Preimplantation diagnosis and HLA typing for haemoglobin disorders

Updates in preimplantation genetic testing (PGT)

Preimplantation genetic testing (PGT) involves taking a biopsy of an early embryo created through in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI). Genetic testing is performed on the biopsy, in order to select which embryo to transfer. PGT began as an experimental procedure in the 1990s, but is now an integral part of assisted human reproduction (AHR). PGT allows for embryo selection which can reduce the risk of transmission of inherited disease and may reduce the chance of implantation failure and pregnancy loss. This is a rapidly evolving area, which raises important ethical issues. This review article aims to give a brief history of PGT, an overview of the current evidence in PGT along with highlighting exciting areas of research to advance this technology.

Evolution and Utility of Preimplantation Genetic Testing for Monogenic Disorders in Assisted Reproduction - A Narrative Review

Preimplantation genetic testing (PGT) for monogenic disorders and assisted reproductive technology have evolved and progressed in tandem. PGT started with single-cell polymerase chain reaction (PCR) followed by fluorescent in situ hybridisation for a limited number of chromosomes, later called 'preimplantation genetic diagnosis (PGD) version 1'. This review highlights the various molecular genetic techniques that have evolved to detect specific inherited monogenic disorders in the preimplantation embryo. Literature review in English was performed in PubMed from 1990 to 2021, using the term 'preimplantation genetic diagnosis'. With whole-genome amplification, multiple copies of embryonic DNA were created. This helped in avoiding misdiagnosis caused by allele dropout. Multiplex fluorescent PCR analysed informative short tandem repeats (STR) and detected mutations simultaneously on automated capillary electrophoresis sequencers by mini-sequencing. Comparative genomic hybridisation (CGH) and array CGH were used for 24 chromosome aneuploidy screening. Subsequently, aneuploidies were detected by next-generation sequencing using single-nucleotide polymorphism arrays, while STR markers were used for haplotyping. 'PGD version 2' included accurate marker-based diagnosis of most monogenic disorders and detection of aneuploidy of all chromosomes. Human leukocyte antigen matching of embryos has important implications in diagnosis and cure of haemoglobinopathies and immunodeficiencies in children by means of matched related haematopoietic stem cell transplantation from an unaffected 'saviour sibling' obtained by PGT.

Third-generation sequencing: any future opportunities for PGT?

PURPOSE

To investigate use of the third-generation sequencing (TGS) Oxford Nanopore system as a new approach for preimplantation genetic testing (PGT).

METHODS

Embryos with known structural variations underwent multiple displacement amplification to create fragments of DNA (average ~ 5 kb) suitable for sequencing on a nanopore.

RESULTS

High-depth sequencing identified the deletion interval for the relatively large HBA1/2--SEA alpha thalassemia deletion. In addition, STRs were able to be identified in the primary sequence data for potential use in conventional PGT-M linkage confirmation. Sequencing of amplified embryo DNA carrying a translocation enabled balanced embryos to be identified and gave the precise identification of translocation breakpoints, offering the opportunity to differentiate carriers from non-carrier embryos. Low-pass sequencing gave reproducible profiles suitable for simple identification of whole-chromosome and segmental aneuploidies.

CONCLUSION

TGS on the Oxford Nanopore is a possible alternative and versatile approach to PGT with potential for performing economical workups where the long read sequencing information can be used for assisting in a traditional PGT workup to design an accurate and reliable test. Additionally, application of TGS has the possibility of providing combined PGT-A/SR or in selected stand-alone PGT-M cases involving pathogenic deletions. Both of these applications offer the opportunity for simultaneous aneuploidy detection to select either balanced embryos for transfer or additional carrier identification. The low cost of the instrument offers new laboratories economical entry into onsite PGT.

Short Tandem Repeats Used in Preimplantation Genetic Testing of Β-Thalassemia: Genetic Polymorphisms For 15 Linked Loci in the Vietnamese Population

BACKGROUND

β-thalassemia is one of the most common monogenic diseases worldwide. Preimplantation genetic testing (PGT) of β-thalassemia is performed to avoid affected pregnancies has become increasingly popular worldwide. In which, the indirect analysis using short tandem repeat (STRs) linking with HBB gene to detect different β-globin (HBB) gene mutation is a simple, accurate, economical and also provides additional control of contamination and allele-drop-out ADO.

