Chromosome balanced translocation in newborn fetus founded during prenatal diagnosis: Three cases reports

RATIONALE

Because of the normal phenotype, carriers of specific chromosomal translocations are often diagnosed only after their development of associated malignancies, recurrent miscarriages, and reproductive difficulties. In this paper, we report primary balanced fetal chromosomal translocations by performing the necessary invasive prenatal diagnosis in couples with previous malformations coupled with prenatal testing suggesting a high risk for trisomy 21.

PATIENT CONCERNS

Case 1 and Case 2 couples had malformed children, and Case 3 couples had a high risk of trisomy 21 on noninvasive preconception serological testing.

DIAGNOSIS AND INTERVENTION

A balanced chromosomal translocation diagnosis was confirmed by karyotyping of fetal cells obtained by amniocentesis.

OUTCOMES

All 3 couples decided to continue their pregnancies after learning about the consequences of the chromosomal abnormalities. Approximately a year after the children were born, the staff of the Prenatal Diagnostic Center followed up with a phone call and found that the children physical development and intelligence were normal.

LESSON

This case report reports healthy chromosomal balanced translocation newborns born to couples with poor maternal history and couples with abnormalities suggested by preconception testing, and followed up with the newborns to provide some experience in prenatal diagnosis and genetic counseling for chromosomal balanced translocations.

Gene sequencing and result analysis of balanced translocation carriers by third-generation gene sequencing technology

Because the total gene copy number remains constant and all genes are normally expressed, carriers of balanced chromosomal translocations usually have a normal phenotype but are able to produce many different types of gametes during meiosis, and unbalanced gametes lead to increased risks of infertility, recurrent spontaneous abortion, stillbirth, neonatal death or malformations and intellectual abnormalities in offspring. The key to balanced translocations lies in finding the breakpoints, but current genetic testing techniques are all short-read sequencing, with the disadvantage of procedural complexity and imprecision for precisely identifying the breakpoints. The latest third-generation sequencing technology overcomes these drawbacks and uses robust long-read sequencing to accurately and rapidly detect genome-wide information and identify breakpoint locations. In this paper, we performed whole genome long-read sequencing using an Oxford Nanopore sequencer to detect the breakpoints of 4 balanced chromosomal translocation carriers. The results showed that employing about ~ 10× coverage confirmed 6 of the 8 breakpoints, of which, 2 had microdeletions/insertions identified near the breakpoints and 4 had breakpoints that disrupted the normal gene structure and were simultaneously tested for genome-wide structural variation (SV). The results show that whole genome long-read sequencing is an efficient method for pinpointing translocation breakpoints and providing genome-wide information, which is essential for medical genetics and preimplantation genetic testing.

Are ovarian responses and the number of transferable embryos different in females and partners of male balanced translocation carriers?

PURPOSE

To compare ovarian response and the number of transferable embryos between women with balanced autosomal translocations and women whose partners carry the translocation (control group). To investigate the predictive value of metaphase II (MII) oocyte number and biopsied embryo number for gaining at lowest one transferable embryo.

DESIGN

We retrospectively analyzed 1942 preimplantation genetic testing for structural rearrangements (PGT-SR) cycles of 1505 balanced autosomal translocation couples over 8 years. All cycles were divided into two subgroups: Robertsonian and reciprocal translocations (ROBT and ReBT). Receiver operator characteristic (ROC) curves were plotted to ascertain a cutoff of MII oocytes and biopsied embryos as predictors of gaining at lowest one transferable embryo.

RESULT

There were no statistical differences in baseline features or ovarian response indicators regarding the number of retrieved/MII oocytes, E2 level on the day of HCG, and ovarian sensitivity index (OSI) between women with balanced autosomal translocations and control group (P > 0.05). A decreased number of transferable embryos were found in women with balanced autosomal translocations regardless of the type of translocation. The cutoff values for gaining at lowest one transferable embryo are 12.5 MII oocytes and 4.5 biopsied embryos, respectively.

CONCLUSION

Women with balanced autosomal translocations have a normal ovarian response, but fewer transferable embryos, meaning that higher gonadotropin (Gn) doses may be required to increase transferable embryos. When fewer than 12.5 MII oocytes or 4.5 blastocysts are obtained in a PGT-SR cycle, couples should be notified that the likelihood of gaining a transferable embryo is low.

Exploration of the interchromosomal effects in preimplantation genetic testing for structural rearrangements based on next-generation sequencing

BACKGROUND

To investigate the interchromosomal effect (ICE) in chromosome translocation carriers.

METHODS

Data on preimplantation genetic testing aneuploidy and structural rearrangements (translocation) were retrospectively collected and classified into a reciprocal translocation group, a Robertsonian translocation group and a control group. According to the carrier's gender and age, all cases underwent further subgroup difference analysis of de novo abnormal embryo rates and the number of chromosomes involved in de novo abnormal embryos.

RESULTS

Among the 283 couples who participated in this study, 1076 blastocysts from 352 cycles were collected, and 246 de novo abnormal embryos were included. There was a significant difference in the rate of de novo abnormal embryos among the three groups (p < .05) but no significant difference in the number of de novo abnormal chromosomes in the abnormal embryos (p > .05). Gender and age (classified by 35 years old) had no effect on the de novo abnormal embryo ratios among the translocation carriers (p > .05). However, the de novo abnormal ratio increased with age. The embryo constitution reflected no significant difference between the translocation groups (p > .05).

CONCLUSION

The ICE was detected for the translocation carriers. The de novo abnormal embryo ratio increased with age. Gender had no effect on the de novo abnormal embryo ratio. Translocation status played a more important role than age and gender.

