Detection of aneuploidy and chromosomal mosaicism in human embryos during preimplantation sex determination by fluorescent in situ hybridisation, (FISH)

Preimplantation diagnosis of inherited disease by embryo biopsy: an update of the world figures

PURPOSE

Cleavage stage embryo biopsy and preimplantation diagnosis was first reported five years ago. The annual collation of the world figures for centres offering this procedure is important to continually assess the efficiency and success of the biopsy, diagnosis and pregnancies obtained.

MATERIALS AND METHODS

Data was collected from 14 centres worldwide. The largest series of diagnosis has been performed for those patients carrying X-linked disease where the embryos have been sexed either by PCR or FISH. PCR has also been used for the specific diagnosis of a number of single gene defects, mainly for cystic fibrosis but also for the diagnosis of Lesch Nyhan syndrome, Fragile X, Duchenne muscular dystrophy, Tay Sachs, haemophilia and RhD blood typing.

RESULTS

For PCR sexing, a total of 62 cycles have been performed with 14 pregnancies, 8 deliveries and 11 babies born. For FISH sexing, 70 cycles have resulted in 15 pregnancies, 8 deliveries and 11 babies born. For the specific diagnosis of single genes defects, a total of 65 cycles resulted in 21 pregnancies, 12 deliveries and 12 babies born. Overall, 197 cycles were performed, with 171 embryo transfers (86%), 50 pregnancies (25% per cycle, 29% per transfer), 28 deliveries and 34 babies born.

CONCLUSIONS

New methods are being developed to increase the scope of preimplantation diagnoses that can be offered. From next year, the biochemical and miscarriage rates will also be recorded.

Allele dropout in sequential PCR and FISH analysis of single cells (cell recycling)

PURPOSE

Our purpose was to investigate the feasability of using sequential PCR and FISH analysis of single cells for preimplantation diagnosis.

METHODS

Protocols for sequential PCR and FISH analysis of a single fibroblast (cell recycling) were optimized for six loci and the rates of allele specific dropout (ADO) were determined.

RESULTS

Conditions that allow reliable genotyping of single cells in lysis buffer were not optimal for amplifying fibroblasts fixed to coverslips. After optimizing conditions, we observed a success rate of 85% for both analyses in sequential PCR-FISH experiments in single cells for the four loci studied. The individual success rates for each technique revealed a slightly higher rate for FISH (91-95%) than for PCR (85-87%) for single cells on coverslips. The presence of two hybridization signals in FISH experiments demonstrated that the failure to amplify both alleles from heterozygous cells on coverslips was due to true ADO, and not the loss of chromosomal material. The ADO rate observed on coverslips varied between 10 and 14%, which is significantly higher than that observed in solution, even after meticulous optimization.

CONCLUSIONS

Sequential PCR and FISH analysis of single cells remains an attractive possibility. However, until the problem of the increased rate of ADO is resolved, cell recycling should be applied to clinical preimplantation genetic analysis.

Detection of aneuploidy in human oocytes and corresponding first polar bodies by fluorescent in situ hybridization

PURPOSE

The purpose of the study was to investigate the reliability of the fluorescent in situ hybridization (FISH) analysis of the first polar body (IPB) for cytogenetic evaluation of human oocytes as a method of choice in preimplantation diagnosis of chromosomal aneuploidies.

DESIGN

Human unfertilized oocytes and their extruded IPB were analyzed using the directly labeled fluorescence alpha-satellite DNA probes to chromosomes X and 18.

RESULTS

Paired signals for chromosomes X and 18 were observed in the second meiotic prophase (MII) of unfertilized oocytes and their extruded IPB. In the series of 156 unfertilized oocytes in which the number of X chromosome- and chromosome 18-specific signals were analyzed in both MII and IPB, five nondisjunction events have been detected, with corresponding signals in MII and their IPB: missing signals in MII corresponded to extra signals in their IPB and extra signals in MII corresponded to missing signals in IPB. In one oocyte chromosome 18 nondisjunction was detected, with both chromosome 18 signals in MII and no chromosome 18 signal in IPB. In four oocytes chromatid malsegregations for chromosome X or chromosome 18 were detected: in two oocytes, three of four chromosome 18 signals were present in MII, with only one in IPB, and in the other two oocytes, three of four chromosome signals were present in MII, with only one left in IPB.

