Preimplantation diagnosis of thalassemias

Development of preimplantation genetic testing for monogenic reference materials using next-generation sequencing

OBJECTIVE

Preimplantation genetic testing for monogenic disorders (PGT-M) has been used for over 20 years to detect many serious genetic conditions. However, there is still a lack of reference materials (RMs) to validate the test performance during the development and quality control of PGT-M.

METHOD

Sixteen thalassemia cell lines from four thalassemia families were selected to establish the RMs. Each family consisted of parents with heterozygous mutations for α- and/or β-thalassemia and two children, at least one of whom carried a homozygous thalassemia mutation (proband). The RM panel consisted of 12 DNA samples (parents and probands in 4 families) and 4 simulated embryos (cell lines constructed from blood samples from the four nonproband children). Four accredited genetics laboratories that offer verification of thalassemia samples were invited to evaluate the performance of the RM panel. Furthermore, the stability of the RMs was determined by testing after freeze‒thaw cycles and long-term storage.

RESULTS

PGT-M reference materials containing 12 genome DNA (gDNA) reference materials and 4 simulated embryo reference materials for thalassemia testing were successfully established. Next-generation sequencing was performed on the samples. The genotypes and haplotypes of all 16 PGT-M reference materials were concordant across the four labs, which used various testing workflows. These well-characterized PGT-M reference materials retained their stability even after 3 years of storage.

CONCLUSION

The establishment of PGT-M reference materials for thalassemia will help with the standardization and accuracy of PGT-M in clinical use.

The successful strategy of comprehensive pre-implantation genetic testing for beta-thalassaemia-haemoglobin E disease and chromosome balance using karyomapping

Thalassaemia is the commonest monogenic disease and causes a health and economic burden worldwide. Karyomapping can be used for pre-implantation genetic testing of monogenic disorders (PGT-M). This study applied karyomapping in two PGT-M cycles and made a comparison to polymerase chain reaction (PCR). Two families at risk of having beta-thalassaemia-haemoglobin E disease offspring decided to join the project and informed consent was obtained. Karyomapping results of family A (beta-thalassaemia (c.41_42delTCTT)-Hb E (c.26G>A) disease) revealed four normal, two beta-thalassaemia traits, one Hb E trait and six affected. Three embryos exhibited unbalanced chromosomes. One normal male embryo was transferred. Karyomapping results of family B (beta-thalassaemia (c.17A>T)-Hb E (c.26G>A) disease) revealed six Hb E traits and three affected. Three embryos were chromosomally unbalanced. One Hb E trait embryo was transferred. Two successful karyomapping PGT-M were performed, including deletion and single-base mutations. Karyomapping provides accuracy as regards the protocol and copy number variation which is common in pre-implantation embryos. Impact StatementWhat is already known on this subject? Thalassaemia syndrome is the commonest monogenic disease and causes a health and economic burden worldwide. Modern haplotyping using SNP array (aSNP) and karyomapping algorithms can be used for pre-implantation genetic testing of monogenic disorders (PGT-M). However, few clinical karyomapping PGT-M cycles have been done and validated so far.What do the results of this study add? Two successful clinical PGT-M cycles for beta-thalassaemia (c.41_42delTCTT and c.17A>T mutations)-haemoglobin E (c.26G>A) disease were performed using karyomapping. The outcome was two healthy babies. Multiplex fluorescent polymerase chain reaction (PCR) with mini-sequencing was also used for confirmation mutation analysis results. PCR confirmed haplotyping results in all embryos. Six embryos from both PGT-M cycles exhibited unbalanced chromosomes evidenced by aSNP.What are the implications of these findings for clinical practice and/or further research? Karyomapping provides accurate information quickly and the outcomes of the study will save time as regards protocol development, provide a usable universal PGT-M protocol and add additional copy number variation (CNV) information, chromosome number variation being a common issue in pre-implantation embryos.

Hemoglobinopathies and preimplantation diagnostics

Hemoglobinopathies constitute some of the most common inherited disorders worldwide. Manifestations are very severe, patient management is difficult and treatment is not easily accessible. Preimplantation genetic testing for monogenic disorders (PGT-M) is a valuable reproductive option for hemoglobinopathy carrier-couples as it precludes the initiation of an affected pregnancy. PGT-M is performed on embryos generated by assisted reproductive technologies and only those found to be free of the monogenic disorder are transferred to the uterus. PGT-M has been applied for 30 years now and β-thalassemia is one of the most common indications. PGT may also be applied for human leukocyte antigen typing to identify embryos that are unaffected and also compatible with an affected sibling in need of hemopoietic stem cell transplantation. PGT-M protocols have evolved from PCR amplification-based, where a small number of loci were analysed, to whole genome amplification-based, the latter increasing diagnostic accuracy, enabling the development of more generic strategies and facilitating multiple diagnoses in one embryo. Currently, numerous PGT-M cycles are performed for the simultaneous diagnosis of hemoglobinopathies and screening for chromosomal abnormalities in the embryo in an attempt to further improve success rates and increase deliveries of unaffected babies.

