Proof of principle and first cases using preimplantation genetic haplotyping--a paradigm shift for embryo diagnosis

Preimplantation Genetic Diagnosis of Androgen Resistance Syndrome Caused by Mutation on the AR Gene in Vietnam

Background

Androgen resistance syndrome or androgen insensitivity syndrome (AIS - Androgen Insensitivity Syndrome, OMIM 300068) is an X-linked recessive genetic syndrome causing disorders of sexual development in males. This disease is caused by mutations in the AR gene located on the X chromosome, which encodes the protein that structures the androgen receptor, with the role of receiving androgens. Mutation of the AR gene causes complete or partial loss of androgen receptor function, thereby androgen not being obtained and exerting its effect on target organs, resulting in abnormalities of the male reproductive system due to this organ system, differentiating towards feminization under the influence of estrogen. Disease prevention can be achieved by using pre-implantation genetic diagnosis, which enables couples carrying the mutation to have healthy offspring.

Aim

To carry out preimplantation genetic diagnosis of androgen resistance syndrome.

Methods

Sanger sequencing was used to detect the mutation in the blood samples of the couple, their son, and 01 embryo that were biopsied on the fifth day based on the findings of next-generation sequencing (NGS) of the affected son. We combined Sanger sequencing and linkage analysis using short tandem repeats (STR) to provide diagnostic results.

Results

We performed preimplantation genetic diagnosis for AIS on an embryo from a couple who had previously had an affected son. Consequently, one healthy embryo was diagnosed without the variant NM_000044: c.796del (p.Asp266IlefsTer30).

Conclusion

We report on a novel variant (NM_000044: c.796del (p.Asp266IlefsTer30)) in the AR gene discovered in Vietnam. The developed protocol was helpful for the preimplantation genetic diagnosis process to help families with the monogenic disease of AIS but wish to have healthy children.

Preimplantation genetic testing for embryos predisposed to hereditary cancer: Possibilities and challenges

Preimplantation genetic testing (PGT), which was developed as an alternative to prenatal genetic testing, allows couples to avoid pregnancies with abnormal chromosomes and the subsequent termination of the affected fetus. Originally used for early onset monogenic conditions, PGT is now used to prevent various types of inherited cancer conditions based on the development of PGT technology, assisted reproductive techniques (ARTs), and in vitro fertilization (IVF). This review provides insights into the potential benefits and challenges associated with the application of PGT for hereditary cancer and provides an overview of the existing literature on this test, with a particular focus on the current challenges related to laws, ethics, counseling, and technology. Additionally, this review predicts the future potential applications of this method. Although PGT may be utilized to predict and prevent hereditary cancer, each case should be comprehensively evaluated. The motives of couples must be assessed to prevent the misuse of this technique for eugenic purposes, and non-pathogenic phenotypes must be carefully evaluated. Pathological cases that require this technology should also be carefully considered based on legal and ethical reasoning. PGT may be the preferred treatment for hereditary cancer cases; however, such cases require careful case-by-case evaluations. Therefore, this study concludes that multidisciplinary counseling and support for patients and their families are essential to ensure that PGT is a viable option that meets all legal and ethical concerns.

Preimplantation Genetic Testing for Genetic Diseases: Limits and Review of Current Literature

Preimplantation genetic testing (PGT) has emerged as a revolutionary technique in the field of reproductive medicine, allowing for the selection and transfer of healthy embryos, thus reducing the risk of transmitting genetic diseases. However, despite remarkable advancements, the implementation of PGT faces a series of limitations and challenges that require careful consideration. This review aims to foster a comprehensive reflection on the constraints of preimplantation genetic diagnosis, encouraging a broader discussion about its utility and implications. The objective is to inform and guide medical professionals, patients, and society overall in the conscious and responsible adoption of this innovative technology, taking into account its potential benefits and the ethical and practical challenges that it presents.

Clinical application of NGS-based SNP haplotyping for PGT-M of methylmalonic acidemia

This study describes a successful case of preimplantation genetic testing for the monogenic disease (PGT-M) of methylmalonic acidemia (MMA). To avoid the transmission of pathogenic mutations and unnecessary pregnancy termination we applied next-generation sequencing (NGS)-based haplotyping on a couple with a previously deceased MMA offspring. After embryo preparation, all samples were amplified successfully by whole genome amplification. We performed preimplantation genetic testing for aneuploidy (PGT-A) to determine the copy number of embryos' chromosomes. PGT-A results showed five blastocysts (2, 11, 14, 15 and 16) with balanced chromosomes (46, XN). Two techniques were used for PGT-M. Sanger sequencing was used to detect the mutations of MMUT gene directly, and NGS-based single nucleotide polymorphism (SNP) haplotyping was used to distinguish the chromosomes that carried the mutation. Sanger sequencing and NGS-based SNP haplotyping confirmed that samples 2 and 15 carried c.730insTT, samples 11 and 15 carried c.1105 C > T and samples 14 and 16 did not carry any mutation. Thus, blastocyst 14 was transferred into the mother's uterus. After prenatal diagnosis at 18 weeks of gestation, a healthy infant without MMUT mutation was born at full term. This study highlights the efficiency of NGS-based SNP haplotyping for PGT-M of MMA.Abbreviations: MMA: methylmalonic acidemia; MMUT: methylmalonyl-CoA mutase; PGT-M: preimplantation genetic testing for monogenic disease; PGD: preimplantation genetic diagnosis; IVF: in vitro fertilization; ADO: allele dropout; WGA: whole genome amplification; SNP: single nucleotide polymorphism; NGS: next-generation sequencing; PND: prenatal diagnosis; ICSI: intracytoplasmic sperm injection; TE: trophectoderm; DOP-PCR: degenerate oligonucleotide primed polymerase chain reaction; PGT-A: preimplantation genetic testing for aneuploidy; PCR: polymerase chain reaction.

