Interchromosomal effect analyses by sperm FISH: incidence and distribution among reorganization carriers

Trisomy 21 with Maternally Inherited Balanced Translocation (15q;22q) in a Female Fetus: A Rare Case of Probable Interchromosomal Effect

Chromosomal rearrangements can interfere with the disjunction and segregation of other chromosome pairs not involved in the rearrangements, promoting the occurrence of numerical abnormalities in resulting gametes and predisposition to trisomy in offspring. This phenomenon of interference is known as the interchromosomal effect (ICE). Here we report a prenatal case potentially generated by ICE. The first-trimester screening ultrasound of the pregnant woman was normal, but the NIPT indicated a high risk for three copies of chromosome 21, thus suspecting trisomy 21 (T21). After a comprehensive clinical evaluation and genetic counseling, the couple decided to undergo amniocentesis. The prenatal karyotype confirmed T21 but also showed a balanced translocation between the long arm of chromosome 15 (q22) and the long arm of chromosome 22. The parents' karyotypes also showed that the mother had the 15;22 translocation. We reviewed T21 screening methods, and we performed a literature review on ICE, a generally overlooked phenomenon. We observed that ours is the first report of a prenatal case potentially due to ICE derived from the mother. The recurrence risk of aneuploidy in the offspring of translocated individuals is likely slightly increased, but it is not possible to estimate to what extent. In addition to supporting observations, there are still open questions such as, how frequent is ICE? How much is the aneuploidy risk altered by ICE?

Higher chromosomal abnormality rate in blastocysts from a subset of patients with pericentric inversion (Inv) 1 variant

The purpose of this study was to evaluate the incidence of unbalanced chromosome rearrangement in blastocyst-stage embryos from carriers of pericentric inversion of chromosome 1 (PEI-1). A total of 98 embryos from 22 PEI-1 carriers were tested for unbalanced rearrangements, originating from inversion carriers, and overall aneuploidy. Logistic regression analysis indicated that the ratio of inverted segment size to chromosome length was a statistically significant risk factor for unbalanced chromosome rearrangement from PEI-1 carriers (p = 0.003). The optimal cut-off values to predict the risk of unbalanced chromosome rearrangement was 36%, with the incidence being 2.0% in the <36% group and 32.7% in the ≥36% group. The unbalanced embryo rate was 24.4% in male carriers compared to 12.3% in female carriers. Inter-chromosomal effect analysis was performed using 98 blastocysts from PEI-1 carriers and 116 blastocysts from age-matched controls. PEI-1 carriers had similar sporadic aneuploidy rates compared to those of age-matched controls at 32.7 vs. 31.9%, respectively. In conclusion, the risk of unbalanced chromosome rearrangement is affected by inverted segment size in PEI-1 carriers.

The effect of carrier characteristics and female age on preimplantation genetic testing results of blastocysts from Robertsonian translocation carriers

PURPOSE

To analyze factors affecting segregation and ploidy results from Robertsonian carriers, and determine chromosomes involved impact chromosome stability during meiosis and mitosis.

METHODS

This retrospective study include 928 oocyte retrieval cycles from 763 couples with Robertsonian translocations undergoing preimplantation genetic testing for structural rearrangements (PGT-SR) using next-generation sequencing (NGS) between December 2012 and June 2020.The segregation patterns of the trivalent of 3423 blastocysts were analyzed according to the carrier's sex and age. A total of 1492 couples who received preimplantation genetic testing for aneuploidy (PGT-A) were included as the control group and matched according to maternal age and testing time stage.

RESULTS

A total of 1728 (50.5%) normal/balanced embryos were identified from 3423 embryos diagnosed. The rate of alternate segregation in male Robertsonian translocation carriers was significantly higher than that in female carriers (82.3% vs. 60.0%, P < 0.001). However, the segregation ratio exhibited no difference between young and older carriers. Further, increasing maternal age decreased the proportion of transferable embryo cycle in both female and male carriers. And the ratio of chromosome mosaic from the Robertsonian translocation carrier group was significantly higher than that in the PGT-A control group (1.2% vs. 0.5%, P < 0.01).

CONCLUSIONS

The meiotic segregation modes were affected by the carrier sex and were independent of the carrier's age. Advanced maternal age decreased the probability of obtaining a normal/balanced embryo. In additional, the Robertsonian translocation chromosome could increase the possibility of chromosome mosaicism during mitosis in blastocysts.

Sperm and Oocyte Chromosomal Abnormalities

Gametogenesis, the process of producing gametes, differs significantly between oocytes and sperm. Most oocytes have chromosomal aneuploidies, indicating that chromosomal aberrations in miscarried and newborn infants are of oocyte origin. Conversely, most structural anomalies are of sperm origin. A prolonged meiotic period caused by increasing female age is responsible for an increased number of chromosomal aberrations. Sperm chromosomes are difficult to analyze because they cannot be evaluated using somatic cell chromosome analysis methods. Nevertheless, researchers have developed methods for chromosome analysis of sperm using the fluorescence in situ hybridization method, hamster eggs, and mouse eggs, allowing for the cytogenetic evaluation of individual sperm. Reproductive medicine has allowed men with severe spermatogenic defects or chromosomal abnormalities to have children. However, using these techniques to achieve successful pregnancies results in higher rates of miscarriages and embryos with chromosomal abnormalities. This raises questions regarding which cases should undergo sperm chromosome analysis and how the results should be interpreted. Here, we reviewed clinical trials that have been reported on oocyte and sperm chromosome analyses. Examination of chromosomal abnormalities in gametes is critical in assisted reproductive technology. Therefore, it is necessary to continue to study the mechanism underlying gametic chromosomal abnormalities.

