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

Comprehensive preimplantation genetic testing for balanced insertional translocation carriers

BACKGROUND

Balanced insertional translocations (BITs) can increase the risk of infertility, recurrent miscarriages or neonatal birth defects due to chromosomal imbalances in gametes. However, studies on preimplantation genetic testing (PGT) for patients carrying BITs are inadequate.

METHODS

A preimplantation genetic genotyping and haplotype analysis approach was developed and implemented in this study. Genome-wide SNP genotyping was performed, followed by core family-based haplotype analysis. The balanced insertion segments in euploid embryos were inferred from the haplotypes inherited from the carrier parent.

RESULTS

A total of 10 BIT carrier couples were enrolled in our study. 15 in vitro fertilisation cycles were conducted, resulting in 73 blastocysts biopsied and subjected to PGT analysis. Among these, 20 blastocysts displayed rearrangement-related imbalances, 13 exhibited de novo aneuploidies, 15 presented a complex anomaly involving both imbalances and additional aneuploidies, while 25 were euploid. Within the euploid embryos, 12 were balanced carrier embryos and 13 were non-carrier embryos. To date, eight non-carrier and one carrier embryos have been transferred, resulting in seven clinical pregnancies. All pregnancies were recommended to perform prenatal diagnosis, our date revealed complete concordance between fetal genetic testing results and PGT results. Presently, five infants have been born from these pregnancies, and two pregnancies are still ongoing.

CONCLUSION

The proposed method facilitates comprehensive chromosome screening and the concurrent identification of balanced insertions or normal karyotypes in embryos. This study offers an effective and universally applicable strategy for BIT carriers to achieve a healthy pregnancy and prevent the transmission of BITs to their offspring.

Extended application of PGT-M strategies for small pathogenic CNVs

PURPOSE

The preimplantation genetic testing for aneuploidy (PGT-A) platform is not currently available for small copy-number variants (CNVs), especially those < 1 Mb. Through strategies used in PGT for monogenic disease (PGT-M), this study intended to perform PGT for families with small pathogenic CNVs.

METHODS

Couples who carried small pathogenic CNVs and underwent PGT at the Reproductive and Genetic Hospital of CITIC-Xiangya (Hunan, China) between November 2019 and April 2023 were included in this study. Haplotype analysis was performed through two platforms (targeted sequencing and whole-genome arrays) to identify the unaffected embryos, which were subjected to transplantation. Prenatal diagnosis using amniotic fluid was performed during 18-20 weeks of pregnancy.

RESULTS

PGT was successfully performed for 20 small CNVs (15 microdeletions and 5 microduplications) in 20 families. These CNVs distributed on chromosomes 1, 2, 6, 7, 13, 15, 16, and X with sizes ranging from 57 to 2120 kb. Three haplotyping-based PGT-M strategies were applied. A total of 89 embryos were identified in 25 PGT cycles for the 20 families. The diagnostic yield was 98.9% (88/89). Nineteen transfers were performed for 17 women, resulting in a 78.9% (15/19) clinical pregnancy rate after each transplantation. Of the nine women who had healthy babies, eight accepted prenatal diagnosis and the results showed no related pathogenic CNVs.

CONCLUSION

Our results show that the extended haplotyping-based PGT-M strategy application for small pathogenic CNVs compensated for the insufficient resolution of PGT-A. These three PGT-M strategies could be applied to couples with small pathogenic CNVs.

A Retrospective Analysis of Robertsonian Translocations from a Single Center in China

Robertsonian translocations (ROBs) are the most common structural chromosomal abnormalities in the general population, with an estimated incidence rate of 1/1000 births. In this study, we retrospectively analyzed the cases of ROBs from September 2015 to August 2022 and totally identified ROB carriers from 84,569 specimens karyotyped in a single accredited laboratory in China, including 189 cases of balanced ROBs and 3 of mosaic ROBs. Microsoft Excel and descriptive statistics were used to record and analyze the collected data. The male/female ratio of ROBs is 1/1.29, with der(13;14) and der(14;21) being the main karyotypes. Among the 192 patients, 7 were lost to follow-up, 82 had given birth, and 103 were childless (such as miscarriage, fetal chromosomal abnormalities, in vitro fertilization (IVF) failure, or divorce). A total of 44 amniocenteses were performed in 42 couples; ROB cases with natural pregnancies showed that the normal karyotype and balanced ROBs of fetal accounted for 66.67% (16/24), while the results of assisted pregnancies showed 90.00% (18/20). This study represents the largest collections of ROBs in Jiangxi population and reminder that the ROB carriers can achieve the ideal outcome for pregnancy with the appropriate genetic guidance and assisted reproductive technologies (ART).

Preimplantation genetic testing: A remarkable history of pioneering, technical challenges, innovations, and ethical considerations

Preimplantation genetic testing (PGT) has emerged as a powerful companion to assisted reproduction technologies. The origins and history of PGT are reviewed here, along with descriptions of advances in molecular assays and sampling methods, their capabilities, and their applications in preventing genetic diseases and enhancing pregnancy outcomes. Additionally, the potential for increasing accuracy and genome coverage is considered, as well as some of the emerging ethical and legislative considerations related to the expanding capabilities of PGT.

The effect of parental carrier of de novo mutated vs. inherited balanced reciprocal translocation on the chance of euploid embryos

OBJECTIVE

To evaluate whether the effect of de novo mutated balanced reciprocal translocation on the rate of euploid embryos varied from inherited balanced reciprocal translocation.