Accurate and scalable variant calling from single cell DNA sequencing data with ProSolo

Accurate single cell mutational profiles can reveal genomic cell-to-cell heterogeneity. However, sequencing libraries suitable for genotyping require whole genome amplification, which introduces allelic bias and copy errors. The resulting data violates assumptions of variant callers developed for bulk sequencing. Thus, only dedicated models accounting for amplification bias and errors can provide accurate calls. We present ProSolo for calling single nucleotide variants from multiple displacement amplified (MDA) single cell DNA sequencing data. ProSolo probabilistically models a single cell jointly with a bulk sequencing sample and integrates all relevant MDA biases in a site-specific and scalable-because computationally efficient-manner. This achieves a higher accuracy in calling and genotyping single nucleotide variants in single cells in comparison to state-of-the-art tools and supports imputation of insufficiently covered genotypes, when downstream tools cannot handle missing data. Moreover, ProSolo implements the first approach to control the false discovery rate reliably and flexibly. ProSolo is implemented in an extendable framework, with code and usage at: https://github.com/prosolo/prosolo.

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.

Preimplantation Genetic Testing for Monogenic Conditions: Is Cell-Free DNA Testing the Next Step?

Genetic assessment of an embryo via preimplantation genetic testing (PGT) represents an important reproductive option for couples wanting to try and improve success rates from in vitro fertilisation (IVF) cycles, as well as reduce their risk of having a child born with a genetic condition. Currently, biopsy of the developing embryo prior to transfer allows genetic assessment of an embryo for either chromosome copy number (aneuploidy [PGT-A] or segmental rearrangement [PGT-SR]) or to avoid the transmission of a single gene condition (monogenic conditions [PGT-M]). However, this technology is invasive and commands considerable resources. Non-invasive PGT (niPGT) offers a potential alternate mode of embryonic analysis. Whilst the utility of niPGT-A has been recently explored, there has been limited consideration of niPGT-M as an option for couples at risk of passing on a single gene or chromosomal condition. This review examines the historical and current clinical context of preimplantation embryonic analysis for monogenic conditions, in addition to important considerations surrounding the origin and analysis of cell-free deoxyribose nucleic acid (cfDNA), whether it is sourced via blastocentesis or spent embryonic culture medium (SCM). Future capabilities of this testing modality will almost certainly be enhanced by integration of whole genome sequencing into everyday practice. In addition, the increased utilisation of reproductive carrier screening as part of standard reproductive healthcare will likely result in the identification of a larger high-risk population. As a result, stratification of limited and highly specialised reproductive genetic resources will be required. Prospective parents should continue to be made aware of the limitations of this technology, with prenatal confirmatory testing remaining an essential part of antenatal care in these patients. However, niPGT-M poses an important alternate testing modality for high-risk couples, particularly in the setting of embryos that cannot be biopsied for traditional PGT-M and as demand for this treatment continues to grow.

A novel monogenic preimplantation genetic testing strategy for sporadic polycystic kidney caused by de novo PKD1 mutation

Autosomal dominant hereditary polycystic kidney disease (ADPKD) is the most common inherited kidney disease that causes end-stage renal disease and kidney failure. Preimplantation genetic testing for monogenic (PGT-M) can effectively prevent the transmission of genetic diseases from parents to the offspring before pregnancy. However, PGT-M currently adopts the single nucleotide polymorphism (SNP) linkage analysis for embryo's pathogenic gene carrying status and linkage analysis requires proband of the family. Here we report a new PGT-M strategy using single sperm SNP linkage analysis for male patient with sporadic ADPKD caused by de novo PKD1 mutation. We recruited five couples with male patient with ADPKD caused by de novo PKD1 mutation, and 39 embryos from six PGT-M cycles were detected. The five couples had at least one embryo that does not carry the PKD1 mutation. Within these five couples, the accuracy of carrier status of embryos was confirmed by amniotic fluid gene detection of two couples and two couples successfully delivered healthy fetuses. Therefore, the new PGT-M strategy of using single sperm SNP linkage analysis was proved to be feasible and effective for male patient with ADPKD caused by de novo PKD1 mutation.

Reproductive options for families at risk of Osteogenesis Imperfecta: a review

Background

Osteogenesis Imperfecta (OI) is a rare genetic disorder involving bone fragility. OI patients typically suffer from numerous fractures, skeletal deformities, shortness of stature and hearing loss. The disorder is characterised by genetic and clinical heterogeneity. Pathogenic variants in more than 20 different genes can lead to OI, and phenotypes can range from mild to lethal forms. As a genetic disorder which undoubtedly affects quality of life, OI significantly alters the reproductive confidence of families at risk. The current review describes a selection of the latest reproductive approaches which may be suitable for prospective parents faced with a risk of OI. The aim of the review is to alleviate suffering in relation to family planning around OI, by enabling prospective parents to make informed and independent decisions.

Main body

The current review provides a comprehensive overview of possible reproductive options for people with OI and for unaffected carriers of OI pathogenic genetic variants. The review considers reproductive options across all phases of family planning, including pre-pregnancy, fertilisation, pregnancy, and post-pregnancy. Special attention is given to the more modern techniques of assisted reproduction, such as preconception carrier screening, preimplantation genetic testing for monogenic diseases and non-invasive prenatal testing. The review outlines the methodologies of the different reproductive approaches available to OI families and highlights their advantages and disadvantages. These are presented as a decision tree, which takes into account the autosomal dominant and autosomal recessive nature of the OI variants, and the OI-related risks of people without OI.

The complex process of decision-making around OI reproductive options is also discussed from an ethical perspective.

Conclusion

The rapid development of molecular techniques has led to the availability of a wide variety of reproductive options for prospective parents faced with a risk of OI. However, such options may raise ethical concerns in terms of methodologies, choice management and good clinical practice in reproductive care, which are yet to be fully addressed.