Risk Factors Affecting Alternate Segregation in Blastocysts From Preimplantation Genetic Testing Cycles of Autosomal Reciprocal Translocations

Reciprocal translocations are the most common structural chromosome rearrangements and may be associated with reproductive problems. Therefore, the objective of this study was to analyze factors that can influence meiotic segregation patterns in blastocysts for reciprocal translocation carriers. Segregation patterns of quadrivalents in 10,846 blastocysts from 2,871 preimplantation genetic testing cycles of reciprocal translocation carriers were analyzed. The percentage of normal/balanced blastocysts was 34.3%, and 2:2 segregation was observed in 90.0% of the blastocysts. Increased TAR1 (ratio of translocated segment 1 over the chromosome arm) emerged as an independent protective factor associated with an increase in alternate segregation (p = 0.004). Female sex and involvement of an acrocentric chromosome (Acr-ch) were independent risk factors that reduced alternate segregation proportions (p < 0.001). Notably, a higher TAR1 reduced the proportion of adjacent-1 segregation (p < 0.001); a longer translocated segment and female sex increased the risk of adjacent-2 segregation (p = 0.009 and p < 0.001, respectively). Female sex and involvement of an Acr-ch enhanced the ratio of 3:1 segregation (p < 0.001 and p = 0.012, respectively). In conclusion, autosomal reciprocal translocation carriers have reduced proportions of alternate segregation in blastocysts upon the involvement of an Acr-ch, female sex, and lower TAR1. These results may facilitate more appropriate genetic counseling for couples with autosomal reciprocal translocation regarding their chances of producing normal/balanced blastocysts.

Effect of parental origin and predictors for obtaining a euploid embryo in balanced translocation carriers

RESEARCH QUESTION

What is the effect of parental origin of translocation and predictors for obtaining a euploid embryo in preimplantation genetic testing for chromosomal structural rearrangements (PGT-SR) for balanced translocation carriers?

DESIGN

A total of 179 PGT-SR cycles and 614 blastocysts from 123 couples carrying a balanced translocation were retrospectively analysed. Next-generation sequencing (NGS) was performed after trophectoderm biopsy.

RESULTS

There were no differences in ovarian stimulation parameters or PGT-SR outcomes regarding the number of oocytes retrieved (11.95 ± 5.71 versus 11.82 ± 6.26), blastulation rate (0.42 ± 0.27 versus 0.45 ± 0.28), biopsy cancellation rate (11.7% versus 12.9%), the number of blastocysts for biopsy (3.70 ± 2.58 versus 4.04 ± 3.51), or the proportion of euploid embryos (23.80% versus 25.42%), aneuploid embryos (58.10% versus 57.52%) and mosaic embryos (18.10% versus 17.06%) between female carriers and male partner carriers. In a multivariate logistic regression model, the number of blastocysts for biopsy (adjusted odds ratio 1.752; 95% confidence interval 1.359-2.259; P < 0.001) was significantly associated with the chance of obtaining at least one euploid embryo. Receiver operating characteristic analysis with a threshold of 3.5 was conducted to calculate the number of blastocysts required for biopsy to obtain at least one euploid embryo.

CONCLUSIONS

The parental origin of translocation does not significantly affect the PGT-SR outcomes for young balanced translocation carriers. At least 3.5 blastocysts are required to obtain one euploid embryo. Couples should be informed that the probability of obtaining one euploid embryo is low when fewer than 4 blastocysts are obtained in one PGT cycle.

Effect of carriers' sex on meiotic segregation patterns and chromosome stability of reciprocal translocations

RESEARCH QUESTION

Does the sex of reciprocal translocation carriers affect meiotic segregation patterns and stability of non-translocated chromosomes during meiosis?

DESIGN

A total of 790 couples who underwent preimplantation genetic testing for reciprocal translocations by using the single nucleotide polymorphism (SNP) array platform between October 2016 and December 2019 were included. Among them, 294 couples had their euploid embryos distinguished between normal euploidies and balanced translocation carriers.

RESULTS

Female translocation carriers had a significantly lower incidence of alternate segregation pattern than male carriers (43.26% versus 47.98%, P = 0.001), but a higher incidence of 3:1 segregation pattern (6.70% versus 4.29%, P < 0.001). Stratified analysis showed only female translocation carriers with acrocentric chromosome (Acr-ch) involved had a lower incidence of alternate segregation pattern and a higher incidence of 3:1 segregation pattern compared with male carriers (41.63% versus 47.73%, P = 0.012; 9.32% versus 5.03%, P = 0.001). In 2233 embryos of 294 couples with identification of normal and balanced embryos, no significant differences were found in the paternal-origin aneuploidy rate (5.61% versus 5.82%, P = 0.861) and the maternal-origin aneuploidy rate (12.82% versus 12.08%, P = 0.673) in both male and female carriers. After excluding segmental aneuploidies, no differences were found between male and female carriers in both paternal-origin aneuploidy rate (2.14% versus 1.75%, P = 0.594) and maternal-origin aneuploidy rate (11.75% versus 11.06%, P = 0.683).

CONCLUSION

The sex of the translocation carriers affected meiotic segregation patterns with no effect on the stability of non-translocated chromosomes during meiosis.

Effects of Gender of Reciprocal Chromosomal Translocation on Blastocyst Formation and Pregnancy Outcome in Preimplantation Genetic Testing

Objective

To determine the effect of gender of reciprocal chromosomal translocation on blastocyst formation and pregnancy outcome in preimplantation genetic testing, including different parental ages.