Professionally responsible management of the ethical and social challenges of antenatal screening and diagnosis of β-thalassemia in a high-risk population

Thalassemias are among the most frequent genetic disorders worldwide. They are an important social and economic strain in high-risk populations. The benefit of β-thalassemia screening programs is growing evident but the capacity to diagnose fetal β-thalassemia exceeds the treatment possibilities and even when treatment before birth becomes feasible, difficult decisions about the relative risks will remain. This paper can be of practical and ethically justified aid when counseling women about screening, diagnosis, and treatment of β-thalassemia. It takes in consideration various social challenges, medical issues such as antenatal screening, preimplantation genetic diagnosis, prenatal diagnosis, non-invasive prenatal testing and prenatal therapy. We also describe the Sardinian experience in applying and promoting high-risk population screening and diagnosis programs and future trends in the management of β-thalassemia.

Successful four-factor preimplantation genetic testing: α- and β-thalassemia, human leukocyte antigen typing, and aneuploidy screening

Our study established an effective next-generation sequencing (NGS) protocol for four-factor preimplantation genetic testing (PGT) using  α- and β-thalassemia, human leukocyte antigen (HLA) typing, and aneuploidy screening. Three couples, in whom both partners were α- and β-double thalassemia carriers, underwent PGT between 2016 and 2018. These individuals sought an opportunity for hematopoietic stem cell transplantation to save their children from β-thalassemia major. A total of 35 biopsied trophectoderm samples underwent multiple displacement amplification (MDA). PGT for α- and β-thalassemia and HLA typing were performed on MDA products using NGS-based single-nucleotide polymorphism (SNP) haplotyping. Although two samples failed MDA, 94.3% (33/35) of samples were successfully amplified, achieving conclusive PGT results. Furthermore, 51.5% (17/33) of the embryos were diagnosed as unaffected non-carriers or carriers. Of the 17 unaffected embryos, nine (52.9%) were tested further  and identified as euploid via NGS-based aneuploid screening, in which five had HLA types matching affected children. One family did not achieve any unaffected euploid embryos. The two other families transferred HLA-matched and unaffected euploid embryos, resulting in two healthy 'savior babies.' NGS-PGT results were confirmed in prenatal diagnosis. Therefore, NGS-SNP was effective in performing PGT for multipurpose detection within a single PGT cycle.

Clinical utility of combined preimplantation genetic testing methods in couples at risk of passing on beta thalassemia/hemoglobin E disease: A retrospective review from a single center

Thalassemia and hemoglobinopathy is a group of hereditary blood disorder with diverse clinical manifestation inherited by autosomal recessive manner. The Beta thalassemia/Hemoglobin E disease (HbE/βthal) causes a variable degree of hemolysis and the most severe form of HbE/βthal disease develop a lifelong transfusion-dependent anemia. Preimplantation genetic testing (PGT) is an established procedure of embryo genetic analysis to avoid the risk of passing on this particular condition from the carrier parents to their offspring. Preimplantation genetic testing for chromosomal aneuploidy (PGT-A) also facilitates the selection of embryos without chromosomal aberration resulting in the successful embryo implantation rate. Herein, we study the clinical outcome of using combined PGT-M and PGT-A in couples at risk of passing on HbE/βthal disease. The study was performed from January 2016 to December 2017. PGT-M was developed using short tandem repeat linkage analysis around the beta globin gene cluster and direct mutation testing using primer extension-based mini-sequencing. Thereafter, we recruited 15 couples at risk of passing on HbE/βthal disease who underwent a combined total of 22 IVF cycles. PGT was performed in 106 embryos with a 3.89% allele drop-out rate. Using combined PGT-M and PGT-A methods, 80% of women obtained satisfactory genetic testing results and were able to undergo embryo transfer within the first two cycles. The successful implantation rate was 64.29%. PGT accuracy was evaluated by prenatal and postnatal genetic confirmation and 100% had a genetic status consistent with PGT results. The overall clinical outcome of successful live birth for couples at risk of producing offspring with HbE/βthal was 53.33%. Conclusively, combined PGT-M and PGT-A is a useful technology to prevent HbE/βthal disease in the offspring of recessive carriers.