CONCLUSIONS

The data suggest the possibility of detecting chromosomal aneuploidy in oocytes through cytogenetic analysis of their corresponding IPB by FISH as a possible approach for preimplantation diagnosis of major chromosomal trisomies.

Chromosome 18 analysis by fluorescence in situ hybridization (FISH) in human blastomeres of abnormal embryos after in vitro fertilization (IVF) attempt

We performed fluorescence in situ hybridization (FISH) with a chromosome 18-specific probe on human abnormal cleaved embryos, fertilized either by two spermatozoa and exhibiting three pronuclei (3 PN) or normally fertilized and exhibiting two pronuclei (2 PN) with subsequent severe fragmentation and/or blocking. The aim of the study was to evaluate the incidence of chromosome 18 anomalies among these embryos in order to evaluate the FISH efficiency on such material and to obtain more precise and complete data than those obtained with classical cytogenetic analysis. For the 3 PN cleaved embryos, FISH confirmed the frequent regulation towards diploidy (25 per cent) and the high frequency of mosaics (53 per cent). For the 2 PN blocked or damaged embryos, FISH permitted chromosome evaluation, which was otherwise impossible with classical cytogenetic techniques: we also found a high mosaic frequency (45 per cent) with these embryos. If this frequency were the same for normally developing embryos, it would be a major obstacle to the reliability of either chromosomal or genetic preimplantation diagnosis.

Assessment of numeric abnormalities of X, Y, 18, and 16 chromosomes in preimplantation human embryos before transfer

OBJECTIVE

Our purpose was to determine the feasibility of ascertaining aneuploidy for chromosomes X, Y, 18, and 16 by use of multiple-probe fluorescence in situ hybridization in blastomeres from preimplantation human embryos.

STUDY DESIGN

A short fluorescence in situ hybridization procedure involving the simultaneous use of four deoxyribonucleic acid probes detected with red, green, blue, or a mixture of red and green fluorochromes was developed to determine numeric abnormalities of chromosomes X, Y, 18, and 16. Embryos underwent biopsy, and all or most cells were analyzed to distinguish true aneuploidy from mosaicism and to assess technique variations within the same embryo (n = 64).

RESULTS

The analysis of all the blastomeres of an embryo was achieved in 91% of the embryos. Successful analyses including biopsy, fixation, and fluorescence in situ hybridization were achieved in 87.8% of the blastomeres. Of the four chromosomes tested, numeric aberrations were found in 23% and 42% of normally and abnormally developing embryos, respectively, including aneuploidy, polyploidy, haploidy, and mosaicism. When diploid embryos containing one or several tetraploid cells are counted as chromosomally abnormal, then 49% and 61% of normally and abnormally developing embryos, respectively, were chromosomally abnormal. Aneuploid embryos consisted of two monosomies for chromosome 16, one for chromosome 18, and a trisomy for chromosome 16. There was a tendency for aneuploidy to increase with maternal age.

CONCLUSIONS

Fluorescence in situ hybridization is a more efficient method than cytogenetic analysis to study specific aneuploidies at preimplantation stages of development in human embryos. In addition, the preimplantation genetic diagnosis of two blastomeres per eight-cell embryo may be sufficient to ensure successful analysis of polyploidy, haploidy, and specific aneuploidies without endangering the survival of the embryo. The technique can be easily modified to consider other chromosomes, including 13 and 21. Because most chromosomally abnormal embryos do not develop to term, the use of this technique may increase the delivery rate per embryo by allowing only transfer of embryos normal for the tested chromosomes. This technique would be most useful for older women undergoing in vitro fertilization, because aneuploidy appears to increase with advancing maternal age.

