Sperm studies in heterozygote inversion carriers: a review

Genome sequencing differentiates a paracentric inversion from a balanced insertion enabling more accurate preimplantation genetic testing

INTRODUCTION

Distinguishing paracentric inversions (PAIs) from chromosomal insertions has traditionally relied on fluorescent in situ hybridization (FISH) techniques, but recent advancements in high-throughput sequencing have enabled the use of genome sequencing for such differentiation. In this study, we present a 38-year-old male carrier of a paracentric inversion on chromosome 2q, inv (2)(q31.2q34), whose partner experienced recurrent miscarriages.

MATERIAL AND METHODS

FISH analysis confirmed the inversion, and genome sequencing was employed for detailed characterization.

RESULTS

Preimplantation genetic testing (PGT) revealed that all assessed embryos were balanced, consistent with the low risk of unbalanced offspring associated with PAIs. While PAI carriers traditionally exhibit low risk of producing unbalanced offspring, exceptions exist due to crossover events within the inversion loop. Although the sample size was limited, the findings align with existing sperm study data, supporting the rare occurrence of unbalanced progeny in PAI carriers.

CONCLUSIONS

This study highlights the possibility of characterizing PAIs using genome sequencing to enable correct reproductive counseling and PGT decisions. Detailed characterization of a PAI is crucial for understanding potential outcomes and guiding PGT strategies, as accurate knowledge of the inversion size is essential for appropriate method selection in PGT. Given the very low risk of unbalanced offspring in PAI carriers, routine PGT may not be warranted but should be considered in specific cases with a history of unbalanced progeny or recurrent miscarriages. This study contributes to our understanding of PAI segregation and its implications for reproductive outcomes.

Exploring the impact of pericentric inversion of chromosome 9 on fertility in sperm donors

Pericentric inversion of chromosome 9 (inv[9]) is a common chromosomal structural variant, but its impact on clinical outcomes remains debated. The screening criteria of sperm banks are rarely mentioned to individuals with inv(9). In this study, we evaluated the fertility of sperm donors with inv(9) who met eligibility criteria for sperm banks (inv[9]-eligible donors). From March 2004 to May 2022, chromosomal analysis of 16 124 sperm donors at CITIC-Xiangya Human Sperm Bank in Hunan Province (Changsha, China) found that 251 (1.6%) had chromosome variations, with inv(9) being the most prevalent at 1.1%. All 169 inv(9)-eligible donors were contacted to collect fertility outcome data, along with 206 eligible donors without inv(9) as controls. In addition, semen samples from inv(9)-eligible donors and eligible donors underwent assessments of sperm fluorescence in situ hybridization (FISH), mitochondrial membrane potential, DNA fragmentation index, acrosome integrity, reactive oxygen species (ROS), and sperm morphology. Results showed that inv(9) did not significantly increase reproductive risks overall. Despite detecting ROS level differences, the clinical impact may be insignificant. This study provides new data on the inv(9) population that can serve as a valuable reference for decision-making by sperm banks as well as for genetic counseling and clinical guidance for individuals carrying inv(9) variant.

Genome sequencing identify chromosome 9 inversions disrupting ENG in 2 unrelated HHT families

Hereditary hemorrhagic telangiectasia (HHT), also known as Rendu-Osler-Weber disease, is a dominant inherited vascular disorder. The clinical diagnosis is based on the Curaçao criteria and pathogenic variants in the ENG and ACVRL1 genes are responsible for most cases of HHT. Four families with a negative targeted gene panel and selected by a multidisciplinary team were selected and whole-genome sequencing was performed according to the recommendations of the French National Plan for Genomic Medicine. Structural variations were confirmed by standard molecular cytogenetic analysis (FISH). In two families with a definite diagnosis of HHT, we identified two different paracentric inversions of chromosome 9, both disrupting the ENG gene. These inversions are considered as pathogenic and causative for the HHT phenotype of the patients. This is the first time structural variations are reported to cause HHT. As such balanced events are often missed by exon-based sequencing (panel, exome), structural variations may be an under-recognized cause of HHT. Genome sequencing for the detection of these events could be suggested for patients with a definite diagnosis of HHT and in whom no causative pathogenic variant was identified.

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 effects of chromosome polymorphism on the clinical outcomes of in vitro fertilization/embryo transfer-assisted reproduction

OBJECTIVE

To investigate the effects of chromosome polymorphism on the clinical outcomes of in vitro fertilization/embryo transfer (IVF/ET)-assisted reproductive technology.

METHODS

The case data of 2740 patients treated between January 2018 and January 2019 were retrospectively analyzed. The patients were organized into two groups: a case group and a control group. In the case group (n = 81), one or both parents were characterized by chromosomal polymorphism; in the control group (n = 2659), both parents had normal chromosome karyotyping. The primary outcomes included clinical pregnancy rate (clinical pregnancy rate of fresh transfer cycles = number of clinical pregnancy cycles/number of fresh embryo transfer cycles × 100%) and live birth rate (live birth rate per fresh transfer cycles = number of live births/numbers of fresh embryo transfer cycles × 100%). The propensity score matching (PSM) method was used for statistical analysis.

RESULTS

After PSM 1:2 matching for the patients in the two groups, 72 patients were successfully matched. The clinical pregnancy rate and live birth rate in the case group were lower than in the control group before PSM (clinical pregnancy rate: 33.30% case group vs. 46.60% control group, p = .020; live birth rate: 30.90% case group vs. 47.90% control group, p = .03). The differences were statistically significant (p < .05). The live birth rate in the case group was also significantly lower than in the control group after PSM (34.98% case group vs. 74.52% control group; p = .028). The correlation coefficient between clinical pregnancy and grouping (i.e. if there was a characteristic chromosome polymorphism) was -.045 (p = .02), while the correlation coefficient between live birth and grouping was -.046.

