First Clinical Application of DNA Microarrays for Translocations and Inversions

Natural selection between day 3 and day 5/6 PGD embryos in couples with reciprocal or Robertsonian translocations

PURPOSE

For translocation carriers, preimplantation genetic diagnosis (PGD) provides the opportunity to distinguish between normal/balanced and unbalanced embryos prior to implantation and, as such, increases the likelihood of a successful ongoing pregnancy. The data presented here compares autosomal reciprocal and Robertsonian translocation segregation patterns in day 3 versus day 5/6 IVF-PGD embryos to determine if there is a difference in the chromosome segregation patterns observed at these developmental time points.

METHODS

A retrospective analysis on PGD translocation carriers at Monash IVF was performed. Segregation patterns were compared between day 3 and day 5/6 embryos to ascertain whether selection against malsegregants exists.

RESULTS

For reciprocal translocations, 1649 day 3 embryos (139 translocations) from 144 couples and 128 day 5/6 embryos (59 translocations) from 60 couples were analysed. Day 3 segregation analysis showed that 22.3% of embryos were normal/balanced (consistent with 2:2 alternate segregation) and 77.7% were unbalanced (malsegregation). Day 5/6 segregation analysis showed that 53.1% of embryos were normal/balanced and 46.9% were unbalanced. For Robertsonian translocations, 847 day 3 embryos (8 translocations) from 54 couples and 193 day 5/6 embryos (6 translocations) from 31 couples were analysed. Day 3 segregation analysis showed that 38.7% of embryos were normal/balanced (consistent with 2:1 alternate segregation) and 61.3% were unbalanced. Day 5/6 segregation analysis showed that 74.1% of embryos were normal/balanced and 25.9% were unbalanced.

CONCLUSIONS

This data demonstrates an increase in the proportion of genetically normal/balanced embryos at day 5/6 of development. This suggests a strong natural selection process between day 3 and day 5/6 in favour of normal/balanced embryos. These findings support performing PGD testing on day 5/6 of embryo development.

Translocations, inversions and other chromosome rearrangements

Chromosomal rearrangements have long been known to significantly impact fertility and miscarriage risk. Advancements in molecular diagnostics are challenging contemporary clinicians and patients in accurately characterizing the reproductive risk of a given abnormality. Initial attempts at preimplantation genetic diagnosis were limited by the inability to simultaneously evaluate aneuploidy and missed up to 70% of aneuploidy in chromosomes unrelated to the rearrangement. Contemporary platforms are more accurate and less susceptible to technical errors. These techniques also offer the ability to improve outcomes through diagnosis of uniparental disomy and may soon be able to consistently distinguish between normal and balanced translocation karyotypes. Although an accurate projection of the anticipated number of unbalanced embryos is not possible at present, confirmation of normal/balanced status results in high pregnancy rates (PRs) and diagnostic accuracy.

Methods for comprehensive chromosome screening of oocytes and embryos: capabilities, limitations, and evidence of validity

Preimplantation aneuploidy screening of cleavage stage embryos using fluorescence in situ hybridization (FISH) may no longer be considered the standard of care in reproductive medicine. Over the last few years, there has been considerable development of novel technologies for comprehensive chromosome screening (CCS) of the human genome. Among the notable methodologies that have been incorporated are whole genome amplification, metaphase and array based comparative genomic hybridization, single nucleotide polymorphism microarrays, and quantitative real-time PCR. As these methods become more integral to treating patients with infertility, it is critical that clinicians and scientists obtain a better understanding of their capabilities and limitations. This article will focus on reviewing these technologies and the evidence of their validity.

Single-cell whole-genome amplification technique impacts the accuracy of SNP microarray-based genotyping and copy number analyses

Methods of comprehensive microarray-based aneuploidy screening in single cells are rapidly emerging. Whole-genome amplification (WGA) remains a critical component for these methods to be successful. A number of commercially available WGA kits have been independently utilized in previous single-cell microarray studies. However, direct comparison of their performance on single cells has not been conducted. The present study demonstrates that among previously published methods, a single-cell GenomePlex WGA protocol provides the best combination of speed and accuracy for single nucleotide polymorphism microarray-based copy number (CN) analysis when compared with a REPLI-g- or GenomiPhi-based protocol. Alternatively, for applications that do not have constraints on turnaround time and that are directed at accurate genotyping rather than CN assignments, a REPLI-g-based protocol may provide the best solution.