The relevance of sperm morphology in male infertility

This brief report concerns the role of human sperm morphology assessment in different fields of male infertility: basic research, genetics, assisted reproduction technologies, oxidative stress. One of the best methods in studying sperm morphology is transmission electron microscopy (TEM) that enables defining the concept of sperm pathology and classifying alterations in non-systematic and systematic. Non-systematic sperm defects affect head and tail in variable ratio, whereas the rare systematic defects are characterized by a particular anomaly that marks most sperm of an ejaculate. TEM analysis and fluorescence in situ hybridization represent outstanding methods in the study of sperm morphology and cytogenetic in patients with altered karyotype characterizing their semen quality before intracytoplasmic sperm injection. In recent years, the genetic investigations on systematic sperm defects, made extraordinary progress identifying candidate genes whose mutations induce morphological sperm anomalies. The question if sperm morphology has an impact on assisted fertilization outcome is debated. Nowadays, oxidative stress represents one of the most important causes of altered sperm morphology and function and can be analyzed from two points of view: 1) spermatozoa with cytoplasmic residue produce reactive oxygen species, 2) the pathologies with inflammatory/oxidative stress background cause morphological alterations. Finally, sperm morphology is also considered an important endpoint in in vitro experiments where toxic substances, drugs, antioxidants are tested. We think that the field of sperm morphology is far from being exhausted and needs other research. This parameter can be still considered a valuable indicator of sperm dysfunction both in basic and clinical research.

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.

Logistic regression analyses of factors affecting the euploidy of blastocysts undergoing in vitro fertilization and preimplantation genetic testing

Embryo chromosomal abnormalities are considered as the main cause of low pregnancy rate for in vitro fertilization (IVF). Recently, a new metric of success in assisted reproductive technology, that is, the ability to achieve at least 1 euploid blastocyst for transfer, has been brought into focus among clinicians. Our study aimed to investigate the effects of different factors on the euploidy of blastocysts undergoing IVF and preimplantation genetic testing (PGT). This retrospective observational study included 493 cycles underwent IVF/intracytroplasmatic sperm injection intended to obtain trophectoderm biopsy for PGT from June 2016 to December 2019 at a single academic fertility center. Logistic regression was adopted to analyze the clinical characteristics and embryonic data related to the ability to achieve at least 1 euploid blastocyst for transfer. The study took 1471 blastocysts from 493 cycles as samples for PGT. Among them, 149 cycles (30.22%) had no euploid blastocyst and 344 cycles (69.78%) had at least 1 euploid blastocyst. A multivariate logistic analysis suggested that maternal age >36, abnormal parental karyotype, nonfirst cycles and blastocysts number per cycle <3 were the risk factors for no euploid blastocyst. The parental karyotype, maternal age, number of cycles, and number of blastocysts per cycle were the dominant factors affecting the ability to achieve at least 1 euploid blastocyst for transfer and therefore could be regarded as potential predictors for genetic counseling.

Sperm chromosome segregation of rob(4;16) and rob(4;16)inv(4) in the brown brocket deer (Mazama gouazoubira)

The genus Mazama stands out among the Neotropical deer due to their wide intra and interspecific karyotypic diversification, which is associated with an accentuated chromosomal fragility. There are reports of heterozygous Robertsonian translocation (RT) carriers in a free-range population of Mazama gouazoubira (brown brocket deer), as well as in captive animals of this and other species of the genus. To analyze possible negative impacts of heterozygous chromosome rearrangements on reproductive fitness of the carriers, we performed an analysis of sperm meiotic segregation in four brown brocket bucks, carriers of a rob(4;16), and compared the results with those of a normal buck. We established a reliable FISH and sperm-FISH protocol for the brown brocket deer using bovine (Bos taurus; diploid number, 2n = 60) whole chromosome painting (WCP) and BAC probes. Using BAC probes, we revealed the presence of a paracentric inversion (PAI) of the fused chromosome 4 in two of the four analyzed RT carriers. The mean frequency of normal/balanced sperm in the translocation carriers was significantly lower than in the normal buck (94.78% vs 98.40%). The mean value of total unbalanced spermatozoa was almost doubled in the RT/PAI carriers (6.68%) when compared to RT carriers (3.76%), but the difference was not statistically significant. This study demonstrated the efficiency of FISH with bovine WCP and BAC probes in the characterization of chromosome rearrangements and gametic segregation patterns in brown brocket deer. Our results indicate a low to moderate increase in the rates of unbalanced meiotic segregation products in brown brocket bucks heterozygous for RT and RT/PAIs.