CONCLUSION

Chromosome polymorphism is weakly negatively correlated with live birth in IVF/ET-assisted reproduction and can significantly reduce the live birth rate of patients.

Do chromosomal inversion carriers really need preimplantation genetic testing?

PURPOSE

This study aimed to evaluate the rates of euploidy, aneuploidy, and mosaicism in preimplantation genetic testing for structural rearrangements (PGT-SR) cycles from chromosomal inversion carriers. In addition, this work also focused on assessing the impact of some contributors on the incidence of parental originating aneuploidy and mosaicism.

METHODS

This retrospective review enrolled chromosomal inversion carrier couples of whom the females were under 38 years old undergoing PGT-SR at a single academic reproductive center. Subgroups were divided according to the gender of carriers, the inversion type, and the semen parameters of male carriers (male factor infertility (MF) or non-MF). Patient demographics, cycle characteristics, and PGT-SR outcomes were compared among subgroups.

RESULTS

A total of 71 PGT-SR cycles from 57 inversion carrier couples were included for analysis. Among the 283 blastocysts, 48.4% were identified as euploidy, 27.9% as aneuploidy, and the remaining 23.7% as mosaicism. Only 32.9% of aneuploid embryos and 1.5% of mosaic embryos involved the parental inversion chromosomes. Notably, the female inversion carriers seemed to produce more parental originating aneuploid embryos than male inversion carriers (45.5% vs 23.9%, p = 0.044).

CONCLUSIONS

The type of inversion and sperm parameters of male chromosomal inversion carriers did not affect the ploidy status of embryos. The incidence of parental originating aneuploidy in inversion carrier couples is lower than expected. For male chromosomal inversion carriers with normal sperm condition whose female partners are under 38 years old, natural conception combined with prenatal diagnosis could be provided as an option during fertility counseling.

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.

Supergene origin and maintenance in Atlantic cod

Supergenes are sets of genes that are inherited as a single marker and encode complex phenotypes through their joint action. They are identified in an increasing number of organisms, yet their origins and evolution remain enigmatic. In Atlantic cod, four megabase-scale supergenes have been identified and linked to migratory lifestyle and environmental adaptations. Here we investigate the origin and maintenance of these four supergenes through analysis of whole-genome-sequencing data, including a new long-read-based genome assembly for a non-migratory Atlantic cod individual. We corroborate the finding that chromosomal inversions underlie all four supergenes, and we show that they originated at different times between 0.40 and 1.66 million years ago. We reveal gene flux between supergene haplotypes where migratory and stationary Atlantic cod co-occur and conclude that this gene flux is driven by gene conversion, on the basis of an increase in GC content in exchanged sites. Additionally, we find evidence for double crossover between supergene haplotypes, leading to the exchange of an ~275 kilobase fragment with genes potentially involved in adaptation to low salinity in the Baltic Sea. Our results suggest that supergenes can be maintained over long timescales in the same way as hybridizing species, through the selective purging of introduced genetic variation.

Atlantic cod carries four supergenes linked to migratory lifestyle and environmental adaptations. Using whole-genome sequencing, the authors show that the genome inversions that underlie the supergenes originated at different times and show gene flux between supergene haplotypes.

Update on genetic screening and treatment for infertile men with genetic disorders in the era of assisted reproductive technology

A genetic etiology of male infertility is identified in fewer than 25% of infertile men, while 30% of infertile men lack a clear etiology, resulting in a diagnosis of idiopathic male infertility. Advances in reproductive genetics have provided insights into the mechanisms of male infertility, and a characterization of the genetic basis of male infertility may have broad implications for understanding the causes of infertility and determining the prognosis, optimal treatment, and management of couples. In a substantial proportion of patients with azoospermia, known genetic factors contribute to male infertility. Additionally, the number of identified genetic anomalies in other etiologies of male infertility is growing through advances in whole-genome amplification and next-generation sequencing. In this review, we present an up-to-date overview of the indications for appropriate genetic tests, summarize the characteristics of chromosomal and genetic diseases, and discuss the treatment of couples with genetic infertility by microdissection-testicular sperm extraction, personalized hormone therapy, and in vitro fertilization with pre-implantation genetic testing.

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.

Genetic mutations contributing to non-obstructive azoospermia

Non-obstructive azoospermia is a distinct diagnosis within male infertility in which no sperm is found in the ejaculate as a result of spermatogenesis failure. Because of the increased prevalence of genetic abnormalities in men with non-obstructive azoospermia, male infertility guidelines recommend screening for karyotype abnormalities and Y chromosome microdeletions in this population. Numerous karyotype abnormalities may be present resulting in impaired spermatogenesis, including: Klinefelter syndrome, translocations, and deletions. Y chromosome microdeletions of the AZFa, AZFb, AZFc subregions all can also result in non-obstructive azoospermia with the possibility of sperm being present if only the AZFc subregion is deleted. While these are the two genetic tests recommended by the guidelines, nearly 50%-80% of non-obstructive azoospermia has no identifiable cause and is deemed idiopathic. Several other genetic defects can lead to non-obstructive azoospermia including Kallmann syndrome, mild androgen insensitivity syndrome, and TEX11. While many additional candidate genes have been proposed, many have yet to be verified or are so infrequent in the population that screening is cost-ineffective. Much research is still required in the genetics of non-obstructive azoospermia and will require multi-institutional initiatives to better understand the genetics of condition.