AIM

This study established microsatellite markers for PGT of Vietnamese β-thalassemia patient.

METHODS

Fifteen (15) STRs gathered from 5 populations were identified by in silico tools within 1 Mb flanking the HBB gene. The multiplex PCR reaction was optimized and performed on 106 DNA samples from at-risk families.

RESULTS

After estimating, PIC values were ≥ 0.7 for all markers, with expected heterozygosity and observed heterozygosity values ranged from 0.81 to 0.92 and 0.53 to 0.86, respectively. One hundred percent of individuals had at least seven heterozygous markers and were found to be heterozygous for at least two markers on either side of the HBB gene.

CONCLUSION

In general, a pentadecaplex marker (all < 1 Mb from the HBB gene) assay was constituted for β-thalassemia PGT on Vietnamese population.

Single-Molecule Sequencing: A New Approach for Preimplantation Testing and Noninvasive Prenatal Diagnosis Confirmation of Fetal Genotype

We investigated the potential of next-generation sequencing (NGS) as an alternative method for preimplantation genetic testing of monogenic disease (PGT-M) with human leukocyte antigen (HLA) matching and for noninvasive prenatal diagnosis follow-up. The case involved parents who were carriers of the Fanconi anemia complementation group G (FANCG) 260delG mutation. After clinical PGT using conventional short tandem repeat and mutation analysis, two euploid disease-free embryos were transferred, resulting in a twin pregnancy. Using the original embryo whole genome amplification products from 10 embryos, NGS confirmed the genotypes of the eight nontransferred embryos for both mutation status and HLA combination. NGS also confirmed that the two transferred embryos, which resulted in a twin pregnancy, were euploid, Fanconi disease free, and HLA matched to their sick sibling. At 15 weeks' gestation, noninvasive prenatal diagnosis of the maternal cell-free DNA determined fetal fractions of 14% and 6.6% for twins 1 and 2, respectively. The maternal plasma FANCG 260delG mutation ratio was measured at 46.2%, consistent with the presence of a carrier fetus and a normal fetus. These findings provide proof of concept that NGS has clinical utility as a safe and effective PGT-M method for embryo genotyping as well as more complex direct HLA matching. In addition, NGS can be used to confirm the original PGT-M and HLA matching embryo results in early pregnancy without the need for invasive prenatal diagnosis.

The first South American case of pre-implantation genetic diagnosis to select compatible embryo for cord blood transplantation as treatment for sickle cell anemia

Sickle cell anemia is an inherited systemic hemoglobinopathy that affects hemoglobin production in red blood cells, leading to early morbidity and mortality. It is caused by a homozygous nucleotide substitution (c.20A>T) in the β-globin gene (HBB) that changes a glutamic acid to a valine in the protein. We present a case report of a fertile couple, both carriers of the sickle cell anemia mutation, with one affected daughter. Six cycles of assisted reproductive techniques were performed, resulting in 53 embryos in cleavage stage. Each embryo was biopsied and analyzed for pre-implantation genetic diagnosis (PGD) by fluorescent polymerase chain reaction, using polymorphic markers of the region of interest followed by capillary electrophoresis in an automated genetic analyzer. HLA Compatible and normal embryos for the mutation represented 3 (5.66%); while the carriers and compatible 6 (11.32%); therefore, embryos matching those of the affected daughter represented 9 (16.98%). A selected embryo in blastocyst stage was transferred, resulting in a healthy male newborn, who had the umbilical cord blood cells collected and stored. The affected daughter was immunosuppressed and received transplanted cells from the umbilical cord blood of her brother; the treatment was successful. Embryo selection using PGD technologies represent the most effective treatment plan for parents who want to have a healthy child, and it could cure another child already affected by inherited hemoglobinopathy.