From Prenatal to Preimplantation Genetic Diagnosis of β-Thalassemia. Prevention Model in 8748 Cases: 40 Years of Single Center Experience

The incidence of β-thalassemia in Sardinia is high and β-39 is the most common mutation. The prevention campaign started in 1977 and was performed in a single center (Microcitemico Hospital, Cagliari, Sardinia, Italy). It was based on educational programs, population screening by hematological and molecular identification of the carriers. Prenatal and pre-implantation diagnosis was offered to couples at risk. 8564 fetal diagnosis procedures using different invasive approaches and analysis techniques were performed in the last 40 years. Trans-abdominal chorionic villous sampling was preferred due to lower complication risks and early diagnosis. Chorionic villous DNA was analyzed by PCR technique. 2138 fetuses affected by β-thalassemia were diagnosed. Women opted for termination of the pregnancy (TOP) in 98.2% of these cases. Pre-implantation genetic diagnosis (PGD) was proposed to couples at risk to avoid TOP. A total of 184 PGD were performed. Initially, the procedure was exclusively offered to infertile couples, according to the law in force. The success rate of pregnancies increased from 11.1% to 30.8% when, crucial law changes were enacted, and PGD was offered to fertile women as well. Forty years of β-thalassemia prevention programs in Sardinia have demonstrated the important decrease of this severe genetic disorder.

Factors associated with continuing emergence of β-thalassemia major despite prenatal testing: a cross-sectional survey

Purpose

Health care initiatives focusing on prenatal testing and premarital genetic screening aiming to reduce the incidence of β-thalassemia have emerged during the last decade. In Palestine, 4% of the population are known thalassemia carriers with new cases continuing to appear despite the availability of prenatal testing. This study aims to identify factors that influence the decision to retain or abort fetuses affected by β-thalassemia in Palestine.

Methods

Convenience sampling was used to select 32 women (72 fetuses) who were at risk of having a baby with β-thalassemia. A questionnaire on prenatal testing, test results, pregnancy outcomes, and factors influencing the decision to terminate the pregnancy were used for this cross-sectional study. The data were analyzed using SPSS version 17.

Results

Among the fetuses screened, 36 (50%) were thalassemia carriers and 20 (28%) had β-thalassemia; 17 (85%) affected fetuses were aborted. Religious beliefs were the most cited reason for opposing abortion while prior experience with β-thalassemia patients and awareness programs promoted abortions. Mothers who opted to retain an affected fetus had modest educational attainment. Higher educational level was significantly associated with the decision to abort an affected fetus (p<0.05).

Conclusion

A religious consensus is needed on the abortion of fetuses affected by β-thalassemia. Improving female education and increasing awareness on thalassemia could help reduce the incidence of β-thalassemia in Palestine and around the world.

Non-invasive pre-implantation aneuploidy screening and diagnosis of beta thalassemia IVSII654 mutation using spent embryo culture medium

BACKGROUND

Cell-free nuclear DNA has been isolated from spent embryo culture medium. Whether this small amount of DNA can be amplified at the whole genome level and the concordance rate of karyotypes and specific alleles between biopsied cells and media has not been evaluated.

METHODS

Seven couples were recruited, 88 donated embryos and their corresponding media were collected for whole genome amplification (WGA). The efficiency of WGA, the concordance of chromosome status, and the HBB gene IVSII654 allele between biopsied cells and media were investigated.

RESULTS

After WGA, the DNA detection rate was 90.90% with a mean concentration of 26.15 ng/μl. The full chromosome concordance rate between biopsied cells and medium was 64.52%, and it increased to 90.00% for diploid blastocyst samples. Analysis of the mutated IVSII654 locus and SNP linkage verified that the DNA present in the medium originated from embryonic cells.

CONCLUSION

We confirmed that nuclear DNA is present in spent culture medium and that the majority of this DNA can be amplified for subsequent analysis. Our results showed that non-invasive embryo genetic testing at the chromosomal-level using medium can concordant to the biopsied cells, but it needs further optimized before use in clinical applications. KEY MESSAGES The aggressive biopsy step during PGD/PGS procedure would have a negative effect on the future development of the embryo. Cell-free nuclear DNA has been observed in spent embryo culture medium, which holds promise for the development of non-invasive PGD/PGS approaches. The presence of DNA in medium, its efficiency for WGA, and the concordance between chromosome status and the HBB gene IVSII654 allele as diagnosed from biopsied cells or medium were investigated. Non-invasive embryo genetic testing at the chromosomal-level and allele site using medium can concordant to the biopsied cells, but it needs further optimized before use in clinical applications.

Pre-implantation genetic diagnosis and screening: now and the future

Since 1989, the year of the first pre-implantation genetic diagnosis (PGD), many developments occurred both in assisted reproduction techniques and in molecular tools. While PGD is a well-established and documented application, pre-implantation genetic screening (PGS) for the detection of aneuploid embryos is still debated due to the presence of mosaicism in the embryo, but especially to the knowledge of the limits that label an embryo as healthy or as appropriate to the life. The aim of this review is to present the state-of-the-art in the field of PGD and PGS, illustrating its benefits and limitations, along with biopsy techniques and the use of new high-throughput technologies.