DESIGN

A retrospective cohort study compared the percentage of euploid embryo and proportion of patients with at least 1 euploid embryo between de novo mutated balanced reciprocal translocation (i.e., the group of de novo mutated carriers) and inherited balanced reciprocal translocation (i.e., the group of inherited carriers).

SETTING

An academic fertility center.

PATIENT(S)

A total of 413 couples with balanced reciprocal translocation (219 female carriers and 194 male carriers) who underwent their first cycle of preimplantation genetic testing for structural rearrangements were included.

INTERVENTION(S)

Carriers of balanced reciprocal translocation either de novo mutated or inherited.

MAIN OUTCOME MEASURE(S)

The percentage of euploid embryo and proportion of patients with at least 1 euploid embryo.

RESULT(S)

The carriers of the de novo mutated balanced reciprocal translocation had a lower percentage of euploid embryos (19.5% vs. 25.5%), and were less likely to have at least 1 euploid embryo (47.1% vs. 60.1%) compared with the carriers of the inherited balanced reciprocal translocation. In the male-carrier subgroup, the percentage of euploid embryos (16.7% vs. 26.7%) and proportion of patients with at least 1 euploid embryo (41.9% vs. 67.5%) were lower among the de novo mutated carriers than those among the inherited carriers. However, in the female-carrier subgroup, there was no statistically significant difference in the percentage of euploid embryos (22.4% vs. 24.4%) or the proportion of patients with at least 1 euploid embryo (52.3% vs. 53.7%) between the de novo mutated carriers and inherited carriers.

CONCLUSION(S)

The de novo mutated balanced reciprocal translocation was associated with a lower percentage of euploid embryos and lower chance of obtaining at least 1 euploid embryo than the inherited balanced reciprocal translocation.

A novel multifunctional haplotyping-based preimplantation genetic testing for different genetic conditions

STUDY QUESTION

Is there an efficient and cost-effective detection platform for different genetic conditions about embryos?

SUMMARY ANSWER

A multifunctional haplotyping-based preimplantation genetic testing platform was provided for detecting different genetic conditions.

WHAT IS KNOWN ALREADY

Genetic disease and chromosomal rearrangement have been known to significantly impact fertility and development. Therefore, preimplantation genetic testing for aneuploidy (PGT-A), monogenic disorders (PGT-M) and structural rearrangements (PGT-SR), a part of ART, has been presented together to minimize the fetal genetic risk and increase pregnancy rate. For patients or their families who are suffering from chromosome abnormality, monogenic disease, unexplained repeated spontaneous abortion or implantation failure, after accepting genetic counseling, they may be suggested to accept detection from more than one PGT platforms about the embryos to avoid some genetic diseases. However, PGT platforms work through different workflows. The high costliness, lack of material and long-time operation of combined PGT platforms limit their application.

STUDY DESIGN, SIZE, DURATION

All 188 embryonic samples from 43 families were tested with HaploPGT platform, and most of their genetic abnormalities had been determined by different conventional PGT methods beforehand. Among them, there were 12 families only carrying structural rearrangements (115 embryos) in which 9 families accepted implantation and 5 families had normal labor ART outcomes, 7 families only carrying monogenic diseases (26 embryos) and 3 families carrying both structural rearrangements and monogenic diseases (26 embryos). Twelve monopronucleated zygotes (1PN) samples and 9 suspected triploid samples were collected from 21 families.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

Here, we raised a comprehensive PGT method called HaploPGT, combining reduced representation genome sequencing, read-count analysis, B allele frequency and haplotyping analysis, to simultaneously detect different genetic disorders in one single test.

MAIN RESULTS AND THE ROLE OF CHANCE

With 80 million reads (80M) genomic data, the proportion of windows (1 million base pairs (Mb)) containing two or more informative single nucleotide polymorphism (SNP) sites was 97.81%, meanwhile the genotyping error rate stabilized at a low level (2.19%). Furthermore, the informative SNPs were equally distributed across the genome, and whole-genomic haplotyping was established. Therefore, 80M was chosen to balance the cost and accuracy in HaploPGT. HaploPGT was able to identify abnormal embryos with triploid, global and partial loss of heterozygosity, and even to distinguish parental origin of copy number variation in mosaic and non-mosaic embryos. Besides, by retrospectively analyzing 188 embryonic samples from 43 families, HaploPGT revealed 100% concordance with the available results obtained from reference methods, including PGT-A, PGT-M, PGT-SR and PGT-HLA.

LIMITATIONS, REASON FOR CAUTION

Despite the numerous benefits HaploPGT could bring, it still required additional family members to deduce the parental haplotype for identifying balanced translocation and monogenic mutation in tested embryos. In terms of PGT-SR, the additional family member could be a reference embryo with unbalanced translocation. For PGT-M, a proband was normally required. In both cases, genomic information from grandparents or parental siblings might help for haplotyping theoretically. Another restriction was that haploid, and diploid resulting from the duplication of a haploid, could not be told apart by HaploPGT, but it was able to recognize partial loss of heterozygosity in the embryonic genome. In addition, it should be noted that the location of rearrangement breakpoints and the situation of mutation sites were complicated, which meant that partial genetic disorders might not be completely detected.