Preimplantation HLA typing: Practical tool for stem cell transplantation treatment of congenital disorders

It is well known that to achieve an acceptable engraftment and survival in stem cell therapy, an human leukocyte antigens (HLA) identical stem cell transplant is strongly required. However, the availability of the HLA matched donors even among family members is extremely limited, so preimplantation HLA typing provides an attractive practical tool of stem cell therapy for children requiring HLA matched stem cell transplantation. The present experience of preimplantation genetic diagnosis (PGD) for HLA typing of over one thousand cases shows that PGD provides the at-risk couples with the option to establish an unaffected pregnancy, which may benefit the affected member of the family with hemoglobinopathies, immunodeficiencies and other congenital or acquired bone marrow failures. Despite ethical issues involved in preimplantation HLA typing, the data presented below show an extremely high attractiveness of this option for the couples with affected children requiring HLA compatible stem cell transplantation.

Preimplantation HLA Typing for Stem Cell Transplantation Treatment of Hemoglobinopathies

Preimplantation genetic diagnosis (PGD) for HLA typing is steadily becoming an option for at risk couples with thalassemic children, requiring HLA matched bone marrow transplantation treatment. The paper presents the world’s largest PGD experience of 475 cases for over 2 dozens thalassemia mutations, resulting in birth of 132 unaffected children. A total of 146 cases were performed together with preimplantation HLA typing, resulting in detection and transfer of HLA matched unaffected embryos in 83 of them, yielding the birth of 16 HLA matched children, potential donors for their affected siblings. The presented experience of HLA matched stem cell transplantation for thalassemia, following PGD demonstrated a successful hematopoietic reconstitution both for younger and older patients. The data show that PGD is an efficient approach for HLA matched stem cell transplantation treatment for thalassemia.

Successful haematopoietic stem cell transplantation in 44 children from healthy siblings conceived after preimplantation HLA matching

Haematopoietic stem cell transplantation (HSCT) remains the best therapeutic option for many acquired and inherited paediatric haematological disorders. Unfortunately, the probability of finding an HLA matched donor is limited. An alternative technique is PGD combined with HLA matching, which offers the possibility of selecting unaffected embryos that are HLA compatible with the sick child, with the aim of possible use of stem cells from the resulting baby in future. Since the first successful report for Fanconi anaemia a decade ago, the therapeutic success of this technique was reported in a few cases and for a limited number of disorders. Here, we report full recovery of 44 sick children who received HSCT from healthy infants conceived after pre-implantation HLA matching for the following 10 indications; beta-thalassaemia, Wiskott-Aldrich syndrome, Fanconi anaemia, sickle cell anaemia, acute myeloid leukaemia, acute lymphoblastic leukaemia, Glanzmann's thrombasthaenia, Diamond-Blackfan anaemia, X-linked adrenoleukodystrophy and mucopolysaccharidosis type I. No serious complications were observed among recipients and donors. Graft failure occurred in four children with beta-thalassaemia where a second HSCT was planned. Preimplantation HLA matching is a reliable technique and provides a realistic option for couples seeking treatment for an affected child when no HLA-matched donor is available.

Experience of preimplantation genetic diagnosis with HLA matching at the University Hospital Virgen del Rocío in Spain: technical and clinical overview

Preimplantation genetic diagnosis (PGD) of genetic diseases, combined with HLA matching (PGD-HLA), is an option for couples at risk of transmitting a genetic disease to select unaffected embryos of an HLA tissue type compatible with that of an existing affected child. Here we present the results of our PGD-HLA program at the Department of Genetics, Reproduction and Fetal Medicine of the University Hospital Virgen del Rocío in Seville. Seven couples have participated in our program because of different indications. Overall, 26 cycles were performed, providing a total of 202 embryos. A conclusive molecular diagnosis and HLA-typing could be assured in 96% of the embryos. The percentage of transfers per cycle was 26.9% and the birth rate per cycle was 7.7% per transfer. Our PGD-HLA program resulted in the birth of 2 healthy babies, HLA-identical to their affected siblings, with successful subsequent haematopoietic stem cell (HSC) transplantations. Both HSC-transplanted children are currently doing well 48 and 21 months following transplantation, respectively. All the procedures, including HSCs umbilical cord transplantation, were performed in our hospital.

