Birth of healthy children after preimplantation diagnosis of beta-thalassemia by whole-genome amplification

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.

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.

Multiple displacement amplification as the first step can increase the diagnostic efficiency of preimplantation genetic testing for monogenic disease for β-thalassemia

AIM

To evaluate whether using multiple displacement amplification (MDA) as the first step can increase the diagnostic efficiency of preimplantation genetic testing for monogenic disease (PGT-M) for β-thalassemia.

METHODS

This is a retrospective cohort study. All included patients underwent PGT-M cycles (n = 307) for β-thalassemia in our center from January 2014 to February 2018. We divided the patients into two groups based on two different detection methods. For the polymerase chain reaction (PCR) group (n = 115), multiplex nested PCR+ reverse dot blot analysis was performed directly after cell lysis. For the MDA group (n = 192), the whole genomes of single cells were directly amplified using MDA and then examined by singleplex PCR + reverse dot blot for β-thalassemia.

RESULTS

A total of 2315 embryos were tested. The overall diagnostic efficiency of the MDA group was significantly higher than that of the PCR group (96.99% vs 88.15%, P < 0.001). The percentage of embryos available for transfer was significantly higher in the MDA group than in the PCR group (74.28% vs 64.98%, P < 0.001). Furthermore, the carrier embryo rate of the MDA group was significantly higher than that of the PCR group (50.11% vs 35.95%, P < 0.001).

CONCLUSION

This study indicates that MDA, as the first step in PGT-M for β-thalassemia, can increase diagnostic efficiency.

Genotyping single-sperm cells by universal MARSALA enables the acquisition of linkage information for combined pre-implantation genetic diagnosis and genome screening

PURPOSE

This paper aims to investigate the feasibility of performing pre-implantation genetic diagnosis (PGD) and pre-implantation genetic screening (PGS) simultaneously by a universal strategy without the requirement of genotyping relevant affected family members or lengthy preliminary work on linkage analysis.

METHODS

By utilizing a universal Mutated Allele Revealed by Sequencing with Aneuploidy and Linkage Analyses (MARSALA) strategy based on low depth whole genome sequencing (~3x), not involving specific primers' design nor the enrichment of SNP markers for haplotype construction. Single-sperm cells and trephectoderm cells from in vitro fertilized embryos from a couple carrying HBB mutations were genotyped. Haplotypes of paternal alleles were constructed and investigated in embryos, and the chromosome copy number profiles were simultaneously analyzed.

RESULTS

The universal MARSALA strategy allows the selection of a euploid embryo free of disease mutations for in uterus transfer and successful pregnancy. A follow-up amniocentesis was performed at 17 weeks of gestation to confirm the PGD/PGS results.

CONCLUSION

We present the first successful PGD procedure based on genotyping multiple single-sperm cells to obtain SNP linkage information. Our improved PGD/PGS procedure does not require genotyping the proband or relevant family members and therefore can be applicable to a wider population of patients when conducting PGD for monogenic disorders.

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.

Whole genome amplification in preimplantation genetic diagnosis

Preimplantation genetic diagnosis (PGD) refers to a procedure for genetically analyzing embryos prior to implantation, improving the chance of conception for patients at high risk of transmitting specific inherited disorders. This method has been widely used for a large number of genetic disorders since the first successful application in the early 1990s. Polymerase chain reaction (PCR) and fluorescent in situ hybridization (FISH) are the two main methods in PGD, but there are some inevitable shortcomings limiting the scope of genetic diagnosis. Fortunately, different whole genome amplification (WGA) techniques have been developed to overcome these problems. Sufficient DNA can be amplified and multiple tasks which need abundant DNA can be performed. Moreover, WGA products can be analyzed as a template for multi-loci and multi-gene during the subsequent DNA analysis. In this review, we will focus on the currently available WGA techniques and their applications, as well as the new technical trends from WGA products.