WIDER IMPLICATIONS OF THE FINDINGS

HaploPGT is an efficient and cost-effective detection platform with high clinical value for detecting genetic status. This platform could promote the application of PGT in ART, to increase pregnancy rate and decrease the birth of children with genetic diseases.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by grants from the National Natural Science Foundation of China (81873478, to L.H.), National Key R&D Program of China (2018YFC1003100, to L.H.), the Natural Science Foundation of Hunan Province (Grant 2022JJ30414, to P.X.), Hunan Provincial Grant for Innovative Province Construction (2019SK4012) and the Scientific Research Foundation of Reproductive and Genetic Hospital of China International Trust & Investment Corporation (CITIC)-Xiangya (YNXM-201910). Haplotyping analysis has been licensed to Basecare Co., Ltd. L.K., Y.M., K.K., D.Z., N.L., J.Z. and R.D. are Basecare Co., Ltd employees. The other authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Detection of a Cryptic 25 bp Deletion and a 269 Kb Microduplication by Nanopore Sequencing in a Seemingly Balanced Translocation Involving the LMLN and LOC105378102 Genes

Preimplantation genetic testing plays a critical role in enabling a balanced translocation carrier to obtain the normal embryo. Identifying the precise breakpoints for the carriers with phenotypic abnormity, allows us to reveal disrupted genes. In this study, a seemingly balanced translocation 46, XX, t (3; 6) (q29; q26) was first detected using conventional karyotype analysis. To locate the precise breakpoints, whole genomes of DNA were sequenced based on the nanopore GridION platform, and bioinformatic analyses were further confirmed by polymerase-chain-reaction (PCR) and copy number variation (CNV). Nanopore sequencing results were consistent with the karyotype analysis. Meanwhile, two breakpoints were successfully validated using polymerase-chain-reaction and Sanger Sequencing. LOC105378102 and LMLN genes were disrupted at the breakpoint junctions. Notably, observations found that seemingly balanced translocation was unbalanced due to a cryptic 269 kilobases (Kb) microduplication and a 25 bp deletion at the breakpoints of chromosome (chr) 6 and chr 3, respectively. Furthermore, 269 Kb microduplication was also confirmed by copy number variation analyses. In summary, nanopore sequencing was a rapid and direct method for identifying the precise breakpoints of a balanced translocation despite low coverage (3.8×). In addition, cryptic deletion and duplication were able to be detected at the single-nucleotide level.

Case Report: A Paternal 20q13.2-q13.32 Deletion Patient With Growth Retardation Improved by Growth Hormone

Interstitial chromosome 20q deletions, containing GNAS imprinted locus, are rarely reported in the past. Hereby, we presented a Chinese boy with a novel 4.36 Mb deletion at paternal 20q13.2-13.32, showing feeding difficulty, malnutrition, short stature, lower limb asymmetry, sightly abnormal facial appearance and mild intellectual abnormality. With 3 years’ growth hormone treatment, his height was increased from 90 to 113.5 cm. This report is the first time to describe the outcome of clinical treatment on a patient with this rare chromosomal 20 long arm interstitial deletion, containing GNAS locus, which may facilitate the diagnosis and treatment of this type of patient in the future.

Identifying Balanced Chromosomal Translocations in Human Embryos by Oxford Nanopore Sequencing and Breakpoints Region Analysis

Background: Balanced chromosomal aberrations, especially balanced translocations, can cause infertility, recurrent miscarriage or having chromosomally defective offspring. Preimplantation genetic testing for structural rearrangement (PGT-SR) has been widely implemented to improve the clinical outcomes by selecting euploid embryos for transfer, whereas embryos with balanced translocation karyotype were difficult to be distinguished by routine genetic techniques from those with a normal karyotype.

Method: In this present study, we developed a clinically applicable method for reciprocal translocation carriers to reduce the risk of pregnancy loss. In the preclinical phase, we identified reciprocal translocation breakpoints in blood of translocation carriers by long-read Oxford Nanopore sequencing, followed by junction-spanning polymerase chain reaction (PCR) and Sanger sequencing. In the clinical phase of embryo diagnosis, aneuploidies and unbalanced translocations were screened by comprehensive chromosomal screening (CCS) with single nucleotide polymorphism (SNP) microarray, carrier embryos were diagnosed by junction-spanning PCR and family haplotype linkage analysis of the breakpoints region. Amniocentesis and cytogenetic analysis of fetuses in the second trimester were performed after embryo transfer to conform the results diagnosed by the presented method.

Results: All the accurate reciprocal translocation breakpoints were effectively identified by Nanopore sequencing and confirmed by Sanger sequencing. Twelve embryos were biopsied and detected, the results of junction-spanning PCR and haplotype linkage analysis were consistent. In total, 12 biopsied blastocysts diagnosed to be euploid, in which 6 were aneuploid or unbalanced, three blastocysts were identified to be balanced translocation carriers and three to be normal karyotypes. Two euploid embryos were subsequently transferred back to patients and late prenatal karyotype analysis of amniotic fluid cells was performed. The outcomes diagnosed by the current approach were totally consistent with the fetal karyotypes.

Conclusions: In summary, these investigations in our study illustrated that chromosomal reciprocal translocations in embryos can be accurately diagnosed. Long-read Nanopore sequencing and breakpoint analysis contributes to precisely evaluate the genetic risk of disrupted genes, and provides a way of selecting embryos with normal karyotype, especially for couples those without a reference.