The role of prenatal diagnosis following preimplantation genetic testing for single-gene conditions: A historical overview of evolving technologies and clinical practice

Preimplantation genetic testing for monogenic conditions (PGT-M) has become a valued reproductive option for couples at risk of having a child with a single gene condition. In line with developments in molecular genetics, there has been an overall trend toward laboratory techniques with higher accuracy in comparison to earlier PGT-M techniques. The recommendation for confirmatory prenatal diagnostic testing has remained a standard component of PGT-M counseling, reflecting the inherent difficulties of testing the limited number of cells obtained from embryo biopsy, as well as recognition of the biological and human factors that may lead to misdiagnosis in a PGT-M cycle. Reported misdiagnosis rates are less than 1 in 200 pregnancies following PGT-M, although updated data regarding newer methods of PGT-M are required. There is limited evidence available regarding clinician and patient behavior in pregnancies resulting from PGT-M cycles. It remains essential that clinicians involved in the care of patients undergoing PGT-M provide appropriate counseling regarding the risks of misdiagnosis and the importance of confirmatory prenatal diagnosis. The nature of PGT-M test design lends itself to cell-free DNA-based noninvasive prenatal testing for monogenic conditions (NIPT-M), which is likely to become a popular method in the near future.

Preimplantation Genetic Testing for Monogenic Disease of Spinal Muscular Atrophy by Multiple Displacement Amplification: 11 unaffected livebirths

Background: Preimplantation genetic testing for monogenic disease (PGT-M) has become an effective method for providing couples with the opportunity of a pregnancy with a baby free of spinal muscular atrophy (SMA). Multiple displacement amplification (MDA) overcomes the innate dilemma of very limited genetic material available for PGT-M. Objective: To evaluate the use of MDA, combined with haplotype analysis and mutation amplification, in PGT-M for families with SMA. Methods: MDA was used to amplify the whole genome from single blastomeres or trophectoderm (TE) cells. Exon 7 of the survival motor neuron gene 1 (SMN1) and eleven STRs markers flanking the SMN1 gene were incorporated into singleplex polymerase chain reaction (PCR) assays on MDA products. Results: Sixteen cycles (19 ovum pick-up cycles) of PGT-M were initiated in 12 couples. A total of 141 embryos were tested: 90 embryos were biopsied at the cleavage stage and 51 embryos were biopsied at the blastocyst stage. MDA was successful on 94.44% (85/90) of the single blastomeres and on 92.16% (47/51) of the TE cells. And the PCR efficiency were 98.4% (561/570) and 100% (182/182), respectively. In addition, the average allele drop-out (ADO) rates were 13.3% (60/392) and 9.8% (11/112), respectively. The results for SMN1 exon 7 were all matched with haplotype analysis, which allowed an accurate diagnosis of 93.62% (132/141) embryos. Twelve families had unaffected embryos available for transfer and a total of 38 embryos were transferred in 20 embryo transfer cycles. Eight transfers were successful, resulting in a clinical pregnancy rate of 40% (8/20) and an implantation rate of 28.95% (11/38). Finally, 11 healthy babies were born. Among them, 5 SMA carriers were singleton live births and 3 SMA carriers had twin births. Conclusion: Careful handling during the MDA procedure can improve subsequent PCR efficiency and reduce the ADO rate. We suggest that this protocol is reliable for increasing the accuracy of the PGT-M for SMA.

Performance comparison of two whole genome amplification techniques in frame of multifactor preimplantation genetic testing

PURPOSE

To compare multiple displacement amplification and OmniPlex whole genome amplification technique performance during array comparative genome hybridization (aCGH), Sanger sequencing, SNaPshot and fragment size analysis downstream applications in frame of multifactor embryo preimplantation genetic testing.

METHODS

Preclinical workup included linked short tandem repeat (STR) marker selection and primer design for loci of interest. It was followed by a family haplotyping, after which an in vitro fertilization preimplantation genetic testing (IVF-PGT) cycle was carried out. A total of 62 embryos were retrieved from nine couples with a confirmed single gene disorder being transmitted in their family with various inheritance traits-autosomal dominant (genes-ACTA2, HTT, KRT14), autosomal recessive (genes-ALOX12B, TPP1, GLB1) and X-linked (genes-MTM1, DMD). Whole genome amplification (WGA) for the day 5 embryo trophectoderm single biopsies was carried out by multiple displacement amplification (MDA) or polymerase chain reaction (PCR)-based technology OmniPlex and was used for direct (Sanger sequencing, fragment size analysis, SNaPshot) and indirect mutation assessment (STR marker haplotyping), and embryo aneuploidy testing by array comparative genome hybridization (aCGH).

RESULTS

Family haplotyping revealed informative/semi-informative microsatellite markers for all clinical cases for all types of inheritance. Indirect testing gave a persuasive conclusion for all embryos assessed, which was confirmed through direct testing. The overall allele dropout (ADO) rate was higher for PCR-based WGA, and MDA shows a better genomic recovery scale. Five euploid embryos were subjected to elective single embryo transfer (eSET), which resulted in four clinical pregnancies and birth of two healthy children, which proved free of disease causative variants running in the family postnataly.

CONCLUSIONS

A developed multifactor PGT protocol can be adapted and applied to virtually any genetic condition and is capable of improving single gene disorder preimplantation genetic testing in a patient-tailored manner thus increasing pregnancy rates, saving costs and increasing patient reliability.

‘Designer babies’ almost thirty years on

The first pregnancies and live births following in vitro fertilisation (IVF) and preimplantation genetic testing (PGT), formerly known as preimplantation genetic diagnosis, were reported in 1990, almost 30 years ago, in several couples at risk of X-linked inherited conditions, which typically only affect boys inheriting the X chromosome with the affected gene from their carrier mothers. At that time, it was only possible to identify the sex of the embryo by amplifying a Y-linked repeat sequence in single cells biopsied at cleavage stages and avoid the transfer of males, half of which would be affected. The extensive publicity surrounding these cases and the perceived risk of using IVF and PGT for desirable characteristics not related to health, such as sex selection, led to the epithet of ‘designer babies’ which continues to resonate to this day. Here, I briefly reflect on how the technology of PGT has evolved over the decades and whether it deserves this reputation. With efficient methods for whole genome amplification and the genomic revolution, we now have highly accurate universal tests that combine marker-based diagnosis of almost any monogenic disorder with the detection of aneuploidy. PGT is now clinically well established and is likely to remain a valuable alternative for couples at risk of having affected children.

