Clinical outcomes following preimplantation genetic testing and microdissecting junction region in couples with balanced chromosome rearrangement

Detection of chromosome aberrations in 17 054 individuals with fertility problems and their subsequent assisted reproductive technology treatments in Central China

STUDY QUESTION

How do the types and frequency of chromosome aberrations in couples in central China affect fertility and ART treatment?

SUMMARY ANSWER

Men with chromosome aberrations or polymorphisms have an increased risk of semen quality impairment and infertility, and couples affected by reciprocal translocations had a lower pregnancy rate compared with other chromosome aberrations.

WHAT IS KNOWN ALREADY

Karyotyping is crucial for patients affected by infertility as chromosome aberrations play an important role in the etiology of male infertility. However, the influence of chromosome aberrations and polymorphisms on sperm motility and morphology remains controversial. Data on ART treatment outcomes in infertile couples affected by chromosome aberrations are insufficient.

STUDY DESIGN, SIZE, DURATION

We conducted a retrospective study involving 17 054 patients affected by infertility who underwent karyotyping in our center between January 2020 and May 2022.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Karyotyping was performed on 17 054 patients with reproductive failure. All patients were from the central regions of China. The following data were collected from a medical records system using patient identification numbers: couples' ages, history of pregnancy and childbirth, type of infertility, years of infertility, cause of infertility, chromosome karyotypes, semen analysis results, assisted reproductive techniques performed, and treatment outcomes of ART.

MAIN RESULTS AND THE ROLE OF CHANCE

The incidence of chromosome aberrations was 2.04%; 2.49% in men and 1.57% in women. By analyzing the relationships between chromosome aberrations/polymorphisms and abnormal semen parameters, we found that there were significantly higher rates of asthenozoospermia, oligospermia, and teratozoospermia among men with Robertsonian translocations and sex chromosomal structural aberrations compared with those with normal karyotypes. Higher rates of asthenozoospermia and teratozoospermia were also observed among men with autosomal reciprocal translocations. The incidence of chromosome aberrations in azoospermic men (13.75%), and in men with cryptozoospermia or severe oligospermia (6.97%) was significantly higher than that in men with mild oligospermia or normospermia (0.88-2.12%). In addition, we found that the progressive movement of sperm is impaired in men with Chromosome 21 polymorphisms compared with men with normal karyotypes (39.46% ± 20.51% vs 48.61% ± 18.76%, P = 0.026). The percentage of morphologically normal forms was lower in the chromosomal polymorphism group than in the normal karyotype group (5.01% ± 2.41% vs 5.59% ± 2.14%, P = 0.001), especially in men with polymorphisms on Chromosome 9 (enlarged Chromosome 9 heterochromatin [9qh+]: 4.48% ± 2.22% vs 5.59% ± 2.14%, P = 0.006; pericentric inversion of Chromosome 9 [inv(9)]: 5.09% ± 3.11% vs 5.59% ± 2.14%, P = 0.008). ART treatment was successful in 36.00% of couples affected by chromosome aberrations. However, couples affected by reciprocal translocations achieved a lower pregnancy rate (24.07%), which may be due to the lower euploidy rates (27.31%) when compared with that in other chromosome aberrations.

LIMITATIONS, REASONS FOR CAUTION

First, although the initial cohort was large, chromosome aberrations were identified in a small number of patients. Second, the observational nature of the study design is limiting. Third, the couples affected by infertility in this study were all outpatients that did not undergo identical comprehensive examinations except for karyotyping, leading to the incomplete collection of medical records. Also, the population included in this study mainly focused on couples affected by infertility, which may not be included in the European Association of Urology (EAU) recommendation on male infertility.

WIDER IMPLICATIONS OF THE FINDINGS

Men with chromosome aberrations or polymorphisms have an increased risk of semen quality impairment and infertility. Constitutional chromosome analysis is recommended for men affected by infertility and severe oligospermia or azoospermia to facilitate early and appropriate guidance for the most suitable treatment. Carriers of chromosome aberrations can achieve acceptable pregnancy outcomes through IVF. However, couples affected by reciprocal translocations have lower pregnancy rates, and more treatment cycles are needed before a successful pregnancy. A possible explanation may be the fewer euploid embryos obtained.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by Grant 2021YFC2700603 from the National Key Research & Development Program of China. The authors declare no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

PGT for structural chromosomal rearrangements in 300 couples reveals specific risk factors but an interchromosomal effect is unlikely

RESEARCH QUESTION

What factors affect the proportion of chromosomally balanced embryos in structural rearrangement carriers? Is there any evidence for an interchromosomal effect (ICE)?

DESIGN

Preimplantation genetic testing outcomes of 300 couples (198 reciprocal, 60 Robertsonian, 31 inversion and 11 complex structural rearrangement carriers) were assessed retrospectively. Blastocysts were analysed either by array-comparative genomic hybridization or next-generation sequencing techniques. ICE was investigated using a matched control group and sophisticated statistical measurement of effect size (φ).

RESULTS

300 couples underwent 443 cycles; 1835 embryos were analysed and 23.8% were diagnosed as both normal/balanced and euploid. The overall cumulative clinical pregnancy and live birth rates were 69.5% and 55.8%, respectively. Complex translocations and female age (≥35) were found to be risk factors associated with lower chance of having a transferable embryo (P < 0.001). Based on analysis of 5237 embryos, the cumulative de-novo aneuploidy rate was lower in carriers compared to controls (45.6% versus 53.4%, P < 0.001) but this was a 'negligible' association (φ < 0.1). A further assessment of 117,033 chromosomal pairs revealed a higher individual chromosome error rate in embryos of carriers compared to controls (5.3% versus 4.9%), which was also a 'negligible' association (φ < 0.1), despite a P-value of 0.007.