Methods

This was a retrospective cohort study that enrolled 1034 couples undergoing preimplantation genetic testing-structural rearrangement on account of a carrier of reciprocal chromosomal translocation from the Reproductive Medicine Center of the First Affiliated Hospital of Zhengzhou University from January 2015 to December 2019. Group A represented 528 couples in which the man was the carrier of reciprocal translocation and group B represented 506 couples in which the woman was the carrier of reciprocal translocation. All patients were divided into two groups according to their age: female age<35 and female age≥35. Furthermore, the differences in blastocyst condition and pregnancy outcome between male and female carriers in each group were further explored according to their father's age.

Results

The blastocyst formation rate of group A (55.3%) is higher than that of group B (50%) and the results were statistically significant (P<0.05). The blastocyst formation rate of group A is higher than that of group B, no matter in young maternal age or in advanced maternal age (P<0.05). The blastocyst formation rate in maternal age<35y and paternal age<30y in group A(57.1%) is higher than that of Group B(50%); Similarly, the blastocyst formation rate in maternal age≥35 and paternal age≥38y(66.7%) is higher than that of Group B(33.3%)(all P<0.05). There was no difference in fertilization rate, aeuploidy rate, clinical pregnancy rate, miscarriage rate and live birth rate between Group A and Group B.

Conclusion

When the carrier of reciprocal translocation is male, the blastocyst formation rate is higher than that of female carrier. While there is no significant difference between the two in terms of fertilization rate, aeuploidy rate, clinical pregnancy rate, miscarriage rate and live birth rate.

Comprehensive assessment of a clinic's experience of preimplantation genetic testing by a cumulative rate

OBJECTIVE

This study aimed to investigate the outcomes of patients who had preimplantation genetic testing for chromosomal structural rearrangement (PGT-SR) or for aneuploidy screening (PGT-A) with different indications.

METHODS

This was a retrospective study at a single center. Pregnancy outcomes of all couples who had PGT from 2014 to 2018 were retrospectively analyzed, and the cumulative pregnancy rates (CPR) and the cumulative live birth/ongoing pregnancy rate (CLB/OPR) per patient with at least one transfer cycle were calculated.

RESULTS

A total of 313 PGT-SR cycles of 255 patients, 22 PGT-sexing cycles of 20 patients, and 190 PGT-A cycles of 168 patients were performed during the period. In PGT-SR, the overall CPR and the CLB/OPR were 68.04% and 59.79%, respectively. In PGT-A, the CPR and CLB/OPR were 67.52% and 58.12%, respectively. We also found that the CPR (93.75%) and CLB/OPR (87.50%) were highest in patients for PGT-sexing with a diagnosis of Y chromosomal microdeletion. In addition, we discovered a significant trend that aneuploidy rate significantly increased with maternal age (p = 0.000) in PGT-A population. No significant difference was found in the mosaicism rate or clinical outcomes among the age groups. Similarly, the significance was absent in the PGT-SR population.

CONCLUSION

We reviewed the CPR and CLB/OPR for different indications since the 24-chromosome technique has been applied in the clinical setting for 4 years in our center. We hope that our results will provide some pointed guidance and a new perspective on outcomes for PGT in certain patients and clinicians.

Conventional ICSI improves the euploid embryo rate in male reciprocal translocation carriers

PURPOSE

To evaluate whether the morphologically normal spermatozoa selected for intracytoplasmic sperm injection (ICSI) under microscope had a higher rate of normal/balanced chromosome contents than that in the whole unselected sperm from reciprocal translocation carriers.

METHODS

Five hundred unselected spermatozoa from each of 40 male translocation carriers were performed with fluorescence in situ hybridization (FISH), to determine the rates of gametes with different meiotic contents of translocated chromosomes. Meanwhile, 3030 biopsied blastocysts from 239 male and 293 female reciprocal translocation carriers were detected with the microarray technique to analyze the rates of embryos with different translocated chromosome contents.

RESULTS

The D3 embryo rate, blastocyst formation rate, and euploid rate of blastocysts were remarkably higher in male carriers than those in female (p = 0.001, p = 0.004, and p = 0.035, respectively). In addition, the percentages of alternate products, which contained normal/balanced chromosome contents, in embryos from male carriers were markedly higher than those in sperm FISH (p = 2.48 × 10^-5 and p = 2.88 × 10^-10), while the percentages of adjacent-2 and 3:1 products were lower than those in sperm FISH (p = 0.003 and p = 5.28 × 10^-44). Moreover, consistent results were obtained when comparing the rates of products in embryos between male and female carriers. Specifically, the incidence of alternate products in male carriers was higher than those in female carriers (p = 0.022). However, no similar differences were seen between sperm and embryos of female carriers.

CONCLUSION

ICSI facilitates the selection of spermatozoa with normal/balanced chromosome contents and improves the D3 embryo rate, blastocyst formation rate, and the euploid embryo rate in male carriers.

Interaction of acrocentric chromosome involved in translocation and sex of the carrier influences the proportion of alternate segregation in autosomal reciprocal translocations

STUDY QUESTION

Are meiotic segregation patterns of reciprocal translocations affected by the combined effect of chromosome type and carrier's sex?

SUMMARY ANSWER

Interaction of an acrocentric chromosome (Acr-ch) involved in the translocation and sex of the carrier influences the proportion of alternate segregation for normal or balanced chromosome contents during meiotic segregation in autosomal reciprocal translocations.