Normal pregnancy after preimplantation DNA diagnosis of a dystrophin gene deletion

To perform preimplantation DNA diagnosis for Duchenne muscular dystrophy (DMD) in a female carrier of a dystrophin gene deletion of exons 3-18, we developed a polymerase chain reaction (PCR)-based assay of exon 17 sequences. Exon 17 was efficiently amplified in all 50 single blastomeres of normal control embryos and in five blastomeres of one male embryo of the DMD carrier obtained after a first preimplantation diagnosis (PID) for gender determination. In ten blastomeres of another two male embryos of the DMD carrier, no PCR signals were observed, probably as a result of the deletion. After intracytoplasmic sperm injection, embryos were analysed for exon 17 and three of the four embryos showing normal PCR signals were replaced, resulting in a singleton pregnancy. Prenatal diagnosis showed a female karyotype and DNA analysis indicated that the fetus was not a DMD carrier.

Single-cell analysis of the RhD blood type for use in preimplantation diagnosis in the prevention of severe hemolytic disease of the newborn

OBJECTIVE

Our purpose was to develop a molecular assay to determine the fetal RhD blood type on single diploid cells, including blastomeres.

STUDY DESIGN

Polymerase chain reaction amplification of a 99 bp deoxyribonucleic acid fragment of the RhD gene or a 113 bp fragment from the RhCE gene was performed from 20 venous blood samples and 20 amniotic fluid samples and from 60 single-cultured lymphoblasts and 12 media blanks mixed in a blinded fashion. This reaction was similarly tested after whole-genome amplification on 10 lymphoblasts and seven human blastomeres.

RESULTS

Deoxyribonucleic acid amplification was successful and correct from all genomic deoxyribonucleic acid samples. Ninety-seven percent of single cells amplified; correct diagnosis was made in 96%. Five blastomeres successfully amplified. No media blanks produced amplified, contaminating deoxyribonucleic acid.

CONCLUSIONS

The RhD blood type can be determined reliably from single cells and can be used for preimplantation genetic diagnosis for the prevention of rhesus hemolytic disease.

Mosaicism of autosomes and sex chromosomes in morphologically normal, monospermic preimplantation human embryos

We have previously detected chromosome abnormalities in human embryos whilst identifying the sex for preimplantation diagnosis of X-linked disease. In this study we assess the incidence of these abnormalities, both for sex chromosomes and autosomes 1 and 17, using dual fluorescent in situ hybridization (FISH). Sixty-nine normally fertilized embryos of good morphology at the 6-10 cell stage (day 3 post-insemination) were examined. The embryos were spread whole using HCl and Tween 20 to dissolve the cytoplasm. Thirty-four embryos were analyzed for the sex chromosomes and 35 for autosomes 1 and 17. All probes were directly labelled with fluorochromes allowing analysis in 2 h. Control lymphocytes demonstrated that the probes were of high specificity. For the sex chromosomes, five embryos were mosaic (15 per cent) with the remaining 29 being uniformly XX or XY. In no case was an XX nucleus found in an otherwise XY embryo, indicating that even though mosaicism for the sex chromosomes is present, such abnormalities would not lead to a misdiagnosis of sex. For the autosomes, 16 embryos were abnormal (46 per cent); one embryo was triploid, one was monosomic for chromosome 1, and ten others were diploid mosaics (three diploid/aneuploid, three diploid/polyploid, and four diploid/haploid). A further four embryos had variable chromosome numbers in the majority of nuclei which appeared to be the result of uncontrolled mitotic division. The presence of haploidy or double monosomy, which occurred in 15 per cent of nuclei, has important implications for the diagnosis of trisomies and dominant disorders.

Cytogenetic and cryobiology of human cocultured embryos: a 3-year experience

PURPOSE

Coculture, which allows good-quality human blastocysts with good yields to be obtained, has been designed mainly to select the best embryos for transfers.

METHODS

In a first attempt during coculture, we have studied by fluorescent in situ hybridization the chromosomic content of the in vitro blocked embryos, using centrometric probes for chromosomes 1, 12, and 18. Close to 37% of the arrested embryos show aneuploidymosaicism.

RESULTS

Freezing cocultured blastocysts gives good recovery rates after transfer (83%). The ongoing pregnancy rates per transfer (19%) are high, and the implantation rate per embryo is 13%. This compares favorably with freezing at an early stage.