Variant haplophasing by long-read sequencing: a new approach to preimplantation genetic testing workups

OBJECTIVE

To apply long-read, third-generation sequencing as a part of a general workup strategy for performing structural rearrangement (PGT-SR) and monogenic disease (PGT-M) embryo testing.

DESIGN

Prospective study.

SETTING

In vitro fertilization unit.

PATIENT(S)

Couples presenting for PGT-SR (n = 15) and PGT-M (n = 2).

INTERVENTION(S)

Blastocyst biopsy with molecular testing for translocation breakpoints or mutations (targets).

MAIN OUTCOME MEASURE(S)

Detailed, parental-phased, single-nucleotide polymorphism (SNP) profiles around targets for selection of informative polymorphic markers to simplify and facilitate clinical preimplantation genetic testing (PGT) designs that enable discrimination between carrier and noncarrier embryos.

RESULT(S)

High definition of chromosome breakpoints together with closely phased polymorphic markers was achieved for all 15 couples presenting for PGT-SR. Similarly, for the two couples presenting for PGT-M, tightly linked informative markers around the mutations were also simply identified. Three couples with translocations t(1;17)(q21;p13), t(3;13)(p25;q21.2), and t(12;13)(q23;q22) proceeded with PGT-SR, requesting preferential identification of noncarrier embryos for transfer. Following selection of a set of informative SNPs linked to breakpoints, we successfully performed PGT-SR tests, resulting in ongoing pregnancies with a noncarrier fetus for all couples. Similarly, with the use of tests based on informative SNPs linked to the parental mutations, one couple proceeded with PGT-M for maple syrup urine disease, resulting in an ongoing pregnancy with a disease-free fetus.

CONCLUSION(S)

For couples contemplating clinical PGT, variant haplophasing around the target reduces the workup process by enabling rapid selection of closely linked informative markers for patient-specific test design.

Preimplantation genetic testing results of blastocysts from 12 non-Robertsonian translocation carriers with chromosome fusion and comparison with Robertsonian translocation carriers

OBJECTIVE

To investigate the effects of non-Robertsonian translocation with chromosome fusion (N-RBCF) on preimplantation embryos.

DESIGN

Case series.

SETTING

University-affiliated center.

PATIENT(S)

Twelve couples with N-RBCF.

INTERVENTION(S)

Assisted reproduction with preimplantation genetic testing in chromosomal structural rearrangement (PGT-SR).

MAIN OUTCOME MEASURE(S)

Normal embryo rate, unbalanced translocation rate.

RESULT(S)

PGT was performed in 12 N-RBCF carriers, of whom 4 carried Y-autosome fusions and 8 autosomal fusions. A total of 12 (63.2%) of 19 blastocysts exhibited normal/balanced embryos, and only one (5.3%) embryo exhibited unbalanced translocations among Y-autosome fusion cases. In contrast to these findings, the percentage of normal/balanced blastocysts in 8 autosomal N-RBCF cases was 28.2% (11/39), whereas the unbalanced translocation rate was 53.8%. Furthermore, the percentage of normal/balanced embryos in the Robertsonian translocation group was significantly higher than that of the 8 autosomal N-RBCF (48.7% vs. 28.2%) cases. The rates of abnormality from chromosomal fusion in the 8 autosomal N-RBCF cases were significantly higher than those noted in the Robertsonian translocation (53.8% vs. 31.4%) subjects. The results of the stratified analysis according to the carrier's sex demonstrated that the rates of unbalanced translocation were significantly higher in the male autosomal N-RBCF subjects than those from the corresponding Robertsonian translocation (55% vs. 19.7%) cases.

CONCLUSION(S)

A low number of unbalanced translocations was identified in blastocysts from N-RBCF subjects who carried the Y fusion. The risk of unbalanced translocation in autosomal N-RBCF was higher than that of the Robertsonian translocation, notably in male carriers.

Meiotic Heterogeneity of Trivalent Structure and Interchromosomal Effect in Blastocysts With Robertsonian Translocations

Background

Robertsonian translocations are common structural rearrangements and confer an increased genetic reproductive risk due to the formation of trivalent structure during meiosis. Studies on trivalent structure show meiotic heterogeneity between different translocation carriers, although the factors causing heterogeneity have not been well elaborated in blastocysts. It is also not yet known whether interchromosomal effect (ICE) phenomenon occurs in comparison with suitable non-translocation control patients. Herein, we aimed to evaluate the factors that cause meiotic heterogeneity of trivalent structure and the ICE phenomenon.

Methods

We designed a retrospective study, comprising 217 Robertsonian translocation carriers and 134 patients with the risk of transmitting monogenic inherited disorders (RTMIDs) that underwent preimplantation genetic testing (PGT). Data was collected between March 2014 and December 2019. The segregation products of trivalent structure were analyzed based on the carrier’s gender, age and translocation type. In addition, to analyze ICE phenomenon, aneuploidy abnormalities of non-translocation chromosomes from Robertsonian translocation carriers were compared with those from patients with RTMIDs.

