Preimplantation diagnosis of single gene disorders by two-step oocyte genetic analysis using first and second polar body

Correlation of the position and status of the polar body from the fertilized oocyte to the euploid status of blastocysts

Polar bodies are tiny cells that are extruded during oocyte meiosis and are generally considered not essential for embryonic development. Therefore, polar bodies have been widely used as important materials for the preimplantation genetic diagnosis of human embryos. Recent studies have shown that polar bodies mediate embryonic development and that their morphology is related to embryo quality and developmental potential. However, the relationship between the emission of the polar body and embryonic euploidy remains unclear. In this study, a total of 1,360 blastocyst trophectoderm (TE) biopsies were performed, and blastocyst ploidy results were correlated with the state of polar bodies. The results showed that polar body angle size and polar body status are not directly related to whether the blastocysts are euploid, aneuploid, or mosaic (p > 0.05). Therefore, in the process of clinical embryo selection, embryologists should not predict the euploidy of blastocysts based on the state of polar bodies, thus affecting embryo selection.

Human in vitro fertilisation and developmental biology: a mutually influential history

This article describes the origins and development of in vitro fertilisation (IVF) and how it was influenced by, and influenced, basic research in developmental biology. It describes the technical and social challenges that confronted the pioneers in this field of study, and the considerable progress that has been made since those early days. It also considers how IVF has contributed, and continues to contribute, to our understanding of early human development.

Improving preimplantation genetic diagnosis (PGD) reliability by selection of sperm donor with the most informative haplotype

BACKGROUND

The study is aimed to describe a novel strategy that increases the accuracy and reliability of PGD in patients using sperm donation by pre-selecting the donor whose haplotype does not overlap the carrier's one.

METHODS

A panel of 4-9 informative polymorphic markers, flanking the mutation in carriers of autosomal dominant/X-linked disorders, was tested in DNA of sperm donors before PGD. Whenever the lengths of donors' repeats overlapped those of the women, additional donors' DNA samples were analyzed. The donor that demonstrated the minimal overlapping with the patient was selected for IVF.

RESULTS

In 8 out of 17 carriers the markers of the initially chosen donors overlapped the patients' alleles and 2-8 additional sperm donors for each patient were haplotyped. The selection of additional sperm donors increased the number of informative markers and reduced misdiagnosis risk from 6.00% ± 7.48 to 0.48% ±0.68. The PGD results were confirmed and no misdiagnosis was detected.

CONCLUSIONS

Our study demonstrates that pre-selecting a sperm donor whose haplotype has minimal overlapping with the female's haplotype, is critical for reducing the misdiagnosis risk and ensuring a reliable PGD. This strategy may contribute to prevent the transmission of affected IVF-PGD embryos using a simple and economical procedure.

TRIAL REGISTRATION

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. DNA testing of donors was approved by the institutional Helsinki committee (registration number 319-08TLV, 2008). The present study was approved by the institutional Helsinki committee (registration number 0385-13TLV, 2013).

Successful implantation and live birth of a healthy boy after triple biopsy and double vitrification of oocyte-embryo-blastocyst

Introduction

Preimplantation genetic diagnosis and/or screening (PGD/PGS) allow the assessment of the genetic health of an embryo before transferring it into the uterus. These techniques require the removal of cellular material (polar bodies, blastomere(s) or trophectoderm cells) in order to perform the proper genetic analysis. We report the implantation and live birth outcome of a vitrified-warmed blastocyst developed after triple biopsy and double vitrification procedures at oocyte, cleavage embryo and blastocyst stage.

Case description

An infertile couple, with family history of β-thalassemia, searched for IVF procedure and PGD. First polar bodies biopsy with subsequent vitrification was uninformative due to meiotic crossing-over, so oocytes were inseminated after warming. Two embryos were obtained and blastomere biopsy was performed on day 3 with inconclusive results on their genetic status. Their culture resulted in one expanded blastocyst stage on day 7 that underwent trophectoderm biopsy and vitrification. This embryo showed to be normal. It was then warmed and transferred in an artificial cycle.

Discussion and Evaluation

Preconception genetic analysis by removal and analysis of the first polar body is technically possible, but the genetic information that we can obtain at this stage may be limited and the oocytes to be inseminated is not predictable. Compared to blastomere biopsy, trophectoderm biopsy has more diagnostic efficiency with respect to both chromosomal mosaicism and PCR accuracy, reducing the problems of amplification failure and allele drop out. Moreover, embryos biopsied at the cleavage stage seem to have lower implantation rate than biopsied blastocyst.

Conclusions

This is the first case report of a live birth obtained from a three step biopsy and double vitrification procedures of a blastocyst. This case report seems also to suggest the harmlessness of all these procedures if carefully performed by a skilled biologist in an IVF lab with quality management system. Finally, our study highlight that blastocyst cryopreserved on day 7 have clinically important potential and embryos that not reach blastocyst stage on day 6 should not to be discharged because they may result in an ongoing pregnancy.

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.