Analysis of sperm chromosomes in six carriers of rare and common Robertsonian translocations

Introduction: Robertsonian translocation (RobT) is the central fusion of the long arms of two acrocentric chromosomes, leading to 45 chromosomes in humans. The most common ones are rob(13;14) and rob(14;21) (91%). Other types of RobT are so-called rare cases. In the general population RobTs occur with a frequency of approximately 0.123%, but among men with reproductive failure this value rises 9-fold. Infertility in RobT carriers is associated with the formation of unbalanced spermatozoa resulting from segregation of the chromosomes involved in trivalent during the meiotic prophase. In spermatozoa of many RobT carriers an increased level of chromosomal aneuploidy is observed. Materials and Methods: We examined the hyperhaploidy level of chromosomes 7, 9, 18, 21, 22, X and Y in spermatozoa of 6 RobT unrelated carriers: two carriers with rare rob(13;15), one with rare rob(13;22), and three of the common rob(13;14). Results were compared with the control data from a group of 7 fertile men with a normal karyotype. Fluorescent in situ hybridization (FISH) was applied. Results: We found an increased level of sperm aneuploidy regarding at least one of the analyzed chromosomes in each of the carriers, while in rare RobTs interchromosomal effect (ICE) was observed. Meiotic segregation pattern of a rare rob(13;15) carrier revealed the 76% of normal /balanced spermatozoa. Disucussion: Due to the relatively high population frequency of RobTs, their influence on reproductive failure, hight risk of imbalancement in prenatal diagnosis (7%), and small amount of data for rare RobTs, each newly characterized case is valuable in genetic counseling.

A Rapid NGS-Based Preimplantation Genetic Testing for Chromosomal Abnormalities in Day-3 Blastomere Biopsy Allows Embryo Transfer Within the Same Treatment Cycle

Nowadays, most of the preimplantation genetic testing (PGT) is performed with a strategy of comprehensive chromosome screening and trophectoderm biopsy. Nevertheless, patients with ovarian insufficiency may not have competent blastocysts. In the present study, we aimed to establish the value of multiple annealing and looping-based amplification cycle (MALBAC)-based next-generation sequencing (NGS) for PGT in day-3 embryos. A total of 94.3% (1168/1239) of embryos yielded informative results, and the overall embryo euploid rate was 21.9% (256/1168). Overall, 225 embryos were transferred in 169 cycles with a clinical pregnancy rate of 49.1% (83/169). The live birth and implantation rates were 47.3% (80/169) and 44.4% (100/225), respectively. Double embryos transfer showed higher clinical pregnancy and live birth rates compared with single embryo transfer, but the implantation rates were similar (44.2% vs. 44.6%, P > 0.05). The euploid rate for reciprocal translocations (16.1%) was significantly lower than that for Robertsonian translocations (28.0%, P < 0.01) and inversions (28.0%, P < 0.01). However, higher percentages of embryos with de novo abnormalities were observed with Robertsonian translocations (23.3%, P < 0.01) and inversions (30.5%, P < 0.01) than with reciprocal translocations (11.6%). We demonstrated that NGS for PGT on day-3 embryos is an effective clinical application, particularly for patients with a diminished ovarian reserve and limited embryos.

Fertility problems in males carrying an inversion of chromosome 10

Chromosomal inversion is closely related to male infertility. Inversion carriers may produce abnormal gametes, which may lead to partial duplication/deletion of the embryonic chromosome and result in spontaneous abortion, a fetus with multiple anomalies, or birth of a malformed child. Genetic counselling remains challenging for these carriers in clinical practice. We report two male carriers with inversion of chromosome 10 and review 26 reported cases. In the first case, 46,XX,inv(10)(p13q22) of the fetal chromosome was found in prenatal diagnosis; this was inherited from the paternal side with 46XY,inv(10)(p13q22). Another case was a male carrier with inv(10)(q21.2q22.1). There have been 25 (89.3%) cases of pericentric inversion and three (10.7%) cases of paracentric inversion involving chromosome 10. Of 28 cases, nine were associated with pregestational infertility of the couples, while the other 19 cases were associated with gestational infertility of the couples or normozoospermia. The breakpoints at 10p15, 10p11, 10q11, and 10q21 were associated with pregestational infertility of the couples. The breakpoints at 10p15, 10p14, 10p13, 10p12, 10p11, 10q11, 10q21, 10q22, 10q23, 10q24, 10q25, and 10q26 were related to gestational infertility of the couples or normozoospermia. Although there is a high risk of infertility or recurrent miscarriages, carriers with inversion of chromosome 10 might produce healthy offspring. Natural pregnancy can be used as a choice for inversion carriers with recurrent spontaneous abortion.

How much, if anything, do we know about sperm chromosomes of Robertsonian translocation carriers?

In men with oligozoospermia, Robertsonian translocations (RobTs) are the most common type of autosomal aberrations. The most commonly occurring types are rob(13;14) and rob(14;21), and other types of RobTs are described as 'rare' cases. Based on molecular research, all RobTs can be broadly classified into Class 1 and Class 2. Class 1 translocations produce the same breakpoints within their RobT type, but Class 2 translocations are predicted to form during meiosis or mitosis through a variety of mechanisms, resulting in variation in the breakpoint locations. This review seeks to analyse the available data addressing the question of whether the molecular classification of RobTs into Classes 1 and 2 and/or the type of DD/GG/DG symmetry of the involved chromosomes is reflected in the efficiency of spermatogenesis. The lowest frequency value calculated for the rate of alternate segregants was found for rob(13;15) carriers (Class 2, symmetry DD) and the highest for rob(13;21) carriers (Class 2, DG symmetry). The aneuploidy values for the rare RobT (Class 2) and common rob(14;21) (Class 1) groups together exhibited similarities while differing from those for the common rob(13;14) (Class 1) group. Considering the division of RobT carriers into those with normozoospermia and those with oligoasthenozoospermia, it was found that the number of carriers with elevated levels of aneuploidy was unexpectedly quite similar and high (approx. 70%) in the two subgroups. The reason(s) that the same RobT does not always show a similar destructive effect on fertility was also pointed out.