WHAT IS KNOWN ALREADY

Carriers of reciprocal translocations are at a significantly increased risk of fertility problems due to the generation of unbalanced gametes in meiotic segregation of a quadrivalent. Previous studies have reported that meiotic segregation patterns of a quadrivalent can be affected by factors such as a carrier's sex and age and the chromosome type. However, the reported proportion of alternate segregation does not differ significantly, except in one study, and whether combined effects between these factors exist is unclear.

STUDY DESIGN, SIZE, DURATION

A retrospective study of array comparative genomic hybridization (aCGH) outcome data from patients with autosomal reciprocal translocations was conducted to analyse meiotic segregation patterns and blastocyst euploidy rates. We enroled 473 couples whose embryos were tested between January 2013 and September 2016.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Meiotic segregation patterns of 2101 blastocysts from 243 female carriers, including 76 cases with translocations involving Acr-ch, and 230 male carriers, including 88 cases with translocations involving Acr-ch, were analysed according to chromosome type, carrier's sex and age.

MAIN RESULTS AND THE ROLE OF CHANCE

In cases with translocations involving the Acr-ch subgroup, the proportion of alternate segregation (53.9 vs 33.4%, P < 0.0001) was significantly higher in male carriers than in female carriers, with the proportion of 3:1 segregation (6.8 vs 16.3%, P < 0.0001) being significantly lower. The proportions of alternate segregation were similar between sexes in cases with translocations not involving the Acr-ch subgroup. Meanwhile, in the female carrier subgroup, the proportion of alternate segregation (33.4 vs 45.2%, P < 0.001) was significantly lower and the proportion of 3:1 segregation (16.3 vs 8.2%, P < 0.001) was significantly higher in cases with translocations involving Acr-ch than in those not. In the male carrier subgroup, the proportion of alternate segregation (53.9 vs 46.9%, P = 0.031) was higher and the proportion of adjacent-1 segregation (27.1 vs 37.3%, P < 0.001) was significantly lower in cases with translocations involving Acr-ch than in those not. Carrier's age did not affect the meiotic segregation patterns. However the euploidy rates were significantly lower in couples with advanced compared to young maternal age respectively.

LIMITATIONS, REASONS FOR CAUTION

Mosaic embryos were not identified using aCGH in this study. Patients with complex chromosome rearrangements and translocations involving sex chromosomes were excluded. Interchromosomal effect was not analysed.

WIDER IMPLICATIONS OF THE FINDINGS

The findings of this study provide detailed information for genetic counselling of couples with autosomal reciprocal translocations on their chances of producing euploid gametes.

STUDY FUNDING/COMPETING INTEREST(S)

This research was supported by the National Key Research and Development Program of China (2016YFC1000202); the National Natural Science Foundation of China (81671522); the Natural Science Foundation of Shandong Province in China (ZR2016HP09); and the Innovative Foundation of Reproductive Hospital Affiliated to Shandong University (20171114, 20171111). No competing interests are declared.

TRIAL REGISTRATION NUMBER

N/A.

Detection of a balanced translocation carrier through trophectoderm biopsy analysis: a case report

BACKGROUND

Balanced translocation carriers are burdened with fertility issues due to improper chromosome segregation in gametes, resulting in either implantation failure, miscarriage or birth of a child with chromosomal disorders. At the same time, these individuals are typically healthy with no signs of developmental problems, hence they often are unaware of their condition. Yet, because of difficulties in conceiving, balanced translocation carriers often turn to assisted reproduction, some of whom may also undergo preimplantation genetic testing for aneuploidy (PGT-A) to improve the likelihood of achieving a successful pregnancy.

CASE REPORT

We describe a female patient, who pursued in vitro fertilization (IVF) treatment coupled with PGT-A following two consecutive miscarriages, unaware of her genetic condition. PGT-A was performed on blastocyst-stage embryos and the results of comprehensive chromosome screening from a first IVF cycle demonstrated reciprocal segmental aberrations on chromosome 7 and chromosome 10 in two out of four embryos. Due to distinct embryo profiles, the couple was then referred for genetic counselling and subsequent parental karyotyping revealed the presence of a previously undetected balanced translocation in the mother.

CONCLUSIONS

These results confirm previous reports that genome-wide PGT-A can facilitate the identification of balanced translocation carriers in IVF patients, providing explanation for poor reproductive outcome and allowing adjustments in treatment strategies.

Next-generation sequencing analysis of embryos from mosaic patients undergoing in vitro fertilization and preimplantation genetic testing

OBJECTIVE

To investigate the effects of parental mosaicism on their preimplantation embryos.

DESIGN

Case series.

SETTING

An institute for reproductive and stem cell engineering.

PATIENT(S)

Sixty-eight mosaic couples.

INTERVENTION(S)

Assisted reproduction with preimplantation genetic testing (PGT).

MAIN OUTCOME MEASURE(S)

Karyotypes, embryo-related chromosomal abnormalities, and PGT results.

RESULT(S)

A total of 209 embryos were obtained from 68 mosaic couples, and 153 (73.21%) of 209 of the total embryos were obtained from 55 mosaic couples with abnormal sex chromosome numbers. Of these 153 embryos, 2 (1.31%) had an abnormal copy number of X chromosome, 1 had mosaicism with 46,XN,+X(mosaic, 40%), 1 (0.65%) had an extra Y chromosome, 3 (1.96%) exhibited both X chromosomal and autosomal abnormalities, and 4 (2.61%) exhibited de novo X chromosome structural abnormalities. A total of 56 (26.79%) of 209 embryos were obtained from mosaic couples (n = 13) with abnormal autosomal structures. Notably, of these 56 embryos, 5 (8.93%) had a 16q21-q24.3 copy number abnormality related to the parental karyotype, with a fragile site at 16q22; 5 (7.14%) exhibited 46,XX,dup(8p23.1-8p11.21) and 46,XY,del(8p22-8p11.21), which were related to the parental karyotype; and 10 (17.86%) were de novo chromosome abnormalities.