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 pregnancy outcome after in vitro fertilisation following Pre-implantation Genetic Diagnosis/Polymerase Chain Reaction screening for single gene disorder (sickle cell anaemia) before embryo transfer: The clinical experience of an in vitro fertilisation clinic in Nigeria

A couple, both carriers of the sickle cell anaemia trait (Genotype HbAS) with an offspring already affected with the genetic disease underwent a Pre-implantation Genetic Diagnosis/Polymerase Chain Reaction screening of biopsied blastomeres. DNA analysis of single blastomeres was carried out to find out indicated a viable intra-uterine pregnancy with embryos which carried the sickle cell mutation, which resulted in a livebirth (HbAS). PGD/PCR in combination with IVF appears to be the most suitable treatment plan for patients who are at a higher risk of reproducing offspring affected with inheritable genetic diseases.

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

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

Regional consensus opinion for the management of Beta thalassemia major in the Arabian Gulf area

Thalassemia syndrome has diverse clinical presentations and a global spread that has far exceeded the classical Mediterranean basin where the mutations arose. The mutations that give rise to either alpha or beta thalassemia are numerous, resulting in a wide spectrum of clinical severity ranging from carrier state to life-threatening, inherited hemolytic anemia that requires regular blood transfusion. Beta thalassemia major constitutes a remarkable challenge to health care providers. The complications arising due to the anemia, transfusional iron overload, as well as other therapy-related complications add to the complexity of this condition. To produce this consensus opinion manuscript, a PubMed search was performed to gather evidence-based original articles, review articles, as well as published work reflecting the experience of physicians and scientists in the Arabian Gulf region in an effort to standardize the management protocol.

Single-cell polymerase chain reaction-based pre-implantation genetic diagnosis using fragment analysis for β-thalassemia in an Indian couple with β-globin gene mutations

Despite advances in diagnostic techniques, approximately 10,000 babies with β-thalassemia major are born annually in India. Pre-implantation genetic diagnosis (PGD), an alternative to prenatal diagnosis, helps in negative selection of affected embryos prior to implantation. Hereby, we report the first successful β-thalassemia PGD pregnancy in an Indian carrier couple. β-Thalassemia mutation analysis by Amplification-Refractory Mutation Sequence (ARMS)-polymerase chain reaction (PCR) in the parents, followed by PGD for β-thalassemia mutation in embryos in two consequent in vitro fertilization (IVF) cycles, with transfer for three β-thalassemia minor embryos, resulted in singleton successful pregnancy, the results of which were confirmed on prenatal diagnosis. With advances in assisted reproductive techniques and molecular diagnosis, PGD for monogenic diseases is feasible in high-risk couples. The methodology in the current study included two rounds of PCR using fluorescently labeled primers, fragment analysis using the ABI 3100 nucleotide sequencer and the GeneMapper software, purification, and concentration of PCR product, which enabled distinct clear peaks making the analysis and interpretation non-ambiguous.

The prevention of thalassemia

The thalassemias are among the most common inherited diseases worldwide, affecting individuals originating from the Mediterranean area, Middle East, Transcaucasia, Central Asia, Indian subcontinent, and Southeast Asia. As the diseases require long-term care, prevention of the homozygous state constitutes a major armament in the management. This article discusses the major prevention programs that are set up in many countries in Europe, Asia, and Australia, often drawing from the experience in Sardinia. These comprehensive programs involve carrier detections, molecular diagnostics, genetic counseling, and prenatal diagnosis. Variability of clinical severity can be attributable to interactions with α-thalassemia and mutations that increase fetal productions. Special methods that are currently quite expensive and not widely applicable are preimplantation and preconception diagnosis. The recent successful studies of fetal DNA in maternal plasma may allow future prenatal diagnosis that is noninvasive for the fetus.

Genotyping of β-globin gene mutations in single lymphocytes: a preliminary study for preimplantation genetic diagnosis of monogenic disorders

