Healthy Baby Born to a Robertsonian Translocation Carrier following Next-Generation Sequencing-Based Preimplantation Genetic Diagnosis: A Case Report

The clinical application of single-sperm-based single-nucleotide polymorphism haplotyping for PGT of patients with genetic diseases

RESEARCH QUESTION

Is there a simple and effective method for male patients with genetic disorders in families with no identified haplotype and with Robertsonian translocations to avoid the transfer of embryos carrying translocated chromosomes?

DESIGN

Single spermatozoa were separated to identify by next-generation sequencing (NGS) those that were genetically abnormal, to establish a sperm-based single-nucleotide polymorphism (SNP) haplotype. Blastocysts that developed to day 5 or 6 were then biopsied for whole genome amplification and screening for chromosomal aneuploidy. Normal embryos were selected by comparison with a single-sperm-based SNP haplotype and were transferred. The results were verified by second trimester amniocentesis.

RESULTS

Two blastocysts obtained from patients with neurofibroma type 1 (NF1) were found to be normal after NGS according to single-sperm-based SNP haplotype analysis (13 SNP sites). Three and one blastocysts, respectively, were obtained from the patients with Robertsonian translocation. Blastocysts B9 and B7 were found to be normal after NGS according to the single-sperm-based SNP haplotype analysis (12 and 13 SNP sites selected on chromosomes 14 and 22 for the first patient; 12 and 9 SNP sites selected on chromosomes 13 and 14 for the second patient). Successful pregnancies after blastocyst transfer occurred in all three patients. The identification of embryos was verified by mid-trimester amniocentesis. All three patient couples successfully delivered healthy babies.

CONCLUSION

This study preliminarily summarized the process of single-sperm-based SNP haplotyping, which could be applied as preimplantation genetic testing for male patients without identified disease-causing haplotypes and with Robertsonian translocations.

Interchromosomal effect in carriers of translocations and inversions assessed by preimplantation genetic testing for structural rearrangements (PGT-SR)

PURPOSE

Balanced carriers of structural rearrangements have an increased risk of unbalanced embryos mainly due to the production of unbalanced gametes during meiosis. Aneuploidy for other chromosomes not involved in the rearrangements has also been described. The purpose of this work is to know if the incidence of unbalanced embryos, interchromosomal effect (ICE) and clinical outcomes differ in carriers of different structural rearrangements.

METHODS

Cohort retrospective study including 359 preimplantation genetic testing cycles for structural rearrangements from 304 couples was performed. Comparative genomic hybridisation arrays were used for chromosomal analysis. The results were stratified and compared according to female age and carrier sex. The impact of different cytogenetic features of chromosomal rearrangements was evaluated.

RESULTS

In carriers of translocations, we observed a higher percentage of abnormal embryos from day 3 biopsies compared with day 5/6 biopsies and for reciprocal translocations compared with other rearrangements. We observed a high percentage of embryos with aneuploidies for chromosomes not involved in the rearrangement that could be attributed to total ICE (aneuploid balanced and unbalanced embryos). No significant differences were observed in these percentages between types of rearrangements. Pure ICE (aneuploid balanced embyos) was independent of female age only for Robertsonian translocations, and significantly increased in day 3 biopsies for all types of abnormalities. Furthermore, total ICE for carriers of Robertsonian translocations and biopsy on day 3 was independent of female age too. High ongoing pregnancy rates were observed for all studied groups, with higher pregnancy rate for male carriers.

CONCLUSION

We observed a higher percentage of abnormal embryos for reciprocal translocations. No significant differences for total ICE was found among the different types of rearrangements, with higher pure ICE only for Robertsonian translocations. There was a sex effect for clinical outcome for carriers of translocations, with higher pregnancy rate for male carriers. The higher incidence of unbalanced and aneuploid embryos should be considered for reproductive counselling in carriers of structural rearrangements.

Preimplantation genetic testing for complex chromosomal rearrangement carriers by next-generation sequencing

RESEARCH QUESTION

Can preimplantation genetic testing (PGT) with next-generation sequencing (NGS) increase the chance of achieving a balanced euploid pregnancy in complex chromosome rearrangement (CCR) carriers?