Investigation of the interchromosomal effects in male carriers with structural chromosomal abnormalities using FISH

OBJECTIVE

The interchromosomal effect (ICE) refers to the uncertainty during meiosis where the rearrangement of the chromosomes affects the segregation of the chromosomes that are not involved in the structural chromosomal abnormalities. The aim of this study is to investigate the existence of ICE in the sperm nuclei of the males who have structural chromosomal abnormalities.

MATERIAL AND METHODS

Nine male individuals who are the carriers of the structural chromosomal abnormalities (patient group) and 14 male individuals who did not have any chromosomal abnormalities (control group) were diagnosed by the classical cytogenetic analysis. The aneuploidy of chromosomes 2, 3, 12, 13, 17, 18, 21, X, and Y in the sperm nuclei was investigated using the fluorescence in situ hybridization (FISH) method in these individuals. The patient group included 5 Robertsonian translocation (ROB) carriers, 3 reciprocal translocation (RCP) carriers, and 1 inversion carrier.

RESULTS

A total of 51921 sperm nuclei were analyzed (19484 from the patient group and 32437 from the control group). While ICE was determined in 4 of 5 patients who were the carriers of ROB and an inversion carrier patient, it was not determined in the patient carrier of RCP.

CONCLUSION

Our results suggest that there is ICE in the male carriers with a structural chromosomal abnormality, which appears to be translocation, breakpoint, chromosome, and patient dependent.

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.

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

OBJECTIVE

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

DESIGN

Retrospective study.

SETTING

University-affiliated center.

PATIENT(S)

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

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE(S)

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

RESULT(S)

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

CONCLUSION(S)

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

Chromosome (re)positioning in spermatozoa of fathers and sons - carriers of reciprocal chromosome translocation (RCT)

Background

Non-random chromosome positioning has been observed in the nuclei of several different tissue types, including human spermatozoa. The nuclear arrangement of chromosomes can be altered in men with decreased semen parameters or increased DNA fragmentation and in males with chromosomal numerical or structural aberrations. An aim of this study was to determine whether and how the positioning of nine chromosome centromeres was (re)arranged in the spermatozoa of fathers and sons – carriers of the same reciprocal chromosome translocation (RCT).

Methods

Fluorescence in situ hybridization (FISH) was applied to analyse the positioning of sperm chromosomes in a group of 13 carriers of 11 RCTs, including two familial RCT cases: t(4;5) and t(7;10), followed by analysis of eight control individuals. Additionally, sperm chromatin integrity was evaluated using TUNEL and Aniline Blue techniques.

Results

In the analysed familial RCT cases, repositioning of the chromosomes occurred in a similar way when compared to the data generated in healthy controls, even if some differences between father and son were further observed. These differences might have arisen from various statuses of sperm chromatin disintegration.

Conclusions

Nuclear topology appears as another aspect of epigenetic genomic regulation that may influence DNA functioning. We have re-documented that chromosomal positioning is defined in control males and that a particular RCT is reflected in the individual pattern of chromosomal topology. The present study examining the collected RCT group, including two familial cases, additionally showed that chromosomal factors (karyotype and hyperhaploidy) have superior effects, strongly influencing the chromosomal topology, when confronted with sperm chromatin integrity components (DNA fragmentation or chromatin deprotamination).

Electronic supplementary material

The online version of this article (10.1186/s12920-018-0470-7) contains supplementary material, which is available to authorized users.

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.

Infertility patients with chromosome inversions are not susceptible to an inter-chromosomal effect

PURPOSE

The aim of this study was to evaluate the incidence of an inter-chromosomal effect (ICE) in blastocyst-stage embryos from carriers of balanced chromosome inversions.

METHODS

Infertility patients (n = 52) with balanced inversions (n = 66 cycles), and maternal age-matched controls that concurrently cycled (n = 66), consented to an IVF cycle with preimplantation genetic testing for aneuploidy (PGT-A). Blastocyst-stage embryos underwent trophectoderm biopsy for PGT-A with only euploid blastocysts transferred in a subsequent frozen embryo transfer. Subtypes of inversions were included in aggregate: paracentric/pericentric, polymorphic/non-polymorphic, male/female carriers, and varying inversion sizes.

RESULTS

The incidence of aneuploidy was not significantly higher for the inversion patients compared to the controls (inversion = 48.8% vs. control = 47.2% ns). Following euploid blastocyst transfer, there were excellent live birth outcomes.

CONCLUSIONS

Carriers of balanced chromosome inversions did not exhibit higher aneuploidy rates for chromosomes that were not involved in the inversion compared to maternal age-matched controls, signifying the absence of an inter-chromosomal effect for this data set. These results provide the largest investigation of blastocyst embryos regarding the debated existence of an ICE resulting from the presence of an inversion during meiosis. However, further studies are warranted to investigate an ICE among inversions subtypes that were outside the scope of this study.