Preimplantation genetic diagnosis for monogenic diseases: overview and emerging issues

Preimplantation genetic diagnosis (PGD) is an established reproductive option for couples at risk of conceiving a pregnancy affected with a known genetic disease, who wish to avoid an (additional) affected child, termination of pregnancy or recurrent miscarriages. Early technologies concentrated on different approaches to direct mutation testing for monogenic diseases using single cell PCR protocols, or sex selection by fluorescent in situ hybridization for X-linked monogenic disease. Development of multiplex fluorescent PCR allowed simultaneously testing of linked markers alongside the mutation test, increasing the accuracy by controlling for contamination and identifying allele drop-out. The advent of highly effective whole genome amplification methods has opened the way for new technologies such as preimplantation genetic haplotyping and microarrays, thus increasing the number of genetic defects that can be detected in preimplantation embryos; the number of cases carried out and the new indications tested increases each year. Different countries have taken very different approaches to legislating and regulating PGD, giving rise to the phenomenon of reproductive tourism. PGD is now being performed for scenarios previously not undertaken using prenatal diagnosis, some of which raise significant ethical concerns. While PGD has benefited many couples aiming to have healthy children, ethical concerns remain over inappropriate use of this technology.

Novel one-step multiplex PCR-based method for HLA typing and preimplantational genetic diagnosis of β-Thalassemia

Preimplantation genetic diagnosis (PGD) of single gene disorders, combined with HLA matching (PGD-HLA), has emerged as a tool for couples at risk of transmitting a genetic disease to select unaffected embryos of an HLA tissue type compatible with that of an existing affected child. Here, we present a novel one-step multiplex PCR to genotype a spectrum of STRs to simultaneously perform HLA typing and PGD for β-thalassemia. This method is being routinely used for PGD-HLA cycles in our department, with a genotyping success rate of 100%. As an example, we present the first successful PGD-HLA typing in Spain, which resulted in the birth of a boy and subsequent successful HSC transplantation to his affected brother, who is doing well 4 years following transplantation. The advantage of our method is that it involves only a round of single PCR for multiple markers amplification (up to 10 markers within the HLA and 6 markers at the β-globin loci). This strategy has allowed us to considerably reduce the optimization of the PCR method for each specific PGD-HLA family as well as the time to obtain molecular results in each cycle.

[Preimplantation diagnosis with HLA typing: birth of the first double hope child in France]

Preimplantation genetic diagnosis (PGD) is authorized in France since 1999. After 10 years, technical results are encouraging. With the development of new technologies, our team is able to diagnosis the large majority of chromosome translocations and 75 monogenic diseases. However, PGD remains limited because of the growing augmentation of demands causing an increasing delay for the first procedure of more than 18 months. Since 2006, 19 couples asked for a PGD with HLA typing. In January 2011, 11 couples have already been included in our PGD program. The birth of the first child after PGD with HLA typing offers new perspectives of treatment for these couples.

ESHRE PGD consortium best practice guidelines for amplification-based PGD

In 2005, the European Society for Human Reproduction and Embryology (ESHRE) PGD Consortium published a set of Guidelines for Best Practice PGD to give information, support and guidance to potential, existing and fledgling PGD programmes. The subsequent years have seen the introduction of a number of new technologies as well as the evolution of current techniques. Additionally, in light of recent advice from ESHRE on how practice guidelines should be written and formulated, the Consortium believed it was timely to revise and update the PGD guidelines. Rather than one document that covers all of PGD, as in the original publication, these guidelines are separated into four new documents that apply to different aspects of a PGD programme, i.e. Organization of a PGD centre, fluorescence in situ hybridization-based testing, Amplification-based testing and Polar Body and Embryo Biopsy for PGD/preimplantation genetic screening. Here, we have updated the sections that pertain to amplification-based PGD. Topics covered in this guideline include inclusion/exclusion criteria for amplification-based PGD testing, preclinical validation of tests, amplification-based testing methods, tubing of cells for analysis, set-up of local IVF centre and Transport PGD centres, quality control/quality assurance and diagnostic confirmation of untransferred embryos.