Preimplantation genetic diagnosis of X-linked Charcot-Marie-Tooth disease by indirect linkage analysis

OBJECTIVE

To present methodical approach of preimplantation genetic diagnosis (PGD) as an option for an unaffected pregnancy in reproductive-age couples who have a genetic risk of the X-linked dominant peripheral neuropathy Charcot-Marie-Tooth type 1 disease.

PATIENTS AND METHODS

We performed PGD of X-linked Charcot-Marie-Tooth type 1 disease using haplotyping/indirect linkage analysis, when during analysis we reach to exclude embryos that carry a high-risk haplotype linked to the causal mutation p.Leu9Phe in the GJB1 gene.

RESULTS

Within the PGD cycle, we examined 4 blastomeres biopsied from cleavage-stage embryos and recommended 3 embryos for transfer. Two embryos were implanted into the uterus; however, it resulted in a singleton pregnancy with a male descendant. Three years later, the couple returned again with spontaneous gravidity. A chorionic biopsy examination of this gravidity ascertained the female sex and a pericentric inversion of chromosome 5 in 70% of the cultivated foetal cells.

CONCLUSION

Using indirect linkage analysis, PGD may help to identify genetic X-linked defects within embryos during screening, thereby circumventing the potential problems with abortion.

Preimplantation Genetic Diagnosis of Multiple Endocrine Neoplasia Type 2A Using Informative Markers Identified by Targeted Sequencing

BACKGROUND

The revised guidelines for the management of medullary thyroid carcinoma recommend that genetic counseling regarding reproductive options, including preimplantation genetic diagnosis (PGD), be considered for all RET mutation carriers of reproductive age to avoid the transmission of multiple endocrine neoplasia type 2 (MEN2). However, the high complexity and cost of PGD have hindered its widespread use. Thus, it is necessary to establish a simple and relatively inexpensive method to facilitate the PGD of MEN2.

PATIENTS AND METHODS

A customized Nimblegen EZ sequence capture array was designed to capture the targeted regions, including the RET gene, and 1 Mb range on each side of the RET gene. Targeted, capture-based next-generation sequencing of three members of one family with MEN2A (the couple and the paternal father) was conducted to identify the informative markers. The diagnosis of the embryos was achieved through haplotype analysis based on informative markers and causative mutation.

RESULTS

Based on the sequencing results, 173 informative markers were detected, which were sufficient for the subsequent use for PGD. Seven informative markers and the causative mutation (RET^C634Y) were selected and subjected to Sanger sequencing. Through haplotype analysis, four embryos without inheritance of the mutation haplotype of the RET gene were diagnosed as unaffected. One unaffected embryo was transferred, with one healthy baby born at 38 gestational weeks.

CONCLUSIONS

Targeted, capture-based next-generation sequencing for identification of informative markers together with Sanger sequencing is an easy and efficient method for the PGD of monogenic diseases such as MEN2.

The SEeMORE strategy: single-tube electrophoresis analysis-based genotyping to detect monogenic diseases rapidly and effectively from conception until birth

BACKGROUND

The development of technologies that detect monogenic diseases in embryonic and fetal samples are opening novel diagnostic possibilities for preimplantation genetic diagnosis (PGD) and prenatal diagnosis (PND) thereby changing laboratory practice. Molecular diagnostic laboratories use different workflows for PND depending on the disease, type of biological sample, the presence of one or more known mutations, and the availability of the proband. Paternity verification and contamination analysis are also performed. The aim of this study was to test the efficacy of a single workflow designed to optimize the molecular diagnosis of monogenic disease in families at-risk of transmitting a genetic alteration.

METHODS

We used this strategy, which we designated "SEeMORE strategy" (Single-tube Electrophoresis analysis-based genotyping to detect MOnogenic diseases Rapidly and Effectively from conception to birth). It consists of a multiplex PCR that simultaneously carries out linkage analysis, direct analysis, maternal contamination and parenthood testing. We analyzed samples from previously diagnosed families for PND (cystic fibrosis or Duchenne muscular dystrophy) without, however, knowing the results.

RESULTS

The results obtained with the SEeMORE strategy concurred with those obtained with traditional PND. In addition, this strategy has several advantages: (i) use of one or a few cells; (ii) reduction of the procedure to 1 day; and (iii) a reduction of at least 2-3-fold of the analytic cost.

CONCLUSIONS

The SEeMORE strategy is effective for the molecular diagnosis of monogenic diseases, irrespective of the amount of starting material and of the disease mutation, and can be used for PND and PGD.

The establishment and application of preimplantation genetic haplotyping in embryo diagnosis for reciprocal and Robertsonian translocation carriers

Background

Preimplantation genetic diagnosis (PGD) is now widely used to select embryos free of chromosomal copy number variations (CNV) from chromosome balanced translocation carriers. However, it remains a difficulty to distinguish in embryos between balanced and structurally normal chromosomes efficiently.

Methods

For this purpose, genome wide preimplantation genetic haplotyping (PGH) analysis was utilized based on single nucleotide polymorphism (SNP) microarray. SNPs that are heterozygous in the carrier and, homozygous in the carrier’s partner and carrier’s family member are defined as informative SNPs. The haplotypes including the breakpoint regions, the whole chromosomes involved in the translocation and the corresponding homologous chromosomes are established with these informative SNPs in the couple, reference and embryos. In order to perform this analysis, a reference either a translocation carrier’s family member or one unbalanced embryo is required. The positions of translocation breakpoints are identified by molecular karyotypes of unbalanced embryos. The recombination of breakpoint regions in embryos could be identified.

Results

Eleven translocation families were enrolled. 68 blastocysts were analyzed, in which 42 were unbalanced or aneuploid and the other 26 were balanced or normal chromosomes. Thirteen embryos were transferred back to patients. Prenatal cytogenetic analysis of amniotic fluid cells was performed. The results predicted by PGH and karyotypes were totally consistent.

Conclusions

With the successful clinical application, we demonstrate that PGH was a simple, efficient, and popularized method to distinguish between balanced and structurally normal chromosome embryos.

Electronic supplementary material

The online version of this article (10.1186/s12920-017-0294-x) contains supplementary material, which is available to authorized users.

Karyomapping and how is it improving preimplantation genetics?

