Objective: The primary objective of this study was to characterize the incidence, origin, and distribution of genome-wide segmental aneuploidy (SA) in preimplantation embryos generated by a high resolution PGT-A pipeline. Design: Approximately 150K trophectoderm biopsy samples were analyzed for this study. PGT-A was performed, and samples were classified based on karyotype. In a subset of samples, full copy-number SA was stratified according to length, location, and origin. Materials and Methods: Biopsy samples were amplified using primary template-directed amplification (PTA), target-enriched and next-generation sequenced. SAs (>5 megabases) were detected and confirmed with a bioinformatics pipeline combining genome-wide copy-number (CN) coverage and allelic balance (AB) from highly polymorphic SNPs. Parental DNA from buccal swabs was used to identify the origin of aneuploidy. Results: SA was observed collectively in 12.9% of samples, with full-copy SA (FCSA) identified in 3.1% samples. FCSA most frequently included a q-arm deletion (36%), followed by q-arm duplication (22%), p-arm deletion (21%), and p-arm duplication (16%). A single intra-chromosomal SA, not involving the distal end of a chromosome, was observed in 5% of cases. A high-resolution map of SAs showed decreasing involvement moving inward from either terminus on most chromosomes. Paternal origin of the SA was observed in 68% of samples versus 31% maternal and 1% biparental inheritance. A single segmental gain or loss was observed in 81% of samples, 19% contained two or more SAs. Interestingly, 11% of samples had both a single deletion and duplication and in 44% of these cases, both events occurred within the same chromosome. The most frequently observed SAs overlapped strongly with known genomic fragile sites and many contained genes significant to embryonic development. Conclusions: The findings of this study provide a highly resolved map of SA across the preimplantation embryonic genome. PGT-A combining CN and AB to accurately detect SA, could be critical to parsing out the clinical significance of sub-chromosomal variation and provide data on underlying causes of embryo failure. Support: Funding provided by CooperSurgical.
Weier et al. (Sun,) studied this question.
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