DESIGN

Six couples underwent PGT at the Clinical Centre of Reproductive Medicine, First Affiliated Hospital, Nanjing Medical University. The CCR carriers in the six couples were: Case A: 46,XY,t(1;4;11)(p31;p16;q22); Case B: 46,XY,t(3;13;5)(p14;q21;p14); Case C: 46,XX,t(6;11;21)(q21;q21;q13); Case D: 46,XX,inv(9)(p12; q13),t(13;15)(q14;q24); Case E: 46,XX,inv(9)(p12;q13),t(7;9)(q22;p22); and Case F: 46,XX,t(2;7)(q21;q36),t(2;4)(p10;q10),t(2;4)(q15;q10). After ovarian stimulation followed by oocyte retrieval and embryo culture, PGT was performed on day 5 or 6 blastocyst biopsies using NGS to identify normal/balanced euploid embryos. Vitrified-warmed single embryo transfers were performed using normal/balanced euploid embryos.

RESULTS

After seven cycles, 84 oocytes were retrieved. Whole genome sequencing by NGS was performed on 25 trophectoderm biosies. Six (24%) embryos were identified as normal/balanced euploid, four were transferred resulting in four live births. Case A, C, D and E each gave birth to a healthy baby after their first cycle. There was no transferable embryo after two cycles for Case B and one cycle for Case F. The implantation rate per transfer was 4/4 and the live birth rate was 4/4.

CONCLUSION

These results strongly support the use of NGS for CCR carriers.

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.

Successful preimplantation genetic diagnosis by targeted next-generation sequencing on an ion torrent personal genome machine platform

Hearing loss may place a heavy burden on the patient and patient's family. Given the high incidence of hearing loss among newborns and the huge cost of treatment and care (including cochlear implantation), prenatal diagnosis is strongly recommended. Termination of the fetus may be considered as an extreme outcome to the discovery of a potential deaf fetus, and therefore preimplantation genetic diagnosis has become an important option for avoiding the birth of affected children without facing the risk of abortion following prenatal diagnosis. In one case, a couple had a 7-year-old daughter affected by non-syndromic sensorineural hearing loss. The affected fetus carried a causative compound heterozygous mutation c.919-2 A>G (IVS7-2 A>G) and c.1707+5 G>A (IVS15+5 G>A) of the solute carrier family 26 member 4 gene inherited from maternal and paternal sides, respectively. The present study applied multiple displacement amplification for whole genome amplification of biopsied trophectoderm cells and next-generation sequencing (NGS)-based single nucleotide polymorphism haplotyping on an Ion Torrent Personal Genome Machine. One unaffected embryo was transferred in a frozen-thawed embryo transfer cycle and the patient was impregnated. To conclude, to the best of our knowledge, this may be the first report of NGS-based preimplantation genetic diagnosis (PGD) for non-syndromic hearing loss caused by a compound heterozygous mutation using an Ion Torrent Personal Genome Machine. NGS provides unprecedented high-throughput, highly parallel and base-pair resolution data for genetic analysis. The method meets the requirements of medium-sized diagnostics laboratories. With decreased costs compared with previous techniques (such as Sanger sequencing), this technique may have potential widespread clinical application in PGD of other types of monogenic disease.

Thirteen years' experience of 893 PGD cycles for monogenic disorders in a publicly funded, nationally regulated regional hospital service

This study provides an overview of preimplantation genetic diagnosis (PGD) for single gene diseases and the management of expanding indications in the context of a fully financially covered service at Montpellier's regional hospital centre. Within the framework of a restrictive law ruling PGD in France, only the parental genetic risk can be studied in embryos (concurrent aneuploidy screening is not allowed). PCR-based techniques were developed combining mutation detection and closely linked short tandem repeat markers within or flanking the affected genes, and set up more than 100 different robust fluorescent multiplex assays for 61 monogenic disorders. This strategy was used to analyse blastomeres from cleavage-stage embryos. Overall, 893 cycles were initiated in 384 couples; 727 cycles proceeded to oocyte retrieval and 608 cycles to embryo transfer, resulting in 184 deliveries. Clinical pregnancy rate per transfer, implantation and miscarriage rates were 33.6%, 25.1% and 8.8%, respectively. Our PGD programme resulted in the birth of 214 healthy babies for 162 out of 358 couples (45.3%), constituting a relevant achievement within an organizational framework that does not allow aneuploidy screening but provides equal access to PGD, both geographically and socioeconomically. This is a rare example of a fully free-of-charge PGD service.