Preventing mucopolysaccharidosis type II (Hunter syndrome): PGD and establishing a Hunter (46, XX) stem cell line

OBJECTIVES

Preimplantation genetic diagnosis (PGD) enables the identification of affected embryos prior to implantation. We present for the first time three families in which either the oocytes or embryos obtained from female carriers of mutations in the iduronate-2-sulfatase (IDS) gene underwent PGD for mucopolysaccharidosis type II (Hunter syndrome). Furthermore, we report the first ever derivation of a Hunter's syndrome (46, XX) human stem cell line from embryos (HESC) carrying the IDS and oculocutaneus albinism type 2 mutations.

METHODS

Combined polar body (PB) 1 and 2 or a single cell of a six- to eight-cell embryo (blastomere) was used for genetic analysis by multiplex polymerase chain reaction assay using six microsatellite polymorphic markers flanking the gene and mutation.

RESULTS

One couple underwent four PB-PGD cycles, with birth of a healthy girl; the second couple with one PB-PGD cycle had healthy twins; the third couple underwent seven cycles of double PGD for Hunter and Albinism syndrome with birth of healthy twins. One novel Hunter 46, XX HESC line was established displaying typical characteristics of HESC cells.

CONCLUSIONS

PGD is a reliable method to prevent pregnancy of children affected with Hunter syndrome. In addition, derived HESC can be further utilized for drug testing and better understanding of the pathogenesis of this syndrome.

Poor correlations in the levels of pathogenic mitochondrial DNA mutations in polar bodies versus oocytes and blastomeres in humans

Because the mtDNA amount remains stable in the early embryo until uterine implantation, early human development is completely dependent on the mtDNA pool of the mature oocyte. Both quantitative and qualitative mtDNA defects therefore may negatively impact oocyte competence or early embryonic development. However, nothing is known about segregation of mutant and wild-type mtDNA molecules during human meiosis. To investigate this point, we compared the mutant levels in 51 first polar bodies (PBs) and their counterpart (oocytes, blastomeres, or whole embryos), at risk of having (1) the "MELAS" m.3243A>G mutation in MT-TL1 (n = 30), (2) the "MERRF" m.8344A>G mutation in MT-TK (n = 15), and (3) the m.9185T>G mutation located in MT-ATP6 (n = 6). Seven out of 51 of the PBs were mutation free and had homoplasmic wild-type counterparts. In the heteroplasmic PBs, measurement of the mutant load was a rough estimate of the counterpart mutation level (R(2) = 0.52), and high mutant-load differentials between the two populations were occasionally observed (ranging from -34% to +34%). The mutant-load differentials between the PB and its counterpart were higher in highly mutated PBs, suggestive of a selection process acting against highly mutated cells during gametogenesis or early embryonic development. Finally, individual discrepancies in mutant loads between PBs and their counterparts make PB-based preconception diagnosis unreliable for the prevention of mtDNA disorder transmission. Such differences were not observed in animal models, and they emphasize the need to conduct thorough studies on mtDNA segregation in humans.

Use of parthenogenetic activation of human oocytes as an experimental model for evaluation of polar body based PGD assay performance

PURPOSE

To develop an experimental model to assess the feasibility of polar body preimplantation genetic diagnosis without requiring oocyte fertilization.

METHODS

First polar body was removed from donated oocytes and second polar body was biopsied after parthenogenetic activation. Molecular analysis on both polar bodies involved a fluorescent multiplex polymerase chain reaction of short-tandem repeat markers, closely linked to genes of interest. Main outcome measures were: allele segregation through polar bodies and haploid nucleus, recombination rates between alleles and frequency of Allele Drop Out.

RESULTS

Twenty-six out of 39 oocytes extruded a second polar body after activation. Ninety-two percent of the first polar bodies and 20 out of 26 (77%) second polar bodies were successfully amplified. Eighty percent of first polar bodies were heterozygous for CFTR and 55% for HBB. Analysis of second polar bodies predicted the genotype of the oocytes in case of heterozygous first polar body, and validated results in homozygous cases. Frequency of allele drop out was 4%.

CONCLUSIONS

Our model confirms that polar body preimplantation genetic diagnosis for single gene disorders can be evaluated using parthenogenetic oocytes and offers an option to set up procedures without requiring oocyte fertilization.

Polar bodies--more a lack of understanding than a lack of respect

Polar bodies are as diverse as the organisms that produce them. Although in many animals these cells often die following meiotic maturation of the oocyte, in other organisms they are an essential and diverse part of embryonic development. Here we highlight some of this diversity and summarize the evolutionary basis for their utility.

Detection and quantification of mRNA in single human polar bodies: a minimally invasive test of gene expression during oogenesis

Proteins and mRNA produced in oogenesis support embryonic development until the zygotic transition, 3 days after fertilization. Since polar bodies can be biopsied with little if any harm to the oocyte, we tested the hypothesis that mRNA originating from expression in the meiotic oocyte is present and detectable in a single polar body prior to insemination. Human oocytes were obtained from patients undergoing controlled ovarian hyperstimulation and intracytoplasmic sperm injection. Immature oocytes were cultured overnight and inspected the following day for maturation. Metaphase II oocytes underwent polar body biopsy followed by reverse transcription without RNA isolation. Sibling oocytes were similarly prepared. Complementary DNA from all samples were pre-amplified over 15 cycles for candidate genes using selective primers. Real-time PCR was performed to detect and quantify relative single-cell gene expression. Polar body mRNA was detected in 11 of 12 candidate genes. Transcripts that were present in greater abundance in the oocyte were more likely to be detected in qPCR replicates from single polar bodies. Pre-amplification of cDNA synthesized without RNA isolation can facilitate the quantitative detection of mRNA in single human polar bodies.