Hemoglobinopathies, especially β-thalassemia (β-thal), represent an important health burden in Mediterranean countries like Turkey. Some couples prefer the option of preimplantation genetic diagnosis (PGD). However, clinical application of PGD, especially for the monogenic disorders is technically demanding. To ensure reliable results, protocols need to be robust and well standardized. Ideally PGD-PCR (polymerase chain reaction) protocols should be based on multiplex and fluorescent PCR for analysis of the disease-causing mutation(s) along with linked markers across the disease-associated locus. In this study, we aimed to constitute a protocol in single cells involving first round multiplex PCR with primers to amplify the region of the β-globin gene containing the most common mutations. Two microsatellites linked to the β-globin gene cluster (D11S4891, D11S2362) and two unlinked (D13S314, GABRB3) microsatellite markers, were used to rule out allele dropout (ADO) and contamination; followed by nested real-time PCR for genotyping the β-globin mutations. We also investigated the allele frequencies and heterozygote rates of these microsatellites in the Turkish population that have not been reported to date. This protocol was tested in 100 single lymphocytes from heterozygotes with known β-globin mutations. Amplification failure was detected in one lymphocyte (1%) and ADO was observed in two lymphocytes (2%). No contamination was detected. All results were concordant with the genotypes of the patients. Overall, this protocol was demonstrated to be sensitive, accurate, reliable and rapid for the detection of β-globin mutations in single cells and shows potential for the clinical application of PGD for hemoglobinopathies in the Turkish population.

Preimplantation genetic diagnosis for α-and β-double thalassemia

PURPOSE

To evaluate the use of multiple displacement amplification (MDA) for preimplantation genetic diagnosis (PGD) of α- and β-double thalassemia.

METHOD

Whole genome of a single cell was directly amplified using MDA and its products were used as templates in fluorescent gap polymerase chain reaction (PCR) analysis of α-thalassemia and in PCR-reverse dot blot analysis, singleplex fluorescent PCR of β-28 and CD17 mutation and HumTH01 for β-thalassemia.

RESULTS

1) MDA from single cell could produce enough DNA templates for the detection of both α and β-thalassemia; 2) The established MDA-PGD protocol for α- and β-double thalassemia was successfully applied in PGD of six embryos, among which, three were transferred, but no pregnancy ensued.

CONCLUSIONS

The use of MDA as a universal step allows for the simultaneous diagnosis of two or more hereditary defects.

Prenatal, noninvasive and preimplantation genetic diagnosis of inherited disorders: hemoglobinopathies

Disorders of hemoglobin synthesis have been used as a prototype for the development of most approaches for prenatal diagnosis (PND). PND for hemoglobinopathies based on molecular analysis of trophoblast or amniocyte DNA has accumulated approximately 30 years of experience. Disadvantages with conventional PND include 'invasive' fetal sampling and the need to terminate affected ongoing pregnancies. New developments are directed towards improving both the timing and/or safety of procedures. Preimplantation genetic diagnosis, an established procedure with 20 years of clinical application, avoids the need to terminate affected pregnancies through the identification and selective transfer of unaffected in vitro fertilization embryos. Approaches towards 'noninvasive' PND, through analyzing fetal cells or free fetal DNA present in the circulation of pregnant women, are a focus of ongoing research. Overall, PND, preimplantation genetic diagnosis (and potentially 'noninvasive' PND) represent valuable reproductive options for couples at risk of having a child affected with a severe inherited disease.

In vitro fertilization (IVF): a review of 3 decades of clinical innovation and technological advancement

In vitro fertilization, popularly referred to as IVF, has captured the attention of the public since its sensational introduction in 1978. Today assisted reproductive technology is available throughout most of the civilized world, and the practice is largely different from that used during the early days. Refinements in laboratory technology and clinical practice have allowed IVF to evolve into a medical procedure that is efficient, safe, readily accessible, and relatively affordable. More than 2 million IVF children have been born to date, and it is likely that continued enhancements will widen its appeal and applicability.

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

Couples at risk for having an affected child with homozygous thalassemia or other serious hemoglobin disorder have various options for prevention. The most used in some countries has been prenatal diagnosis with a choice of termination of pregnancy. A more recent addition is preimplantation genetic diagnosis (PGD). In this article, this method is described and reviewed.

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.

First Successful Preimplantation Genetic Diagnosis in Singapore – Avoidance of -Thalassaemia Major

Introduction: We report on the first successful preimplantation genetic diagnosis (PGD) in Singapore. Clinical Picture: A couple who are -thalassaemia carriers and have an affected daughter requested for PGD. Treatment: Two cycles of PGD were performed on the couple. -thalassaemia mutations were detected using a nested PCR and minisequencing strategy, and unaffected embryos were selected for transfer. Outcome: A singleton pregnancy was achieved in the second PGD cycle, resulting in the birth of a healthy baby boy with carrier genotype. Conclusions: This case report documents the first successful PGD in Singapore, involving a couple at-risk of transmitting -thalassaemia major. Key words: Beta-thalassaemia, Multiplex minisequencing, Polymerase chain reaction, Preimplantation genetic diagnosis

Preliminary Data on Preimplantation Genetic Diagnosis for Hemoglobinopathies in Turkey

Hemoglobinopathies are the most common genetic diseases in Turkey. Sickle cell anemia is prevalent in the Cukurova region but beta-thalassemia (thal) is seen all over the country. The incidence of sickle cell trait is 10% and beta-thal trait is 3.7% in this region. The families at risk for hemoglobinopathies have come to our center for prenatal diagnosis since 1992. In 15 years, 1,593 fetuses were examined. Four hundred and ten fetuses were found to be homozygous or compound heterozygous for sickle cell anemia and beta-thal. Some mothers had affected fetuses several times. Preimplantation genetic diagnosis (PGD) is an option to avoid the termination of a pregnancy. Studies for PGD of sickle cell anemia were done at Cukurova University Hospital, Cukurova, Adana, Turkey.