Singling out genetic disorders and disease

Preimplantation genetic diagnosis (PGD) involves testing of single cells biopsied from oocytes and/or embryos generated in vitro. As only embryos unaffected for a given genetic condition are transferred to the uterus, it avoids prenatal diagnosis and termination of pregnancy. Follow-up data from PGD pregnancies, deliveries and children show an acceptable live birth rate and, so far, no detrimental effects of the procedure have been observed. Of course, the long-term health outcome is currently unknown. PGD was first performed in 1990 and remained an experimental procedure for a number of years. Now, two decades later, it is regarded as an established alternative to prenatal diagnosis: its use has expanded, the range of applications has broadened, and continuous technical progress in single-cell testing has led to high levels of efficiency and accuracy. The current gold standard methods (single-cell multiplex-PCR for monogenic diseases and interphase fluorescence in situ hybridization for chromosomal aberrations) are being replaced by single-cell whole genome amplification and array technology. These generalized methods substantially reduce the pre-PGD workload and allow more automated genome-wide analysis. The implementation of laboratory accreditation schemes brings the field at the same level of routine diagnostics. This article reviews the state of the art and considers indications, accuracy and current technical changes in the field of PGD.

Simplified PGD of common determinants of haemoglobin Bart's hydrops fetalis syndrome using multiplex-microsatellite PCR

The high incidence of double-gene deletions in α-thalassaemia increases the risk of having pregnancies with homozygous α(0)-thalassaemia, the cause of the lethal haemoglobin (Hb) Bart's hydrops fetalis syndrome. Preimplantation genetic diagnosis (PGD) has played an important role in preventing such cases. However, the current gap-PCR based PGD protocol for deletional α-thalassaemia requires specific primer design for each specific deletion. A universal PGD assay applicable to all common deletional determinants of Hb Bart's hydrops fetalis syndrome has been developed. Microsatellite markers 16PTEL05 and 16PTEL06 within the α-globin gene cluster were co-amplified with a third microsatellite marker outside the affected region in a multiplex-PCR reaction and analysed by capillary electrophoresis. Eight informed couples at risk of having Hb Bart's hydrops fetalis were recruited in this study and all patients underwent standard procedures associated with IVF. A total of 47 embryos were analysed. Three pregnancies were achieved from three couples, with the births of two healthy babies and one ongoing pregnancy. This work has successfully adapted an earlier protocol and developed a simple and reliable single-cell assay applicable to PGD of Hb Bart's hydrops fetalis syndrome regardless of type of deletion. Alpha-thalassaemia is one of the most common inheritable disorders worldwide. It is a blood disorder that, in its lethal form caused by deletion of all four copies of the α-globin gene, results in the demise of the affected fetus, a condition referred to as haemoglobin (Hb) Bart's hydrops fetalis syndrome. Preimplantation genetic diagnosis (PGD) has played an important role in preventing such cases. Current PGD protocols for deletional α-thalassaemia utilize a strategy called gap-PCR, which requires the different assays for different deletion types. We have developed a universal PGD assay applicable to all common deletional determinants of Hb Bart's hydrops fetalis syndrome based on microsatellite marker analysis. Eight informed couples at risk of having Hb Bart's hydrops fetalis were recruited in this study and all patients underwent standard procedures associated with IVF. Forty-five embryos were analysed in total. Three pregnancies were achieved from three couples, with the births of two healthy babies and one pregnancy still ongoing. We have successfully adapted our earlier protocol and developed a simple and reliable single cell assay applicable to PGD of Hb Bart's hydrops fetalis syndrome regardless of the type of deletion.

Preimplantation genetic diagnosis for haematologic conditions

PURPOSE OF REVIEW

This review will inform the clinician about the application, success rates and limitations of preimplantation genetic diagnosis (PGD) for haematologic disease to enable clinicians to offer couples with reproductive risk a realistic view of possible treatments. The molecular techniques used to diagnose disease mutations are described, including the newest technologies using whole genome amplification (WGA) and preimplantation genetic haplotyping (PGH) of embryos. The history and ethics involved in performing PGD together with human leukocyte antigen (HLA) testing (PGD-H) to create matched siblings suitable for haematopoietic stem cell transplant (HSCT) are discussed.

RECENT FINDINGS

The greatest diagnostic hurdle in PGD is the paucity of molecular material in the single embryonic cell. WGA allows amplification of the entire genome, which greatly simplifies mutation analysis and increases the possibilities of multiple simultaneous genetic diagnoses. PGH can be applied to the amplified material, and may enable the application of PGD to the less common haematological mutations, and the diagnosis of nonaffected male progeny in cases of X-linked haematologic diseases.