Predicting aneuploidy in human oocytes: key factors which affect the meiotic process

BACKGROUND

To estimate the incidence of aneuploidy in relation to patients' characteristics, the type of hormonal stimulation and their response to induction of multiple follicular growth, 4163 first polar bodies (PB1s) were analyzed.

METHODS

Five hundred and forty four infertile couples underwent 706 assisted conception cycles (640 with poor prognosis indications and 66 controls) in which chromosomal analysis of PB1 for the chromosomes 13, 15, 16, 18, 21 and 22 was performed. Results were evaluated in a multivariate analysis.

RESULTS

The proportion of normal oocytes was directly correlated (P < 0.01) with (i) the number of mature oocytes and (ii) the establishment of a clinical pregnancy; and inversely correlated (P < 0.01) with (i) female age, (ii) causes of female infertility (endometriosis, abortions, ovulatory factor), (iii) poor prognosis indications (female age, number of previous cycles, multiple poor prognosis indications), (iv) number of FSH units per oocyte and (v) number of FSH units per metaphase II oocyte. There was a weak significance of frequency (P < 0.05) between type of abnormality (originated by chromatid predivision, chromosome non-disjunction or combined mechanisms in the same oocyte) and groups of the studied variables, rather than to a specific abnormality or a specific chromosome.

CONCLUSIONS

The type of infertility had a significant effect on errors derived from the first meiotic division, whose incidence was significantly higher in the presence of endometriosis or of an ovulatory factor, and in women that experienced repeated abortions. Each aneuploidy event was found to be dependent not on a specific variable, but on groups of variables. In addition, the tendency of chromosomal abnormalities to occur simultaneously implies that the deriving aneuploidies can be of any type.

Preimplantation genetic diagnosis in an HIV-serodiscordant couple carrier for sickle cell disease: lessons from a case report

Since 1999, the Erasme Hospital Fertility Clinic has carried a special programme for patients with HIV seropositivity. The philosophy of the programme is to give access to these patients in a secure environment to the same technological facilities available to any other patients. Many of these patients being native from sub-Saharan countries, they are often sickle cell disease (SCD) carriers, a common autosomal recessive disorder in these regions, and a severe affection in homozygotes. We hereby report, for the first time, the birth of a healthy sickle haemoglobin (HbS) heterozygous baby after preimplantation genetic diagnosis (PGD) for SCD in an HIV-serodiscordant couple of HbS mutation carriers with longstanding infertility. The prospective mother was 35 years old and HIV positive with an undetectable viral load under highly active antiretroviral therapy. One carrier embryo was transferred and resulted in the birth of a healthy HbS carrier baby girl. Despite stimulation difficulties, sometimes described in HIV patients, PGD represents an interesting additional technology, especially in populations where the coexistence of both diseases is frequent. PGD could even be preferred to prenatal diagnosis for couples of HbS carriers if the woman is HIV positive, as invasive prenatal samplings carry a risk of materno-foetal viral transmission.

Blastocyst biopsy versus cleavage stage biopsy and blastocyst transfer for preimplantation genetic diagnosis of β-thalassaemia: a pilot study

BACKGROUND

Trophectoderm biopsy at the blastocyst stage is an emerging approach in preimplantation genetic diagnosis (PGD). This study aimed to compare genotyping success and implantation rates in PGD cycles for beta-thalassaemia following biopsy at the cleavage versus the blastocyst stage, with transfer of blastocysts.

METHODS

This pilot study included 20 cycles: Group A: 10 cycles, day 3 blastomere biopsy, day 5 transfer; Group B: 10 cycles, day 5 trophectoderm biopsy, day 6 transfer. Standard-assisted reproduction and laser biopsy procedures were used. Biopsied cells were genotyped using real-time PCR multiplexed with fluorescent microsatellite analysis.

RESULTS

In Group A, 131 fertilized eggs developed to 101 embryos suitable for single blastomere biopsy; 76/101 blastomeres were diagnosed (75.2%), 30 unaffected blastocysts were transferred resulting in six pregnancies (eight fetal hearts, 26.7% implantation rate). In Group B, 128 fertilized eggs developed to 53 blastocysts for trophectoderm biopsy (four to five cells), with 50/53 blastocysts diagnosed (94.3%), 21 unaffected blastocysts transferred and 6 pregnancies initiated (10 fetal hearts, 47.6% implantation rate). Overall, nine pregnancies reached >10 weeks gestation and were confirmed unaffected by prenatal diagnosis, with 12 healthy babies born.

CONCLUSIONS

This pilot study suggests that trophectoderm biopsy and blastocyst transfer may be more advantageous than cleavage stage biopsy with respect to outcome of PGD for monogenic diseases.