Recombinant Chromosome 7 Driven by Maternal Chromosome 7 Pericentric Inversion in a Girl with Features of Silver-Russell Syndrome

Maternal uniparental disomy of chromosome 7 is present in 5-10% of patients with Silver-Russell syndrome (SRS), and duplication of 7p including GRB10 (Growth Factor Receptor-Bound Protein 10), an imprinted gene that affects pre-and postnatal growth retardation, has been associated with the SRS phenotype. Here, we report on a 17 year old girl referred to array-CGH analysis for short stature, psychomotor delay, and relative macrocephaly. Array-CGH analysis showed two copy number variants (CNVs): a ~12.7 Mb gain in 7p13-p11.2, involving GRB10 and an ~9 Mb loss in 7q11.21-q11.23. FISH experiments performed on the proband's mother showed a chromosome 7 pericentric inversion that might have mediated the complex rearrangement harbored by the daughter. Indeed, we found that segmental duplications, of which chromosome 7 is highly enriched, mapped at the breakpoints of both the mother's inversion and the daughter's CNVs. We postulate that pairing of highly homologous sequences might have perturbed the correct meiotic chromosome segregation, leading to unbalanced outcomes and acting as the putative meiotic mechanism that was causative of the proband's rearrangement. Comparison of the girl's phenotype to those of patients with similar CNVs supports the presence of 7p in a locus associated with features of SRS syndrome.

Clinical outcomes of Preimplantation genetic testing (PGT) application in couples with chromosomal inversion, a study in the Chinese Han population

BACKGROUND

Chromosomal inversion was considered to have adverse effects on pregnancy outcomes through abnormal gametogenesis. The purpose of this retrospective study was to investigate whether preimplantation genetic testing (PGT) improves pregnancy outcomes for couples with chromosomal inversion.

METHODS

A total of 188 cycles from 165 couples with one chromosomal inversion carrier were divided into two groups: PGT (136 cycles, 125 couples) and non-PGT (52 cycles, 50 couples). Biochemical pregnancy, clinical pregnancy, ongoing pregnancy, miscarriage and live birth rates of their first transfer cycles, as well as cumulative live birth rates of each cycle and euploidy rates, were analyzed.

RESULTS

There were no statistically significant differences in the pregnancy outcomes between the two groups. The euploidy rate of pericentric inversion carriers was not higher than that of paracentric inversion carriers in PGT group (60.71% vs 50.54%, P = 0.073). Similarly, the euploid rate of male carriers was not higher than that of female carriers (61.2% vs 56.1%, P = 0.256).

CONCLUSIONS

Due to limitation of retrospective study and small sample size, our current data showed that PGT cannot provide prominent benefits for inversion carriers in the Chinese Han population. Further prospective randomized controlled trials are needed to evaluate the effects of PGT.

Chromosomal polymorphisms associated with reproductive outcomes after IVF-ET

Purpose

This study aimed to investigate the effect of the detail type of chromosomal polymorphisms (1/9/16qh^+/−, D/G group polymorphisms, and inv(9)) on the IVF-ET outcomes.

Methods

A total of 1335 infertile couples undergoing IVF/ICSI were enrolled and comprehensively analyzed the correlation between three detail types of chromosomal polymorphisms (1/9/16qh^+/−, D/G group polymorphisms, and inv(9)) and the outcome of IVF/ICSI embryo transfer. The fertilized rate, cleaved embryo rate, good-quality embryo rate, clinical pregnancy rate, implantation rate, and early stage miscarriage rate were compared between the chromosomal polymorphisms groups and the control group.

Results

Both the inv(9) and D/G group chromosomal polymorphisms related to female infertility significantly lead to a lower 2PN cleavage rate (86.44% vs. 97.58% and 90.67% vs. 97.58%, respectively, P < 0.05) undergoing IVF insemination, the inv(9) adversely increasing the early miscarriage rate, either undergoing IVF (21.4% vs. 3.0%, P < 0.05) or ICSI (50.0% vs. 2.0%, P < 0.05) insemination, female carriers (23.08% vs. 2.87%, P < 0.05) or male carriers (44.44% vs. 2.87%, P < 0.05). For D/G groups, ICSI insemination may increase the implantation rate (44.8% vs. 23.69%, P < 0.05) and clinical pregnancy rate (78.6% vs. 40.65%, P < 0.05). 1/9/16qh^+/− had no apparent adverse effect on the patient’s clinical outcomes.

Conclusions

Our study suggests that chromosome karyotype analysis is necessary for IVF patients in clinical practice; we should afford individual genetic counseling suggestion according to the polymorphism types.

Prenatal diagnosis and molecular cytogenetic characterization of partial dup(18q)/del(18p) due to a paternal pericentric inversion 18 in a fetus with multiple anomalies

OBJECTIVE

We present prenatal diagnosis of rec(18)dup(18q)inv(18)(p11.2q21.2)pat owing to paternal pericentric inversion in a fetus.

CASE REPORT

A 37-year-old woman was diagnosed with multiple anomalies on a prenatal ultrasound scan at 17 weeks and 5 days of gestation. She underwent amniocentesis at 20 weeks and 2 days. Conventional karyotyping of amniocyte showed 46, XX, der(18). She was thus referred for genetic counseling; cytogenetic analysis revealed a 46, XY karyotype, inv(18)(p11.2q21.2), of the father. Therefore, based on the results of the father, the fetal karyotype was defined as 46, XX, rec(18)dup(18q)inv(18)(p11.2q21.2)pat. Array comparative genomic hybridization of amniocytes to obtain specific information showed a 3-Mb deletion of 18p11.31p11.32 (136227_3100353)x1 and a 23.7-Mb duplication of 18q21.31-q23 (54222717_77957375) × 3.

