Preimplantation embryo biopsy: detection of trisomy in a single cell biopsied from a four-cell mouse embryo

Diagnosis of inherited disease before implantation

The diagnosis of inherited disease in affected embryos before implantation is now possible using in vitro fertilization (IVF), embryo biopsy and DNA analysis. This enables pregnancies to be established with unaffected embryos following transfer to the uterus avoiding the possibility of terminating a pregnancy diagnosed as affected later in gestation. Pregnancies have been established with female embryos in women carrying X-linked recessive genetic defects affecting boys by identifying the sex of embryos either by DNA amplification of Y-specific sequences or by dual fluorescent in situ hybridization (FISH) with X- and Y-specific probes to interphase nuclei. The predominant ΔF508 deletion causing cystic fibrosis (CF) has also been detected by DNA amplification from single cells and the first pregnancy and birth of a child successfully screened for a single gene defect achieved. The prospects for applying preimplantation diagnosis to other chromosomal and single gene defects are reviewed.

The role of paternal chromosomes and sperm morphology on the outcome of intracytoplasmic sperm injection

The study investigated the possible relationship between the X/Y chromosomes bearing spermatozoa and the outcome of intracytoplasmic sperm injection (ICSI) therapy and morphological appearance/shape (Tygerberg criteria) of the sperm cell injected into the oocyte during ICSI therapy and fertilisation. Thirty-nine patients were recruited for the study from an assisted reproductive programme. Semen samples were prepared by using gradient centrifugation techniques. Prior to injection sperm images were captured using high-quality video graphic equipment. Sperm selection was based on the concept of 'best-looking' spermatozoa i.e. spermatozoa lacking gross and obvious malformations such as broken necks, cytoplasmic droplets, amorphous or elongated heads. Photomicrographs of each sperm cell were produced from video footage. The photographical material was used to determine the basic shape and the actual length-to-width ratio of the injected sperm heads. Embryo biopsies and fluorescent in situ hybridisation (FISH) was performed on 12 randomly selected couples from a set of 39. Embryos were evaluated on day 3 for development and embryo transfer. Embryo biopsies and FISH analyses were performed on those embryos that showed no developmental potential following injection. It was found that 70% of the embryos that showed no developmental potential were Y chromosome-bearing embryos. The sperm selection process for ICSI based on the approach of choosing the 'best-looking' spermatozoon in the ejaculate seems to provide cells that can be classified as normal based on the length-to-width ratio set by the World Health Organization for normal cells.

Human preimplantation diagnosis: needs, efficiency and efficacy of genetic and chromosomal analysis

One of the limitations of existing assisted reproduction practices is that couples at genetic risk to their offspring have to face the abortion of an affected fetus following prenatal diagnosis. This is not acceptable as a measure to avoid a congenital disease in many communities or ethnic groups, where there is a great need for a method to diagnose and avoid the affected embryo before implantation and establishment of the pregnancy. In fact, preimplantation diagnosis is needed also for those who accept prenatal diagnosis as an option to avoid the birth of an affected child, because in most of the cases the couples are at high (25-50%) risk of having a child with a recessive or dominant disease, leading to their unfortunate experience of undergoing two or more abortions of wanted pregnancies. Two methods for preimplantation genetic diagnosis (PGD) have been recently developed and implemented in the framework of IVF. PGD can be performed by micromanipulation and biopsy of the first polar body before fertilization, or by blastomere biopsy before implantation of the pre-embryo. Another potentially realistic approach is blastocyst biopsy, which is still under development and has not yet been tested in clinical practice. Available data suggest that preimplantation diagnosis is safe, as no detrimental effects have been observed in studies on the viability of biopsied pre-embryos. Genetic analysis of biopsied gametes and blastomeres is now possible by DNA analysis, while enzyme analysis and preimplantation diagnosis of chromosomal disorders are still at the research stage. The accuracy of DNA analysis in preimplantation diagnosis is clear from available data on the outcome of preimplantation diagnosis: eight children free of genetic disease have been born following preimplantation diagnosis of cystic fibrosis, haemophilia A and other X-linked conditions. However, two misdiagnoses have been also described, showing the need for further development and improvement in the accuracy, efficiency and efficacy of DNA analysis in single cells. A particularly important implication for assisted reproduction practices can be expected from the further development and improvement of methods for preimplantation cytogenetic analysis. Although the efficiency and efficacy of these methods are not yet acceptable for application in clinical practice, considerable progress has been made, providing clear evidence for their feasibility in the near future. In spite of the high cost of the preimplantation diagnostic technique at present, its development is highly justified for high risk families as it provides a wider range of options for avoiding the risk of having an affected child.(ABSTRACT TRUNCATED AT 400 WORDS)

Clinical experience with preimplantation diagnosis of sex by dual fluorescent in situ hybridization

PURPOSE

Our purpose was to assess the clinical application of dual fluorescent in situ hybridization (FISH) for the diagnosis of sex in the human preimplantation embryo.