Results

We found that the percentage of male carriers with alternate segregation pattern was significantly higher [P < 0.001, odds ratio (OR) = 2.95] than that in female carriers, while the percentage of adjacent segregation pattern was lower (P < 0.001, OR = 0.33). By contrast, no difference was observed between young and older carriers when performing stratified analysis by age. Furthermore, segregation pattern was associated with the D;G chromosomes involved in Robertsonian translocation: the rate of alternate segregation pattern in Rob(13;14) carriers was significantly higher (P = 0.010, OR = 1.74) than that in Rob(14;21) carriers, whereas the rate of adjacent segregation pattern was lower (P = 0.032, OR = 0.63). Moreover, the results revealed that the trivalent structure could significantly increase the frequencies of chromosome aneuploidies 1.30 times in Robertsonian translocation carriers compared with patients with RTMIDs (P = 0.026), especially for the male and young subgroups (P = 0.030, OR = 1.35 and P = 0.012, OR = 1.40), while the mosaic aneuploidy abnormalities presented no statistical difference.

Conclusions

Our study demonstrated that meiotic segregation heterogeneity of trivalent structure is associated with the carrier’s gender and translocation type, and it is independent of carrier’s age. ICE phenomenon exists during meiosis and then increases the frequencies of additional chromosome abnormalities.

Predictive Prenatal Diagnosis for Infantile-onset Inflammatory Bowel Disease Because of Interleukin-10 Signalling Defects

OBJECTIVES

Advances in genetic technologies provide opportunities for patient care and ethical challenges. Clinical care of patients with rare Mendelian disorders is often at the forefront of those developments. Whereas in classical polygenic inflammatory bowel disease (IBD), the predictive value of genetic variants is very low, predictive prenatal genetic diagnosis can inform families at high risk of severe genetic disorders. Patients with IL-10 signalling defects because of pathogenic variants in IL10RA, Il10RB, and IL10 develop severe infantile onset inflammatory bowel disease that is completely penetrant and has a high morbidity and substantial mortality despite treatment.

METHODS

We performed a survey among tertiary specialist paediatric centers of 10 countries on the utilization of predictive prenatal genetic diagnosis in IL-10 signalling defects. We retrospectively report prenatal genetics in a series of 8 families.

RESULTS

International variation in legislation, guidelines, expert opinion, as well as cultural and religious background of families and clinicians results in variable utilization of preimplantation and prenatal genetic testing for IL-10 signalling defects. Eleven referrals for prenatal diagnosis for IL-10 signalling defects were identified across 4 countries. We report on 8 families who underwent prenatal preimplantation monogenic testing after in vitro fertilization (n = 2) and/or by amniocentesis/chorion villus sampling (n = 6). A genetic diagnosis was established in 1 foetus and excluded in 7 foetuses (all IL10RA variants).

CONCLUSIONS

Prenatal genetic testing for IL10R-defects is feasible, yet the legal and ethical considerations are complex and controversial. In some countries, predictive genetics for IL-10-related signalling defects is entering clinical practice.

Feasibility study of using unbalanced embryos as a reference to distinguish euploid carrier from noncarrier embryos by single nucleotide polymorphism array for reciprocal translocations

OBJECTIVES

To study the feasibility of using unbalanced embryos as a reference in distinguishing euploid carrier and noncarrier embryos by single nucleotide polymorphism (SNP) array-based preimplantation genetic testing (PGT) for reciprocal translocations.

METHODS

After comprehensive chromosome screening (CCS), euploid embryos were identified as normal or carriers using a family member as a reference. Next, unbalanced embryos were used as a reference, and the results were compared with the previous ones. Karyotypes of transferred embryos were validated by prenatal diagnosis.

RESULTS

Of 995 embryos from 110 couples, 288 were found to be euploid. Using a family member as a reference, 142 and 144 embryos were tested to be euploid noncarrier and carrier respectively, and the remaining 2 embryos were undetermined. When unbalanced embryos were selected as references, all the results were consistent with the previous ones. A total of 107 embryos were transferred, resulting in 66 clinical pregnancies. Karyotypes of prenatal diagnosis were all in accordance with the results of tested embryos.

CONCLUSIONS

SNP array-based haplotyping is a rapid and effective way to distinguish between euploid carrier and noncarrier embryos. In case no family member is available as a reference, unbalanced embryos can be used for identification of euploid carrier and noncarrier embryos.

A systematic review on concurrent aneuploidy screening and preimplantation genetic testing for hereditary disorders: What is the prevalence of aneuploidy and is there a clinical effect from aneuploidy screening?

INTRODUCTION

In assisted reproductive technology, aneuploidy is considered a primary cause of failed embryo implantation. This has led to the implementation of preimplantation genetic testing for aneuploidy in some clinics. The prevalence of aneuploidy and the use of aneuploidy screening during preimplantation genetic testing for inherited disorders has not previously been reviewed. Here, we systematically review the literature to investigate the prevalence of aneuploidy in blastocysts derived from patients carrying or affected by an inherited disorder, and whether screening for aneuploidy improves clinical outcomes.

MATERIAL AND METHODS

PubMed and Embase were searched for articles describing preimplantation genetic testing for monogenic disorders and/or structural rearrangements in combination with preimplantation genetic testing for aneuploidy. Original articles reporting aneuploidy rates at the blastocyst stage and/or clinical outcomes (positive human chorionic gonadotropin, gestational sacs/implantation rate, fetal heartbeat/clinical pregnancy, ongoing pregnancy, miscarriage, or live birth/delivery rate on a per transfer basis) were included. Case studies were excluded.

