Clinical outcomes in carriers of complex chromosomal rearrangements: a retrospective analysis of comprehensive chromosome screening results in seven cases

Case report: Optical genome mapping revealed double rearrangements in a male undergoing preimplantation genetic testing

Chromosome rearrangement is one of the main causes of abortion. In individuals with double chromosomal rearrangements, the abortion rate and the risk of producing abnormal chromosomal embryos are increased. In our study, preimplantation genetic testing for structural rearrangement (PGT-SR) was performed for a couple because of recurrent abortion and the karyotype of the male was 45, XY der (14; 15)(q10; q10). The PGT-SR result of the embryo in this in vitro fertilization (IVF) cycle showed microduplication and microdeletion at the terminals of chromosomes 3 and 11, respectively. Therefore, we speculated whether the couple might have a cryptic reciprocal translocation which was not detected by karyotyping. Then, optical genome mapping (OGM) was performed for this couple, and cryptic balanced chromosomal rearrangements were detected in the male. The OGM data were consistent with our hypothesis according to previous PGT results. Subsequently, this result was verified by fluorescence in situ hybridization (FISH) in metaphase. In conclusion, the male’s karyotype was 45, XY, t(3; 11)(q28; p15.4), der(14; 15)(q10; q10). Compared with traditional karyotyping, chromosomal microarray, CNV-seq and FISH, OGM has significant advantages in detecting cryptic and balanced chromosomal rearrangements.

Chromosomal segregation analysis and HOST-based sperm selection in a complex reciprocal translocation carrier

INTRODUCTION

Complex chromosomal rearrangements (CCRs) involve two or more chromosomes and at least three breakpoints. Due to their complexity, they are associated with a high number of unbalanced gametes, whose fertilization is often incompatible with viable fetal development. Preimplantation genetic diagnosis (PGD) is usually offered to those patients and typically shows modest results considering the high number of unbalanced embryos. We previously showed that a sperm selection process using the hypo-osmotic swelling test (HOST) allows for an 83% reduction in the proportion of unbalanced spermatozoa (US) in male rearrangements carriers. This is the first report of the use of this procedure in a CCR carrier.

CASE DESCRIPTION

We report on the case of a 36-year-old male t(4;7;14)(q12;p21;q11.2) carrier who presented to our center for infertility. Sperm fluorescent in situ hybridization showed an 88% proportion of unbalanced spermatozoa. After hypo-osmotic incubation and selection of spermatozoa with a specific flagellar conformation, the proportion of unbalanced spermatozoa dropped to 15%.

DISCUSSION

In the present case, we show that it is possible to select chromosomally balanced prior to in vitro fertilization in male CCR carriers. This technique has the potential of increasing the proportion of euploid embryos and therefore the chances of healthy pregnancy and birth.

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.

Analysis of complex chromosomal rearrangements using a combination of current molecular cytogenetic techniques

BACKGROUND

Using combined fluorescence in situ hybridization (FISH) and high-throughput whole-genome sequencing (WGS) molecular cytogenetic technology, we aim to analyze the junction breakpoints of complex chromosome rearrangements (CCR) that were difficult to identify by conventional karyotyping analysis and further characterize the genetic causes of recurrent spontaneous abortion.

RESULTS

By leveraging a combination of current molecular techniques, including chromosome karyotype analysis, FISH, and WGS, we comprehensively characterized the extremely complex chromosomal abnormalities in this patient with recurrent spontaneous abortions. Here, we demonstrated that combining these current established molecular techniques is an effective and efficient workflow to identify the structural abnormalities of complex chromosomes and locate the rearrangement of DNA fragments.

CONCLUSIONS

In conclusion, leveraging results from multiple molecular and cytogenetic techniques can provide the most comprehensive genetic analysis for genetic etiology research, diagnosis, and genetic counseling for patients with recurrent spontaneous abortion and embryonic abortion.

Evaluation of Laser Confocal Raman Spectroscopy as a Non-Invasive Method for Detecting Sperm DNA Contents

RESEARCH QUESTION

Is Raman spectroscopy an efficient and accurate method to detect sperm chromosome balance state by DNA content differences?