Screening oocytes by polar body biopsy

Preimplantation genetic aneuploidy screening performed by polar body biopsy has become a frequently used method, especially as in several countries only preconceptional genetic diagnosis is allowed. To penetrate the zona pellucida, mechanical, chemical and laser-assisted techniques have been introduced. In this paper, the advantages, disadvantages, efficacy and safety of these techniques are elucidated.

Preimplantation genetic diagnosis for Marfan syndrome

OBJECTIVE

To develop and apply efficient and reliable protocols for preimplantation genetic diagnosis (PGD) for Marfan syndrome.

DESIGN

Two mutation-specific protocols were developed, and the markers D15S1028, D15S992, D15S196, D15S576, D15S123, and D15S143 were used to set up four multiplex polymerase chain reactions (PCRs).

SETTING

Research Center Reproduction and Genetics.

PATIENT(S)

Ten couples carrying mutations in the FBN1 gene.

INTERVENTION(S)

Six PGD protocols were developed for 10 couples, and 7 of them underwent a total of 16 clinical cycles.

MAIN OUTCOME MEASURE(S)

Amplification, allele drop-out (ADO), and contamination rates during the preclinical assays. DNA analyses of blastomeres from embryos biopsied during PGD cycles.

RESULT(S)

Six different protocols were set up, with the main objective being to to use one protocol for several couples. A total of 16 PGD cycles were performed, which resulted in the delivery of an unaffected boy and three ongoing pregnancies.

CONCLUSION(S)

The development of single-cell multiplex PCRs for linked markers and its use in PGD reduce the workload of the genetic diagnostic laboratory as well as the average waiting time for patients. This approach also allows for the simultaneous and accurate detection of recombination, contamination, and ADO, thereby increasing the reliability of the diagnosis.

Pre-embryonic diagnosis for Sandhoff disease

Embryos found to be abnormal during preimplantation genetic diagnosis (PGD) are discarded or analysed to confirm the diagnosis. To overcome this limitation, which is unacceptable in some communities and ethnic groups, pre-embryonic genetic diagnosis has been introduced, involving sequential first and second polar body analysis followed by transfer of embryos deriving from the mutation-free oocytes, while removing from culture and freezing the mutant oocytes at the pronuclear stage. The technique is applied here to PGD of Sandhoff disease caused by 16-kb deletion of the hexosaminidase B gene for a couple with a religious objection to discarding embryos irrespective of embryo genotype. Of 16 oocytes tested in a standard IVF protocol for 16-kb deletion, simultaneously with five linked polymorphic markers, eight were predicted mutant and frozen prior to syngamy, with the remaining eight, found to be free of mutation, further cultured and confirmed unaffected using blastomere biopsy. The transfer of two of these embryos resulted in birth of an unaffected child, demonstrating feasibility of pre-embryonic diagnosis to avoid embryo discard.

Frequency and distribution of chromosome abnormalities in human oocytes

It was previously shown that more than half of the human oocytes obtained from IVF patients of advanced reproductive age are aneuploid, due to meiosis I and meiosis II errors. The present paper further confirms that 61.8% of the oocytes tested by fluorescent probes specific for chromosomes 13, 16, 18, 21 and 22 are abnormal, representing predominantly chromatid errors, which are the major source of aneuploidy in the resulting embryos. Almost half of the oocytes with meiosis I errors (49.3%) are prone to sequential meiosis II errors, which may lead to aneuploidy rescue in 30.8% of the cases. Half of the detected aneuploidies (49.8%) are of complex nature with involvement of two or more chromosomes, or the same chromosome in both meiotic divisions. The aneuploidy rates for individual chromosomes are different, with a higher prevalence of chromosome 21 and 22 errors. The origin of aneuploidy for the individual chromosomes is also not random, with chromosome 16 and 22 errors originating more frequently in meiosis II, and chromosome 18, 13 and 21 errors in meiosis I. There is an age dependence not only for the overall frequency of aneuploidies, but also for each chromosome error, aneuploidies originating from meiosis I, meiosis II, and both meiosis I and meiosis II errors, as well as for different types of aneuploidies. The data further suggest the practical relevance of oocyte aneuploidy testing for detection and avoidance from transfer of the embryos deriving from aneuploid oocytes, which should contribute significantly to the pregnancy outcomes of IVF patients of advanced reproduction age.

First pregnancy and life after preimplantation genetic diagnosis by polar body analysis for mucopolysaccharidosis type I

Preimplantation genetic diagnosis (PGD) may help couples at risk to avoid pregnancies with known genetic diseases. In Germany, the only option to perform PGD is the analysis of polar bodies (PB). Mucopolysaccharidosis type I (MPS I) is an autosomal recessive lysosomal storage disorder. Q70X is one of the frequent diseases causing mutations of alpha-L-iduronidase (IDUA), leading to a severe phenotype with mental retardation and various somatic abnormalities, and making a request for PGD is understandable. Using five polymorphic DNA markers from the vicinity of IDUA, PGD on first PB was performed for a consanguineous couple, both heterozygotes of the Q70X mutation of IDUA. Sixteen first PB were obtained by laser assisted hatching of the zona pellucida. Genotyping led to the conclusion that 3/16 oocytes carried wild-type IDUA alleles. Only one of these oocytes showed pronucleus formation after intracytoplasmic sperm injection and was transferred on day 2 after oocyte retrieval. A singleton pregnancy was established. Prenatal diagnosis showed a fetus heterozygous for Q70X. For MPS I, PB analysis is a feasible way to perform PGD and it may be an acceptable alternative for couples with moral objections to embryo selection, or for countries in which genetic testing of the embryo is prohibited.