RESULTS

Of the 26 identified studies, none were randomized controlled trials, three were historical cohort studies with a reference group not receiving aneuploidy screening, and the remaining were case series. In weighted analysis, 34.1% of 7749 blastocysts were aneuploid. Screening for aneuploidy reduced the proportion of embryos suitable for transfer, thereby increasing the risk of experiencing a cycle without transferable embryos. In pooled analysis the percentage of embryos suitable for transfer was reduced from 57.5% to 37.2% following screening for aneuploidy. Among historical cohort studies, one reported significantly improved pregnancy and birth rates but did not control for confounding, one did not report any statistically significant difference between groups, and one properly designed study concluded that preimplantation genetic testing for aneuploidy enhanced the chance of achieving a pregnancy while simultaneously reducing the chance of miscarriage following single embryo transfer.

CONCLUSIONS

On average, aneuploidy is detected in 34% of embryos when performing a single blastocyst biopsy derived from patients carrying or affected by an inherited disorder. Accordingly, when screening for aneuploidy, the risk of experiencing a cycle with no transferable embryos increases. Current available data on the clinical effect of preimplantation genetic testing for aneuploidy performed concurrently with preimplantation genetic testing for inherited disorders are sparse, rendering the clinical effect from preimplantation genetic testing for aneuploidy difficult to access.

Location of Balanced Chromosome-Translocation Breakpoints by Long-Read Sequencing on the Oxford Nanopore Platform

Genomic structural variants, including translocations, inversions, insertions, deletions, and duplications, are challenging to be reliably detected by traditional genomic technologies. In particular, balanced translocations and inversions can neither be identified by microarrays since they do not alter chromosome copy numbers, nor by short-read sequencing because of the unmappability of short reads against repetitive genomic regions. The precise localization of breakpoints is vital for exploring genetic causes in patients with balanced translocations or inversions. Long-read sequencing techniques may detect these structural variants in a more direct, efficient, and accurate manner. Here, we performed whole-genome, long-read sequencing using the Oxford Nanopore GridION sequencer to detect breakpoints in six balanced chromosome translocation carriers and one inversion carrier. The results showed that all the breakpoints were consistent with the karyotype results with only ~10× coverage. Polymerase chain reaction (PCR) and Sanger sequencing confirmed 8 out of 14 breakpoints; however, other breakpoint loci were slightly missed since they were either in highly repetitive regions or pericentromeric regions. Some of the breakpoints interrupted normal gene structure, and in other cases, micro-deletions/insertions were found just next to the breakpoints. We also detected haplotypes around the breakpoint regions. Our results suggest that long-read, whole-genome sequencing is an ideal strategy for precisely localizing translocation breakpoints and providing haplotype information, which is essential for medical genetics and preimplantation genetic testing.

Preimplantation genetic diagnosis (PGD) and genetic testing for aneuploidy (PGT-A): status and future challenges

The world's first in vitro fertilization (IVF) baby was born in July 1978 in the UK. Since then, more than 7 million infants have been born worldwide as a result of IVF. Preimplantation genetic diagnosis (PGD) was introduced in the late 1980s for couples at risk of transmitting a genetic abnormality to their children. From the mid-1990s, this technology has been employed as an embryo selection tool for patients undergoing IVF and has been known as preimplantation genetic screening (PGS). The aim of this practice has been to identify and select euploid embryos for transfer, in order to increase efficacy of IVF cycle, ensure higher implantation rates or at least decreased time to pregnancy. In the early days, fluorescent in situ hybridization (FISH) technology was used for genetic analysis. New advancements in both biopsy and cytogenetic have made possible the improvement of PGD and PGT-A analysis. Currently, a variety of technologies have been implemented to individuate euploid embryos to be preferentially transferred in IVF treatments. The purpose of this review is to clarify the differences between PGD and PGT-A, and to discuss current indications and requirements for embryo biopsy and genetic methodologies used.

Prenatal identification of partial 3q duplication syndrome

BACKGROUND

The 3q duplication syndrome is a result of duplication of a large fragment of the long arm of chromosome 3, mainly 3q21-qter, and in most cases it is diagnosed only after birth. The phenotypic consequences resulting from genetic imbalance are an important source of information for genetic counselling, especially in prenatal diagnostics. However, in most cases it is impossible to define them precisely because the final clinical presentation is a result of an overlap, usually due to different sizes of deletions and/or duplications not only chromosome 3 but also of translocation partner chromosome. In this article, we present a prenatal diagnosis of the 3q duplication syndrome in a foetus, arising from a balanced insertion ins (7,3)(q21.2;q12.3q29) carried by the mother.

CASE PRESENTATION

The article presents a case of a 29-year-old woman referred to the Genetic Outpatient Clinic for consultation in the 12th week of her fifth pregnancy with a diagnosis of generalised hydrops foetalis. The analysis of karyotype using GTG technique and FISH allowed diagnosis of a balanced aberration in the mother, and determined the type of chromosomal rearrangement, which allowed the identification of the origin of the additional genetic material in the foetus and the previous malformed child of the same couple. The use of molecular karyotyping techniques (FISH and aCGH) allowed a precise determination of the size of the imbalanced fragments in the affected siblings.

CONCLUSIONS

The aCGH technique is particularly valuable for the diagnostics of submicroscopic deletions and duplications, if no imbalanced chromosomal aberrations are detected by routine cytogenetic tests. It is also a valuable technique for identifying and fully characterizing genetic material of unknown origin, which can't be identified using routine cytogenetic techniqes. However, it does not allow identification of balanced aberrations in carriers.