Successful preimplantation genetic diagnosis for alpha- and beta-thalassemia in China

METHODS & RESULTS

In southern China, the average carrier rates of alpha-thalassemia and beta-thalassemia in the population are as high as 10.3% and 2.8%, respectively. Because of the high rates, they are known as 'social diseases' in some regions. In this study, the fluorescent gap PCR, which can detect the alpha-thalassemia Southeast Asia deletion (SEA deletion), was applied in four clinical applications of preimplantation genetic diagnosis (PGD) on four couples, among whom both partners were alpha-thalassemia carriers. Two patients became pregnant and two healthy babies were born, which confirmed the PGD results. The single cell multiplex nested PCR followed by reverse dot blot (RDB), which can simultaneously detect the 16 beta-thalassemia mutations in the Chinese population, was applied in four clinical PGD cycles on four couples among whom both partners were beta-thalassemia carriers. One pregnancy was achieved and it resulted in a live healthy birth, which confirmed the results of PGD. The amplification efficiencies of the two protocols described above were 89.5% and 93.9%, respectively. The allele drop-out (ADO) rates of these two protocols were 5.9% and 10.9%, respectively.

CONCLUSION

These studies represent the successful applications of PGD protocols that can detect more than 95% of alpha- and beta -thalassemia mutations in the Chinese population.

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.

Preimplantation diagnosis and HLA typing for haemoglobin disorders

Haemoglobin disorders are among the most frequent indications for preimplantation genetic diagnosis (PGD), introduced as an important option to couples at risk for producing offspring with thalassaemia and sickle cell disease. Previous experience mainly included PGD for beta-thalassaemia, while PGD for alpha-thalassaemia resulting in an unaffected pregnancy has not been reported. This study presents the results of the world's largest experience of 197 PGD cycles for haemoglobin disorders, which includes PGD for alpha-thalassaemia, resulting in 53 clinical pregnancies and birth of 45 healthy children, with five still ongoing. Fifty-four of these cycles were performed in combination with HLA typing, allowing the birth of thalassaemia-free children who were also HLA identical to the affected sibling, with successful stem cell transplantation in one case. As an increasing proportion of patients requesting PGD with HLA typing are of advanced reproductive age, aneuploidy testing was performed simultaneously with PGD. The results show that PGD has now become a practical approach for prevention of haemoglobin disorders, and is gradually being used also for improving access to HLA compatible stem cell transplantation for this group of diseases.

Outcomes of Preimplantation Genetic Diagnosis Therapy in Treatment of β-Thalassemia: A Retrospective Analysis

Thalassemia is one of the most common single-gene disorders that can be cured by hematopoietic stem cell transplantation (HCT) from a human leukocyte antigen (HLA)-identical sibling donor. In families that have an affected child, preimplantation genetic diagnosis (PGD) can be used to select an unaffected, HLA-identical embryo. In brief, this procedure requires in vitro fertilization, oocyte retrieval, fertilization, and blastomere biopsy for identification of unaffected HLA-identical embryos. After delivery, umbilical cord blood from the sibling donor is collected for HCT. The objective of this study was to determine the outcomes of families using PGD therapy for cure of beta-thalassemia and to review the limitations of PGD therapy. Families affected with beta-thalassemia who attempted PGD therapy were retrospectively identified and reviewed for indication, attempted cycles, successful pregnancy, and transplantation outcomes. Eight identified families affected by thalassemia underwent PGD. The diagnosis of their affected children included six cases of beta-thalassemia major and two cases of transfusion-dependent hemoglobin E-beta-thalassemia patients. A total of 14 cycles of PGD were attempted, ranging from one to four attempts per family. Following successful identification of HLA-identical cells, two pregnancies occurred, of which one resulted in engraftment of a beta-thalassemia child. PGD therapy offers the possibility of recruiting a suitable donor for HCT, yet is limited by financial cost due to labor-intensive techniques, low probability of obtaining an HLA-matched unaffected embryo, variable implantation capacity, and significant emotional impact. Improvements in PGD therapy's efficacy and cost will make this a more viable option for affected families.

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.