Chromosomal scan of single sperm cells by combining fluorescence-activated cell sorting and next-generation sequencing

PURPOSE

The purpose of this study was to develop a feasible approach for single sperm isolation and chromosome analysis by next-generation sequencing (NGS).

METHODS

Single sperm cells were isolated from semen samples of normozoospermic male and an infertile reciprocal translocation (RcT) carrier with the 46,XY,t(7;13)(p12;q12.1) karyotype using the optimized fluorescence-activated cell sorting (FACS) technique. Genome profiling was performed using NGS.

RESULTS

Following whole-genome amplification, NGS, and quality control, the final chromosome analysis was performed on 31 and 6 single cell samples derived from the RcT carrier and normozoospermic male, respectively. All sperm cells from normozoospermic male showed a normal haploid 23-chromosome profile. For the RcT carrier, the sequencing data revealed that 64.5% of sperm cells harbored different variants of chromosome aberrations, involving deletion of 7p or 7q, duplication of 7p, and duplication of 13q, which is concordant with the expected chromosome segregation patterns observed in balanced translocation carriers. In one sample, a duplication of 9q was also detected.

CONCLUSIONS

We optimized FACS protocol for simple and efficient isolation of single human sperm cells that subsequently enabled a successful genome-wide chromosome profiling and identification of segmental aneuploidies from these individual cells, following NGS analysis. This approach may be useful for analyzing semen samples of infertile men or chromosomal aberration carriers to facilitate the reproductive risk assessment.

The tumor suppressor BRCA1-BARD1 complex localizes to the synaptonemal complex and regulates recombination under meiotic dysfunction in Caenorhabditis elegans

Breast cancer susceptibility gene 1 (BRCA1) and binding partner BRCA1-associated RING domain protein 1 (BARD1) form an essential E3 ubiquitin ligase important for DNA damage repair and homologous recombination. The Caenorhabditis elegans orthologs, BRC-1 and BRD-1, also function in DNA damage repair, homologous recombination, as well as in meiosis. Using functional GFP fusions we show that in mitotically-dividing germ cells BRC-1 and BRD-1 are nucleoplasmic with enrichment at foci that partially overlap with the recombinase RAD-51. Co-localization with RAD-51 is enhanced under replication stress. As cells enter meiosis, BRC-1-BRD-1 remains nucleoplasmic and in foci, and beginning in mid-pachytene the complex co-localizes with the synaptonemal complex. Following establishment of the single asymmetrically positioned crossover on each chromosome pair, BRC-1-BRD-1 concentrates to the short arm of the bivalent. Localization dependencies reveal that BRC-1 and BRD-1 are interdependent and the complex fails to properly localize in both meiotic recombination and chromosome synapsis mutants. Consistent with a role for BRC-1-BRD-1 in meiotic recombination in the context of the synaptonemal complex, inactivation of BRC-1 or BRD-1 enhances the embryonic lethality of mutants defective in chromosome synapsis. Our data suggest that under meiotic dysfunction, BRC-1-BRD-1 stabilizes the RAD-51 filament and alters the recombination landscape; these two functions can be genetically separated from BRC-1-BRD-1's role in the DNA damage response. Together, we propose that BRC-1-BRD-1 serves a checkpoint function at the synaptonemal complex where it monitors and modulates meiotic recombination.

Sperm fluorescent in situ hybridisation study of interchromosomal effect in six Tunisian carriers of reciprocal and Robertsonian translocations

Carriers of structural chromosomal anomalies, translocations and inversions are at increased risk of aneuploid gametes production. Besides the direct effect on the involved chromosomes, these rearrangements might disturb the segregation of other structurally normal chromosomes during meiosis. Such event is known as interchromosomal effect. In this study, six male carriers of translocations, four reciprocals and two Robertsonians, were investigated. In addition, seven fertile men with normal 46,XY karyotypes and normal sperm characteristics were enrolled as a control group. Spermatic fluorescent in situ hybridisation specific for chromosomes X, Y, 18, 21 and 22 was carried out. The Mann-Whitney U-test was used to compare the aneuploidy rates between patients and controls. All translocation carriers showed significantly increased frequencies of disomy of all investigated chromosomes, and diploid gametes compared with the control group (p < .05). However, disomy XY was not significantly different between controls and patients (p > .05). We have also observed a considerable interindividual variability in disomy and diploidy rates. These results confirm that the interchromosomal effect seems to exist and could contribute to higher rates of abnormal prenatal aneuploidy, resulting in a small increase in the risk of miscarriage and birth of children with congenital abnormalities and a potential reduction in fertility.

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.

Comprehensive Genome Profiling of Single Sperm Cells by Multiple Annealing and Looping-Based Amplification Cycles and Next-Generation Sequencing from Carriers of Robertsonian Translocation

Robertsonian translocation (RT) is a common cause for male infertility, recurrent pregnancy loss, and birth defects. Studying meiotic recombination in RT-carrier patients helps decipher the mechanism and improve the clinical management of infertility and birth defects caused by RT. Here we present a new method to study spermatogenesis on a single-gamete basis from two RT carriers. By using a combined single-cell whole-genome amplification and sequencing protocol, we comprehensively profiled the chromosomal copy number of 88 single sperms from two RT-carrier patients. With the profiled information, chromosomal aberrations were identified on a whole-genome, per-sperm basis. We found that the previously reported interchromosomal effect might not exist with RT carriers. It is suggested that single-cell genome sequencing enables comprehensive chromosomal aneuploidy screening and provides a powerful tool for studying gamete generation from patients carrying chromosomal diseases.