DESIGN

Semen samples were provided by diploid healthy men, and the analysis parameters met the current World Health Organization standards. The DNA content was assessed by analysis of the corresponding spectra obtained from a laser confocal Raman spectroscope. The sperm sex chromosome information was obtained by fluorescence in situ hybridization (FISH). Comparative analysis was performed between FISH results and Raman spectral analysis results.

RESULTS

Different parts of the sperm head showed different spectral signal intensities, which indicated that there were different chemical components. Standard principal component analysis (PCA) can preliminarily classify sperm with different DNA contents into two groups. Further analysis showed that there were significant differences in the 785 DNA backbone peaks and 714-1,162 cm^-1 DNA skeleton regions among sperm with different DNA contents. The peak and regional peak of the DNA skeleton of X sperm were significantly higher than those of Y sperm (X vs. Y, p < 0.05). The above sperm types were confirmed by FISH. ROC curve analysis shows that there is a correlation between the Raman spectrum data and FISH results.

CONCLUSION

Raman spectroscopy can identify X and Y sperms by analyzing the DNA content difference. However, the accuracy of the detection still needs to be improved. Nevertheless, Raman spectroscopy has a potential application value in the field of sperm aneuploidy detection and may even be used as a non-invasive predictor of sperm aneuploid state in preimplantation genetic testing (PGT-A).

The Relationship between Human Embryo Parameters and De Novo Chromosomal Abnormalities in Preimplantation Genetic Testing Cycles

DESIGN

In total, 456 PGT cycles, including 283 PGT-SR cycles and 173 PGT-A cycles, were assessed through comprehensive chromosome screening (CCS) from January 2017 to June 2020 at the Department of Reproductive Medicine of the Third Affiliated Hospital of Zhengzhou University. Trophectoderm (TE) biopsies were sequenced using next-generation sequencing (NGS). The incidence of de novo chromosome abnormalities was calculated, and the relationships between de novo chromosome abnormality rates and maternal age, number of oocytes retrieved, and parameters of cleavage-stage embryos and blastocyst-stage embryos were investigated.

RESULTS

The incidence of de novo chromosome abnormalities was 28.0% (318/1,135) in the PGT-SR cycles and 36.3% (214/590) in the PGT-A cycles, which increased with maternal age in both PGT-SR cycles (P = 0.018) and PGT-A cycles (P < 0.001). The incidence of de novo chromosome abnormalities was related to TE grade (P < 0.001), internal cell mass grade (P = 0.002), and development speed (day 5 vs. day 7: P < 0.001) of blastocyst-stage embryos. The incidence of de novo chromosomal abnormalities was irrelevant to the number of oocytes retrieved and the parameters of the embryo at the cleavage stage.

CONCLUSION

Blastocysts with higher morphology scores and faster progression had a lower incidence of de novo chromosome abnormalities, especially complex chromosome abnormalities. De novo chromosome abnormalities may negatively affect the morphological grading of blastocysts. Our findings will provide valuable information to the fertility doctor for embryo selection in non-PGT cycles.

The genetic cause of intellectual deficiency and/or congenital malformations in two parental reciprocal translocation carriers and implications for assisted reproduction

PURPOSE

To elucidate the genetic cause of intellectual deficiency and/or congenital malformations in two parental reciprocal translocation carriers and provide appropriate strategies of assisted reproductive therapy (ART).

MATERIALS AND METHODS

Two similar couples having a child with global developmental delay/intellectual disability symptoms attended the Reproductive and Genetic Hospital of CITIC-Xiangya (Changsha, China) in 2017 and 2019, respectively, in order to determine the cause(s) of the conditions affecting their child and to seek ART to have a healthy baby. Both of the healthy couples were not of consanguineous marriage, denied exposure to toxicants, and had no adverse life history. This study was approved by the Institutional Ethics Committee of the Reproductive & Genetic Hospital of CITIC-Xiangya, and written informed consent was obtained from the parents. Genetic diagnoses were performed by karyotype analysis, breakpoint mapping analysis of chromosomal translocation(s), single-nucleotide polymorphism (SNP) microarray analysis, and whole-exome sequencing (WES) for the two children and different appropriate reproductive strategies were performed in the two families.