CONCLUSIONS

We observed that the quality of the endometrium is always the limiting step, as first of all we observed wide variations according to the hormonal preparation of the patients. Moreover the implantation per embryo in the pregnant patients is very high (57%), indicating that most of the losses are directly related to the receptivity of the endometrium.

Preimplantation diagnosis

Research towards preimplantation diagnosis of genetic disease was initiated in the UK in the mid 1980s with the aim of helping those couples who would prefer selection to occur at this stage rather than during pregnancy. Following in vitro fertilisation, (IVF), biopsy and removal of 1 or 2 of the totipotent cells from the cleavage stage 3 day old embryo provides the material for molecular genetic diagnosis without interfering with development. Earliest applications were in the avoidance of X-linked disease by sexing embryos and selecting females for transfer to the mother. Initially, polymerase chain reaction (PCR) amplification of DNA from the biopsied blastomeres was performed using primers specific for sequences derived from the Y chromosome and this led to the birth of several normal girls. To reduce the risk of misdiagnosis due to amplification failure, PCR based methods for sexing the embryo now employ both X and Y specific sequences, but the preferred method is currently considered to be fluorescent in situ hybridisation (FISH) with fluorochrome labelled DNA probes to the embryonic nuclei that have been fixed and spread on slides. Dual FISH with probes from X and Y chromosomes allows unequivocal diagnosis of sex and determination of chromosome copy number, avoiding transfer of embryos with abnormal numbers of sex chromosomes, including those with only the maternal X that would be at 50% risk for the X-linked disease. The application of FISH for preimplantation diagnosis has also led to the realisation that chromosomal mosaicism is common at the cleavage stage of development, a finding that has important implications for diagnosis of both dominant single gene disorders and trisomies, as well as for our understanding of early human development. Cloning and sequencing of the relevant genes has enabled the development of methods for the diagnosis of certain recessive single gene disorders in cleavage stage embryos. PCR based methods have to be developed for each condition, sometimes for each family if there is heterogeneity. Preimplantation diagnosis has been successful so far for cystic fibrosis, Tay Sachs disease, and Lesch-Nyhan syndrome. Worldwide, 32 pregnancies have been established following all types of preimplantation diagnosis and with 29 babies born, there is no evidence for any adverse effect on development.

New methods in cytogenetics

Developments in the technique of fluorescence in situ hybridization (FISH) now permit hybridization of sequences ranging from 1 kb to whole genomes. The technique can be used in applications from coarse mapping of whole chromosomes to high-resolution analysis of extended strands of DNA. The complexity, and hence the coverage, of 'paints' prepared by amplification is being improved to the extent that such methods are used in cloning strategies for the generation of region-specific probes. Interphase analysis and comparative genomic hybridization are becoming important tools in cancer cytogenetics, and the potential for routine analysis of fetal cells obtained from maternal blood may provide a fresh approach to prenatal cytogenetic screening. Functional studies of gene activity and nuclear organization are now also possible.

Complex genetic counseling and exclusion of Duchenne muscular dystrophy in a twin pregnancy after in vitro fertilization (IVF)

A twin pregnancy following in vitro fertilization-embryo transfer coincidentally at risk for the X-linked recessive Duchenne muscular dystrophy is described. First-trimester prenatal diagnosis by transabdominal chorionic villus samplings on the dichorionic placentae and molecular linkage analysis could exclude the disorder in both fetuses. Genetic counseling and prenatal diagnosis were particularly complex due to the twin pregnancy, the need for linkage analysis, and confined placental mosaicism 45,X/46XX in one of the fetuses. All parties should be aware that additional invasive diagnostic procedures in the second trimester might be required. It is proposed that, in similar situations, only one, arguably two, fertilized egg be transferred at a time to facilitate prenatal diagnosis and decision making for these rare couples. This problem, however, may be increasingly overcome by preimplantation diagnosis.

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.

Techniques in current use in prenatal diagnosis

Prenatal diagnosis is now offered to the majority of pregnant women in Europe and the United States. Advances in obstetric and laboratory techniques mean that increasing numbers of conditions can be diagnosed prenatally; indeed, gene carriers can be identified before pregnancy in some cases. Current obstetric and laboratory techniques for prenatal screening and diagnosis of genetic disorders are discussed.