Genomic DNA in human blastocoele fluid

Blastocentesis: a source of DNA for preimplantation genetic testing. Results from a pilot study

OBJECTIVE

To investigate the presence of DNA in blastocyst fluids (BFs) and to estimate whether the chromosomal status predicted by its analysis corresponds with the ploidy condition in trophectoderm (TE) cells, the whole embryo, and that predicted by polar bodies (PBs) or blastomeres.

DESIGN

Prospective study.

SETTING

In vitro fertilization unit.

PATIENT(S)

Seventeen couples undergoing preimplantation genetic screening with the use of array comparative genomic hybridization on PBs (n = 12) or blastomeres (n = 5).

INTERVENTION(S)

BFs and TE cells were retrieved from 51 blastocysts for separate chromosomal analysis.

MAIN OUTCOME MEASURE(S)

Presence of DNA in BFs and assessment of the corresponding chromosome condition; correlation with the results in TE cells and those predicted by the analysis done at earlier stages.

RESULT(S)

DNA was detected in 39 BFs (76.5%). In 38 of 39 cases (97.4%) the ploidy condition of BFs was confirmed in TE cells, and the rate of concordance per single chromosome was 96.6% (904/936). In relation to the whole embryo, the ploidy condition corresponded in all cases with a per-chromosome concordance of 98.1%. The testing of PBs and blastomeres had 93.3% and 100% prediction of BF ploidy condition with a concordance per chromosome of 93.5% and 94%, respectively.

CONCLUSION(S)

Blastocentesis could represent an alternative source of material for chromosomal testing, because the BF is highly predictive of the embryo ploidy condition and chromosome content. Our data confirm the relevance of the oocyte and of the early-cleavage embryo in determining the ploidy condition of the resulting blastocyst.

[Update on preimplantation genetic diagnosis and screening]

Recent advancement in both human embryology and genomics has created a completely new situation for practical and widespread application of preimplantation genetic diagnosis and screening with a dramatic effect on assisted reproduction. The mapping of the first human genome and the advancement in sequencing technology and bioinformatics has led to the discovery of the exact genetic background of exponentially increasing number of diseases. In parallel, methods for culturing human embryos have also radically improved, enabling the late transfer, and the procedure of vitrification the safe cryopreservation. In consequence, refined genetic analyses have become available from blastocyst biopsy followed by the application of novel genomic methods. Furthermore, some studies suggest that by the selection of aneuploid embryos the pregnancy- and birth-rates can be increased. The amount and the depth of information obtainable from the embryos raise several technical and ethical questions that can be answered by further prospective randomized trials.

Non-invasive pre-implantation genetic diagnosis of X-linked disorders

Pre-implantation genetic diagnosis (PGD) is a powerful clinical tool to identify embryos with or at risk of specific genetic diseases before implantation in utero after in vitro fertilization (IVF). PGD is performed on embryo biopsies that are obtained by aspiration of one or two cells from pre-implantation embryos at day 3 or day 5/6 of culture. However this is a traumatic method that cannot be avoided because non-invasive procedures to assess the genetic status of pre-implantation embryos are not available yet. We hypothesize that cell-free nucleic acids, which are released by embryos in the culture medium during the IVF procedure, could be used for genetic screening. To test our hypothesis we will focus first on X-linked disorders because these single-gene diseases due to the presence of defective genes on the X chromosome are dominant in males. Therefore the objective here is to discriminate between female (XX) and male (XY) embryos by detecting Y chromosome-specific sequences in cell-free nucleic acids. Using culture medium from embryos we are able to discriminate between male and female embryos. This opens new avenues for the development of a non-invasive PGD method.

Detection of monogenic disorders and chromosome aberrations by preimplantation genetic diagnosis

This chapter highlights the methodologies of single cell genetic diagnosis along with the strengths and weaknesses of existing techniques.

New advances of preimplantation and prenatal genetic screening and noninvasive testing as a potential predictor of health status of babies

The current morphologically based selection of human embryos for transfer cannot detect chromosome aneuploidies. So far, only biopsy techniques have been able to screen for chromosomal aneuploidies in the in vitro fertilization (IVF) embryos. Preimplantation genetic diagnosis (PGD) or screening (PGS) involves the biopsy of oocyte polar bodies or embryonic cells and has become a routine clinical procedure in many IVF clinics worldwide, including recent development of comprehensive chromosome screening of all 23 pairs of chromosomes by microarrays for aneuploidy screening. The routine preimplantation and prenatal genetic diagnosis (PND) require testing in an aggressive manner. These procedures may be invasive to the growing embryo and fetus and potentially could compromise the clinical outcome. Therefore the aim of this review is to summarize not only the new knowledge on preimplantation and prenatal genetic diagnosis in humans, but also on the development of potential noninvasive embryo and fetal testing that might play an important role in the future.

Could time-lapse embryo imaging reduce the need for biopsy and PGS?

PURPOSE

To review relevant studies examining the relationship between embryo morpho-kinetics and aneuploidy.

METHODS

Search of Pubmed and Medline using relevant keywords pertaining to morphology, morphokinetics and embryonic aneuploidy, as well as examination of various reference lists and conference proceedings.

RESULTS

An abundance of publications, both preliminary and peer-reviewed, have emerged regarding the usefulness of time-lapse imaging in tracking embryo development and improving embryo selection. Recently, these publications have explored ability to not only predict blastocyst formation and implantation, but also the ability to detect embryonic chromosomal aneuploidy. Of the two peer-reviewed retrospective studies on morpho-kinetics and embryonic aneuploidy, one demonstrates that early cleavage timings can indicate chromosomal complement, while the other demonstrates that key events following the maternal-zygotic transition can be markers of aneuploidy. A recent paper also demonstrates improved outcomes following IVF using a selection algorithm to identify embryos at "low risk" of chromosomal abnormalities. However, the predictive nature of these events and timings is far from ideal. Additionally, results may be dependent upon the day of biopsy and method utilized for chromosomal assessment.

CONCLUSION

With continued effort, the combination of multiple morphologic endpoint assessments and developmental timings and refinement of modeling systems may improve the predictive ability to determine embryonic aneuploidy. This may help select a subset of embryos that are less likely to carry chromosomal abnormalities and improve assisted reproductive outcomes. However, embryo biopsy, followed by preimplantation genetic screening/comprehensive chromosomal screening still remains the most reliable method to assess chromosomal complement of preimplantation embryos.