Validation of array comparative genome hybridization for diagnosis of translocations in preimplantation human embryos

Fluorescent in-situ hybridization (FISH) for preimplantation genetic diagnosis (PGD) of structural chromosome abnormalities has limitations, including carrier testing, inconclusive results and limited aneuploidy screening. Array comparative genome hybridization (CGH) was used in PGD cases for translocations. Unbalances could be identified if three fragments were detectable. Smallest detectable fragments were ∼6 Mbp and ∼5 Mbp for blastomeres and trophectoderm, respectively. Cases in which three or more fragments were detectable by array CGH underwent PGD by FISH and concordance was obtained in 53/54 (98.1%). The error rate for array CGH was 1.9% (1/54). Of 402 embryos analysed, 81 were normal or balanced, 92 unbalanced but euploid, 123 unbalanced and aneuploid and 106 balanced but aneuploid. FISH with additional probes to detect other aneuploidies would have missed 28 abnormal embryos in the reciprocal group and 10 in the Robertsonian group. PGD cases (926) were retrospectively reviewed for reciprocal translocations performed by FISH to identify which could have been analysed by array CGH. This study validates array CGH in PGD for translocations and shows that it can identify all embryos with unbalanced reciprocal and Robertsonian translocations. Array CGH is a better approach than FISH since it allows simultaneous screening of all chromosomes for aneuploidy.