Clinical application of multiple displacement amplification in preimplantation genetic diagnosis

Multiple displacement amplification (MDA) is a technique used in the amplification of very small amounts of DNA. MDA is reported to yield large quantities of high-quality DNA. The applicability of MDA to single cells was recently demonstrated as a potential technique for preimplantation genetic diagnosis (PGD). This paper shows the first clinical application of MDA in PGD. Two cycles of PGD were performed in two diseases, resulting in two pregnancies. All the diagnoses given on blastomeres were confirmed on the non-transferred whole embryos. The blastomere diagnosis was coupled with short tandem repeat (STR) analysis (16 loci) in all cycles. Allelic drop-out (ADO) assessment and amplification efficiency were evaluated on 40 single lymphocytes derived from parents of each disease. ADO and amplification failure were 10.3 and 2.2% for beta-thalassaemia and 17.9 and 2.2% for cystic fibrosis respectively. HLA matching for A, B and DR was performed successfully on single cell for the beta-thalassaemia family using similar methods to genomic DNA. The PGD protocol used in all diseases consists of MDA amplification, followed by a standard polymerase chain reaction protocol. Although HLA matching was not applied to embryos, its feasibility was shown on single cell DNA amplified by MDA. Altogether, these data show the simplicity and reliability of performing PGD in combination with HLA matching and STR analysis using MDA.

Preimplantation diagnosis (PGD)--a European clinician's point of view

This paper describes the current status of preimplantation diagnosis from the viewpoint of an experienced clinician specialized in reproductive medicine. Current progress and international experiences with different applications and techniques are being reviewed on the basis of the literature. Particular interest is focused on possible advantages of routinely diagnosing major chromosome aneuploidies in preimplantation-embryos of patients undergoing in vitro fertilization and embryo transfer. Last but not least, a short survey of the international guidelines and legislation is compared to the situation in the author's country, Austria, where it is currently unclear whether preimplantation diagnosis is allowed or not.

Preimplantation genetic diagnosis for β-thalassaemia: the Sardinian experience

OBJECTIVES

To report the experiences on preimplantation genetic diagnosis (PGD) in couples at risk for beta-thalassaemia in Sardinia.

METHODS

23 couples at risk for beta-thalassaemia were included in the PGD programme with a total of 42 cycles performed. Among these, 11 couples were fertile, while the remaining 12 had associated fertility problems. In vitro Fertilization (IVF), PGD and prenatal genetic molecular confirmation protocols and results are reported.

RESULTS

All the patients followed the protocol of ovarian stimulation, oocyte retrieval, intracytoplasmic sperm injection (ICSI), embryo biopsy and genetic analysis. A total of 272 oocytes were fertilized in the regular way, and embryo biopsy was performed on 202 embryos. Out of these 202 embryos, 192 (95%) were successful. The genetic diagnosis was performed on 150 embryos (78.1%). Ninety-eight were identified as unaffected and 75 were transferred in 31 cycles. In the infertile patient group, two biochemical pregnancies (11.1% per transfer), in the fertile patient group, four clinical pregnancies, two twin and two singleton pregnancies (30.8% per transfer), were obtained. The genetic molecular results were confirmed in all pregnancies by first-trimester chorionic villus sampling (CVS).

CONCLUSION

Our study shows that PGD for beta-thalassaemia is an available procedure for couples who wish to avoid termination of pregnancy, except in cases where the IVF cycle efficiency is very poor.

Advances in preimplantation genetic diagnosis

Strategies for preimplantation genetic diagnosis (PGD) have become increasingly complex. For single gene disorders it is now usual for several DNA fragments to be simultaneously amplified using multiplex-PCR. This allows redundant diagnostic loci to be analyzed, reducing the chance of misdiagnosis due to allele dropout (ADO). Additionally, hypervariable 'fingerprinting' loci can be amplified, revealing the presence of DNA contaminants. Chromosomal screening has also increased in complexity. Current FISH techniques investigate up to nine chromosomes per cell and are offered to an increasingly wide range of patients, including women of advanced reproductive age and those with a history of repeated spontaneous abortion. Technical limitations, which preclude a full assessment of all chromosomes using FISH, have encouraged the development alternative tests. These include nuclear conversion, comparative genomic hybridization (CGH) and the use of DNA microarray 'chip' technology. This paper discusses technical innovations that have improved the scope and accuracy of PGD, as well as the emergence of new indications for PGD that are sometimes considered controversial (e.g. HLA-typing).