Retrospective analysis of meiotic segregation pattern and interchromosomal effects in blastocysts from inversion preimplantation genetic testing cycles

OBJECTIVE

To determine factors affecting unbalanced chromosomal rearrangement originating from parental inversion and interchromosomal effect occurrence in blastocysts from inversion carriers.

DESIGN

Retrospective study.

SETTING

University-affiliated center.

PATIENT(S)

Couples with one partner carrying inversion underwent preimplantation genetic testing for chromosomal structural rearrangement cycles.

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE(S)

Unbalanced rearrangement embryo rate, normal embryo rate, interchromosomal effect.

RESULT(S)

Preimplantation genetic testing was performed for 576 blastocysts from 57 paracentric (PAI) and 94 pericentric (PEI) inversion carriers. The percentage of normal/balanced blastocysts was significantly higher in PAI than PEI carriers (70.4% vs. 57.5%). Logistic regression indicated the inverted segment size ratio was a statistically significant risk factor for abnormality from parental inversion in both PEI and PAI. The optimal cutoff values to predict unbalanced rearrangement risk were 35.7% and 57%. In PAI, rates of abnormality from parental inversion were 0% and 12.1% in the <35.7% and ≥35.7% groups, respectively, with no gender difference. For PEI, the rates of abnormality from parental inversion were 7.9% and 33.1% in the <57% and ≥57% groups, respectively. In the ≥57% group, the rate of unbalanced rearrangement was significantly higher from paternal than maternal inversion (43.3% vs. 23.6%). In inversion carriers, 21,208 chromosomes were examined, and 187 (0.88%) malsegregations were identified from structurally normal chromosomes. In controls, 56,488 chromosomes were assessed, and 497 (0.88%) aneuploidies were identified, indicating no significant difference.

CONCLUSION(S)

The risk of unbalanced rearrangement is affected by the ratio of inverted segment size in both PAI and PEI carriers and is associated with gender.

BasePhasing: a highly efficient approach for preimplantation genetic haplotyping in clinical application of balanced translocation carriers

BACKGROUND

Preimplantation genetic testing (PGT) has already been applied in chromosomally balanced translocation carriers to improve the clinical outcome of assisted reproduction. However, traditional methods could not further distinguish embryos carrying a translocation from those with a normal karyotype prior to implantation.

METHODS

To solve this problem, we developed a method named "Chromosomal Phasing on Base level" (BasePhasing), which based on Infinium Asian Screening Array-24 v1.0 (ASA) and a specially phasing pipeline. Firstly, by comparing the number of single nucleotide polymorphism (SNP) loci in different minor allele frequencies (MAFs) and in 2Mbp continuous windows of ASA chip and karyomap-12 chip, we verified whether ASA could be adopted for genome-wide haplotype linkage analysis. Besides, the whole gene amplification (WGA) of 3-10 cells of GM16457 cell line was used to verify whether ASA chip could be used for testing of WGA products. Finally, two balanced translocation families were utilized to carry out BasePhasing and to validate the feasibility of its clinical application.

RESULTS

The average number of SNP loci in each window of ASA (473.2) was twice of that of Karyomap-12 (201.2). The coincidence rate of SNP loci in genomic DNA and WGA products was about 97%. The 5.3Mbp deletion was detected positively in cell line GM16457 of both genomic DNA and WGA products, and haplotype linkage analysis was performed in genome wide successfully. In the two balanced translocation families, 18 blastocysts were analyzed, in which 8 were unbalanced and the other 10 were balanced or normal chromosomes. Two embryos were transferred back to the patients successfully, and prenatal cytogenetic analysis of amniotic fluid was performed in the second trimester. The results predicted by BasePhasing and prenatal diagnosis were totally consistent.

CONCLUSIONS

Infinium ASA bead chip based BasePhasing pipeline shows good performance in balanced translocation carrier testing. With the characteristics of simple operation procedure and accurate results, we demonstrate that BasePhasing is one of the most suitable methods to distinguish between balanced and structurally normal chromosome embryos from translocation carriers in PGT at present.

Analysis of segregation patterns of quadrivalent structures and the effect on genome stability during meiosis in reciprocal translocation carriers

STUDY QUESTION

Do specific factors affect the segregation patterns of a quadrivalent structure and can the quadrivalent affect genome stability during meiosis?

SUMMARY ANSWER

Meiotic segregation patterns can be affected by the carrier's gender and age, location of breakpoints and chromosome type, and the quadrivalent structure can increase genome instability during meiosis.

WHAT IS KNOWN ALREADY

Carriers of reciprocal translocations have an increased genetic reproductive risk owing to the complex segregation patterns of a quadrivalent structure. However, the results of previous studies on the factors that affect segregation patterns seem to be contradictory, and the effect of a quadrivalent on genome stability during meiosis is unknown.

STUDY DESIGN, SIZE, DURATION

We designed a retrospective study to analyze the segregation patterns of 24 chromosomes from reciprocal translocation and non-translocation patients. Data for 356 reciprocal translocation carriers and 53 patients with the risk to transmit monogenic inherited disorders (RTMIDs) undergoing PGD-single nucleotide polymorphism array analysis were collected. The study was performed between March 2014 and July 2017.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Segregation patterns of a quadrivalent in 1842 blastocysts from 466 assisted reproduction cycles of reciprocal translocation carriers were analyzed according to the location of chromosome breakpoints, the carrier's gender and age, and chromosome type. In addition, to analyze the effect of quadrivalent structure on genome stability, segregation products of chromosomes which are not involved in the translocation from translocation carriers were compared with those of 23 pairs of chromosomes in 318 blastocysts from 72 assisted reproduction cycles of patients with RTMIDs.