CONCLUSION

Maternal serum screening produces normal results for 18p-/18q+ syndrome, but it can be diagnosed by fluorescent in situ hybridization, quantitative-fluorescent polymerase chain reaction, or array comparative genomic hybridization test by observing abnormal findings on ultrasound.

Recombination suppression in heterozygotes for a pericentric inversion induces the interchromosomal effect on crossovers in Arabidopsis

During meiosis, recombination ensures allelic exchanges through crossovers (COs) between the homologous chromosomes. Advances in our understanding of the rules of COs have come from studies of mutations including structural chromosomal rearrangements that, when heterozygous, are known to impair COs in various organisms. In this work, we investigate the effect of a large heterozygous pericentric inversion on male and female recombination in Arabidopsis. The inversion was discovered in the Atmcc1 mutant background and was characterized through genetic and next-generation sequencing analysis. Reciprocal backcross populations, each consisting of over 400 individuals, obtained from the mutant and the wild type, both crossed with Landsberg erecta, were analyzed genome-wide by 143 single-nucleotide polymorphisms. The negative impact of inversion became evident in terms of CO loss in the rearranged chromosome in both male and female meiosis. No single-CO event was detected within the inversion, consistent with a post-meiotic selection operating against unbalanced gametes. Cytological analysis of chiasmata in F₁ plants confirmed that COs were reduced in male meiosis in the chromosome with inversion. Crossover suppression on the rearranged chromosome is associated with a significant increase of COs in the other chromosomes, thereby maintaining unchanged the number of COs per cell. The CO pattern observed in our study is consistent with the interchromosomal (IC) effect as first described in Drosophila. In contrast to male meiosis, in female meiosis no IC effect is visible. This may be related to the greater strength of interference that constrains the CO number in excess of the minimum value imposed by CO assurance in Arabidopsis female meiosis.

Pericentric inversion (Inv) 9 variant-reproductive risk factor or benign finding?

Purpose

To report the unbalanced chromosome rearrangement rate and overall aneuploidy rate in day 5/6 embryos from a series of patients who underwent in vitro fertilization (IVF) with preimplantation genetic testing for structural rearrangements (PGT-SR) for the pericentric inversion 9 variant, inv(9)(p11q13) or inv(9)(p12q13), with concurrent 24 chromosome preimplantation genetic testing for aneuploidy (PGT-A).

Methods

This was a retrospective cohort analysis. IVF cycles and embryo biopsies were performed by referring clinics. Fifty-two trophectoderm biopsy samples from seven couples were sent to a single lab for PGT-SR for an inversion 9 variant with concurrent 24 chromosome PGT-A using single-nucleotide polymorphism (SNP) microarrays with bioinformatics.

Results

The unbalanced rearrangement rate for this embryo cohort was 0/52 (0.0%); mean maternal age per embryo was 33.3 years (range 21–39 years). The overall euploid rate was 61.5% and aneuploidy rate was 38.5%.

Conclusions

Chromosome 9 pericentric inversions did not result in unbalanced structural rearrangements in day 5/6 embryo samples, supporting that this population variant is not associated with increased reproductive risks.

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.

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.

Improved de novo genomic assembly for the domestic donkey

Donkeys and horses share a common ancestor dating back to about 4 million years ago. Although a high-quality genome assembly at the chromosomal level is available for the horse, current assemblies available for the donkey are limited to moderately sized scaffolds. The absence of a better-quality assembly for the donkey has hampered studies involving the characterization of patterns of genetic variation at the genome-wide scale. These range from the application of genomic tools to selective breeding and conservation to the more fundamental characterization of the genomic loci underlying speciation and domestication. We present a new high-quality donkey genome assembly obtained using the Chicago HiRise assembly technology, providing scaffolds of subchromosomal size. We make use of this new assembly to obtain more accurate measures of heterozygosity for equine species other than the horse, both genome-wide and locally, and to detect runs of homozygosity potentially pertaining to positive selection in domestic donkeys. Finally, this new assembly allowed us to identify fine-scale chromosomal rearrangements between the horse and the donkey that likely played an active role in their divergence and, ultimately, speciation.

A sex-chromosome inversion causes strong overdominance for sperm traits that affect siring success

Male reproductive success depends on the competitive ability of sperm to fertilize the ova, which should lead to strong selection on sperm characteristics. This raises the question of how heritable variation in sperm traits is maintained. Here we show that in zebra finches (Taeniopygia guttata) nearly half of the variance in sperm morphology is explained by an inversion on the Z chromosome with a 40% allele frequency in the wild. The sperm of males that are heterozygous for the inversion had the longest midpieces and the highest velocity. Furthermore, such males achieved the highest fertility and the highest siring success, both within-pair and extra-pair. Males homozygous for the derived allele show detrimental sperm characteristics and the lowest siring success. Our results suggest heterozygote advantage as the mechanism that maintains the inversion polymorphism and hence variance in sperm design and in fitness.