RESULTS

Karyotype analysis revealed that both patients carried parental reciprocal translocations [46,XY,t(7;16)(p13;q24)pat and 46,XY,t(13;17)(q12.3;p11.2)pat, respectively]. Follow-up breakpoint mapping analysis showed no interruption of associated genes, and SNP microarray analysis identified no significant copy number variations (CNVs) in the two patients. Moreover, WES results revealed that patients 1 and 2 harbored candidate compound heterozygous mutations of MCOLN1 [c.195G>C (p.K65N) and c.1061G>A (p.W354*)] and MCPH1 [c.877A>G (p.S293G) and c.1869_1870delAT (p.C624*)], respectively, that were inherited from their parents and not previously reported. Furthermore, the parents of patient 1 obtained 10 embryos during ART cycle, and an embryo of normal karyotype and non-carrier of observed MCOLN1 mutations according to preimplantation genetic testing for structural rearrangement and monogenic defect was successfully transferred, resulting in the birth of a healthy boy. The parents of patient 2 chose to undergo ART with donor sperm to reduce the risk of recurrence.

CONCLUSIONS

Systematic genetic diagnosis of two carriers of inherited chromosomal translocations accompanied by clinical phenotypes revealed their cause of disease, which was critical for genetic counseling and further ART for these families.

The influence of balanced complex chromosomal rearrangements on preimplantation embryonic development potential and molecular karyotype

BACKGROUND

Balanced complex chromosome rearrangements (BCCR) are balanced chromosomal structural aberrations that involve two or more chromosomes and at least three breakpoints. It is very rare in the population. The objective is to explore the difference of influence of three types of BCCR on early embryonic development and molecular karyotype.

RESULTS

Twelve couples were recruited including four couples of three-way rearrangements carriers (group A), three couples of double two-way translocations carriers (group B) and five couples of exceptional CCR carriers (group C). A total of 243 oocytes were retrievedin the seventeen preimplantation genetic testing (PGT) cycles, and 207 of these were available for fertilization. After intracytoplasmic sperm injection, 181oocytes normally fertilized. The rates of embryos forming on day3 in three groups were 87.88, 97.78 and77.14%, which was significantly different (P = 0.01). Compared with group B, the rate of embryo formation was statistically significantly lower in group C (P = 0.01). Furthermore, the rates of high-quality blastocysts in three group were 14.71, 48.15 and 62.96%, respectively, which was significantly different (P = 0.00). Compared with group B andC, the rate of high-quality blastocysts in group A was statistically significantly lower (P = 0.00;P = 0.00). Comprehensive chromosome analysis was performed on 83 embryos, including 75 trophectodermcellsand 8 blastomeres. Except 7 embryos failed to amplify, 9.01%embryos were diagnosed as euploidy, and 90.91% were diagnosed as abnormal. As for group A, the euploid embryo rate was 10.71%and the abnormal embryo rate was 89.29%. In group B,the euploid embryo rate was 3.85%, the abnormal embryo rate was 96.15%. The euploid embryo rate was 13.04%, the abnormal embryo rate was 86.96% in group C. There were no significant differences among the three groups (P = 0.55).

CONCLUSIONS

The lowest rate of high quality blastocysts has been for three-way rearrangements and the lowest rate of euploidy has been for double two-way translocations, although no significant difference. Different types of BCCR maybe have little effect on the embryonic molecular karyotype. The difference of influence of BCCR on early embryonic developmentandmolecular karyotypeshould be further studied.

Chromoanasynthesis: another way for the formation of complex chromosomal abnormalities in human reproduction

Chromoanasynthesis has been described as a novel cause of massive constitutional chromosomal rearrangements. Based on DNA replication machinery defects, chromoanasynthesis is characterized by the presence of chromosomal duplications and triplications locally clustered on one single chromosome, or a few chromosomes, associated with various other types of structural rearrangements. Two distinct mechanisms have been described for the formation of these chaotic genomic disorders, i.e. the fork stalling and template switching and the microhomology-mediated break-induced replication. Micronucleus-based processes have been evidenced as a causative mechanism, thus, highlighting the close connection between segregation errors and structural rearrangements. Accumulating data indicate that chromoanasynthesis is operating in human germline cells and during early embryonic development. The development of new tools for quantifying chromoanasynthesis events should provide further insight into the impact of this catastrophic cellular phenomenon in human reproduction.