SUMMARY

PGD to exclude embryos carrying serious haematologic disease is a viable alternative to prenatal diagnosis for couples who wish to avoid having affected children and for whom therapeutic termination of affected pregnancies is unacceptable. PGD is not available for all haematologic mutations, is expensive, time consuming and does not guarantee a pregnancy. PGD-H is more diagnostically and ethically challenging, especially when there is the time constraint of urgent provision of HLA-matched stem cells for a sick sibling. To date there is only a handful of reported cases of successful HSCT from siblings created by embryo selection. The evolving technology of PGH following WGA may increase the diagnostic scope and availability of PGD in the future, but certain limitations will remain.

Advances in the prevention and treatment are changing thalassemia from a fatal to a chronic disease. experience from a Cyprus model and its use as a paradigm for future applications

Thalassemia is endemic in Cyprus with a frequency of 1 in 6 persons being a heterozygote and about 1 in 1,000 a homozygous thalassemia major patient. Cyprus has been a pioneer nation in reducing and almost eliminating the number of births of thalassemia major patients by introducing prenatal and antenatal diagnosis. The risks associated with bone marrow transplantation (BMT) make transfusion and chelation therapy the major form of treatment for the vast majority of thalassemia patients. Improved transfusion techniques, diagnostic methods, iron chelation and supportive therapy have increased the quality of life and survival of patients, some of whom are exceeding 50 years of age. The introduction of effective chelation therapy protocols using primarily deferiprone (L1) in combination with deferoxamine (DFO) resulted in the reduction of iron overload induced cardiac failures, which is the main cause of death in thalassemia major. Despite their chronic condition and tedious clinical management many patients are successful professionals, married and have children. The advancement in treatment is transforming thalassemia from a fatal to a chronic condition and some families are opting for giving birth to a thalassemic child rather than abortion.

PGD for monogenic disorders: aspects of molecular biology

Preimplantation genetic diagnosis (PGD) for monogenic diseases has known a considerable evolution since its first application in the early 1990s. Especially the technical aspects of the genetic diagnosis itself, the single-cell genetic analysis, has constantly evolved to reach levels of accuracy and efficiency nearing those of genetic diagnosis on regular DNA samples. In this review, we will focus on the molecular biological techniques that are currently in use in the most advanced centers for PGD for monogenic disorders, including multiplex polymerase chain reaction (PCR) and post-PCR diagnostic methods, whole genome amplification (WGA) and multiple displacement amplification (MDA). As it becomes more and more clear that when it comes to ethically difficult indications, PGD goes further than prenatal diagnosis (PND), we will also briefly discuss ethical issues.

PGD of beta-thalassaemia and HLA haplotypes using OmniPlex whole genome amplification

A strategy was developed using the OmniPlex technology of whole genome amplification for preimplantation genetic diagnosis (PGD) of single gene diseases and human leukocyte antigen (HLA) haplotypes. The amplified genomic DNA library was subsequently examined separately for mutation analysis with mini-sequence and for short tandem repeat (STR) markers within the HLA loci. To evaluate the reliability of the protocol prior to PGD, tests of 50 single lymphocytes revealed an amplification efficiency of 92-96% and allele drop-out (ADO) rate of 6-16%. The strategy was validated in one beta-thalassaemia family having an affected boy. The couple underwent three cycles of ovarian stimulation and intracytoplasmic sperm injection for PGD. On 16 embryos tested, the amplification efficiency was 88-94% and ADO was 6-19%. Two cycles of embryo transfer were performed, and one pregnancy was achieved. The genotypes of the fetus were shown to be unaffected and HLA-identical, in agreement with PGD, by chorionic villus sampling. The cord blood stem cells from the newborn can be used to treat the affected sibling. This study demonstrates the first successful application of OmniPlex whole genome amplification in PGD of a single gene disorder for selecting unaffected and HLA-compatible embryos.

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.