A Peruvian Child with 18p-/18q+ Syndrome and Persistent Microscopic Hematuria

Chromosome 18 pericentric inversion carriers could have offspring with recombinant chromosomes, leading to patients with clinical variable manifestations. Patients with 18p-/18q+ rearrangements share some clinical characteristics, while other characteristics differ. Factors for such divergence include the length of the inverted segment, among others. Here, we describe a Peruvian child with dysmorphic features, intellectual disability persistent microscopic hematuria, aortic pseudocoarctation, and descending aorta arteritis, among others. Karyotype analysis of family members determined the mother as the carrier of a pericentric inversion: 18[inv(18)(p11.2q21.3)]. This child carries a recombinant chromosome 18, with chromosomal microarray analysis detecting two genomic imbalances in patient's chromosome 18: one duplicated region and one deleted segment in the large and the short arms, respectively. Persistent microscopic hematuria has not been reported among 18p-/18q+ phenotypes. Our patient elucidates that other factors play significant and yet unknown roles for not fulfilling the proposed genotype-phenotype correlation associated with hemizygosity in this type of recombinant chromosome 18 or presenting these features as the patient ages.

Chromosomal polymorphisms are associated with female infertility and adverse reproductive outcomes after infertility treatment: a 7-year retrospective study

Data from 19,950 women were retrospectively analysed to determine the effect of chromosomal polymorphisms on female infertility and pregnancy outcome; fertile women were used as controls. Frequency of chromosomal polymorphisms and adverse pregnancy outcomes were compared between groups. A significantly higher incidence of chromosomal polymorphisms was found in total infertile patients, and patients with tubal infertility, ovulatory dysfunction, cervical and uterine abnormalities, and unexplained infertility compared with controls (5.53% [P < 0.001], 4.86% [P = 0.012] 5.40% [P < 0.001], 5.75% [P < 0.001] and 8.51% [P < 0.001], versus 3.74%, respectively). Infertile women had a higher incidence of 9qh+ and inv(9) compared with controls (P < 0.001 and P = 0.027). Logistic regression analysis showed an effect of chromosomal polymorphisms on female infertility (adjusted OR 1.662, 95% CI 1.551 to 1.796, P < 0.001). All couples reported a phenotypically normal baby. In control and tubal infertility groups, miscarriage rates were higher in women with chromosomal polymorphisms than in women with normal chromosomes (4.95% versus 0.96%, P = 0.001 and 6.17% versus 1.08%, P < 0.001). Preterm birth rate showed a similar trend. Chromosomal polymorphisms adversely affected spontaneous miscarriage rates (adjusted OR 1.625, 95% CI 1.514 to 1.769, P = 0.005).

Prenatal diagnosis and molecular cytogenetic characterization of rec(10)dup(10p)inv(10)(p11.2q26.3) in a fetus associated with paternal pericentric inversion

OBJECTIVE

We present prenatal diagnosis and molecular cytogenetic characterization of a recombinant chromosome 10 in a fetus associated with a paternal pericentric inversion.

CASE REPORT

A 35-year-old woman underwent amniocentesis at 18 weeks of gestation because of an advanced maternal age. Amniocentesis revealed a karyotype of 46,XY,der(10)del(10) (q26.3)dup(10)(p11.2p15). She underwent repeat amniocentesis at 21 weeks of gestation and array comparative genomic hybridization revealed a 31.65-Mb duplication of chromosome 10p15.3-p11.22 and a 3.07-Mb deletion of chromosome 10q26.3. Prenatal ultrasound findings were unremarkable. She was referred for genetic counseling and cytogenetic analysis revealed a karyotype of 46,XY,inv(10)(p11.2q26.3) in the father and a karyotype of 46,XX in the mother. The pregnancy was subsequently terminated, and a fetus was delivered with prominent facial dysmorphism. Postnatal cytogenetic analysis of the placenta revealed a karyotype of 46,XY, rec(10)dup(10p)inv(10)(p11.2q26.3). Fluorescence in situ hybridization analysis revealed a duplication of terminal 10p and a deletion of terminal 10q in the recombinant chromosome 10. Array comparative genomic hybridization analysis of the cord blood and umbilical cord confirmed the prenatal diagnosis.

CONCLUSION

Prenatal diagnosis of a recombinant chromosome because of an advanced maternal age should alert the possibility of a paternal pericentric inversion.

Fitness consequences of polymorphic inversions in the zebra finch genome

Background

Inversion polymorphisms constitute an evolutionary puzzle: they should increase embryo mortality in heterokaryotypic individuals but still they are widespread in some taxa. Some insect species have evolved mechanisms to reduce the cost of embryo mortality but humans have not. In birds, a detailed analysis is missing although intraspecific inversion polymorphisms are regarded as common. In Australian zebra finches (Taeniopygia guttata), two polymorphic inversions are known cytogenetically and we set out to detect these two and potentially additional inversions using genomic tools and study their effects on embryo mortality and other fitness-related and morphological traits.

Results

Using whole-genome SNP data, we screened 948 wild zebra finches for polymorphic inversions and describe four large (12–63 Mb) intraspecific inversion polymorphisms with allele frequencies close to 50 %. Using additional data from 5229 birds and 9764 eggs from wild and three captive zebra finch populations, we show that only the largest inversions increase embryo mortality in heterokaryotypic males, with surprisingly small effect sizes. We test for a heterozygote advantage on other fitness components but find no evidence for heterosis for any of the inversions. Yet, we find strong additive effects on several morphological traits.

Conclusions

The mechanism that has carried the derived inversion haplotypes to such high allele frequencies remains elusive. It appears that selection has effectively minimized the costs associated with inversions in zebra finches. The highly skewed distribution of recombination events towards the chromosome ends in zebra finches and other estrildid species may function to minimize crossovers in the inverted regions.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-016-1056-3) contains supplementary material, which is available to authorized users.

