49. Molecular PGT-M for VUS in the genomic era: to do or not to do?

Abstract

Introduction The new chromosomal microarray CMA technology, allows the identification of genetic defects in many disorders that would previously have escaped detection. Alongside the benefits, it exposes us to copy number variants (CNV) whose pathogenic is unclear Variants of unknown significance (VUS). In our cohort we reviewed all files of couples that applied for PGT-M at our clinic with a finding of VUS. We aimed to characterize these VUS and the cases in which PGT-M was decided upon. Materials and methods A retrospective cohort study in the Zohar Unit for PGT-M, Shaare Zedek medical center, 2014-2019. Files of all couples with a finding of VUS among those who applied for PGT-M with any CMA findings were reviewed. VUS were classified (likely pathogenic, VUS, likely benign) according to the American collage of medical genetics and Genomics classification at time of first consultation and to date (December 2018). Pathogenic variants were not included in the study. PGT-M was performed on blastromeres of throphoectoderm biopsy by PCR using surrounding polymorphic markers. For all microduplications, FISH was performed prior to the PGT-M in order to confirm the tandem location. Results Of 45 couples requesting PGT-M for CMA findings, 24 (53%) presented with VUS. VUS was an isolated finding in 54% of cases and as an additional finding to a known pathogenic mutation in 46%. The mean age of women was 29.8. Half the couples had children at the time of PGT-M consultation. 11 couples (46%) had a termination of pregnancy (TOP) due to VUS; three solely for the VUS and eight for VUS accompanying a sonographic finding in a prenatal screening. Indications for detecting the VUS were as follows- 33% amniocentesis for maternal request not otherwise indicated, 50% amniocentesis for a prenatal ultrasound finding, 25% had a CMA testing due to an affected child and another 12.5% for a CMA finding on a previously aborted fetus. Out of 30 VUS detected, 33% were defined VUS, 26% likely benign VUS and 40% likely pathogenic VUS. 19 VUS (63%) were microduplications (size ranging 31-2800Kbp) and 11 (37%) were microdeletions (size ranging 57-1200Kbp). Reviewing VUS classifications up to date- 33% remained unchanged, 20% were more severely defined and 46% were less severely defined. Based on genetic counseling, PGT-M was assigned for 17/30 CNVs (56%), 13(76.4%) of which were isolated VUS. 11/13 cases of isolated VUS were performed to date with a mean number of: 1.5 IVF cycles per couple (1-3), 8.3 embryos biopsied (1-15) and a mean of 2.9 wild type embryos per couple (0-6). Of 6 couples who had an embryo transfer at our institution there were 4 clinical pregnancies. Conclusions The genomic era allows the detection of varies VUS whose definition is submitted to changes as more information is gathered. Couples are already performing TOP and requesting PGT-M for VUS including likely benign VUS. It is thus of great importance to carefully use guidelines for the interpretation of these findings while counseling couples and determining the justification to practice PGT-M for their VUS finding.