Detection and quantitation of chromosomal mosaicism in human blastocysts using copy number variation sequencing.

OBJECTIVE: Currently, our understanding of the nature and reproductive potential of blastocysts associated with trophectoderm (TE) lineage chromosomal mosaicism is limited. The objective of this study was to first validate copy number variation sequencing (CNV-Seq) for measuring the level of mosaicism and second, examine the nature and level of mosaicism in TE biopsies of patient's blastocysts.

METHOD: TE biopy samples were analysed by array comparative genomic hybridization (CGH) and CNV-Seq to discriminate between euploid, aneuploid and mosaic blastocysts.

RESULTS: Using artificial models of TE mosaicism for five different chromosomes, CNV-Seq accurately and reproducibly quantitated mosaicism at levels of 50% and 20%. In a comparative 24-chromosome study of 49 blastocysts by array CGH and CNV-Seq, 43 blastocysts (87.8%) had a concordant diagnosis and 6 blastocysts (12.2%) were discordant. The discordance was attributed to low to medium levels of chromosomal mosaicism (30-70%) not detected by array CGH. In an expanded study of 399 blastocysts using CNV-Seq as the sole diagnostic method, the proportion of diploid-aneuploid mosaics (34, 8.5%) was significantly higher than aneuploid mosaics (18, 4.5%) (p < 0.02).

CONCLUSION: Mosaicism is a significant chromosomal abnormality associated with the TE lineage of human blastocysts that can be reliably and accurately detected by CNV-Seq.