism, all day 3 aneuploid embryos were again diagnosed as abnormal after re-analysis on trofectoderm cells, confirming at the end the previous results regardless of exact genetic conformation. Embryos suitable for transfer were identified in 17 cycles (73.9%), with transfer of 22 embryos (mean 1.3±0.5). Twelve couples achieved a clinical pregnancy (70.6% per ET), with a total of 14 embryos implanted (63.6% per transferred embryo). Three patients delivered 3 healthy babies, while the other pregnancies (2 twins and 7 singletons) are currently ongoing beyond 20 weeks of gestation. CONCLUSIONS: The data obtained demonstrates that array-CGH is able to detects chromosome imbalances on embryos. Unlike some alternative techniques, this approach does not need prior pre-clinical workup for validation of the PGD protocol, reducing the time required for initiation of treatment for translocation couples. It also provides the added benefit of simultaneous aneuploidy screening of all 24 chromosomes. Array-CGH has the potential to overcome several inherent limitations of FISH-based tests, providing improvements in terms of test performance, automation, sensitivity, and reliability.