INTRODUCTION

Preimplantation genetic diagnosis and screening (PGD/PGS) has been applied clinically for >25 years however inherent drawbacks include the necessity to tailor each case to the trait in question, and that technology to detect monogenic and chromosomal disorders respectively is fundamentally different. Areas covered: The area of preimplantation genetics has evolved over the last 25 years, adapting to changes in technology and the need for more efficient, streamlined diagnoses. Karyomapping allows the determination of inheritance from the (grand)parental haplobocks through assembly of inherited chromosomal segments. The output displays homologous chromosomes, crossovers and the genetic status of the embryos by linkage comparison, as well as chromosomal disorders. It also allows for determination of heterozygous SNP calls, avoiding the risks of allele dropout, a common problem with other PGD techniques. Manuscripts documenting the evolution of preimplantation genetics, especially those investigating technologies that would simultaneously detect monogenic and chromosomal disorders, were selected for review. Expert commentary: Karyomapping is currently available for detection of single gene disorders; ~1000 clinics worldwide offer it (via ~20 diagnostic laboratories) and ~2500 cases have been performed. Due an inability to detect post-zygotic trisomy reliably however and confounding problems of embryo mosaicism, karyomapping has yet to be applied clinically for detection of chromosome disorders.

The clinical application of preimplantation genetic diagnosis for the patient affected by congenital contractural arachnodactyly and spinal and bulbar muscular atrophy

PURPOSE

To investigate the usefulness of preimplantation genetic diagnosis (PGD) for the patient affected by congenital contractural arachnodactyly (CCA) and spinal and bulbar muscular atrophy (SBMA).

METHODS

Multiple displacement amplification (MDA) was performed for whole genome amplification (WGA) of biopsied trophectoderm (TE) cells. Direct mutation detection by sequencing and next-generation sequencing (NGS)-based single nucleotide polymorphism (SNP) haplotyping were used for CCA diagnosis. Direct sequencing of the PCR products and sex determination by amplification of sex-determining region Y (SRY) gene were used for SBMA diagnosis. After PGD, the unaffected blastocyst (B4) was transferred in the following frozen embryo transfer (FET).

RESULTS

In this PGD cycle, sixteen MII oocytes were inseminated by ICSI with testicular spermatozoa. Four blastocysts (B4, B5, B10, B13) were utilized for TE cell biopsy on day 5 after ICSI. After PGD, B4 was unaffected by CCA and SBMA. B5 was affected by CCA and carried SBMA. B10 was unaffected by CCA and carried SBMA. B13 was affected by CCA and unaffected by SBMA. B4 was the only unaffected blastocyst and transferred into the uterus for the subsequent FET cycle. The accuracy of PGD was confirmed by amniocentesis at 21 weeks of gestation. A healthy boy weighing 2850 g was born by cesarean section at the 38th week of gestation.

CONCLUSIONS

PGD is a valid screening tool for patienst affected of CCA and SBMA to prevent transmission of these genetic diseases from parents to children.

The Past, Present, and Future of Preimplantation Genetic Testing

Preimplantation genetic testing (PGT) of oocytes and embryos is the earliest form of prenatal testing. PGT requires in vitro fertilization for embryo creation. In the past 25 years, the use of PGT has increased dramatically. The indications of PGT include identification of embryos harboring single-gene disorders, chromosomal structural abnormalities, chromosomal numeric abnormalities, and mitochondrial disorders; gender selection; and identifying unaffected, HLA-matched embryos to permit the creation of a savior sibling. PGT is not without risks, limitations, or ethical controversies. This review discusses the techniques and clinical applications of different forms of PGT and the debate surrounding its associated uncertainty and expanded use.

Clinical Considerations of Preimplantation Genetic Diagnosis for Monogenic Diseases

Purpose

The aim of this study was to explore factors contribute to the success of PGD cycles for monogenic diseases.

Methods

During a 3-year period (January 2009 to December 2012), 184 consecutive ICSI-PGD cycles for monogenic diseases reaching the ovum pick-up and fresh embryo-transfer stage performed at the Reproductive Medicine Center of The First Affiliated Hospital Of Sun Yat-sen University were evaluated.

Results

ICSI was performed on 2206 metaphase II oocytes, and normal fertilization and cleavage rates were 83.4% (1840/2206) and 96.2% (1770/1840), respectively. In the present study, 60.5% (181/299) of day 3 good-quality embryos developed into good-quality embryos on day 4 after biopsy. Collectively, 42.9% clinical pregnancy rate (79/184) and 28.5% implantation rate (111/389) were presented. In the adjusted linear regression model, the only two significant factors affecting the number of genetically unaffected embryos were the number of biopsied embryos (coefficient: 0.390, 95%CI 0.317–0.463, P = 0.000) and basal FSH level (coefficient: 0.198, 95%CI 0.031–0.365, P = 0.021). In the adjusted binary logistic regression model, the only two significant factors affecting pregnancy outcome were the number of genetically available transferable embryos after PGD (adjusted OR 1.345, 95% CI 1.148–1.575, P = 0.000) and number of oocyte retrieved (adjusted OR 0.934, 95% CI 0.877–0.994, P = 0.031).

Conclusion

There should be at least four biopsied embryos to obtain at least one unaffected embryos in a PGD system for patients with single gene disorder and under the condition of basal FSH level smaller than 8.0mmol/L. Moreover, if only a low number (< 4) of biopsied embryos are available on day 3, the chance of unaffected embryos for transfer was small, with poor outcome.

A simple strategy for reducing false negatives in calling variants from single-cell sequencing data

Due to the growth of interest in single-cell genomics, computational methods for distinguishing true variants from artifacts are highly desirable. While special attention has been paid to false positives in variant or mutation calling from single-cell sequencing data, an equally important but often neglected issue is that of false negatives derived from allele dropout during the amplification of single cell genomes. In this paper, we propose a simple strategy to reduce the false negatives in single-cell sequencing data analysis. Simulation results show that this method is highly reliable, with an error rate of 4.94×10^-5, which is orders of magnitude lower than the expected false negative rate (~34%) estimated from a single-cell exome dataset, though the method is limited by the low SNP density in the human genome. We applied this method to analyze the exome data of a few dozen single tumor cells generated in previous studies, and extracted cell specific mutation information for a small set of sites. Interestingly, we found that there are difficulties in using the classical clonal model of tumor cell growth to explain the mutation patterns observed in some tumor cells.

