Mirjana Martic1, Sophie Falle1, Katerina Mitsiou1, Maria Kemeridis1, Sharyn Stock-Myer1
1 Virtus Diagnostics, Melbourne IVF, 344 Victoria Parade, East Melbourne 3002
The 24sure+ BAC array Comparative Genomic Hybridisation (CGH) system has been the first commonly available technology for many years used to detect unbalanced segregants in the embryos of reciprocal translocation carriers in Preimplantation Genetic Diagnosis (PGD) programs. Next generation sequencing (NGS) based testing has recently been introduced and widely accepted for aneuploidy testing. Here we present the application and limitation of a NGS based chromosome testing system, VeriSeq (Illumina, USA) on single cells and trophectoderm (TE) samples for reciprocal translocation carriers.
Aliquots of whole genome amplified DNA (Sureplex, Illumina, USA) from either single cells or TE samples of embryos diagnosed as unbalanced using arrayCGH, were subjected to NGS. Amplified samples were from carriers of 15 different reciprocal translocations with varied sizes of the unbalanced segments. The chromosome status of these samples was analysed and concordance determined.
Thirteen single blastomeres and 27 TE samples were amplified with 100% efficiency and results were obtained on 100% of amplified samples. NGS confirmed clinical diagnosis predicted by arrayCGH in all samples. Although individual segmental imbalances were detected in all samples, two unbalanced segments smaller than 6 Mb were not as apparent in the NGS profile as they were in the arrayCGH. Additionally, the NGS system was able to detect full aneuploidy and mosaicism of other chromosomes not involved in the translocation.
The NGS system is a reliable alternative to array CGH to detect large unbalanced chromosome segments as well as full aneuploidy and mosaicism of any other chromosome in single blastomeres and TE samples. In reciprocal translocation carriers in which unbalanced segments are smaller than 6 Mb, trophectoderm biopsy has to be requested and the confirmation of results by array CGH is strongly recommended.
Mirjana is a Preimplantation Genetics Laboratory manager at Virtus Diagnostics. She completed her Medical degree at the University of Zagreb, Croatia and her PhD at the University of Melbourne. Initially, she worked as an embryologist at Melbourne IVF and for the last 13 years she has been working in Preimplantation Genetics.