RESULTS

Over a 2-year period, 18 couples at risk of transmitting X-linked recessive disorders underwent preimplantation diagnosis of embryo sex by dual FISH with X and Y chromosome-specific DNA probes. A total of 27 in vitro fertilization (IVF) treatment cycles led to nine pregnancies; 7 reached the stage of clinical recognition, of which 2 spontaneously aborted. There were five live births, three singleton and two twin: none in disagreement with the diagnosed sex. The diagnosis was corroborated in 51 of the 74 nontransferred embryos. The efficiency of the procedure improved throughout the four treatment cycles. This was reflected in the increased proportion of double embryo transfers (from 50% in series 1 and 2 to 100% in series 3 and 4), with a consequent improvement in pregnancy rate (from 28 to 71% per embryo transfer). The excess of male embryos (male:female, 60:40 overall) and the high proportion of biopsied embryos with abnormal numbers of X and Y chromosome signals (14.5%) effectively reduced the number of normal female embryos available for transfer.

CONCLUSION

Dual FISH is an efficient technique for determination of the sex of human preimplantation embryos and the additional ability to detect abnormal chromosome copy numbers, which is not possible via the polymerase chain reaction, (PCR), makes FISH the preferred technique.

Cell allocation in twin half mouse embryos bisected at the 8-cell stage: implications for preimplantation diagnosis

Previous work in the mouse and human has shown that removal of cells from 2- and 4-cell embryos disproportionately reduces the inner cell mass (ICM), from which the fetus is derived, suggesting that preimplantation biopsy at these stages would be inadvisable. Here we have examined allocation in twin half mouse embryos produced by bisection at the 8-cell stage. Half embryos and intact zona-free control embryos were differentially labeled at the time of cavitation using polynucleotide-specific fluorochromes, and the numbers of cells in the ICM and trophectoderm (TE) counted. Adding the numbers of cells in the twin halves together, the numbers of ICM cells are not significantly different from those in intact controls. In contrast, numbers of TE cells were significantly higher (P < 0.01), producing a small increase in the total cell number of half embryos. There is no concomitant decrease in ICM cell number. We propose that as the surface area of a half embryo is greater than half an intact control, TE cells in half embryos divide faster in order to reach an optimal packing density similar to that in intact control embryos. Furthermore, we suggest that preimplantation biopsy only be performed at the 8-cell stage or later.

Viability of preimplantation embryos

Only about 10% of embryos obtained after in vitro fertilization (IVF) are able to implant after transfer in utero. Detecting the viable embryos is therefore the prerequisite condition to increase the overall efficiency of the technique. Zygote and embryo morphology is partly related to their viability. Indeed, fertilized oocytes with a timely fertilization and pronuclear growth, leading to embryos with equally sized blastomeres reaching at least the 4-cell stage about 42 h after insemination, have the best chance of implanting. The metabolic approach, although requiring sensitive microassays, seems promising. Indeed, in a small series 100% of the pregnancies were predicted when the level of interleukin 1-alpha was > 60 pg/ml and the suppressive level (antiproliferative activity using tumour cell lines) was > 20% in the supernatant of transferred embryos. Lastly, invasive assessment of the chromosome status of embryos should allow us in future to discard severely abnormal embryos, thus increasing the success rate of IVF.

Dual fluorescent in situ hybridisation for simultaneous detection of X and Y chromosome-specific probes for the sexing of human preimplantation embryonic nuclei

Dual fluorescent in situ hybridisation has been used for the simultaneous detection of X and Y chromosome-specific probes in single cleavage nuclei from disaggregated 4- to 7-cell human embryos. Based on the presence of a Y signal or 2 X signals in the absence of a Y, 89% of poor quality metaphases and 72% of interphase nuclei could be classified as male or female. With further refinements, this technique will offer a credible alternative to the polymerase chain reaction for the diagnosis of sex in human preimplantation embryos in families segregating for X-linked genetic disease.