Preimplantation diagnosis of Lesch-Nyhan using mini-sequencing primer extension

Lesch-Nyhan syndrome (LN) is a severe X-linked disorder of males characterized by hyperuricaemia, choreoathetosis, spasticity, mental retardation and self-mutilation. The disorder is caused by a wide spectrum of mutations distributed throughout the hypoxanthine phosphoribosyltransferase (HPRT) gene. Female carriers of LN display no clinical symptoms but are at 50% risk of passing on the affected gene to their male offspring. A couple who had a boy with LN were referred to Monash IVF for preimplantation genetic diagnosis (PGD) because the woman had undergone tubal ligation and the couple wanted to have another child. A test was developed for the causative mutation IVS8+6 T-->G mutation based on minisequencing primer extension that also incorporated the co-analysis of an informative tetranucleotide marker in intron 3 of the HPRT gene to identify allelic dropout. All four biopsied embryos from their first IVF cycle were diagnosed as unaffected, and transfer of two embryos in the cohort with the highest morphological quality resulted in a singleton pregnancy and the birth of a healthy girl. Direct mutation detection by mini-sequencing and parallel analysis of an informative linked marker provides an alternative strategy for molecular diagnosis of point mutations that will have useful application in PGD for other single gene disorders.

Real-time PCR for single-cell genotyping in sickle cell and thalassemia syndromes as a rapid, accurate, reliable, and widely applicable protocol for preimplantation genetic diagnosis

Sickle-cell and beta-thalassemia syndromes are priority genetic diseases for prevention programs involving population screening with the option of prenatal diagnosis for carrier couples. Preimplantation genetic diagnosis (PGD) represents a specialized alternative to prenatal diagnosis and is most appropriately used for couples with an unsuccessful reproductive history and/or undergoing assisted reproduction. However, clinical application of PGD has been hindered by difficulties in reliably transferring molecular diagnostic protocols to the single-cell level. We standardized and validated a protocol involving first-round multiplex PCR, amplifying the region of the beta-globin gene containing most of the common disease mutations world-wide and two unlinked microsatellite markers (GABRB3 and D13S314), followed by: 1) analysis of beta-globin genotypes with real-time PCR and 2) microsatellite sizing to exclude chance contamination. The protocol was standardized on 100 single lymphocytes from a beta-thalassemia heterozygote, including 15 artificially contaminated samples, the latter demonstrated through microsatellite analysis. PCR failure and allele drop-out (ADO) were observed in one (uncontaminated) sample each (1.2%). A pilot study in six clinical PGD cycles with five different beta-globin genotype interactions achieved results (in 5-6 hr) in 46 out of 50 single blastomeres (92%), all concordant with results from an established PGD method applied simultaneously; microsatellite analysis detected only parental alleles, excluding contamination. Beta-globin genotypes were also confirmed in two blastomeres through prenatal diagnosis (twin pregnancy), and in 11 out of 12 spare embryos, revealing one incident of ADO. Overall, the protocol proved to be sensitive, accurate, reliable, rapid, and applicable for many genotype interactions, with internal monitoring of contamination, thus fulfilling all requirements for clinical PGD application.

Single-cell sequencing and mini-sequencing for preimplantation genetic diagnosis

There is increasing interest in the use of preimplantation genetic diagnosis (PGD) as an alternative to routine prenatal diagnosis. However, the costs associated with development and testing of new PGD protocols have forced some PGD centres to limit the number of diseases for which PGD is offered. One of the main factors in the design of new protocols, which affects cost and accuracy, is the choice of the mutation-detection technique. We have assessed the reliability of DNA sequencing and mini-sequencing for clinical diagnosis at the single-cell level and have found them to be rapid and accurate. Extensive optimisation for individual mutations is not usually necessary when employing these versatile techniques and consequently a smaller investment of time and resources should be required during development of new protocols. Additionally, we report single-cell protocols for the diagnoses of cystic fibrosis, sickle cell anaemia and beta-thalassaemia, which utilise mini-sequencing. Unlike most mutation-detection techniques, mini-sequencing permits analysis of very small DNA fragments. Small amplicons experience low allele dropout (ADO) rates, and consequently this approach could potentially improve the reliability of PGD.

Current status of preimplantation diagnosis for single gene disorders

Preimplantation genetic diagnosis (PGD) has become an established procedure for avoiding the birth of affected children with single gene disorders. PGD is performed through polar body or blastomere biopsy, which has no deleterious effect on pre- and post-implantation development. This review describes the most recent developments and current changes in the spectrum of conditions for which PGD has been applied. The most recent applications of PGD include congenital malformations, blood group incompatibility and an increasing number of late onset disorders with genetic predisposition, all of which have not previously been diagnosed using PGD. Despite ethical concerns, PGD has also been used for preselection of unaffected and HLA matched embryos, and recently for preimplantation HLA matching without testing for the causative gene. This extends the practical value of PGD, with its utility being no longer limited to prevention of single gene disorders, by expanding it to treatment of siblings requiring stem cell transplantation.