CONCLUSION(S)

Our data demonstrate that the risk of embryo-related chromosome abnormalities in mosaic patients with abnormal sex chromosomes is very low. Therefore, PGT may not need to be recommended for mosaic patients with abnormal copy numbers of sex chromosomes, especially for patients with financial difficulties. By contrast, the mosaic patients with structural abnormalities of autosomes may have a relatively high risk of abnormal embryos with an unbalanced segment of the involved chromosomes. Thus, PGT is highly recommended for mosaic patients with autosomal structure abnormalities, especially those with a fragile site at 16q22.

Analysis of meiotic segregation modes in biopsied blastocysts from preimplantation genetic testing cycles of reciprocal translocations

Purpose

To analyse the meiotic segregation modes of chromosomal structural rearrangements (PGT-SR) of reciprocal translocation in biopsied blastocysts from preimplantation genetic testing and to investigate whether any features of reciprocal translocation, such as carrier gender or the presence of acrocentric chromosomes or terminal breakpoints, affect meiotic segregation modes.

Methods

Comprehensive chromosomal screening was performed by next generation sequencing (NGS) on 378 biopsied blastocysts from 102 PGD cycles of 89 reciprocal translocation carriers. The segregation modes of a quadrivalent in 378 blastocysts were analysed according to the carrier’s gender, chromosome type and the location of chromosome breakpoints.

Results

The results showed that 122 out of 378 blastocysts (32.3%) were normal or balanced, 209 (55.3%) were translocated chromosomal abnormalities, and 47 (12.4%) were abnormalities of non-translocated chromosomes. The proportion of translocated chromosomal abnormalities in translocations without acrocentric chromosomes was significantly higher than that in blastocysts from carriers with acrocentric chromosomes (14.8% versus 5.9%, P = 0.032). Translocation with acrocentric chromosomes exhibited a significantly higher proportion of 3:1 segregation (24.8% versus 5.1%, P < 0.0001) and a lower rate of 2:2 segregation (70.3% versus 87.0%, P = 0.00028) compared with the proportions in blastocysts from carriers without acrocentric chromosomes. The frequency of adjacent-2 segregation was significantly different in translocations with terminal breakpoints compared to the frequency in blastocysts from carriers without terminal breakpoints (6.7% versus 15.5%, P = 0.013).

Conclusions

This study indicates that the segregation modes in blastocysts were affected by the presence of acrocentric chromosomes and terminal breakpoints, but not by the carrier’s sex. Our data may be useful for predicting the segregation pattern of a reciprocal translocation and could support genetic counselling for balanced translocation carriers for PGT cycles using blastocyst biopsy.

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.

Evaluation of preimplantation genetic testing based on next-generation sequencing for balanced reciprocal translocation carriers

RESEARCH QUESTION

Can next-generation sequencing (NGS) based on copy number variation sequencing (CNV-Seq) identify normal/balanced embryos in balanced reciprocal translocation carriers and what are their reproductive outcomes?

DESIGN

One hundred couples with balanced reciprocal translocation who underwent a total of 134 preimplantation genetic testing (PGT) cycles between January 2015 and October 2017 were evaluated. Trophectoderm cells of blastocysts were biopsied for CNV-Seq-based NGS. All the balanced/normal blastocysts were vitrified and cryopreserved. Single balanced/normal blastocysts were warmed and transferred in the subsequent frozen embryo transfer (FET) cycle.

RESULTS

During the study period, 400 blastocysts were analysed by NGS-PGT, of which 109 (27.25%) were balanced and euploid. A total of 52 blastocysts were transferred in the FET cycle. Clinical pregnancy was confirmed in 34 women (65.38%), with a miscarriage rate of 2.94%; 26 healthy term babies were born, including 24 singletons and one set of twins, while eight couples had ongoing pregnancies. Amniocentesis revealed a fetal chromosome status that was consistent with the NGS-PGT results. Female carriers had a significantly higher blastocyst rate than did the male carriers (37.01% versus 31.27%, P = 0.04). The transferable blastocyst rate was higher in couples treated with gonadotrophin-releasing hormone (GnRH) antagonist than in those treated with GnRH agonist (38.20% versus 24.37%, P = 0.01). However, neither carrier sex nor ovarian stimulation protocol influenced the clinical pregnancy rate.

CONCLUSIONS

CNV-Seq-based NGS is an efficient and reliable PGT method for balanced reciprocal translocation.

Time-lapse imaging reveals delayed development of embryos carrying unbalanced chromosomal translocations

PURPOSE

The purpose of the study was to compare the morphokinetic parameters of embryos carrying balanced chromosomal translocations with those carrying unbalanced chromosomal translocations using time-lapse microscopy.

METHODS

The study group included 270 embryos that underwent biopsies on day 3 for preimplantation genetic diagnosis (PGD) for chromosomal translocations in our unit between 2013 and 2015. All embryos were incubated under time-lapse microscopy and evaluated for timing of developmental events up to day 5. The timing of these events was compared between balanced and unbalanced embryos, potentially viable and nonviable variants, and maternal versus paternal inheritance of the translocation.