Meiotic pairing and gene expression disturbance in germ cells from an infertile boar with a balanced reciprocal autosome-autosome translocation

Individuals carrying balanced constitutional reciprocal translocations generally have a normal phenotype, but often present reproductive disorders. The aim of our research was to analyze the meiotic process in an oligoasthenoteratospermic boar carrying an asymmetric reciprocal translocation involving chromosomes 1 and 14. Different multivalent structures (quadrivalent and trivalent plus univalent) were identified during chromosome pairing analysis. Some of these multivalents were characterized by the presence of unpaired autosomal segments with histone γH2AX accumulation sometimes associated with the XY body. Gene expression in spermatocytes was studied by RNA-DNA-FISH and microarray-based testis transcriptome analysis. Our results revealed a decrease in gene expression for chromosomes 1 and 14 and an up-regulated expression of X-chromosome genes for the translocated boar compared with normal individuals. We hypothesized that the observed meiotic arrest and reproductive failure in this boar might be due to silencing of crucial autosomal genes (MSUC) and disturbance of meiotic sex chromosome inactivation (MSCI). Further analysis revealed abnormal meiotic recombination (frequency and distribution) and the production of a high rate of unbalanced spermatozoa.

A rare Robertsonian translocation rob(14;22) carrier with azoospermia, meiotic defects, and testicular sperm aneuploidy

Male infertility is a serious problem in an increasing number of couples. We report an infertile man with non-obstructive azoospermia and karyotype 45,XY,rob(14;22). The immunofluorescence analysis of his testicular tissue using antibodies to SYCP1, SYCP3, HORMAD2, MLH1, and centromeres showed delayed synapsis of the chromosomes involved in the translocation, a varying extent of trivalent asynapsis and its association with sex chromosomes. The mean frequency of meiotic recombination per cell was within the range of normal values. Fluorescence in situ hybridization (FISH) with probes for chromosomes 14 and 22 revealed 5.83% of chromosomally abnormal testicular spermatozoa. FISH with probes for chromosomes X, Y, and 21 showed frequencies of disomic and diploid testicular spermatozoa increased when compared to ejaculated sperm of healthy donors, but comparable with published results for azoospermic patients. PGD by FISH for the translocation and aneuploidy of chromosomes X, Y, 13, 18, and 21 showed a normal chromosomal complement in one out of three analyzed embryos. A healthy carrier girl was born after the embryo transfer. This study shows the benefits of preimplantation genetic diagnosis in a case of a rare Robertsonian translocation carrier with azoospermia and a relatively low frequency of chromosomally unbalanced testicular spermatozoa.

Co-Occurence of Reciprocal Translocation and COL2A1 Mutation in a Fetus with Severe Skeletal Dysplasia: Implications for Genetic Counseling

Achondrogenesis type II is an autosomal-dominant disease leading to severe micromelic dwarfism. Here, we report on the postmortem identification of a de novo heterozygous mutation in the COL2A1 gene (c.1529G>A, p.Gly510Asp) in a fetus who presented with generalized hydrops fetalis and severe micromelia during prenatal sonographic examinations. Initially, a reciprocal translocation t(4;17)(q31;p13) was detected in this fetus by chorionic villus sampling. Subsequent chromosomal analysis of maternal and paternal blood showed that the patient's mother was carrier of the same reciprocal translocation. SNP array analysis of the fetus did not provide evidence for chromosomal imbalances or CNVs that could be associated with the fetal phenotype. The coexistence of a cytogenetic (reciprocal translocation) and a molecular genetic (COL2A1 mutation) abnormality in the fetus carries important implications for genetic counseling.

Meiotic and sperm aneuploidy studies in three carriers of Robertsonian translocations and small supernumerary marker chromosomes

OBJECTIVE

To study the meiotic behaviour of one carrier of a small supernumerary marker chromosome (sSMC): 47,XY,+mar; one carrier of a Robertsonian translocation (ROB): 45,XY,rob(13;21) (q10;q10); and one carrier of both a sSMC and a ROB: 46,XY,rob(13;21) (q11.1;q11.1),+mar.

DESIGN

Case-control study.

SETTING

University-affiliated research center and hospital.

PATIENT(S)

Subfertile men with ROB and sSMC.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The chromosomal origin of the sSMC was assessed by multiplex fluorescence in situ hybridization. The segregation of the ROB and sSMC in sperm and possible interchromosomal effects were examined by fluorescence in situ hybridization. Synapsis, meiotic recombination, and meiotic inactivation were investigated in ejaculate spermatocytes of the 47,XY,+mar and 45,XY,rob(13;21) carriers using immunostaining.

