CLINICAL UTILITY OF HUMAN REVIEW: EXPERIENCE WITH PREVIOUSLY UNKNOWN REARRANGEMENT CARRIERS USING FAST-SEQS, A NEXT-GENERATION SEQUENCING PGT ASSAY

Abstract

To report clinical preimplantation genetic testing (PGT) experience identifying previously unknown balanced rearrangement carriers using the FAST-SeqS NGS-based PGT assay. Trophectoderm biopsies were analyzed using our modified FAST-SeqS NGS-based PGT method and bioinformatics pipeline, which detects whole chromosome and segmental aneuploidies (≥10Mb), most types of polyploidy, and many instances of single chromosome uniparental isodisomy. A retrospective analysis of all embryos from patients where we suspected a parental balanced rearrangement (PBR) based on PGT-A results was performed, as identified by a recommendation for follow-up testing, either by traditional karyotyping or fluorescent in situ hybridization (FISH), on their PGT-A report. We analyzed ∼244,700 embryos from ∼39,750 patients undergoing PGT testing. Of those patients, 170 (0.43%) specifically ordered PGT-SR testing due to a known PBR. In addition, based on the PGT-A results, we suspected a previously unidentified PBR in 181 patients (0.46%). The vast majority (151/181) of patients received a recommendation on their first PGT-A cycle, with a range of 2-15 biopsies; however, 30 patients were not identified until subsequent cycles. This was due to a combination of low number of biopsies per cycle, common whole-chromosome aneuploidies, and identification of only one translocation segment. We received follow-up test results for 88 couples; all but ten (88.6%) were found to carry a PBR. Among identified PBRs, balanced reciprocal translocations were the most common (72/78); of note, due to size, three patients required FISH to demonstrate the PBR. The remaining PBRs were Robertsonian translocations and pericentric inversions (three each). The putative PBRs in the remaining ten patients may require higher resolution testing (FISH) or may be restricted to the gonads; alternatively, the pattern of abnormalities seen in the biopsies was due to random chance. Most PBR carriers are unaware of their rearrangement until karyotype analyses are performed, typically as part of an infertility workup or after an unbalanced rearrangement is detected in a pregnancy, products of conception, or child. Many IVF centers only recommend karyotype analysis after two or more miscarriages or in cases of an abnormal semen analysis. Therefore, there are patients undergoing IVF who unknowingly carry a PBR, some of whom may choose to pursue PGT-A to help increase their chances of a successful pregnancy. Astute analysis of their PGT-A results may lead to detection of the PBR. With the advances of PGT-A technology allowing for routine detection of segmental aneuploidy, more PBR carriers will be picked up through routine PGT-A testing, providing couples with an answer to their “unexplained” infertility.