Birth of a healthy infant following trophectoderm biopsy from blastocysts for PGD of beta-thalassaemia major

PGD is a well accepted reproductive choice for couples at genetic risk and involves the diagnosis and transfer of unaffected IVF embryos. PGD for monogenetic diseases is most commonly accomplished by the biopsy of one or two blastomeres from cleavage stage embryos, followed by PCR-based protocols. However, PCR-based DNA analysis of one or two cells is subject to several problems, including total PCR failure, or failure of one allele to amplify. Trophectoderm biopsy at the blastocyst stage enables the removal of more than two cells for diagnosis while being non-invasive to the inner cell mass which is destined for fetal development. The aim of this study was to develop a safe, reliable technique for the biopsy of trophectoderm cells from human blastocysts. This case report demonstrates that removal of trophectoderm cells prior to blastocyst transfer is compatible with implantation and development to term. Here we report successful PGD for beta-thalassaemia following trophectoderm cell biopsy from blastocysts and the birth of a healthy infant.

Outcome of laser-assisted polar body biopsy and aneuploidy testing

Polar body biopsy and subsequent fluorescence in-situ hybridization (FISH) analysis allows detection of maternally derived chromosomal aneuploidies in human oocytes during IVF treatment. The development of a diode laser technique for the partial opening of the zona pellucida has stimulated the use of this technique to assist polar body biopsy. Laser-assisted polar body biopsy was performed in 140 IVF cycles from patients of advanced maternal age (> or =35 years). A total of 921 oocytes were treated by a laser for partial zona opening and polar body removal. FISH was performed for chromosomes 13, 16, 18, 21 and 22 and results were available for 903 oocytes (98%). In all, 443 oocytes (49.1%) were euploid and of these, 293 were fertilized. A total of 214 embryos were transferred in 120 embryo transfer cycles (1.78 per embryo transfer) resulting in 27 clinical pregnancies (22.5% per embryo transfer) with an implantation rate of 15.4%. Subsequently, five women aborted (18.5%) and 24 healthy children were born from the remaining 22 pregnancies, which gives a take home baby rate of 18.3% per transfer cycle. It is concluded that polar body biopsy using a diode laser system is as efficient as standard polar body biopsy using zona drilling.

ESHRE PGD Consortium ‘Best practice guidelines for clinical preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS)’

Among the many educational materials produced by the European Society of Human Reproduction and Embryology (ESHRE) are guidelines. ESHRE guidelines may be developed for many reasons but their intent is always to promote best quality practices in reproductive medicine. In an era in which preimplantation genetic diagnosis (PGD) has become a reality, we must strive to maintain its efficacy and credibility by offering the safest and most effective treatment available. The dominant motivators for the development of current comprehensive guidelines for best PGD practice were (i) the absence of guidelines and/or regulation for PGD in many countries and (ii) the observation that no consensus exists on many of the clinical and technical aspects of PGD. As a consequence, the ESHRE PGD Consortium undertook to draw up guidelines aimed at giving information, support and guidance to potential, fledgling and established PGD centres. The success of a PGD treatment cycle is the result of great attention to detail. We have strived to provide a similar level of detail in this document and hope that it will assist staff in achieving the best clinical outcome for their patients.

Preimplantation diagnosis for ornithine transcarbamylase deficiency

Ornithine transcarbamylase (OTC) deficiency is a severe X-linked metabolic disorder leading to hyperammonaemia and death shortly after birth. Prenatal diagnosis for OTC deficiency is available, but may require termination of pregnancy if affected. Thus there is a need for an option for pre-pregnancy testing, to pre-select OTC deficiency-free embryos for transfer, thus avoiding prenatal diagnosis and pregnancy termination. Preimplantation genetic diagnosis (PGD) for OTC deficiency has been developed, using sequential first and second polar body analysis; it was applied in a woman carrying the R26Q mutation in the exon 1 of OTC gene. The first and second polar bodies were removed following maturation and fertilization of oocytes in a standard IVF protocol, and analysed using a multiplex nested PCR. R26Q mutation was tested simultaneously with linked markers in six zygotes, resulting in detection of the embryos with a mutation-free maternal contribution; these were transferred back to the patient, yielding pregnancy and birth of a healthy child. This is the first PGD for OTC deficiency resulting in the birth of an unaffected child.

Preimplantation diagnosis for long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency is a fatal autosomal recessive metabolic disorder, presenting during infancy. Preimplantation genetic diagnosis (PGD) provides an option for establishing an unaffected pregnancy, avoiding the risk for termination of pregnancy following prenatal diagnosis. The method for pre-selection of mutation-free oocytes for LCHAD deficiency was developed by testing the first and second polar body removed from oocytes by micromanipulation techniques in the framework of in-vitro fertilization. To avoid misdiagnosis, testing was done using hemi-nested polymerase chain reaction (PCR), with outer primers designed to lie outside the pseudogene, eliminating false priming. Four of 12 tested oocytes were predicted to be unaffected, based on the heterozygous first and mutant second polar body. The embryos resulting from these mutation-free oocytes were replaced, yielding a singleton clinical pregnancy and birth of a healthy child following confirmation by prenatal diagnosis.