RESULT(S)

In the 47,XY,+mar and 46,XY,rob(13;21),+mar carriers, the sSMC was found in 13.5% and 11.5 % of sperm, respectively. Analysis of meiotic segregation of chromosome 13 and 21 showed that 91.2% of sperm were normal/balanced in the 46,XY,rob(13;21),+mar case, whereas 88.4% of sperm were normal/balanced in the 45,XY,rob(13;21) case. Interchromosomal effects involving the sex chromosomes were found in both sSMC carriers. Both 47,XY,+mar and 45,XY,rob(13;21) carriers showed decreased global recombination, impaired synapsis, and an association of abnormal chromosomes with the XY body.

CONCLUSION(S)

Carriers of marker chromosomes produce sperm with markers at frequencies lower than theoretically expected. Carriers of ROB and sSMC showed decreased recombination, impaired synapsis, and association of abnormal chromosomes with the XY body, which may contribute to an interchromosomal effect. Using immunofluorescence techniques to analyze ejaculate-derived spermatocytes from subfertile men provides a novel technique for examining meiosis without the need for a testicular biopsy.

Is the interchromosomal effect present in embryos derived from Robertsonian and reciprocal translocation carriers particularly focusing on chromosome 10 rearrangements?

The aim of this study was to analyse the possible occurrence of the interchromosomal effect (ICE) in human preimplantation embryos obtained from Robertsonian and reciprocal translocation carriers focusing on ones with chromosome 10 rearrangements who were undergoing preimplantation genetic diagnosis (PGD) and to investigate whether offering aneuploidy screening would be beneficial to these patients. Cleavage stage embryos from translocation carriers undergoing PGD were biopsied. Multicolour fluorescence in situ hybridisation for the chromosomes involved in the translocation in addition to nine more chromosomes (13, 15, 16, 17, 18, 21, 22, X and Y) was used in the analysis. The control group involved embryos obtained from age-matched patients undergoing preimplantation genetic screening (PGS). Cumulative aneuploidy rate in embryos derived from both Robertsonian and reciprocal translocation carriers was found to be similar with the control group. Therefore no ICE was observed in cleavage stage embryos obtained from these carriers. More than half of the embryos with chromosome 10 rearrangements had aneuploidy for which an increased aneuploidy rate was more apparent in male carriers. Thus, it is possible that there is a risk of ICE in reciprocal carriers with chromosome 10 rearrangements. This study showed that there is no ICE in embryos derived from Robertsonian and reciprocal translocation carriers. However high rates of aneuploidy in structurally normal chromosomes were detected in embryos derived from these carriers and thus aneuploidy screening in addition to PGD may increase the pregnancy rates of these patients.

Sperm aneuploidy in infertile male patients: a systematic review of the literature

Males with abnormal karyotypes and subgroups of fertile and infertile males with normal karyotypes may be at risk of producing unbalanced or aneuploid spermatozoa. Biological, clinical, environmental and other factors may also cause additional sperm aneuploidy. However, increased risk of sperm aneuploidy is directly related to chromosomally abnormal embryo production and hence to poor reproductive potential. This systemic literature review focuses on the identification of these males because this is an essential step in the context of assisted reproduction. This research may allow for a more personalised and, hence, more accurate estimation of the risk involved in each case, which in turn will aid genetic counselling for affected couples and help with informed decision-making.

Sperm FISH and chromatin integrity in spermatozoa from a t(6;10;11) carrier

Complex chromosome rearrangements (CCRs) are structurally balanced or unbalanced aberrations involving more than two breakpoints on two or more chromosomes. CCRs can be a potential reason for genomic imbalance in gametes, which leads to a drastic reduction in fertility. In this study, the meiotic segregation pattern, aneuploidy of seven chromosomes uninvolved in the CCR and chromatin integrity were analysed in the ejaculated spermatozoa of a 46,XY,t(6;10;11)(q25.1;q24.3;q23.1)mat carrier with asthenozoospermia and a lack of conception. The frequency of genetically unbalanced spermatozoa was 78.8% with a prevalence of 4:2 segregants of 38.2%, while the prevalence of the adjacent 3:3 mode was 35.3%. Analysis of the aneuploidy of chromosomes 13, 15, 18, 21, 22, X and Y revealed an approximately fivefold increased level in comparison with that of the control group, indicating the presence of an interchromosomal effect. Sperm chromatin integrity status was evaluated using chromomycin A3 and aniline blue staining (deprotamination), acridine orange test and TUNEL assay (sperm DNA fragmentation). No differences were found when comparisons were made with a control group. We suggest that the accumulation of genetically unbalanced spermatozoa, significantly increased sperm aneuploidy level and decreased sperm motility (20%, progressive) were not responsible for the observed lack of reproductive success in the analysed infertile t(6;10;11) carrier. Interestingly, in the case described herein, a high level of sperm chromosomal imbalance appears not to be linked to sperm chromatin integrity status.

Balanced chromosomal translocations in men: relationships among semen parameters, chromatin integrity, sperm meiotic segregation and aneuploidy

PURPOSE

To analyse relationships between semen parameters, sperm chromatin integrity and frequencies of chromosomally unbalanced, disomic and diploid sperm in 13 Robertsonian and 37 reciprocal translocation carriers and to compare the results with data from 10 control donors.

METHODS

Conventional semen analysis, Sperm Chromatin Structure Assay and FISH with probes for chromosomes involved in the individual translocations and for chromosomes X, Y, 7, 8, 13, 18 and 21.

