Whole-genome analysis for managing the preimplantation genetic testing of a putative rare and complex interchromosomal reciprocal insertion: thorough investigations for a straightforward interpretation

Abstract Research Question To analyze whether whole-genome investigations should be considered systematically before a complex chromosomal abnormality PGT-SR management is performed using conventional cytogenetic techniques. Design A male carrying a putative rare interchromosomal reciprocal insertion (IRI) 46,XY,ins(14;?)(q11;?).ish der(14)ins(14;22)(q11.2;q11.2q11.2)(xcp14+,xcp22+,N25+,3’TRA/D+),der(22)ins(22;14)(q11.2;q11.2q11.2)(xcp22+,xcp14+,N25-,5’TRA/D+), and his partner were referred to our center for PGT analysis after three spontaneous miscarriages. Whole-genome sequencing was used to distinguish between the proposed IRI and an alternative explanation of reciprocal translocation. Fluorescence in situ hybridization (FISH) were used to detect all chromosome segments involved in this chromosomal rearrangement, to identify transferable normal/balanced embryos. Results Whole-genome sequencing (WGS) allowed the determination of the number of chromosomal breakpoints involved in chromosomal rearrangement between chromosomes 14 and 22. Finally, only two breakpoints were identified instead of four in IRI rearrangements, which suggests a reciprocal translocation rearrangement (rcp). A probe strategy was established to highlight all chromosomal imbalances, whether IRI or reciprocal translocation, and PGT cycles were achieved. Conclusion Conventional cytogenetic techniques are not capable of identifying all complex chromosomal rearrangements, especially those involving centromeric regions and short arms of acrocentric chromosomes. The advent of new sequencing technologies has allowed for a better appreciation of genome complexity. In this study, whole-genome analysis provided additional information to explain the occurrence of genomic events and confirmed that the initial diagnosis of IRI identified by conventional cytogenetic techniques was, in fact, a simple reciprocal translocation. A reliable PGT-SR strategy was proposed for this couple to achieve their parental project.