Detection of a balanced translocation carrier through trophectoderm biopsy analysis: a case report

Derivative and non-derivative aneuploidy rates in PGT tested blastocysts from carriers of structural rearrangements

RESEARCH QUESTION

What is the likelihood of having an euploid embryo when undergoing preimplantation genetic testing for structural rearrangements (PGT-SR)?

DESIGN

PGT-SR data from 364 couples (2822 trophectoderm biopsies) with a reciprocal translocation (RecT, n = 263), Robertsonian translocation (RobT, n = 79) or inversion (Inv, n = 22) were analysed retrospectively. Rates of euploid, derivative aneuploid or non-derivative aneuploid were evaluated for each cycle, stratified by the type of rearrangement and parent of origin.

RESULTS

Inv had the highest rate of euploid embryos (47.0-52.5%), followed by RobT (34.1-45.2%) and RecT (24.0-28.2%). The rates of euploid embryos were significantly lower for carriers of RobT and RecT compared with age-matched controls (57.6-59.0%). Maternal versus paternal rearrangements had significantly higher rates of derivative-abnormal findings for RobT (41.6% versus 20.2%) and RecT (60.2% versus 52.7%). Aneuploidies involving other chromosomes did not differ significantly in frequency between rearrangement carriers (38.1-41.9%) and age-matched controls (40.6-42.4%).

CONCLUSIONS

Data from this study demonstrated that Inv carriers have the highest rates of euploid embryos among all carriers of chromosomal rearrangements, that maternal rearrangements confer a higher risk of abnormal embryos, and that evidence for an interchromosomal effect on aneuploidy rates was not present in this cohort. This analysis of over 2700 PGT-SR biopsies enabled generation of likelihood-of-transfer tables stratified by type of translocation, parent of origin, and number of biopsies, which can be used to help counsel patients pursuing PGT-SR.

High-resolution PGT-A results in incidental identification of patients with small pathogenic copy number variants

PURPOSE

This study aimed to evaluate whether a high-throughput high-resolution PGT-A method can detect copy number variants (CNVs) that could have clinical implications for patients and their embryos.

METHODS

A prospective analysis of PGT-A cases was conducted using a high-resolution SNP microarray platform with over 820,000 probes. Cases where multiple embryos possessed the same segmental imbalance were identified, and preliminary PGT-A reports were issued recommending either parental microarray or conventional karyotyping to identify CNVs or translocations.

RESULTS

Analysis of 6080 sequential PGT-A cases led to identification of 41 cases in which incidental findings were observed (0.7%) and parental testing was recommended. All cases, in which parental studies were completed, confirmed the original PGT-A incidental findings. In 2 of the cases, parental studies indicated a pathogenic variant with clinical implications for the associated embryos. In one of these cases, the patient was identified as a carrier of a duplication in chromosome 15q11.2:q11.2 (SNRPN + +), which is associated with autism spectrum disorder. In the second case, the patient was heterozygous positive for an interstitial deletion of 3p26.1:p26.3, which is associated with 3p deletion syndrome and had clinical implications for the patient and associated embryos. In each case, parental studies were concordant with PGT-A findings and revealed the presence of an otherwise unknown CNV.

CONCLUSION

High-throughput high-resolution SNP array-based PGT-A has the ability to detect previously unknown and clinically significant parental deletions, duplications, and translocations. The use of cost-effective SNP array-based PGT-A methods may improve the effectiveness of PGT by identifying and preventing previously unknown pathogenic CNVs in children born to patients seeking in vitro fertilization.