Polar body-based preimplantation diagnosis for X-linked disorders

Preimplantation diagnosis for X-linked disorders has been performed predominantly by gender determination, which, however, leads to the discarding of 50% unaffected male embryos. In an attempt to identify X-linked mutation-free embryos for transfer, the present authors introduced preimplantation genetic diagnosis (PGD), using a sequential first and second polar body analysis, as an alternative to gender determination. This method was offered to eight couples at risk for having children with X-linked disorders, including haemophilia B, fragile-X syndrome (FMR1), myotubular myotonic dystrophy (MTMD), ornithine transcarbamylase (OTC) deficiency and X-linked hydrocephalus. The first and second polar bodies were removed following maturation and fertilization of oocytes in a standard IVF protocol and analysed using a multiplex nested polymerase chain reaction (PCR), involving testing for mutations simultaneously with linked markers. Overall, 13 PGD cycles were performed, resulting in the detection of 25 embryos with the predicted mutation-free maternal contribution; these embryos were transferred back to the patients in all cycles, yielding four clinical pregnancies. Four children were born following these pregnancies, including three unaffected and one with misdiagnosis as a result of allele dropout (ADO), which was predictable in the case of FMR1. Presented results demonstrate the clinical usefulness of the specific polar body testing for X-linked disorders as an alternative to PGD by gender determination.

Direct comparison of detection systems used for the development of single-cell genetic tests in preimplantation genetic diagnosis

PURPOSE

Single-cell polymerase chain reaction (PCR) requires efficient amplification and accurate detection. We compare the accuracy of heteroduplex, fluorescent-fragment, and fluorescent single-strand conformation polymorphism (F-SSCP) analysis as detection systems for analysis of a PCR assay developed for preimplantation genetic diagnosis.

METHODS

A single-cell, fluorescent multiplex PCR assay was developed for the cystic fibrosis delta F508 mutation and the short tandem repeat, D21S11. Detection systems were compared by analyzing blinded PCR products.

RESULTS

Amplification rates for cystic fibrosis were 89% by heteroduplex and 91% by fragment analysis, while it was 72% for D21S11 by fragment analysis. No difference in allele dropout was detected for cystic fibrosis by any method (2%). Overall accuracy was high, > 97%, although SSCP was the least accurate.

CONCLUSIONS

Heteroduplex and fragment analysis proved equal in the diagnosis of a single amplified locus. We determined that fragment analysis allows maximal accuracy of detection and permits analysis of a second loci, controlling for DNA contamination and allelic dropout.

Aspects of biopsy procedures prior to preimplantation genetic diagnosis

Today, preimplantation genetic diagnosis (PGD) is offered in over 40 centres worldwide for an expanded range of genetic defects causing disease. This very early form of prenatal diagnosis involves the detection of affected embryos by fluorescent in situ hybridization (FISH) (sex determination or chromosomal defects) or by polymerase chain reaction (PCR) (monogenic diseases) prior to implantation. Genetic analysis of the embryos involves the removal of some cellular mass from the embryos (one or two blastomeres at cleavage-stage or some extra-embryonic trophectoderm cells at the blastocyst stage) by means of an embryo biopsy procedure. Genetic analysis can also be performed preconceptionally by removal of the first polar body. However, additional information is then often gained by removal of the second polar body and/or a blastomere from the embryo. Removal of polar bodies or cellular material from embryos requires an opening in the zona pellucida, which can be created in a mechanical way (partial zona dissection) or chemical way (acidic Tyrode's solution). However, the more recent introduction of laser technology has facilitated this step enormously. Different biopsy procedures at different preimplantation stages are reviewed here, including their pros and cons and their clinical applications. The following aspects will also be discussed: safety of zona drilling by laser, use of Ca2+/Mg2+-free medium for decompaction, and removal of one or two cells from cleavage-stage embryos.

Human germline gene therapy reconsidered

This paper reevaluates the notion of human germline gene therapy (HGLGT) in light of developments in biomedicine, biotechnology, and ethical and policy analysis. The essay makes the following key points. First, because the distinction among "therapy," "prevention," and "enhancement" is not clear in human genetics, "gene therapy" is an inadequate descriptor of the process and goals of germline genetic alterations. The alternate use of the phrase "human germline genome modification" (HGLGM) could avoid a misleading label. Second, procedures that could be construed as genetic "enhancement" may not be as morally problematic as some have supposed, once one understands that the boundaries between therapy, prevention, and enhancement are not obvious in genetic medicine. Third, HGLGM might be the medically and morally most appropriate way of avoiding the birth of a child with a genetic disease in only a small range of cases. Fourth, there are still many ethical and scientific problems relating to the safety and efficacy of HGLGM.