Live birth after PGD with confirmation by a comprehensive approach (karyomapping) for simultaneous detection of monogenic and chromosomal disorders

Preimplantation genetic diagnosis (PGD) for monogenic disorders has the drawback of time and cost associated with tailoring a specific test for each couple, disorder, or both. The inability of any single assay to detect the monogenic disorder in question and simultaneously the chromosomal complement of the embryo also limits its application as separate tests may need to be carried out on the amplified material. The first clinical use of a novel approach ('karyomapping') was designed to circumvent this problem. In this example, karyomapping was used to confirm the results of an existing PGD case detecting both chromosomal abnormalities and a monogenic disorder (Smith-Lemli-Opitz [SLO] syndrome) simultaneously. The family underwent IVF, ICSI and PGD, and both polar body and cleavage stage biopsy were carried out. Following whole genome amplification, array comparative genomic hybridisation of the polar bodies and minisequencing and STR analysis of single blastomeres were used to diagnose maternal aneuploidies and SLO status, respectively. This was confirmed, by karyomapping. Unlike standard PGD, karyomapping required no a-priori test development. A singleton pregnancy and live birth, unaffected with SLO syndrome and with no chromosome abnormality, ensued. Karyomapping is potentially capable of detecting a wide spectrum of monogenic and chromosome disorders and, in this context, can be considered a comprehensive approach to PGD.

Revisited diagnostics of hereditary epidermolysis bullosa

Hereditary epidermolysis bullosa is a big group of hereditary diseases with the main manifestations in the form of blisters on the skin and mucous coat after slight mechanical injuries. It is not always possible to diagnose this disease based on the clinical picture. The article discusses current laboratory diagnostics methods for hereditary epidermolysis bullosa including immunofluorescence antigen mapping (IFM), transmission electron microscopy (TEM) and genetic analysis (molecular or DNA diagnostics) as well as their advantages and disadvantages. TEM determines the micro splitting level and nature of ultrafine changes in the area of the dermoepidermal junction; at the same time, such tests need special expensive equipment. Substantial experience is also needed to analyze the resulting submicroscopic images. IFM determines whether expression of the affected protein related to the disease development is reduced or absent; however, invalid (false positive or false negative) results can be obtained in patients with the reduced expression of the affected protein. Genetic analysis plays a key role for prenatal diagnostics. Therefore, to make an exact diagnosis of hereditary epidermolysis bullosa, it is expedient to apply IFM, TEM and genetic analysis. The need to set an exact diagnosis of the disease is related to the fact that the promising treatment methods being currently developed are aimed at treating patients with certain forms of the disease.

Preimplantation genetic diagnosis for cystic fibrosis: the Montpellier center's 10-year experience

This study provides an overview of 10 years of experience of preimplantation genetic diagnosis (PGD) for cystic fibrosis (CF) in our center. Owing to the high allelic heterogeneity of CF transmembrane conductance regulator (CFTR) mutations in south of France, we have set up a powerful universal test based on haplotyping eight short tandem repeats (STR) markers together with the major mutation p.Phe508del. Of 142 couples requesting PGD for CF, 76 have been so far enrolled in the genetic work-up, and 53 had 114 PGD cycles performed. Twenty-nine cycles were canceled upon in vitro fertilization (IVF) treatment because of hyper- or hypostimulation. Of the remaining 85 cycles, a total of 493 embryos were biopsied and a genetic diagnosis was obtained in 463 (93.9%), of which 262 (without or with a single CF-causing mutation) were transferable. Twenty-eight clinical pregnancies were established, yielding a pregnancy rate per transfer of 30.8% in the group of seven couples with one member affected with CF, and 38.3% in the group of couples whose both members are carriers of a CF-causing mutation [including six couples with congenital bilateral absence of the vas deferens (CBAVD)]. So far, 25 children were born free of CF and no misdiagnosis was recorded. Our test is applicable to 98% of couples at risk of transmitting CF.

Preimplantation Genetic Diagnosis: Prenatal Testing for Embryos Finally Achieving Its Potential

Preimplantation genetic diagnosis was developed nearly a quarter-century ago as an alternative form of prenatal diagnosis that is carried out on embryos. Initially offered for diagnosis in couples at-risk for single gene genetic disorders, such as cystic fibrosis, spinal muscular atrophy and Huntington disease, preimplantation genetic diagnosis (PGD) has most frequently been employed in assisted reproduction for detection of chromosome aneuploidy from advancing maternal age or structural chromosome rearrangements. Major improvements have been seen in PGD analysis with movement away from older, less effective technologies, such as fluorescence in situ hybridization (FISH), to newer molecular tools, such as DNA microarrays and next generation sequencing. Improved results have also started to be seen with decreasing use of Day 3 blastomere biopsy in favor of polar body or Day 5 trophectoderm biopsy. Discussions regarding the scientific, ethical, legal and social issues surrounding the use of sequence data from embryo biopsy have begun and must continue to avoid concern regarding eugenic or inappropriate use of this technology.

Molecular cytogenetics: making it safe for human embryonic stem cells to enter the clinic

Regenerative therapies based on transplantation of cells derived from human embryonic stem cells (hESC) are currently being prepared for clinical trials. Unfortunately, recent evidence indicates that many kinds of changes can occur to hESC during expansion in culture, and alterations to the growth control mechanisms may be required to establish hESC lines at all. Changes in the genome and epigenome can affect the validity of in vitro and animal studies, and put transplant recipients at increased risk of cancer. New molecular cytogenetic technologies enable us to examine the whole human genome with ever-finer resolution. This review describes several techniques for whole-genome analysis and the information they can provide about hESC lines. Adoption of high-resolution genotyping into routine characterization may prevent highly discouraging clinical outcomes.

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.