Statistical analysis of six STR loci located in MHC region in Iranian population for preimplantation genetic diagnosis

We studied allele frequency and other statistical parameters of six short-tandem repeat (STR) loci: D6S265, D6S439, D6S105, D6S82-1, MICA, and MOGd, which are located in major histocompatibility complex (MHC) region (6p21.3) in 101 Iranian individuals. STR polymorphisms were analysed by PCR and polyacrylamide gel electrophoresis and subsequent comparison with standard (allelic) ladders. Exact tests of Hardy-Weinberg equilibrium were performed for the six loci. All loci, except the MOGd (P = 0.4291), were in Hardy-Weinberg equilibrium. These data may be useful in PGD-HLA matching and forensic science.

PGD-derived human embryonic stem cell lines as a powerful tool for the study of human genetic disorders

Human embryonic stem (ES) cells are derived from the inner cell mass (ICM) of blastocyst embryos. They are established from spare embryos that have been obtained by in vitro fertilization (IVF) and donated for research purposes. The ICM-derived cell lines have two unique properties, they can be propagated indefinitely in culture and have the potential to develop into practically any cell type in vitro and in vivo. Human embryonic stem (hES) cells carrying specific mutations can be used as a valuable tool for studying genetic disorders in human. One favorable approach to obtain such mutant ES cell lines is their derivation from affected preimplantation genetic diagnosed (PGD) embryos. This review focuses on the importance of deriving human ES cell lines from genetically abnormal embryos, especially in cases where no good cellular and/or animal models exist.

The future (r)evolution of preimplantation genetic diagnosis/human leukocyte antigen testing: ethical reflections

There has been increasing support for combining preimplantation genetic diagnosis (PGD) for specific diseases with a test for human leukocyte antigens (HLA) because the generation of HLA-matched umbilical cord blood cells may save the life of a diseased sibling. To date, this procedure has taken place in the context of conceiving another child--PGD/HLA testing type 1. However, it may well become possible to perform PGD/HLA testing outside this context, that is, to select matched embryos from which embryonic stem cells could be derived and used in cell therapy--PGD/HLA testing type 2. A proactive ethical analysis is needed and is presented in this article. Although PGD/HLA testing type 1 can be morally justified, the risks, pitfalls, and practical limitations of this procedure make it necessary to develop alternative strategies. PGD/HLA testing type 2 may provide an alternative strategy. From an ethical point of view, the controversial issue is that this procedure creates embryos purely for instrumental use. However, given the dominant view that the preimplantation embryo has only limited moral value, this alternative may be as morally justified as PGD/HLA testing type 1.

Preimplantation diagnosis for immunodeficiencies

Preimplantation genetic diagnosis (PGD) has become an established procedure for the detection of single gene disorders, and has recently been performed together with human leukocyte antigen (HLA) typing for couples with children affected by genetic disorders that require HLA-identical stem cell transplantation therapy. For these couples, PGD can ensure the birth of an unaffected child, and because HLA-matched stem cell transplantation improves or completely restores the immune system, this child may also serve as a potential stem cell donor for affected siblings. This paper presents the first cumulative experience (18 cycles) of PGD for detection of the following immunodeficiencies: Wiscott-Aldrich syndrome, X-linked hyper-IgM syndrome (HIGM), X-linked hypohidrotic ectodermal dysplasia with immune deficiency (HED-ID), ataxia telangiectasia and Omenn syndrome, resulting in the transfer of unaffected embryos in 13 cycles and the birth of seven unaffected children, with one healthy pregnancy ongoing. HLA-identical stem cells from some of these children have been used for transplantation therapy, resulting in the restoration of normal function in siblings with HIGM and HED-ID.

IVF, IVM, natural cycle IVF, minimal stimulation IVF – time for a rethink

Considerable changes are afoot in the practice of assisted human conception. Doubts about its methods, especially over endocrinology, concern its complexity and its expense. IVF has spread worldwide since its beginnings in the UK, but its current practice, termed routine IVF, is being challenged by simpler routines. These include natural cycle IVF, which has been in the background for many years, minimal stimulation IVF, where doses of hormones are reduced, and the in-vitro maturation of human oocytes ready for fertilization in vitro (IVM). These three approaches are now practised in increasing numbers of IVF clinics, and may well replace routine IVF. The events leading to current interest in these methods will be discussed briefly in this review.