The evolution of reproductive isolation in the Drosophila yakuba complex of species

In the Drosophila melanogaster subgroup, the yakuba species complex, D. yakuba, D. santomea and D. teissieri have identical mitochondrial genomes in spite of nuclear differentiation. The first two species can be readily hybridized in the laboratory and produce fertile females and sterile males. They also form hybrids in natural conditions. Nonetheless, the third species, D. teissieri, was thought to be unable to produce hybrids with either D. yakuba or D. santomea. This in turn posed the conundrum of why the three species shared a single mitochondrial genome. In this report, we show that D. teissieri can indeed hybridize with both D. yakuba and D. santomea. The resulting female hybrids from both crosses are fertile, whereas the hybrid males are sterile. We also characterize six isolating mechanisms that might be involved in keeping the three species apart. Our results open the possibility of studying the history of introgression in the yakuba species complex and dissecting the genetic basis of interspecific differences between these three species by genetic mapping.

The Largest Paracentric Inversion, the Highest Rate of Recombinant Spermatozoa. Case Report: 46,XY, inv(2)(q21.2q37.3) and Literature Review

Carriers of inversions involving euchromatic regions are at risk of having unbalanced offspring due to meiotic crossover. In carriers, recombination can occur during gametogenesis and cause genetically unbalanced sperm and subsequently unbalanced embryos. Here we present segregation analysis results of an infertile male with 46,XY,inv(2) (q21.2q37.3) using fluorescent in situ hybridization (FISH) on sperm cells. This is the largest paracentric inversion (PAI) reported so far in a meiotic segregation analysis study. Sperm FISH revealed 28.0% recombinant spermatozoa rate for chromo-some 2, which was the highest rate in PAI carriers in the literature. Our results indicate a clear correlation between the size of the inverted segment and the frequency of the recombinant spermatozoa. The results of the FISH analysis with the information of unbalanced spermatozoa rate can provide accurate counseling on the genetic risk of infertility.

Relatives with opposite chromosome constitutions, rec(10)dup(10p)inv(10)(p15.1q26.12) and rec(10)dup(10q)inv(10)(p15.1q26.12), due to a familial pericentric inversion

Large pericentric inversions in chromosome 10 are rare chromosomal aberrations with only few cases of familial inheritance. Such chromosomal rearrangements may lead to production of unbalanced gametes. As a result of a recombination event in the inversion loop, 2 recombinants with duplicated and deficient chromosome segments, including the regions distal to the inversion, may be produced. We report on 2 relatives in a family with opposite terminal chromosomal rearrangements of chromosome 10, i.e. rec(10)dup(10p)inv(10) and rec(10)dup(10q)inv(10), due to familial pericentric inversion inv(10)(p15.1q26.12). Based on array-CGH results, we characterized the exact genomic regions involved and compared the clinical features of both patients with previous reports on similar pericentric inversions and regional differences within 10p and 10q. The fact that both products of recombination are viable indicates a potentially high recurrence risk of unbalanced offspring. This report of unbalanced rearrangements in chromosome 10 in 2 generations confirms the importance of screening for terminal imbalances in patients with idiopathic intellectual disability by molecular cytogenetic techniques such as FISH, MLPA or microarrays. It also underlines the necessity for FISH to define structural characteristics of such cryptic intrachromosomal rearrangements and the underlying cytogenetic mechanisms.

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.

Different segregation patterns in five carriers due to a pericentric inversion of chromosome 1

Pericentric inversion can produce recombinant gametes; however, meiotic segregation studies on the relationship between the frequency of recombinants and the inverted segment size are rare. Triple-color fluorescence in situ hybridization (FISH) was performed to analyze the meiotic behavior in five inv(1) carriers with different breakpoints. Recombination gametes were absent in Patient 1, whereas the percentages of the recombinants in Patients 2, 3, 4, and 5 were of 9.2%, 15.3%, 17.3%, and 40.9%, respectively. A significant difference was present for the frequencies of the recombinant spermatozoa among the five patients (p < 0.001). For each patient, the frequency of the two types of recombinant gametes (dup(1p)/del(1q) or del(1p)/dup(1q)) did not exhibit a significant difference in comparison with the expected 1:1 ratio (p > 0.05). The meiotic segregation of nine inv(1) carriers (including those presented in this paper) is now available. A significant correlation was discovered between the rate of recombination and the proportion of the chromosome implicated in the inversion (R = 0.9435, p < 0.001). The frequency of the recombinant gametes was directly related to the proportion of the chromosome that was inverted. Sperm-FISH allowed an additional comprehension of the patterns of meiotic segregation and provided accurate genetic counseling.

Discontinuous gradient centrifugation (DGC) decreases the proportion of chromosomally unbalanced spermatozoa in chromosomal rearrangement carriers

STUDY QUESTION

Can the proportion of unbalanced spermatozoa in chromosomal rearrangement carriers be decreased through the use of discontinuous gradient centrifugation (DGC)?

SUMMARY ANSWER

DGC significantly decreases the proportion of genetically unbalanced spermatozoa in chromosomal rearrangement carriers.

WHAT IS KNOWN ALREADY

Chromosomal rearrangement carriers present with a certain proportion of unbalanced gametes, which can lead to miscarriages or malformations in the offspring. There is presently no known way to select the balanced spermatozoa and use them for IVF.

STUDY DESIGN, SIZE, DURATION

The proportion of unbalanced spermatozoa after DGC was compared with that before DGC in 21 patients with a chromosomal rearrangement. At least 500 spermatozoa were analysed per observation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Twenty-one male patients with a chromosomal rearrangement were included in this prospective study. They initially consulted for infertility, recurrent miscarriages or a history of abnormal pregnancy. The samples were split into two, with one part undergoing DGC and the other being immediately fixed. Fluorescence in situ hybridization was performed to establish the chromosome segregation pattern of each spermatozoon.