RESULTS

The PGD analysis found that 209 (77%) of the 270 biopsied embryos carried an unbalanced translocation. Embryos carrying unbalanced translocations, which are expected to lead to implantation failure or miscarriage, cleaved less synchronously and were delayed in time of cleavage to the 4-cell stage (t4) and in time of start of blastulation (tSB) compared with balanced embryos (P < 0.05). Furthermore, embryos carrying nonviable translocations demonstrated a significant delay at the time of pronuclei fading (tPNf) compared with those carrying potentially viable translocations (P < 0.05). Embryos whose unbalanced translocations were of maternal origin were significantly delayed in most of the morphokinetic parameters (including tPNf, t2, t3, t4, t6, t7, t8, cc2, s2, and tSB) compared with embryos carrying balanced translocations (P < 0.05).

CONCLUSIONS

Embryos carrying unbalanced chromosomal translocations mainly of maternal origin undergo delayed development and asynchronous cleavage that may lead to implantation failure or miscarriage.

Preliminary analysis of numerical chromosome abnormalities in reciprocal and Robertsonian translocation preimplantation genetic diagnosis cases with 24-chromosomal analysis with an aCGH/SNP microarray

PURPOSE

The aim of this study was to determine whether an interchromosomal effect (ICE) occurred in embryos obtained from reciprocal translocation (rcp) and Robertsonian translocation (RT) carriers who were following a preimplantation genetic diagnosis (PGD) with whole chromosome screening with an aCGH and SNP microarray. We also analyzed the chromosomal numerical abnormalities in embryos with aneuploidy in parental chromosomes that were not involved with a translocation and balanced in involved parental translocation chromosomes.

METHODS

This retrospective study included 832 embryos obtained from rcp carriers and 382 embryos from RT carriers that were biopsied in 139 PGD cycles. The control group involved embryos obtained from age-matched patient karyotypes who were undergoing preimplantation genetic screening (PGS) with non-translocation, and 579 embryos were analyzed in the control group. A single blastomere at the cleavage stage or trophectoderm from a blastocyst was biopsied, and 24-chromosomal analysis with an aCGH/SNP microarray was conducted using the PGD/PGS protocols. Statistical analyses were implemented on the incidences of cumulative aneuploidy rates between the translocation carriers and the control group.

RESULTS

Reliable results were obtained from 138 couples, among whom only one patient was a balanced rcp or RT translocation carrier, undergoing PGD testing in our center from January 2012 to June 2014. For day 3 embryos, the aneuploidy rates were 50.7% for rcp carriers and 49.1% for RT carriers, compared with the control group, with 44.8% at a maternal age < 36 years. When the maternal age was ≥ 36 years, the aneuploidy rates were increased to 61.1% for rcp carriers, 56.7% for RT carriers, and 60.3% for the control group. There were no significant differences. In day 5 embryos, the aneuploidy rates were 24.5% for rcp carriers and 34.9% for RT carriers, compared with the control group with 53.6% at a maternal age < 36 years. When the maternal age was ≥ 36 years, the aneuploidy rates were 10.7% for rcp carriers, 26.3% for RT carriers, and 57.1% for the control group. The cumulative aneuploidy rates of chromosome translocation carriers were significantly lower than the control group. No ICE was observed in cleavage and blastocyst stage embryos obtained from these carriers. Additionally, the risk of chromosomal numerical abnormalities was observed in each of the 23 pairs of autosomes or sex chromosomes from day 3 and day 5 embryos.

CONCLUSION

There was not enough evidence to prove that ICE was present in embryos derived from both rcp and RT translocation carriers, regardless of the maternal age. However, chromosomal numerical abnormalities were noticed in 23 pairs of autosomes and sex chromosomes in parental structurally normal chromosomes. Thus, 24-chromosomal analysis with an aCGH/SNP microarray PGD protocol is required to decrease the risks of failure to diagnose aneuploidy in structurally normal chromosomes.

Clinical outcomes for couples containing a reciprocal chromosome translocation carrier without preimplantation genetic diagnosis

OBJECTIVE

To evaluate the pregnancy outcomes of couples containing a carrier of a reciprocal chromosome translocation (RCT) after assisted reproductive technology without preimplantation genetic diagnosis.

METHODS

A retrospective study was performed using data for couples with an RCT carrier and control couples with a normal karyotype (1:4 ratio) who underwent assisted reproductive technology cycles at a Chinese fertility center in 2010-2011. The embryos were fertilized via in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). Only the first pick-up cycles were used for analysis. Clinical variables were compared.

RESULTS

Compared with the control group (n=164), the RCT group (n=41) had a marginally lower clinical pregnancy rate (46.3% [19/41] vs 54.3% [89/164]), implantation rate (21.7% [23/106] vs 26.9% [118/438]), multiple-gestation pregnancy rate (21.1% [4/19] vs 32.6% [29/89]), and delivery rate (36.6% [15/41] vs 47.6% [78/164]), whereas the spontaneous abortion rate was slightly higher (21.1% [4/19] vs 12.4% [11/89]). However, none of these differences were significant.

CONCLUSION

The clinical outcomes for RCT carriers were acceptable after IVF/ICSI without performing preimplantation genetic diagnosis, indicating that this approach might comprise a feasible alternative fertility treatment for RCT carriers.

14q32.3-qter trisomic segment: a case report and literature review

BACKGROUND

Segmental duplication of the long arm of chromosome 14 (14q) has commonly been reported to affect the proximal segment of 14q, while distal duplication is a rare condition and often associated with segmental monosomy of other chromosomes.