CONCLUSIONS

These findings suggest that rearrangement type, female age and sex of the carrier have significant impacts on the proportion of transferable embryos. Careful examination of structural rearrangement carriers and controls indicated little or no evidence for an ICE. This study helps to provide a statistical model for investigating ICE and an improved personalized reproductive genetics assessment for structural rearrangement carriers.

Carrier screening and PGT for an autosomal recessive monogenic disorder: insights from virtual trials

PURPOSE

To assess the costs and benefits of carrier screening and preimplantation genetic testing (PGT) for recessive autosomal monogenic disorders for couples attempting assisted conception.

METHODS

A simulated first full cycle for women less than 35 years transferring embryos one at a time. The effect of testing on pregnancy outcomes was evaluated for different reporting scenarios. A Monte Carlo method utilising 1000 trials for 10,000 couples, testing 4, 16 and 38 genes, was used to assess the numbers likely to be at high risk and to estimate the incremental cost of screening and PGT to avoid an affected child.

RESULTS

PGT for high-risk couples: testing embryos only for the monogenic condition avoided 1 affected pregnancy for 4 cycles started. Combined with testing for chromosomal aneuploidy: ranking test results avoided 1 adverse pregnancy (affected, biochemical, clinical miscarriage) from 3 cycles started; 1 in 2 when excluding from transfer all embryos with an abnormal test result, within 1 in 25 fewer women achieving an unaffected live birth. Carrier screening for 4, 16 and 38 gene scenarios, where 1:250, 1:196 and 1:29 couples were at high risk: the incremental cost to prevent 1 affected live birth was estimated to be less than GBP 1,150,000 (US $1,587,000), < 836,642 (1,154,566) and < 137,794 (190,156), respectively, in 95% of trials.

CONCLUSIONS

Carrier screening combined with PGT, with and without testing for unrelated chromosomal abnormalities, for couples attempting assisted conception is complex but likely to be effective and also expensive.

PGT-SR (reciprocal translocation) using trophectoderm sampling and next-generation sequencing: insights from a virtual trial

PURPOSE

The objective of this virtual study was to simulate a full cycle and assess the costs and benefits to a couple with a reciprocal translocation, using current techniques for preimplantation genetic testing and comparing reporting every chromosome with only reporting those involved in the rearrangement.

METHODS

A simulation was constructed for women under the age of 35 years, where vitrified-warmed embryos were transferred one at a time in a first full cycle following preimplantation genetic testing using next-generation sequencing and sampling the trophectoderm at the blastocyst stage. The effect on pregnancy outcomes (live birth, clinical miscarriage and biochemical pregnancy) was evaluated for different reporting strategies for embryo transfer to (i) report only the rearranged chromosomes and transfer embryos with a normal or balanced test result for the translocation (targeted), or (ii) report every chromosome and exclude from transfer all embryos with an abnormal test result (exclusion), or (iii) exclude only those consistent with an unbalanced translocation and/or unrelated non-mosaic whole-chromosome aneuploidy and assign those with samples consistent with a normal or balanced translocation complement and unrelated mosaic aneuploidy or segmental imbalance (embryos of uncertain reproductive potential) a lower transfer priority (ranking). The number of individual women whom might benefit by avoiding an adverse pregnancy outcome (biochemical pregnancy, clinical miscarriage) or be disadvantaged by not achieving a live birth was evaluated. The financial cost of the different reporting strategies and the time taken to complete a cycle were also considered.

RESULTS

The simulation showed that compared to only reporting the translocation chromosomes (targeted reporting), testing every chromosome and ranking embryos by test result for transfer was a cost-effective strategy to avoid an adverse pregnancy without compromising the chance of a live birth. Excluding from transfer embryos with a test result consistent with a normal or balanced translocation complement of uncertain reproductive potential was an inferior strategy because it resulted in fewer live births from a full cycle. Reporting only the translocation chromosomes was an inferior strategy because it was less effective than ranked reporting of every chromosome to avoid an adverse pregnancy. Compared to targeted reporting, the ranked and exclusion strategies marginally reduced the overall cost and time taken to complete a full cycle. The ranking strategy avoided 1 adverse pregnancy for 12 cycles started, compared to 1 in 10 for the exclusion strategy which also resulted in 1 in 22 fewer women achieving a live birth. A minority (< 10%) of couples benefited by avoiding at least 1 adverse pregnancy whilst also reducing the time and cost for a complete cycle; most (> 70% ) couples received no benefit additional to targeted reporting and had the same outcome for pregnancy, time and cost.

CONCLUSIONS

The primary objective of PGT-SR for couples with a reciprocal translocation is to avoid a pregnancy with a chromosomally unbalanced product of the translocation and to reduce the risk of miscarriage, at least to that expected for couples with normal karyotypes. Trophectoderm sampling at the blastocyst stage with testing using NGS is an effective approach; however, ranking and excluding from transfer embryos with abnormal test results for unrelated chromosomes is problematical and is likely to be detrimental to achieving a live birth. Targeted reporting, where only the results of the chromosomes involved in the translocation are known, should be preferred to achieve a live birth. A best effort should be made to follow up and investigate all pregnancies following PGT-SR. Once the reproductive outcome is known (biochemical pregnancy, clinical pregnancy, live birth), the chromosomes unrelated to the rearrangement can be analysed as an experimental study. The risk/benefit of avoiding an adverse pregnancy vs reducing the chance of a healthy delivery should be a decision for each individual couple and informed by appropriate genetic counselling for their specific translocation and history.