DNA amplification using phi29 DNA polymerase validates gene polymorphism analysis from buccal mucosa samples

Venous blood is currently the most common source of DNA for gene polymorphism screening; however, blood sampling is invasive and difficult to perform in general dental treatment. Buccal mucosa samples provide an alternative source of DNA, but it is frequently difficult to effectively amplify the DNA owing to the small amounts of sample material obtained. This study was performed to establish a method for performing total genomic DNA amplification from buccal mucosa samples using phi29 DNA polymerase. Total genomic DNA was isolated from buccal mucosa samples obtained from healthy subjects and was amplified using phi29 DNA polymerase. To determine the suitability of the extracted DNA for genotyping, polymerase chain reaction and restriction fragment length polymorphism analyses were performed for the IL-1 gene polymorphism. Genotyping of the IL-1 polymorphism was successful using the amplified DNA from a buccal mucosa, but genotyping was unsuccessful using the unamplified control because of low DNA purity. The method of extracting DNA from a buccal mucosa is painless, simple, minimally invasive, and rapid. Genomic DNA from a buccal mucosa can be amplified by phi29 DNA polymerase in sufficient quantity and quality to conduct gene polymorphism analyses.

New multiplex PCR-based protocol allowing indirect diagnosis of FSHD on single cells: can PGD be offered despite high risk of recombination?

Molecular pathophysiology of facioscapulohumeral muscular dystrophy (FSHD) involves the heterozygous contraction of the number of tandemly repeated D4Z4 units at chromosome 4q35.2. FSHD is associated with a range of 1-10 D4Z4 units instead of 11-150 in normal controls. Several factors complicate FSHD molecular diagnosis, especially the cis-segregation of D4Z4 contraction with a 4qA allele, whereas D4Z4 shortening is silent both on alleles 4qB and 10q. Discrimination of pathogenic 4q-D4Z4 alleles from highly homologous 10q-D4Z4 arrays requires the use of the conventional Southern blot, which is not suitable at the single-cell level. Preimplantation genetic diagnosis (PGD) is a frequent request from FSHD families with several affected relatives. We aimed to develop a rapid and sensitive PCR-based multiplex approach on single cells to perform an indirect familial segregation study of pathogenic alleles. Among several available polymorphic markers at 4q35.2, the four most proximal (D4S2390, D4S1652, D4S2930 and D4S1523, <1.23 Mb) showing the highest heterozygote frequencies (67-91%) were selected. Five recombination events in the D4S2390-D4S1523 interval were observed among 144 meioses. In the D4S2390-D4Z4 interval, no recombination event occurred among 28 FSHD meioses. Instead, a particular haplotype segregated with both clinical and molecular status, allowing the characterization of an at-risk allele in each tested FSHD family (maximal LOD score 2.98 for theta=0.0). This indirect protocol can easily complement conventional techniques in prenatal diagnosis. Although our multiplex PCR-based approach technically fulfils guidelines for single-cell analysis, the relatively high recombination risk hampers its application to PGD.

Cryopreservation of human embryonic stem cells with a new bulk vitrification method

To increase the manipulation efficiency and storage capability of vitrified human embryonic stem cells, a new bulk vitrification method was established using transformed cryovials. This method vitrified a large number of cell clumps, as opposed to those cryopreserved by a slow-freezing method with conventional cryovials at one time (round). After warming, vitrified human embryonic stem cells exhibited a much higher survival rate than the slow-freezing cells. The vitrified stem cells continued to express markers of pluripotency and formed teratomas in mice with severe combined immunodeficiency, confirming the pluripotency of vitrified-warmed human embryonic stem cell clumps. The new bulk vitrification method is superior to and more practical than the open pulled straw vitrification method and the slow-freezing method for the cryopreservation of human embryonic stem cells.

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.

Preimplantation genetic diagnosis for beta-thalassemia using single-cell DNA analysis for codons 17 and 26 of beta-globin gene

BACKGROUND

Preimplantation genetic diagnosis (PGD) of monogenic autosomal hereditary disorders following assisted conception usually involves the removal of one or two blastomeres from preimplantation embryos. However, the amount of DNA from a single blastomere is insufficient to amplify the region of interest. Hence, the whole genome amplification (WGA) method is performed prior to amplifying the genes of interest before analysis of DNA material through polymerase chain reaction (PCR).

METHODS

In the present study we report that WGA from a single blastomere extracted from unwanted preimplantation human embryos (obtained from 10 infertile couples) could positively yield microgram quantities of amplified DNA allowing PCR analysis for codons 17 and 26 of the beta-globin gene that cause the beta-thalassemia disorder. We developed a rapid and highly specific technique of single-cell PCR to amplify a specific region on the beta-globin gene for codon 17 (AAG-->TAG) and codon 26 (GAG-->AAG) by using single-cell PCR.