MAIN RESULTS AND THE ROLE OF CHANCE

DGC significantly decreased the proportion of unbalanced spermatozoa in all but 1 of the 21 chromosomal rearrangement carriers (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

Although DGC reduces the proportion of unbalanced spermatozoa in ejaculates from patients with chromosome rearrangements this elimination is only partial and some abnormal spermatozoa remain. Means to exclude these spermatozoa to ensure that only balanced ones are used in IVF remain to be discovered. The motility and morphology of the sperm before and after DGC were not measured.

WIDER IMPLICATIONS OF THE FINDINGS

Used in IVF or intrauterine insemination, DGC could decrease the chance that a man carrying a chromosomal rearrangement will father an abnormal fetus.

Meiotic recombination, synapsis, meiotic inactivation and sperm aneuploidy in a chromosome 1 inversion carrier

Disrupted meiotic behaviour of inversion carriers may be responsible for suboptimal sperm parameters in these carriers. This study investigated meiotic recombination, synapsis, transcriptional silencing and chromosome segregation effects in a pericentric inv(1) carrier. Recombination (MLH1), synapsis (SYCP1, SYCP3) and transcriptional inactivation (γH2AX, BRCA1) were examined by fluorescence immunostaining. Chromosome specific rates of recombination were determined by fluorescence in-situ hybridization. Furthermore, testicular sperm was examined for aneuploidy and segregation of the inv(1). Our findings showed that global recombination rates were similar to controls. Recombination on the inv(1) and the sex chromosomes were reduced. The inv(1) associated with the XY body in 43.4% of cells, in which XY recombination was disproportionately absent, and 94.3% of cells displayed asynapsed regions which displayed meiotic silencing regardless of their association with the XY body. Furthermore, a low frequency of chromosomal imbalance was observed in spermatozoa (3.4%). Our results suggest that certain inversion carriers may display unimpaired global recombination and impaired recombination on the involved and the sex chromosomes during meiosis. Asynapsis or inversion-loop formation in the inverted region may be responsible for impaired spermatogenesis and may prevent sperm-chromosome imbalance.

De novo partial trisomy 18p and partial monosomy 18q in a patient with anorectal malformation

Anorectal malformations (ARM) encompass a broad clinical spectrum which ranges from mild anal stenosis to severe anorectal anomalies such as complex cloacal malformations. The overall incidence of ARM is around 1 in every 2,500 live births. Although causative genes for a few syndromic forms have been identified, the molecular genetic background of most ARM remains unknown. The present report describes a patient with a de novo 13.2-Mb deletion of chromosome 18q22.3-qter and a 2.2-Mb de novo duplication of chromosomal region 18pter-p11.32 located at the telomeric end of chromosome 18q. The patient presented with ARM and the typical features of 18q- syndrome (De-Grouchy syndrome). The combination of a partial duplication of the short arm and a partial deletion of the long arm of chromosome 18 has been described in 16 previous cases. However, this is the first report of an association between this complex chromosomal rearrangement and ARM.

Cri-du-Chat Syndrome Cytogenetically Cryptic Recombination Aneusomy of Chromosome 5: Implications in Recurrence Risk Estimation

Cri-du-chat syndrome is caused by haploinsufficiency of the genes on the distal part of the short arm of chromosome 5, and characteristic features include microcephaly, developmental delays, and a distinctive high-pitched mewing cry. Most cri-du-chat syndrome cases result from a sporadic de novo deletion that is associated with a low recurrence risk. On rare occasions, however, cri-du-chat syndrome with 5p monosomy can be accompanied by 5q trisomy. This combination is virtually always associated with parental large pericentric inversions. Among previously reported cri-du-chat syndrome cases with 5p monosomy accompanied by 5q trisomy, the aneusomy of chromosome 5 in all but one case was cytogenetically visible using G-banding. When an accompanying 5q trisomy is detected, a significant recurrence risk is expected. We here report on a patient with cri-du-chat syndrome phenotype who initially exhibited a normal karyotype on G-banding but in whom molecular analysis using multiplex ligation-dependent probe amplification and array comparative genomic hybridization revealed a 5p deletion accompanied by a 5q duplication. Parental chromosomal testing led to the identification of a very large pericentric inversion, of which breakpoints resided at the terminal regions of 5p15.31 and 5q35.1. This information was vital for counseling the family regarding the significantly high recurrence risk.

Proteomics and the genetics of sperm chromatin condensation

Spermatogenesis involves extremely marked cellular, genetic and chromatin changes resulting in the generation of the highly specialized sperm cell. Proteomics allows the identification of the proteins that compose the spermatogenic cells and the study of their function. The recent developments in mass spectrometry (MS) have markedly increased the throughput to identify and to study the sperm proteins. Catalogs of thousands of testis and spermatozoan proteins in human and different model species are becoming available, setting up the basis for subsequent research, diagnostic applications and possibly the future development of specific treatments. The present review intends to summarize the key genetic and chromatin changes at the different stages of spermatogenesis and in the mature sperm cell and to comment on the presently available proteomic studies.