CASE PRESENTATION

We report the clinical and genetic characterization of a 4-year-old male patient with 14q32.3-qter trisomy resulting from an adjacent segregation of a paternal reciprocal translocation (14;21)(q32.1;p12). The child shows minor facial anomalies, severe developmental delay, growth retardation, and a history of congenital hypothyroidism and neonatal transitory hyperglycemic crises.

CONCLUSIONS

To the best of our knowledge, only 15 other cases of segmental 14q trisomy were documented. We compared molecularly defined cases to identify a minimal common duplicated region and to find genes with a hypothetical role in the phenotype. The presented case supports the previous suggestion of a pure "distal 14q partial duplication" and underlines the clinical variability.

Prenatal Detection and Postnatal Follow-Up of Segmental Aneusomies of Chromosome 13 in 4 Consecutive Pregnancies in an Ethnic South Indian Family With a Maternally Inherited Balanced Translocation

OBJECTIVE

To assess the postnatal clinical manifestation of an antenatally detected unbalanced rearrangement involving chromosome 13 in an ethnic South Indian couple.

METHODS

We used conventional cytogenetics on fetal cells obtained from prenatal specimens and on peripheral blood lymphocytes from consanguineous family members to ascertain the chromosomal abnormalities.

RESULTS

We report the reproductive outcomes of a maternally inherited chromosome translocation involving chromosome 9 and 13 and the informed decisions of the couple, after genetic counseling in India, regarding their 4 pregnancies.

CONCLUSION

This case report highlights the current practice in India of offering prenatal diagnosis and preimplantation genetic diagnosis to individuals who are carriers of balanced translocations, to reduce the risk of conceiving chromosomally abnormal offspring.

Intellectual disability secondary to a 16p13 duplication in a 1;16 translocation. Extended phenotype in a four-generation family

We describe a large family from the Gaza Strip presented with multiple congenital anomalies. The proband was presented with intellectual disability and multiple congenital anomalies including cleft palate, low-set ears, everted upper lip, diaphragmatic hernia, and arthrogryposis. Pedigree analysis showed 19 affected patients over five generations, only 6 were alive and 11 individuals were obligate carriers. The proband had an apparently normal karyotype, although FISH studies showed a derivative chromosome 1 with duplication of 16p13.3 and deletion of the 1p subtelomere. Her father however had a balanced translocation. The seven affected patients had a similar phenotype, one of them died before genetic testing was carried out and the living six patients had the same unbalanced translocation. Array CGH revealed an 8.8 Mb duplication in 16p13 and 200,338 bp deletion in 1p36.3. Accordingly, intellectual disability, hypertelorism, cupped ears, everted upper lip, and limb anomalies were presenting clinical features of the 16p13 duplication syndrome while deep set eyes were perhaps related to the 1p terminal deletion. Prevention of recurrent intellectual disability in this family can be achieved through carrier detection and prenatal genetic diagnosis.

Poor embryo development and preimplantation genetic diagnosis outcomes of translocations involving chromosome 10: Do we blame genetics?

Balanced reciprocal translocation carriers are usually phenotypically normal. Although the reproductive risk of these carriers varies, they generally have a lower chance to produce normal or balanced gametes. Preimplantation genetic diagnosis (PGD) is offered to these patients to increase their chances of becoming pregnant by selecting a balanced embryo for transfer. This study aimed to analyse the development and the PGD outcome of the embryos obtained from reciprocal translocation carriers focusing on ones with chromosome 10 rearrangements. In total, 27 reciprocal translocation carriers underwent 31 cycles of PGD. PGD was performed using multicolour fluorescence in situ hybridisation for 298 embryos and of these 136 were obtained from couples carrying translocations involving chromosome 10 rearrangements. Carriers of translocations involving chromosome 10 rearrangements have a lower chance of producing normal or balanced embryos compared with the carriers with other rearrangements. The development of embryos obtained from the patients with chromosome 10 rearrangements was impaired and only a limited number of embryos developed to the blastocyst stage.

Quadrivalent asymmetry in reciprocal translocation carriers predicts meiotic segregation patterns in cleavage stage embryos

The effect of quadrivalent geometry on meiotic behaviour was evaluated. Segregation patterns of 404 cleavage stage embryos from 40 reciprocal translocation carriers undergoing 75 PGD cycles were analysed according to the asymmetric degree of quadrivalent. The percentage of alternate products with severe asymmetric quadrivalents was significantly lower than patients with mild asymmetric quadrivalents (22.5% versus 38.7%, P = 0.001). The incidence of 3:1 products was significantly higher in patients with severe compared with mild asymmetric quadrivalents (23.1% versus 12.2%, P = 0.004). The incidence of adjacent 1 (25.8% versus 24.3%), 2 (11.5% versus 12.6%) and 4:0/other segregation products (17.0% versus 12.2%) were not statistically significantly different between embryos from patients with severe or mild asymmetric quadrivalents. After adjusting for the confounder of sex using a logistic regression model, the odds of alternate embryos is about one-half for carriers classified as severe (OR 0.456, 95% CI 0.291 to 0.705), and the odds of 3:1 embryos is 2.2 times higher for carriers with severe asymmetric quadrivalents (OR 2.235, 95% CI 1.318 to 3.846). Our results suggest that the meiotic segregation pattern is related to the degree of asymmetry of specific quadrivalents. Severe asymmetric quadrivalents increases the risk of abnormal embryos.

Can Characteristics of Reciprocal Translocations Predict the Chance of Transferable Embryos in PGD Cycles?