RESULTS

About 249 bp of amplicon for codon 17 and about 200 bp of amplicon for codon 26 were successfully amplified. No mutations were observed. Analyzed embryos were not transferred back to patients because the embryos used as samples were wasted embryos.

CONCLUSIONS

Compared to other approaches for prenatal diagnosis, PGD is rapid and suitable as a noninvasive clinical tool for identifying genetic disorders for the purpose of reducing selective miscarriages and moral dilemmas. We opine that DNA extraction and amplification can be successfully performed by using single-cell PCR to diagnose genetic diseases before pregnancy.

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.

Improved multiple displacement amplification with phi29 DNA polymerase for genotyping of single human cells

The ability to genotype multiple loci of single cells would be of significant benefit to investigations of cellular processes such as oncogenesis, meiosis, fertilization, and embryogenesis. We report a simple two-step, single-tube protocol for whole-genome amplification (WGA) from single human cells using components of the GenomiPhi V2 DNA Amplification kit. For the first time, we demonstrate reliable generation of 4-7 microg amplified DNA from a single human cell within 4 h with a minimum amount of artifactual DNA synthesis. DNA amplified from single cells was genotyped for 13 heterozygous short tandem repeats (STRs) and 7 heterozygous single nucleotide polymorphisms (SNPs), and the genotyping results were compared with purified genomic DNA. Accuracy of genotyping (percent of single-cell amplifications genotyped accurately for any particular STR or SNP) varied from 37% to 100% (with an average of 80%) for STRs and from 89% to 100% (averaging 94%) for SNPs. We suggest that the method described in this report is suitable for WGA from single cells, the product of which can be subsequently used for many applications, such as preimplantation genetic analysis (PGD).

Whole genome amplification from a single cell: a new era for preimplantation genetic diagnosis

Preimplantation genetic diagnosis (PGD) is a technique used for determining the genetic status of a single cell biopsied from embryos or oocytes. Genetic analysis from a single cell is both rewarding and challenging, especially in PGD. The starting material is very limited and not replaceable, and the diagnosis has to be made in a very short time. Different whole genome amplification (WGA) techniques have been developed to specifically increase the DNA quantities originating from clinical samples with limited DNA contents. In this review, currently available WGA techniques are introduced and, among them, multiple displacement amplification (MDA) is discussed in detail. MDA generates abundant assay-ready DNA to perform broad panels of genetic assays through its ability to rapidly amplify genomes from single cells. The utilization of MDA for single-cell molecular analysis is expanding at a high rate, and MDA is expected to soon become an integral part of PGD.

Evaluation of whole genome amplification methods using postmortem brain samples

The importance of examining genomic DNA derived from human brain has been highlighted by recent findings such as the possible link between DNA methylation and behavior or mental disorders, as well as the possible genomic differences between neurons from the same individual caused by transposons and aneuploidy. Consequently, obtaining a sufficient amount of genomic DNA derived from human brain is a critical issue for further research. Whole genome amplification (WGA) methods, by which genomic DNA is typically amplified on the order of 10(4)-10(6), will be a valuable tool for providing a sufficient amount of DNA for various molecular genetic studies. Here we evaluated three methods, including both PCR-based and non-PCR based WGA, as well as DNA extraction methods using frozen postmortem brain tissue. We found that WGA products from postmortem brains can be used in molecular genetic analysis, if a particular protocol for DNA extraction is used, and the most appropriate method for WGA depends on the state of the genomic DNA to be amplified.

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.

Multiple displacement amplification to create a long-lasting source of DNA for genetic studies

In many situations there may not be sufficient DNA collected from patient or population cohorts to meet the requirements of genome-wide analysis of SNPs, genomic copy number polymorphisms, or acquired copy number alternations. When the amount of available DNA for genotype analysis is limited, high performance whole-genome amplification (WGA) represents a new development in genetic analysis. It is especially useful for analysis of DNA extracted from stored histology slides, tissue samples, buccal swabs, or blood stains collected on filter paper. The multiple displacement amplification (MDA) method, which relies on isothermal amplification using the DNA polymerase of the bacteriophage phi29, is a recently developed technique for high performance WGA. This review addresses new trends in the technical performance of MDA and its applications to genetic analyses. The main challenge of WGA methods is to obtain balanced and faithful replication of all chromosomal regions without the loss of or preferential amplification of any genomic loci or allele. In multiple comparisons to other WGA methods, MDA appears to be most reliable for genotyping, with the most favorable call rates, best genomic coverage, and lowest amplification bias.