Amplification of DNA sequences in polar bodies from human oocytes for diagnosis of mitochondrial disease

When a preovulatory oocyte reinitiates meiosis, it sheds a cytoplasmic fragment containing mitochondria and a redundant set of chromosomes. We have detected DNA sequences from both the mitochondrial and nuclear genomes in polar bodies from unfertilised human oocytes, demonstrating the feasibility of diagnosing mitochondrial diseases before conception.

Prepregnancy genetic testing for age-related aneuploidies by polar body analysis

Current practice for prevention of chromosomal aneuploidies involves prenatal screening and termination of pregnancy, a procedure that is not universally acceptable. We introduced prepregnancy genetic testing by sampling and fluorescence in situ hybridization (FISH) analysis of the first and second polar body (PB), to avoid fertilization and transfer of embryos resulting from aneuploid oocytes. In 395 in vitro fertilization (IVF) patients of advanced maternal age, the first and second PBs were removed following their extrusion from oocytes and studied by FISH, using probes specific for chromosomes 13, 18, and 21, to detect and avoid the transfer of oocytes with common aneuploidies. Overall, 3,651 oocytes obtained from 598 IVF cycles were available for FISH analysis, with 2,952 showing interpretable FISH results (80.9%). The analysis revealed 1,271 (43.1%) oocytes with aneuploidy, which were excluded from transfer and subjected to follow-up FISH analysis to confirm PB diagnosis in the cleavage or blastocyst stage embryos. Only embryos originating from 1,681 aneuploidy-free oocytes were transferred back to patients, resulting in 119 pregnancies overall, from which 78 healthy children have already been born, 35 were spontaneously aborted, and 16 are ongoing, after confirming PB diagnosis by prenatal diagnosis. The results demonstrate that PB-based preimplantation diagnosis may be used for prepregnancy screening in women with age-related risk for common aneuploidies.

Prepregnancy testing for single-gene disorders by polar body analysis

Preventive measures for single-gene disorders are currently based on carrier screening in pregnancy and prenatal diagnosis. Although this has been extremely effective for preventing new cases of common inherited conditions, the major limitation is still termination of 25% of wanted pregnancies following detection of affected fetuses. To overcome this important problem, we developed a method for prepregnancy genetic testing that involves DNA analysis of the first and second polar bodies, which are extruded during maturation and fertilization of oocytes. We offered this option to 28 couples at risk for having children with single-gene disorders. Fifty clinical cycles were performed from these patients for the following conditions: 20 for cystic fibrosis, 18 for thalassemia, 6 for sickle cell disease, 2 each for Gaucher disease and LCHAD (long-chain 3-hydroxyacyl-COA dehydrogenase deficiency), and 1 each for hemophilia B and phenylketonuria. Oocytes obtained from these patients using in vitro fertilization procedures (IVF) were tested by a sequential multiplex nested PCR analysis of the first and second polar body to detect the gene involved simultaneously with linked polymorphic markers. A total of 191 of 399 oocytes with predicted genotype were mutation free and preselected for fertilization and transfer. In all but three cycles, one to three unaffected embryos with predicted unaffected genotypes were transferred, resulting in 20 pregnancies, from which 19 healthy children have been born. The follow-up analysis of embryos resulting from oocytes with predicted affected genotype, confirmed the diagnosis in 97% of cases, demonstrating the reliability of prepregnancy diagnosis of single-gene defects by polar body analysis.

Screening oocytes and preimplantation embryos for aneuploidy

Pregnancy and live birth rates following in-vitro fertilization decline rapidly with advancing maternal age partly because of an increase in age-related aneuploidies occurring in female meiosis. Screening oocytes or preimplantation embryos for common aneuploidies is now possible by polar body or cleavage stage biopsy and multicolour fluorescence in-situ hybridization.

Birth of healthy children after preimplantation diagnosis of thalassemias

BACKGROUND

Preimplantation genetic diagnosis (PGD) allows couples at risk of having children with thalassemia to ensure the healthy outcome of their pregnancy.

METHODS

Seventeen PGD clinical cycles were initiated for Cypriot couples at risk of having children with different thalassemia mutations, including IVSI-110, IVSI-6, and IVS II-745. Unaffected embryos for transfer were selected by testing oocytes, using first and second polar body (PB) removal and nested polymerase chain reaction analysis followed by restriction digestion.

RESULTS

Unaffected embryos were selected in 16 of 17 PGD cycles. Of 166 oocytes studied from these cycles, 110 were analyzed by sequential analysis of both the first and the second PB, resulting in preselection and transfer of 45 unaffected embryos. This resulted in seven pregnancies and in the birth of five healthy thalassemia-free children. The embryos predicted to have inherited the affected allele were not transferred. Analysis of these embryos confirmed the PB diagnosis.

CONCLUSIONS

Sequential first and second PB testing of oocytes is reliable for PGD of thalassemia and is a feasible alternative to prenatal diagnosis in high-risk populations.

Accuracy of preimplantation diagnosis of single-gene disorders by polar body analysis of oocytes

PURPOSE

A number of pitfalls in single-cell DNA analysis, including undetected DNA contamination, undetected allele drop out, and preferential amplification, may lead to misdiagnosis in preimplantation genetic diagnosis of single-gene disorders.