Translocation carriers have an increased risk of miscarriage or the birth of a child with congenital anomalies. Preimplantation genetic diagnosis (PGD) is performed in translocation carriers to select for balanced embryos and, thus, increase the chance of an ongoing pregnancy. However, a common experience is that reciprocal translocation carriers produce a high percentage of unbalanced embryos, which cannot be transferred. Therefore, the pregnancy rates in PGD in this patient group are low. In a cohort of 85 reciprocal translocation carriers undergoing PGD we have searched for cytogenetic characteristics of the translocations that can predict the percentage of balanced embryos. Using shape algorithms, the most likely segregation mode per translocation was determined. Shape algorithm, breakpoint location, and relative chromosome segment sizes proved not to be independent predictors of the percentage of balanced embryos. The ratio of the relative sizes of the translocated segments of both translocation chromosomes can give some insight into the chance of transferable embryos: Very asymmetrical translocations have a higher risk of unbalanced products (p = 0.048). Counseling of the couples on the pros and cons of all their reproductive options remains very important.

Comparison of reproductive outcome, including the pattern of loss, between couples with chromosomal abnormalities and those with unexplained repeated miscarriages

AIM

Chromosomal abnormalities are an important cause of repeated miscarriage. Several studies have discussed the association between chromosomal abnormalities and repeated miscarriage. This study attempts to describe the pattern of miscarriage in this group of women and the eventual pregnancy outcome of couples with chromosomal abnormalities compared with couples with unexplained repeated pregnancy loss.

MATERIAL AND METHODS

This was a retrospective study involving 795 couples with repeated miscarriages.

RESULTS

Out of 795 couples, 28 (3.52%) were found to have a chromosomal abnormality (carrier group). Over half (65.5%) of the chromosomal abnormalities were balanced reciprocal translocations. After referral, this carrier group had a total of 159 pregnancies, leading to 36 live births (22.6%) among 18 couples. The after referral miscarriage rate in the chromosomal anomaly group (55.6%) was significantly (P < 0.01) higher than that in the unexplained recurrent miscarriage group (28.1%). In couples with chromosomal anomaly, the miscarriages were more likely to occur between 6 and 12 weeks' gestation.

CONCLUSIONS

The encouraging cumulative live birth rate of 64.3% for couples with chromosomal anomaly and repeated miscarriage suggests that further attempts at natural conception are a viable option.

Chromosome segregation analysis in human embryos obtained from couples involving male carriers of reciprocal or Robertsonian translocation

The objective of this study was to investigate the frequency and type of chromosome segregation patterns in cleavage stage embryos obtained from male carriers of Robertsonian (ROB) and reciprocal (REC) translocations undergoing preimplantation genetic diagnosis (PGD) at our reproductive center. We used FISH to analyze chromosome segregation in 308 day 3 cleavage stage embryos obtained from 26 patients. The percentage of embryos consistent with normal or balanced segregation (55.1% vs. 27.1%) and clinical pregnancy (62.5% vs. 19.2%) rates were higher in ROB than the REC translocation carriers. Involvement of non-acrocentric chromosome(s) or terminal breakpoint(s) in reciprocal translocations was associated with an increase in the percent of embryos consistent with adjacent 1 but with a decrease in 3∶1 segregation. Similar results were obtained in the analysis of nontransferred embryos donated for research. 3∶1 segregation was the most frequent segregation type in both day 3 (31%) and spare (35%) embryos obtained from carriers of t(11;22)(q23;q11), the only non-random REC with the same breakpoint reported in a large number of unrelated families mainly identified by the birth of a child with derivative chromosome 22. These results suggest that chromosome segregation patterns in day 3 and nontransferred embryos obtained from male translocation carriers vary with the type of translocation and involvement of acrocentric chromosome(s) or terminal breakpoint(s). These results should be helpful in estimating reproductive success in translocation carriers undergoing PGD.

First births after preimplantation genetic diagnosis of structural chromosome abnormalities using comparative genomic hybridization and microarray analysis

BACKGROUND

Balanced chromosomal rearrangements represent one of the most frequent indications for preimplantation genetic diagnosis (PGD). Although fluorescence in situ hybridization (FISH) has been successfully employed for diagnosis in such cases, this approach usually restricts assessment of the chromosomes involved in the rearrangement. Furthermore, with FISH-based strategies, it is sometimes necessary to create patient-specific protocols, increasing the waiting time and costs. In the current study, we explored the use of two comprehensive chromosome screening methods, conventional metaphase comparative genomic hybridization (CGH) and microarray-CGH (aCGH), as alternatives for PGD of chromosome rearrangements.

METHODS

The study included 16 patients who underwent 20 cycles of PGD for a variety of chromosome rearrangements (reciprocal or Robertsonian translocations or inversions). Testing was performed at various embryonic stages using CGH (9 cases) or aCGH (11 cases).

RESULTS

Results were obtained for 121 out of 132 samples (91.7%). Of the diagnosed samples, 48.8% were found to carry abnormalities associated with the rearrangement, either alone or in combination with other chromosomal abnormalities. A further 28.9% of samples were normal/balanced for the rearranged chromosomes, but affected by aneuploidy for other chromosomes. Only 22.3% of samples were chromosomally normal. Of the 15 patients who completed their treatment cycles, 5 became pregnant after one or two cycles resulting in four healthy births. The delivery rate per cycle was 21% (27% per embryo transfer).

CONCLUSIONS

This is the first study to describe the clinical application of comprehensive chromosome screening applied to polar bodies, blastomeres or trophectoderm cells from patients carrying inversions and translocations. Using these techniques, most patients requesting PGD for a chromosome rearrangement can be treated using a single protocol. Additionally, the detection of abnormalities affecting chromosomes unrelated to the rearrangement may assist in the selection of viable embryos for transfer.