RESULTS

Normal semen parameters were found in 30.8 % of Robertsonian and 59.5 % of reciprocal translocation carriers. The rates of unbalanced sperm were 12.0 % in Robertsonian and 55.1 % in reciprocal translocation carriers with no difference between normospermic patients and those showing altered semen parameters. Significantly increased frequencies of spermatozoa showing defects in chromatin integrity and condensation, aneuploidy for chromosomes not involved in a translocation and diploidy were detected in translocation carriers with abnormal semen parameters. Normospermic reciprocal translocation carriers showed an increase in chromosome 13 disomy compared to the control group. There was no relationship between gametic and somatic aneuploidy in 12 translocation carriers studied by FISH on sperm and lymphocytes. The frequency of motile sperm was negatively correlated with the frequency of sperm showing disomy, diploidy and defective chromatin condensation.

CONCLUSIONS

Abnormal semen parameters can serve as indicators of an additional risk of forming spermatozoa with defective chromatin and aneuploidy in translocation carriers.

Accumulation of numerical and structural chromosome imbalances in spermatozoa from reciprocal translocation carriers

STUDY QUESTION

Is there a relationship between the occurrence of specific segregation modes and the production of additional numerical abnormalities in spermatozoa from reciprocal translocation carriers?

STUDY ANSWER

The production of aneuploid and diploid spermatozoa tends to be associated with an unbalanced segregation outcome of the rearranged chromosomes.

WHAT IS KNOWN ALREADY

Carriers of reciprocal translocations have an increased genetic reproductive risk as a consequence of producing higher numbers of unbalanced spermatozoa. These imbalances can originate during the segregation of the rearranged chromosomes and also from the occurrence of interchromosomal effects (ICEs). Usually, the outcome of both events is studied independently by means of sperm fluorescent in situ hybridization (FISH).

STUDY DESIGN, SIZE, DURATION

We designed a sequential FISH protocol based on two successive hybridization rounds to study the segregation outcome of the rearranged chromosomes and the presence of additional numerical abnormalities in the same sperm nuclei. The study was performed between February 2010 and February 2012.

MATERIALS, SETTING, METHODS

Sperm samples from eight reciprocal translocation carriers were processed for FISH analysis. Numerical abnormalities for chromosomes X, Y, 13, 18 and 21 were evaluated in the first hybridization round. The aneuploid and diploid nuclei were relocated and analysed for the segregation outcome of the rearranged chromosomes in the second hybridization round. In every carrier, another population of non-selected spermatozoa was also analysed with the aim of defining the general segregation outcome of each reorganization event.

MAIN RESULTS AND THE ROLE OF CHANCE

Overall, the selected population of aneuploid and diploid spermatozoa showed significant increased frequencies of unbalanced segregation modes of the rearranged chromosomes (3:1, 4:0 and 'other') when compared with the non-selected population of spermatozoa. A P-value of <0.05 was chosen to determine if differences observed were statistically significant.

LIMITATIONS, REASONS FOR CAUTION

FISH only allows the analysis of a limited number of chromosomes. Information about the content of additional chromosomes would have been useful in order to broaden the number of aneuploid spermatozoa population, and to infer a more accurate possible mechanism for generating chromosomal imbalances.

WIDER IMPLICATIONS OF THE FINDINGS

There was no previous data about a relationship between chromosomal numerical abnormalities and segregation of rearranged chromosomes. Our findings are consistent with a possible gathering of chromosomal abnormalities in a given nucleus. This information can be used towards a better understanding of the meiotic mechanisms involved in non-disjunction events in gametes from reciprocal translocation carriers. Also, it would help to provide a better reproductive genetic risk assessment in these patients.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by funding of projects SAF2010-2241 (Ministerio de Ciencia e Innovación, Spain), SGR2009-282 (Generalitat de Catalunya, Spain) and UAB CF-180034 (Universitat Autònoma de Barcelona, Spain). The authors declare the lack of competing interests in this study.

Sperm meiotic segregation, aneuploidy and high risk of delivering an affected offspring in carriers of non-Robertsonian translocation t(13;15)

PURPOSE

To determine the percentage of unbalanced spermatozoa and an interchromosomal effect in two carriers of balanced translocations t(13;15)(q32;q26) and t(13;15)(q32;p11.2).

METHODS

Sperm nuclei analysis by fluorescent in situ hybridization for detection of percentage of unbalanced spermatozoa and sperm with disomy of chromosomes X, Y, 8, 18, 21 and diploidy.

RESULTS

The incidence of unbalanced spermatozoa was 50.5 % and 44.6 % in patient 1 (P1) and patient 2 (P2), respectively. Partial disomy of chromosome 13 was detected in 13.4 % and 21.3 % of sperm in P1 and P2, respectively. The unbalanced karyotype der(15)t(13;15) was found previously in a son of P1 and in two adult relatives, and prenatally in the family of P2. This demonstrates a high risk of delivering an affected offspring. Significantly increased frequencies of chromosomes 8, 18, X and XY disomy and diploidy were observed in P2, which might either indicate an interchromosomal effect or be related to his asthenoteratozoospermia.

CONCLUSIONS

Since the proportions of unbalanced spermatozoa and the risk of delivering an affected offspring are high, prenatal or preimplantation genetic diagnosis is recommended for such patients.