Next-generation Sequencing and Karyotype Analysis for the Diagnosis of Robertsonian Translocation Type Trisomy 13: A Case Report

Trisomy 13 (Patau syndrome) is the third most common autosomal trisomy with a prevalence between 1 in 10,000 - 20,000 live births. Robertsonian translocations represent the largest number of chromosomal aberrations in human population with an incidence of 1.23 in 1000 live birth and translocation 13;14 is one of the most frequent Robertsonian translocations (approximately 75%). We sampled umbilical vein blood from a 27-yr-old woman whose ultrasonography findings revealed congenital heart defects, single ventricle, polycystic kidney, median cleft lip and palate and holoprosencephaly at gestational age of 23+6 weeks for karyotype and sequencing during intra-amniotic cavity injection of acrinol for labor induction. Next-generation sequencing indicated 47,XN,+13 and karyotype was identified as 46,XN,+13,rob (13;14). An unexpected problem becomes more and more obvious in human cytogenetics - it seems to become difficult to decide how and when to use the "molecular cytogenetics" or "traditional karyotype analysis". Molecular cytogenetics, such as next-generation sequencing and array-based comparative genomic hybridization (array-CGH), can detect microdeletions and micro-duplications, but it cannot detect balanced translocations. For this case, we cannot find balanced translocations by Molecular cytogenetics. The purpose of this case is that molecular cytogenetics cannot replace the traditional karyotype analysis, but can serve as a useful complement for G-banding to be used in the clinical cytogenetic diagnosis.

Präimplantationsdiagnostik – methodische Aspekte

Die Präimplantationsdiagnostik erfordert eine enge und vertrauensvolle interdisziplinäre Zusammenarbeit zwischen hoch qualifizierten Fachärzten und Naturwissenschaftlern aus Humangenetik und Reproduktionsmedizin. In einem sehr engen Zeitfenster müssen komplexe Laborabläufe standardisiert und qualitätsgesichert umgesetzt werden. In diesem Beitrag sollen orientierende Empfehlungen zur Umsetzung kurz vorgestellt werden. Zentral haben wir häufigere Problemsituationen thematisiert, welche bereits bei der Indikationsstellung wie auch bei den nachfolgenden Schritten in der genetischen Analyse, Datenauswertung und Befunderstellung mögliche Fehlerquellen darstellen. Ziel unserer verantwortlichen Arbeit an den PID-Zentren sollte eine hohe Geburtenrate bei hoher Diagnosesicherheit mit möglichst wenigen schonenden Behandlungszyklen sein.

Recent advances in preimplantation genetic diagnosis and screening

Preimplantation genetic diagnosis/screening (PGD/PGS) aims to help couples lower the risks of transmitting genetic defects to their offspring, implantation failure, and/or miscarriage during in vitro fertilization (IVF) cycles. However, it is still being debated with regard to the practicality and diagnostic accuracy of PGD/PGS due to the concern of invasive biopsy and the potential mosaicism of embryos. Recently, several non-invasive and high-throughput assays have been developed to help overcome the challenges encountered in the conventional invasive biopsy and low-throughput analysis in PGD/PGS. In this mini-review, we will summarize the recent progresses of these new methods for PGD/PGS and discuss their potential applications in IVF clinics.

Clinical applications of MARSALA for preimplantation genetic diagnosis of spinal muscular atrophy

Conventional PCR methods combined with linkage analysis based on short tandem repeats (STRs) or Karyomapping with single nucleotide polymorphism (SNP) arrays, have been applied to preimplantation genetic diagnosis (PGD) for spinal muscular atrophy (SMA), an autosome recessive disorder. However, it has limitations in SMA diagnosis by Karyomapping, and these methods are unable to distinguish wild-type embryos with carriers effectively. Mutated allele revealed by sequencing with aneuploidy and linkage analyses (MARSALA) is a new method allowing embryo selection by a one-step next-generation sequencing (NGS) procedure, which has been applied in PGD for both autosome dominant and X-linked diseases in our group previously. In this study, we carried out PGD based on MARSALA for two carrier families with SMA affected children. As a result, one of the couples has given birth to a healthy baby free of mutations in SMA-causing gene. It is the first time that MARSALA was applied to PGD for SMA, and we can distinguish the embryos with heterozygous deletion (carriers) from the wild-type (normal) ones accurately through this NGS-based method. In addition, direct mutation detection allows us to identify the affected embryos (homozygous deletion), which can be regarded as probands for linkage analysis, in case that the affected family member is absent. In the future, the NGS-based MARSALA method is expected to be used in PGD for all monogenetic disorders with known pathogenic gene mutation.