The inner cell mass confirms deletion syndromes detected in trophectoderm biopsies

Abstract

Deletion syndromes are defined as clinically recognizable genetic disorders characterized by a small chromosomal deletion, with a frequency of 0.5% in prenatal testing and 1 in 700 newborns. The cumulative effect of the imbalance on multiple independent disease genes within the deletion region determines the overall phenotype including, among others, developmental delay, intellectual disability and dysmorphic features. Many deletion syndromes have a corresponding duplication syndrome that is generally more rare and associated with a milder phenotype. Deletions and duplications are typically random events that occur during gametogenesis. The aim of this study was to evaluate the clinical reliability of diagnosing chromosomal deletions in blastocyst trophectoderm (TE) biopsies. Prospective blinded single-center study. A total of 26 blastocysts identified with small chromosome deletions, using the VeriSeq™ NGS platform (Illumina), were donated with patient consent (mean maternal age = 36.3 ±4.0years; mean paternal age = 38.6 ±6.1years). Each blastocyst was re-biopsied into three separate segments that were individually, blindly re-analyzed using the same VeriSeq™ NGS platform performed at the same genetic laboratory (n=96 samples). After un-blinding, all four segments were compiled together for a complete picture of every individual human blastocyst, including representatives of the inner cell mass (ICM) and TE. The overall incidence of partial aneuploidy following TE biopsy of 10,783 human blastocysts was observed at 1% (n=110). The blinded re-analysis of 26 blastocysts with small chromosome deletions, validated the reliability of the original deletion diagnosis in 24 (92.3%) of the embryos. The small chromosome deletion was observed throughout the entire embryo, including all ICM and TE segments, for 14 blastocysts (53.9%). The remaining blastocysts displayed evidence of potential mitotic cell division errors with either a diploid cell line in 1 TE segment (n=6; 23%), or the reverse small chromosome duplication in the re-biopsy ICM and TE segments (n=4; 15.4%). Examples of the clinically recognizable genetic disorders diagnosed in these 26 human blastocysts include chromosome 1q41-q42 deletion syndrome, chromosome 1p36 deletion syndrome, Cri-du-chat syndrome (end of chromosome 5p deletion) and chromosome 8q21.3-q22.1 deletion syndrome. This novel study validated the reliability of diagnosing chromosomal deletion syndromes in blastocyst biopsies. Our re-analysis results confirmed the original partial aneuploidy diagnosis to be present throughout the corresponding blastocyst with no preferential allocation to trophectoderm cells. These observed embryonic chromosomal deletions have been clearly associated with clinically recognizable genetic disorders.