METHODS

Preimplantation genetic diagnosis was performed by sequential first and second polar body analysis of oocytes in 26 couples at risk for having children with various single-gene disorders. Mutant genes were amplified simultaneously with linked polymorphic markers, and only embryos resulting from the mutation-free oocytes predicted by polar body analysis with confirmation by polymorphic marker testing were transferred back to patients.

RESULTS

Overall 529 oocytes from 48 clinical cycles (26 patients) were tested, resulting in the transfer of 106 embryos in 44 clinical cycles. As many as 46 (9.6%) instances of allele dropout were observed, the majority (96%) of which were detected. Seventeen unaffected pregnancies were established, of which nine resulted in the birth of an unaffected child, and the rest are ongoing.

CONCLUSIONS

A high accuracy of preimplantation genetic diagnosis of single-gene disorders is achieved by application of sequential analysis of the first and second polar body and multiplex polymerase chain reaction.

Prevention of age-related aneuploidies by polar body testing of oocytes

PURPOSE

We previously demonstrated that aneuploidy-free oocytes may be preselected by testing the first and second polar bodies removed from oocytes following their maturation and fertilization. The present paper describes the results of the application of the method in 659 in vitro fertilization cycles from patients of advanced maternal age.

METHODS

Using micromanipulation techniques, 3943 oocytes were tested by polar body sampling and fluorescent on situ hybridization analysis using specific probes for chromosomes 13, 18, and 21.

RESULTS

Fluorescent in situ hybridization results were available for 3217 (81.6%) of 3943 oocytes studied, of which 1388 (43.1%) had aneuploidies; 35.7% of the aneuploidies were of first meiotic division origin, and 26.1% of second meiotic division origin. Most errors in the first meiotic division were represented by chromatid malsegregation. The transfer of embryos deriving from 1558 of 1829 aneuploidy-free oocytes in 614 treatment cycles resulted in 131 clinical pregnancies and 88 healthy children born after confirmation of the polar body diagnosis.

CONCLUSIONS

Polar body testing of oocytes provides an accurate and reliable approach for prevention of age-related aneuploidies in in vitro fertilization patients of advanced maternal age.

Allele dropout in polar bodies and blastomeres

PURPOSE

Because allele dropout (ADO) is frequently observed in single-cell polymerase chain reaction analysis, it is important to develop a method for efficient detection of ADO, in order to avoid possible misdiagnosis in preimplantation diagnosis.

METHODS

We introduced a simultaneous amplification of mutant genes and linked polymorphic markers, such as a 4-bp repeat (GATT) at the 3' end of intron 6 in the cystic fibrosis (CF) gene and a short tandem repeat at the 5' end of the beta-globin gene. Three types of single heterozygous cells were studied for the amplification of both alleles, including 150 blastomeres, 1615 fibroblasts, and 170 first polar bodies, obtained from patients at risk for having children with cystic fibrosis (delta F-508 mutation) or sickle cell disease.

RESULTS

ADO rates of as high as 33.3% for delta F-508 mutation and 22.8% for beta-globin gene were observed in single blastomeres, compared to 7.1 and 7.7% in single fibroblasts and 5.9 and 9.6% in first polar bodies, respectively. The application of simultaneous amplification of the above linked polymorphic markers allowed detection of more than half of the cases of ADO in blastomeres (19.4% for cystic fibrosis and 12.3% for beta-globin gene) and almost all ADOs in polar bodies, particularly when the two-step sequential analysis of the first and second polar body was applied in preimplantation diagnosis of single gene disorders.

CONCLUSIONS

Simultaneous amplification of linked polymorphic markers in single-cell DNA analysis of single-gene defects is an efficient method for avoiding the risk of misdiagnosis in preimplantation diagnosis.

Preimplantation diagnosis of thalassemias

PURPOSE

Preimplantation genetic diagnosis (PGD) is an important option for couples at risk of having children with beta-globin mutations to avoid selective abortions of affected fetuses following prenatal diagnosis.

METHODS

We performed PGD for thalassemia in 12 clinical cycles (IVS1-110, and IVS-745 mutations) using biopsy of the first and second polar bodies (PBs) extruded from oocytes during maturation and fertilization, coupled with nested polymerase chain reaction analysis and restriction digestion.

RESULTS

A total of 118 oocytes was obtained, of which 78 had results for both the first and the second PBs. This resulted in the selection and transfer of 30 unaffected embryos (2.5 embryos per cycle). To avoid a possible misdiagnosis due to allele dropout (ADO), we have also introduced simultaneous detection of two highly polymorphic linked markers, a short tandem repeat immediately at the 5' end of the globin gene and HUMTH01 which is a syntenic short tandem repeat. The application of multiplex polymerase chain reaction of the beta-globin gene and linked polymorphic markers enabled detection of ADO in five first PBs, thus avoiding the transfer of potentially affected embryos resulting from their corresponding oocytes.

CONCLUSIONS

Confirmation studies of the embryos resulting from the oocytes predicted to contain an affected gene confirmed the diagnosis in 98% of the cases, thus demonstrating the accuracy and reliability of PB PGD of thalassemia mutations. The application of PB analysis in six patients resulted in two ongoing pregnancies with a thalassemia-free fetus already confirmed in both of them by prenatal diagnosis.