Telomere-centromere-driven genomic instability contributes to karyotype evolution in a mouse model of melanoma

Aneuploidy and chromosomal instability (CIN) are hallmarks of most solid tumors. These alterations may result from inaccurate chromosomal segregation during mitosis, which can occur through several mechanisms including defective telomere metabolism, centrosome amplification, dysfunctional centromeres, and/or defective spindle checkpoint control. In this work, we used an in vitro murine melanoma model that uses a cellular adhesion blockade as a transforming factor to characterize telomeric and centromeric alterations that accompany melanocyte transformation. To study the timing of the occurrence of telomere shortening in this transformation model, we analyzed the profile of telomere length by quantitative fluorescent in situ hybridization and found that telomere length significantly decreased as additional rounds of cell adhesion blockages were performed. Together with it, an increase in telomere-free ends and complex karyotypic aberrations were also found, which include Robertsonian fusions in 100% of metaphases of the metastatic melanoma cells. These findings are in agreement with the idea that telomere length abnormalities seem to be one of the earliest genetic alterations acquired in the multistep process of malignant transformation and that telomere abnormalities result in telomere aggregation, breakage-bridge-fusion cycles, and CIN. Another remarkable feature of this model is the abundance of centromeric instability manifested as centromere fragments and centromeric fusions. Taken together, our results illustrate for this melanoma model CIN with a structural signature of centromere breakage and telomeric loss.

Predictive value of sperm-FISH analysis on the outcome of preimplantation genetic diagnosis (PGD) for a pericentric inversion inv5(p15.3q11.2) carrier

BACKGROUND

Pericentric inversions (PIs) are structural chromosomal abnormalities, potentially associated with infertility or multiple miscarriages. More rarely, at meiosis, odd numbers of genetic recombinations within the inversion loop produce recombinant gametes which may lead to aneusomy of recombination in the offspring.

METHODS

We report a FISH segregation analysis of an inv5(p15.3q11.2) carrier, both in sperm and blastomeres. In sperm, we directly evaluated the proportion of recombinant gametes and compared the results with chromosomal abnormalities found in blastomeres collected from embryos obtained following a preimplantation genetic diagnosis (PGD) procedure.

RESULTS

A total of 7006 sperm nuclei were analyzed. The size of the inverted segment represented 27% of the total length of chromosome 5. The frequencies of balanced chromosomes (normal or inverted), recombinant chromosomes and unbalanced combinations were 97.1, 0.17 and 2.73%, respectively. Of six embryos, PGD FISH analysis revealed that one was a balanced embryo, whereas five were unbalanced and there were no recombinants.

CONCLUSIONS

This study demonstrated the value of sperm-FISH analysis in providing reproductive genetic counseling for PI carriers. Our study also highlights the clinical relevance of performing PGD instead of prenatal diagnosis.

Clinical Review#: State of the art for genetic testing of infertile men

Intracytoplasmic sperm injection (ICSI) now provides fertility in many cases of severe idiopathic spermatogenic failure and obstructive azoospermia. Genetic causes must be sought by systematic evaluation of infertile men and affected couples informed about the implications of such diagnoses for assisted reproductive technology outcome and their potential offspring. This review discusses established and emerging genetic disorders related to fertility practice. Chromosomal anomalies are found in about 7% men with idiopathic spermatogenic failure, predominantly numerical/structural in azoospermic men and translocations/inversions in oligospermic men. Routine karyotyping of men with sperm densities less than 10 million/ml, even in the absence of other clinical presentations, is recommended because infertility is associated with higher rates of aneuploidy in ejaculated or testicular sperm and increased chromosomal defects in ICSI offspring. The long arm of the Y chromosome microdeletions are the most common recognized genetic cause of infertility and are found in about 4% men with sperm densities less than 5 million/ml. Routine testing using strict quality assurance procedures is recommended. Azoospermia factor (AZF)-c deletions, the most common form of the long arm of the Y chromosome microdeletions, are usually associated with low levels of sperm in the ejaculate or in testis biopsies, whereas men with AZFa or AZFb+c deletions usually produce no testicular sperm. When AZF-deleted sperm are available and used for ICSI, fertility defects in male offspring seem inevitable. Bilateral congenital absence of the vas is associated with heterozygosity for cystic fibrosis transmembrane receptor mutations making routine gene screening and genetic counseling of the couple essential. Testing for less common genetic associations/defects linked with different reproductive dysfunction may be applicable to specific patients but have not entered routine practice.

Identical cryptic partial monosomy 20pter and trisomy 20qter in three adult siblings due to a large maternal pericentric inversion: detection by MLPA and breakpoint mapping by SNP array analysis

Genotypic and phenotypic data are presented on three adult siblings with mild to moderate mental retardation and mild dysmorphic features. All three siblings showed a chromosome 20 gain at the q-telomere and loss at the p-telomere in routine subtelomeric MLPA screening. Analysis of GTG-banded chromosomes did not detect any abnormalities, but subtelomeric fluorescent in situ hybridization (FISH) confirmed cryptic partial monosomy of chromosome region 20p13 --> 20pter and cryptic partial trisomy of chromosome region 20q13.33 --> 20qter. Furthermore, FISH analysis in the mother showed a cryptic inv(20)(p13q13.33). This explained the cytogenetic mechanism underlying the chromosomal imbalance in the three children, that is, the meiotic formation of a recombinant chromosome 20 due to crossing-over in the inverted segment. All three children thus carried a rec(20)dup(20q)inv(20)(p13q13.33)mat chromosome. SNP array analysis enabled rapid and detailed imbalance sizing and showed a 1.06 Mb loss in 20p13 and a 2.51 Mb gain in 20q13.33, comprising 21 and 78 genes, respectively. The maternal inversion is the largest described thus far for chromosome 20, comprising 94.4% of its length. Such large inversions result in a particularly high risk for live-born unbalanced offspring because the partial monosomy and trisomy segments are small. Moreover, the inversion size is directly related to the percentage of unbalanced gametes due to high crossing-over change within the inverted segment. The fact that all three children carry an identical chromosomal rearrangement has consequences for genetic counseling for carriers of large pericentric inversions, as the recurrence risk is very high.