Preimplantation genetic diagnosis: its role in prevention of deafness

Deafness is a global problem. In India deafness ranges from 4 % in urban to 11 % in rural and slum areas, out of which 50 % is conductive hearing loss hence curable. Genetic transmission accounts for 50 % of the cases of congenital deafness, and of these, around 30 % are syndromic and 70 % are non-syndromic. Genetic counseling is going to make aware the parents of all appropriate treatments. Preimplantation genetic diagnosis can help to have a baby free from genetic deafness. Procedure is almost safe, harmless, non-invasive and ethically acceptable. While Amniocentesis is a non-invasive method, prenatal genetic testing through Chorionic villous sampling is invasive. The connexin 26 (CX26W 24X) mutations are the most common cause of non-syndromic hearing loss and easy to identify by polymerase chain reaction. There is always co-morbidity after cochlear implantation and the person remains handicapped while baby after PGD shall be having healthy normal life and person prone to environmental factors may be counseled and guided to prevent deafness in next generation. Public must be made aware of noise pollution, tobacco toxicity and consanguinity. The Obstetrician and Pediatrician apart from ENT surgeon should be involved to prevent antenatal or neonatal deafness.

Evaluation of PCR-based preimplantation genetic diagnosis applied to monogenic diseases: a collaborative ESHRE PGD consortium study

Preimplantation genetic diagnosis (PGD) for monogenic disorders currently involves polymerase chain reaction (PCR)-based methods, which must be robust, sensitive and highly accurate, precluding misdiagnosis. Twelve adverse misdiagnoses reported to the ESHRE PGD-Consortium are likely an underestimate. This retrospective study, involving six PGD centres, assessed the validity of PCR-based PGD through reanalysis of untransferred embryos from monogenic-PGD cycles. Data were collected on the genotype concordance at PGD and follow-up from 940 untransferred embryos, including details on the parameters of PGD cycles: category of monogenic disease, embryo morphology, embryo biopsy and genotype assay strategy. To determine the validity of PCR-based PGD, the sensitivity (Se), specificity (Sp) and diagnostic accuracy were calculated. Stratified analyses were also conducted to assess the influence of the parameters above on the validity of PCR-based PGD. The analysis of overall data showed that 93.7% of embryos had been correctly classified at the time of PGD, with Se of 99.2% and Sp of 80.9%. The stratified analyses found that diagnostic accuracy is statistically significantly higher when PGD is performed on two cells versus one cell (P=0.001). Se was significantly higher when multiplex protocols versus singleplex protocols were applied (P=0.005), as well as for PGD applied on cells from good compared with poor morphology embryos (P=0.032). Morphology, however, did not affect diagnostic accuracy. Multiplex PCR-based methods on one cell, are as robust as those on two cells regarding false negative rate, which is the most important criteria for clinical PGD applications. Overall, this study demonstrates the validity, robustness and high diagnostic value of PCR-based PGD.

Familial haplotyping and embryo analysis for Preimplantation genetic diagnosis (PGD) using DNA microarrays: a proof of principle study

PURPOSE

Development of PGD assays for molecular disorders is based on analysis of a familial mutation together with linked polymorphic STR markers; a process which is lengthy and requires the identification of multiple informative markers prior to PGD analysis. On the other hand, whole genome amplification (WGA), in conjunction with microarray platforms, allows the use of a universal assay for the analysis of a very large number of SNP markers at once. The aim of this study was to test high throughput pre-PGD familial haplotyping for in-case blastomere analysis in order to eliminate time-consuming pre-case preparations for each family.

METHODS

A PGD cycle was performed for a couple with paternal Charcot Marie Tooth 1A (CMT1A) using a classic multiplex nested PCR approach. Mutant embryos from the case were blindly reanalyzed, as single or multi-cell biopsies, using a multiple displacement amplification-based WGA protocol and microarray SNP analysis. In parallel, relevant genomic DNA samples from the family were also analyzed by SNP microarray.

RESULTS

After applying a 'unique informative allele' selection algorithm to the data, this array-based assay reconfirmed the initial diagnosis in all samples.

CONCLUSIONS

We describe a PGD method that is both accurate and feasible during the time-frame required for embryo transfer. This strategy greatly reduces the time for pre-case haplotype preparation.

PGD for hereditary breast and ovarian cancer: the route to universal tests for BRCA1 and BRCA2 mutation carriers

Preimplantation Genetic Diagnosis (PGD) is a method of testing in vitro embryos as an alternative to prenatal diagnosis with possible termination of pregnancy in case of an affected child. Recently, PGD for hereditary breast and ovarian cancer caused by BRCA1 and BRCA2 mutations has found its way in specialized labs. We describe the route to universal single-cell PGD tests for carriers of BRCA1/2 mutations. Originally, mutation-specific protocols with one or two markers were set up and changed when new couples were not informative. This route of changing protocols was finalized after 2 years with universal tests for both BRCA1 and BRCA2 mutation carriers based on haplotyping of, respectively, 6 (BRCA1) and 8 (BRCA2) microsatellite markers in a multiplex PCR. Using all protocols, 30 couples had a total of 47 PGD cycles performed. Eight cycles were cancelled upon IVF treatment due to hypostimulation. Of the remaining 39 cycles, a total of 261 embryos were biopsied and a genetic diagnosis was obtained in 244 (93%). In 34 of the 39 cycles (84.6%), an embryo transfer was possible and resulted in 8 pregnancies leading to a fetal heart beat per oocyte retrieval of 20.5% and a fetal heart beat per embryonic transfer of 23.5%. The preparation time and costs for set-up and validation of tests are minimized. The informativity of microsatellite markers used in the universal PGD-PCR tests is based on CEPH and deCODE pedigrees, making the tests applicable in 90% of couples coming from these populations.