Optimization and evaluation of single-cell whole-genome multiple displacement amplification

The scarcity of genomic DNA can be a limiting factor in some fields of genetic research. One of the methods developed to overcome this difficulty is whole genome amplification (WGA). Recently, multiple displacement amplification (MDA) has proved very efficient in the WGA of small DNA samples and pools of cells, the reaction being catalyzed by the phi29 or the Bst DNA polymerases. The aim of the present study was to develop a reliable, efficient, and fast protocol for MDA at the single-cell level. We first compared the efficiency of phi29 and Bst polymerases on DNA samples and single cells. The phi29 polymerase generated accurately, in a short time and from a single cell, sufficient DNA for a large set of tests, whereas the Bst enzyme showed a low efficiency and a high error rate. A single-cell protocol was optimized using the phi29 polymerase and was evaluated on 60 single cells; the DNA obtained DNA was assessed by 22 locus-specific PCRs. This new protocol can be useful for many applications involving minute quantities of starting material, such as forensic DNA analysis, prenatal and preimplantation genetic diagnosis, or cancer research.

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.

The use of whole genome amplification in the study of human disease

The availability of large amounts of genomic DNA is of critical importance for many of the molecular biology assays used in the analysis of human disease. However, since the amount of patient tissue available is often limited and as particular foci of interest may consist of only a few hundred cells, the yield of DNA is often insufficient for extensive analysis. To address this problem, several whole genome amplification (WGA) methodologies have been developed. Initial WGA approaches were based on the polymerase chain reaction (PCR). However, recent reports have described the use of non-PCR-based linear amplification protocols for WGA. Using these methods, it is possible to generate microgram quantities of DNA starting with as little as 1mg of genomic DNA. This review will provide an overview of WGA approaches and summarize some of the uses for amplified DNA in various high-throughput genetic applications.

Molecular diagnosis of inherited disorders: lessons from hemoglobinopathies

Hemoglobinopathies constitute a major health problem worldwide, with a high carrier frequency, particularly in certain regions where malaria has been endemic. These disorders are characterized by a vast clinical and hematological phenotypic heterogeneity. Over 1,200 different genetic alterations that affect the DNA sequence of the human alpha-like (HBZ, HBA2, HBA1, and HBQ1) and beta-like (HBE1, HBG2, HBG1, HBD, and HBB) globin genes are mainly responsible for the observed clinical heterogeneity. These mutations, together with detailed information about the resulting phenotype, are documented in the globin locus-specific HbVar database. Family studies and comprehensive hematological analyses provide useful insights for accurately diagnosing thalassemia at the DNA level. For this purpose, numerous techniques can provide accurate, rapid, and cost-effective identification of the underlying genetic defect in affected individuals. The aim of this article is to review the diverse methodological and technical platforms available for the molecular diagnosis of inherited disorders, using thalassemia and hemoglobinopathies as a model. This article also attempts to shed light on issues closely related to thalassemia diagnostics, such as prenatal and preimplantation genetic diagnoses and genetic counseling, for better-quality disease management.

Thirteen years' experience of preimplantation diagnosis: report of the Fifth International Symposium on Preimplantation Genetics

Preimplantation genetic diagnosis (PGD) has been further developed into a practical option for avoiding the birth of affected children, representing an important complement to traditional prenatal diagnosis. More than 1000 unaffected children have been born after PGD, suggesting the accuracy and safety of the procedure, which is currently also used with the establishment of potential donor progeny for stem cell treatment of siblings. Together with progress in the establishment of embryonic stem (ES) cells, this may contribute to the development and application of stem cell therapy. The accumulated experience of thousands of PGD cycles for poor prognosis IVF patients provides further evidence of the improvement of clinical outcome, particularly obvious from the reproductive history of PGD patients. A high prevalence of aneuploidies in oocytes and embryos may affect the accuracy of PGD for single gene disorders, making aneuploidy testing an important part of PGD for causative genes and preimplantation human leukocyte antigen (HLA) typing. A sequential sampling of both oocytes and the resulting embryos may improve accuracy of aneuploidy testing and may also allow the detection and avoidance of transfer of embryos with uniparental disomies. Current developments and application of nuclear transfer and sperm duplication techniques, and microarray technology, may also contribute to the improvement of PGD and help in the development of PGD for genetic expression disorders.