Preimplantation HLA typing with aneuploidy testing

Preimplantation HLA typing has been introduced for the treatment of affected siblings, requiring HLA-identical stem cell transplantation. This was applied either in combination with preimplantation genetic diagnosis (PGD) to ensure that the preselected HLA-matched embryos were also free of the genetic disorder, or without PGD, with the only purpose of selecting and transferring the HLA-matched embryos. Because patients requesting preimplantation HLA typing are usually of advanced reproductive age, aneuploidy testing allows not only the avoidance of the birth of children with chromosomal disorders, but also improvement of the reproductive outcome, which is still not sufficiently high in preimplantation HLA typing at the present time. This study presents the results of the first experience of preimplantation HLA typing combined with aneuploidy testing, demonstrating feasibility and impact of aneuploidy testing on the accuracy and outcome of preimplantation HLA typing. Of a total of 138 cycles performed, 87 were combined with PGD and 52 without testing for the causative gene, of which aneuploidy testing was performed in 27 cycles, allowing the preselection and transfer of only those HLA-matched embryos that were also euploid. Although the euploid HLA-identical embryos were available for transfer in only half of these cycles, pregnancy and birth of unaffected HLA-identical children were observed in approximately half of these cycles, suggesting the potential usefulness of incorporating aneuploidy testing into preimplantation HLA typing.

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 genetics: Improving access to stem cell therapy

There has been progress in the application of stem cell transplantation for treatment of an increasing number of severe congenital and acquired bone marrow disorders, currently restricted by the availability of human leukocyte antigen (HLA)-matched related donors. Preimplantation HLA typing has recently been introduced to improve the access to stem cell therapy for inherited bone marrow failures. Preimplantation genetic diagnosis (PGD) provides an option not only for avoiding an affected pregnancy with thalassemia and other inherited disorders but also for preselection of the HLA-compatible donors for affected siblings. Multiple short tandem repeat markers throughout the HLA region are applied for this purpose, allowing 100% accuracy of HLA typing, through picking up possible recombination in the HLA region, as well as the copy number of chromosome 6, which affect accuracy of preimplantation HLA typing. Present experience of preimplantation HLA typing includes preimplantation HLA typing in 180 cycles, 122 of which were done as part of PGD for Fanconi anemia, thalassemia, Wiscott-Aldrich syndrome, hyper-immunoglobulin M syndrome, hypohidrotic ectodermal dysplasia with immune deficiency, and X-linked adrenoleukodystrophy, and 58 for the sole purpose of HLA typing for leukemias and for aplastic and Diamond-Blackfan anemia. The applied method resulted in the accurate preselection and transfer of 100% HLA-matched embryos, yielding already three dozen clinical pregnancies and the birth of two dozen HLA-matched children to the siblings requiring stem cell transplantation. Successful therapy with HLA-matched stem cells, obtained from these PGD children, has been achieved already for Diamond-Blackfan anemia hypohidrotic ectodermal dysplasia with immune deficiency and thalassemia.

Cryopreservation of biopsied embryos at the blastocyst stage

BACKGROUND

The availability of an efficient cryopreservation program is especially important in the case of embryos that have undergone blastomere biopsy for PGD. Unfortunately, the freezing/thawing of biopsied embryos has given disappointing results when performed at the cleavage stage. In this study, embryos diagnosed as normal after PGD were grown to the blastocyst stage, frozen and thawed for successive frozen embryo transfer.

METHODS

A total of 34 patients performed a thawing cycle in which 47 blastocysts were thawed. The cryopreservation solutions were based on HEPES-buffered medium supplemented with human serum albumin (HSA), sucrose and 1,2-propanediol. The same protocol was applied to embryos from 88 IVF/ICSI patients, which underwent 92 thawing cycles with 150 thawed blastocysts.

RESULTS

The survival rate was similar in the two groups (53% after PGD and 58% in IVF/ICSI cycles), as well as the cumulative pregnancy rate per patient (59% after PGD versus 47% in IVF/ICSI cycles), despite a higher maternal age and a lower proportion of embryos available for transfer or cryopreservation in the PGD group.

CONCLUSIONS

Neither the survival rate nor the subsequent development and chances of implantation, differed between embryos frozen at the blastocyst stage following biopsy and those frozen intact.