MAIN RESULTS AND THE ROLE OF CHANCE

The percentage of adjacent-2 products with severe asymmetric quadrivalent was significantly higher than those with mild asymmetric quadrivalent (P = 0.020) while, in contrast, the incidence of 4:0/others was lower (P = 0.030). The frequencies of adjacent-1, adjacent-2 and 3:1 products differed between male and female carriers (P < 0.001, P = 0.015 and P = 0.001, respectively), and also for adjacent-1 and 4:0/others products in young versus older carriers (P = 0.04 and P = 0.002, respectively). In addition, adjacent-1 products of a quadrivalent with an acrocentric chromosome were significantly higher than those of a quadrivalent without an acrocentric chromosome (P = 0.001). Moreover, a quadrivalent could significantly increase the frequencies of abnormal chromosomes compared to patients with RTMIDs (P = 0.048, odds ratio (OR) = 1.43, 95% CI = 1.01-2.43), especially for the male carriers (P = 0.018, OR = 1.58, 95% CI = 1.08-2.25). In contrast, for older carriers, no difference was found in both aneuploidy and segmental anomalies compared to patients with RTMIDs.

LIMITATIONS, REASONS FOR CAUTION

The study contained appropriate controls, yet the analysis was limited by a small number of control patients and embryos.

WIDER IMPLICATIONS OF THE FINDINGS

Until now, there had been no definite report about the effect of quadrivalents on genome stability in reciprocal translocation carriers compared with control samples, and in the present study the large sample size ensured a detailed analysis of factors with a possible impact on segregation patterns. These data provide a better insight into the meiotic mechanisms involved in non-disjunction events in gametes from reciprocal translocation carriers. In addition, our results will help to provide each reciprocal translocation carrier couple undergoing PGD with more appropriate genetic counseling and a better understanding of the large numbers of abnormal embryos with chromosome aneuploidy.

STUDY FUNDING/COMPETING INTEREST(S)

The research was supported by the Research Funding of Shanghai Ji Ai Genetics & IVF Institute and the authors declare a lack of competing interests in this study.

The application of PGT-A for carriers of balanced structural chromosomal rearrangements

The aim of this study was to analyze differences in chromosomal aberrations and euploidy in embryos of each translocation type and gender of carrier in the case series of 10 couples with balanced translocations who underwent IVF with embryos trophectoderm (TE) biopsy and PGT-A to detect chromosomal aberrations. This is a Case Series (Retrospective study). In each case, controlled ovarian hyperstimulation, oocyte insemination with intracytoplasmic sperm injection (ICSI) and cultivation gave multiple blastocysts, that underwent trophectoderm (TE) biopsy with PGT-A analysis using aCGH and NGS. Number of total unbalanced translocations compared to the number of sporadic aneuploid embryos was 39.6% to 39.6% (50% to 50% of all 37 aneuploid embryos). The highest euploidy rate was in male carrier group - 26.7% and the lowest in the Robertsonian translocation carrier group - 18.2%. Sporadic aneuploidy - 68.2% was highest in Robertsonian translocation carrier group and lowest in female group - 11.1%. Chromosomal aberrations related to translocation were highest in female carrier group - 77.8% and lowest in Robertsonian translocation carrier group - 13.6%. Our study showed that expectancy of total embryo aneuploidy rates will be higher in carriers, than in people with normal karyotype. The prevalence of chromosomal aberrations related to translocation was 4.5 times higher in Reciprocal carrier group than in Robertsonian translocation carrier group. Among maternal and paternal carrier groups, the embryos from female carriers had the lowest euploidy rate, unbalanced translocation rate 4.7 times higher than in the male carrier group and higher total aneuploidy rates.

Preimplantation genetic testing of Robertsonian translocation by SNP array-based preimplantation genetic haplotyping

OBJECTIVES

The present study attempted to confirm a method that distinguishes a balanced Robertsonian translocation carrier embryo from a truly normal embryo in parallel with comprehensive chromosome screening (CCS).

METHODS

Comprehensive chromosome screening was performed in 107 embryos from 11 couples carrying Robertsonian translocations. Among them, embryos from 2 families had been transferred before the diagnosis of translocation, which resulted in successful pregnancies; embryos from the remaining families were transferred after the identification of translocations. The single nucleotide polymorphism (SNP) genotypes were acquired on a genome-wide basis, and breakpoint regions and flanking were assessed by establishing haplotypes. The predicted karyotypes from the transferred embryos were confirmed by prenatal diagnosis.

RESULTS

Among the 9 families finally undergoing translocation diagnosis, the amniotic cell karyotypes of 3 families were concordant with the results predicted by preimplantation genetic haplotyping, revealing a good consistency rate. After CCS, the euploid embryos from 2 other families could not be further detected because of the absence of abnormal embryos as probands.

CONCLUSIONS

Molecular karyotypes and haplotypes could be established with SNP microarray simultaneously in each embryo. SNP array-based PGT can simultaneously complete the CCS and identify Robertsonian translocation carriers, thus making it possible to prevent Robertsonian translocations from being passed to subsequent generations.