Preimplantation genetic diagnosis in genomic regions with duplications and pseudogenes: long-range PCR in the single-cell assay

Long-range PCR is generally employed for the analysis of disease-causing mutations in genes with homologous pseudogene copies. However, long-range PCR is challenging when performed on single cells, as in preimplantation genetic diagnosis (PGD) of monogenic disorders. PGD on single cells requires concurrent analysis of a mutation together with multiple linked polymorphic markers from closely related family members to prevent misdiagnosis. In PGD cases involving childless de novo mutation carriers, linkage cannot be performed based on family members but rather must first be identified in single gametes. This can be an especially difficult task if the mutation to be assayed lies in a duplicated genomic region because gene-specific long-range PCR must be coupled with short-range PCR analysis of genetic markers on single cells. Here, we describe a novel method by which accurate PGD of pseudogene-homologous mutations can be achieved. Essentially, we performed whole genome amplification on single sperm or blastomeres followed by haplotype construction and long-range PCR-based mutation analysis. This original and universal strategy was used to establish allelic association for two different mutations in genes with one or more pseudogene copies (IKBKG and PKD1). The method was also sensitive enough to detect unexpected germline mosaicism in one mutation carrier.

Strategy for the creation of clinical grade hESC line banks that HLA-match a target population

Here, we describe a pre-derivation embryo haplotyping strategy that we developed in order to maximize the efficiency and minimize the costs of establishing banks of clinical grade hESC lines in which human leukocyte antigen (HLA) haplotypes match a significant proportion of the population. Using whole genome amplification followed by medium resolution HLA typing using PCR amplification with sequence-specific primers (PCR-SSP), we have typed the parents, embryos and hESC lines from three families as well as our eight clinical grade hESC lines and shown that this technical approach is rapid, reliable and accurate. By employing this pre-derivation strategy where, based on HLA match, embryos are selected for a GMP route on day 3-4 of development, we would have drastically reduced our cGMP laboratory running costs.

Preimplantation genetic diagnosis and deafness

Deafness in India ranges from 4.0 % in urban and 4.0-11 % in rural and slum areas, out of which 50 % are of conductive hearing loss hence curable. In the congenital hearing loss the incidence of syndromic hearing loss is only 30 %, rest 70 % are non syndromic. Genetic counseling is going to make aware the parents. Preimplantation genetic diagnosis can help to have a baby free from genetic deafness. Procedure is almost safe, harmless, non-invasive and ethically acceptable. While by genetic testing through prenatal genetic testing, amniocentesis and chorionic villous sampling is invasive and termination of pregnancy is difficult, social and ethical issue. The connexin 26 (CX26W 24X) has been observed as most common and easy to identify by polymerase chain reaction. There is always co morbidity after cochlear implantation and the person remains handicapped while baby after PGD shall be having healthy normal life and person prone to environmental factors may be counseled and guided to prevent deafness in next generation. Public must be made aware of noise pollution, tobacco toxicity and consanguinity. The obstetrician and pediatrician apart from ENT surgeon should be involved to prevent antenatal or neonatal deafness.

A short and simple improved-primer extension preamplification (I-PEP) procedure for whole genome amplification (WGA) of bovine cells

Embryo transfer is a reproductive technique that has a major impact on the dissemination of economically important genes and the rate of genetic gain in breeding schemes. In recent years, there has been increasing interest in the use of sexed and genotyped embryos in commercial embryo transfer programs. Marker/gene assisted selection (MAS/GAS) projects can be performed in the pre-implantation stage through mass production of characterized embryos. Biopsy of a few cells in the morulla stage is essential for pre-implantation genetic diagnosis (PGD), in which sex determination, evaluation of disease genes, and genotyping for candidate genes are performed. Limited quantity of cells and low amount of DNA restrict the use of multiple molecular analyses in PGD programs. Recently, whole genome amplification (WGA) techniques promise to overcome this problem by providing sufficient input DNA for analysis. Among several techniques proposed for WGA, the primer extension pre-amplification (PEP) and the improved-primer extension pre-amplification (I-PEP) methods are the most commonly used. However, these methods are time-consuming and need more than 12 h amplification cycles. Since the time is a critical parameter in the successful characterized embryo transfer, the shortening of diagnosis time is highly desirable. In this study, we developed a short and simple I-PEP procedure (~3 h) and evaluated its performance for the amplification of bovine genomic DNA. We assessed short WGA procedure by polymerase chain reaction (PCR) amplification of 7 specific loci. The results indicated that the short procedure possesses enough sensitivity for the molecular genetic analysis of 1 input cell. Although the efficiency of the method was 100%, there was an inconsistency between genomic DNA (gDNA) and whole genome amplification product (wgaDNA) genotypes for kappa-casein locus; that is, however, most likely due to allele drop-out (ADO) or false homozigocity. The results of this study indicate that with the application of reliable methods, WGA-amplified bovine DNA will be a useful source for sexing and genotyping bovine embryos in several quantitative trait locus (QTL) markers.

Preimplantation testing: Transition from genetic to genomic diagnosis

Preimplantation genetic testing refers to the procedure to determine the genetic status of embryos formed by in vitro fertilization (IVF) prior to initiating a pregnancy. Traditional genetic methods for preimplantation genetic diagnosis (PGD) examine distinct parts of an individual genome, require the development of a custom assay for every patient family, and are time consuming and inefficient. In the last decade technologies for whole-genome amplification (WGA) from single cells have led to innovative strategies for preimplantation testing. Applications of WGA technology can lead to a universal approach that uses single-nucleotide polymorphisms (SNPs) and mutations across the entire genome for the analysis. Single-cell WGA by multiple displacement amplification has enabled a linkage approach to PGD known as “preimplantation genetic haplotyping”, as well as microarray-based techniques for preimplantation diagnosis. The use of microarrays in preimplantation diagnosis has provided genome-wide testing for gains or losses of single chromosomes (aneuploidies) or chromosomal segments. Properly designed randomized controlled trials are, however, needed to determine whether these new technologies improve IVF outcomes by increasing implantation rates and decreasing miscarriage rates. In genotype analysis of single cells, allele dropout occurs frequently at heterozygous loci. Preimplantation testing of multiple cells biopsied from blastocysts, however, can reduce allele dropout rates and increase the accuracy of genotyping, but it allows less time for PGD. Future development of fast SNP microarrays will enable a universal preimplantation testing for aneuploidies, single-gene disorders and unbalanced translocations within the time frame of an IVF cycle.