Recombination in a male carrier of two reciprocal translocations involving chromosomes 14, 14', 15, and 21 leading to balanced and unbalanced rearrangements in offspring

Familial Infertility (Azoospermia and Cryptozoospermia) in Two Brothers-Carriers of t(1;7) Complex Chromosomal Rearrangement (CCR): Molecular Cytogenetic Analysis

Structural aberrations involving more than two breakpoints on two or more chromosomes are known as complex chromosomal rearrangements (CCRs). They can reduce fertility through gametogenesis arrest developed due to disrupted chromosomal pairing in the pachytene stage. We present a familial case of two infertile brothers (with azoospermia and cryptozoospermia) and their mother, carriers of an exceptional type of CCR involving chromosomes 1 and 7 and three breakpoints. The aim was to identify whether meiotic disruption was caused by CCR and/or genomic mutations. Additionally, we performed a literature survey for male CCR carriers with reproductive failures. The characterization of the CCR chromosomes and potential genomic aberrations was performed using: G-banding using trypsin and Giemsa staining (GTG banding), fluorescent in situ hybridization (FISH) (including multicolor FISH (mFISH) and bacterial artificial chromosome (BAC)-FISH), and genome-wide array comparative genomic hybridization (aCGH). The CCR description was established as: der(1)(1qter->1q42.3::1p21->1q42.3::7p14.3->7pter), der(7)(1pter->1p2 1::7p14.3->7qter). aCGH revealed three rare genes variants: ASMT, GARNL3, and SESTD1, which were ruled out due to unlikely biological functions. The aCGH analysis of three breakpoint CCR regions did not reveal copy number variations (CNVs) with biologically plausible genes. Synaptonemal complex evaluation (brother-1; spermatocytes II/oligobiopsy; the silver staining technique) showed incomplete conjugation of the chromosomes. Associations between CCR and the sex chromosomes (by FISH) were not found. A meiotic segregation pattern (brother-2; ejaculated spermatozoa; FISH) revealed 29.21% genetically normal/balanced spermatozoa. The aCGH analysis could not detect smaller intergenic CNVs of few kb or smaller (indels of single exons or few nucleotides). Since chromosomal aberrations frequently do not affect the phenotype of the carrier, in contrast to the negative influence on spermatogenesis, there is an obvious need for genomic sequencing to investigate the point mutations that may be responsible for the differences between the azoospermic and cryptozoospermic phenotypes observed in a family. Progeny from the same parents provide a unique opportunity to discover a novel genomic background of male infertility.

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

BACKGROUND

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

RESULTS

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

CONCLUSIONS

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

Cryptic breakpoint identified by whole-genome mate-pair sequencing in a rare paternally inherited complex chromosomal rearrangement

Background

Precise characterization of apparently balanced complex chromosomal rearrangements in non-affected individuals is crucial as they may result in reproductive failure, recurrent miscarriages or affected offspring.

Case presentation

We present a family, where the non-affected father and daughter were found, using FISH and karyotyping, to be carriers of a three-way complex chromosomal rearrangement [t(6;7;10)(q16.2;q34;q26.1), de novo in the father]. The family suffered from two stillbirths, one miscarriage, and has a son with severe intellectual disability. In the present study, the family was revisited using whole-genome mate-pair sequencing. Interestingly, whole-genome mate-pair sequencing revealed a cryptic breakpoint on derivative (der) chromosome 6 rendering the rearrangement even more complex. FISH using a chromosome (chr) 6 custom-designed probe and a chr10 control probe confirmed that the interstitial chr6 segment, created by the two chr6 breakpoints, was translocated onto der(10). Breakpoints were successfully validated with Sanger sequencing, and small imbalances as well as microhomology were identified. Finally, the complex chromosomal rearrangement breakpoints disrupted the SIM1, GRIK2, CNTNAP2, and PTPRE genes without causing any phenotype development.

Conclusions

In contrast to the majority of maternally transmitted complex chromosomal rearrangement cases, our study investigated a rare case where a complex chromosomal rearrangement, which most probably resulted from a Type IV hexavalent during the pachytene stage of meiosis I, was stably transmitted from a fertile father to his non-affected daughter. Whole-genome mate-pair sequencing proved highly successful in identifying cryptic complexity, which consequently provided further insight into the meiotic segregation of chromosomes and the increased reproductive risk in individuals carrying the specific complex chromosomal rearrangement. We propose that such complex rearrangements should be characterized in detail using a combination of conventional cytogenetic and NGS-based approaches to aid in better prenatal preimplantation genetic diagnosis and counseling in couples with reproductive problems.

Array CGH detection of a novel cryptic deletion at 3q13 in a complex chromosome rearrangement

Complex chromosome rearrangements (CCRs) are extremely rare in humans. About 20% of the apparently balanced CCRs have an abnormal phenotype and the degree of severity correlates with a higher number of breakpoints. Several studies using FISH and microarray technologies have shown that deletions in the breakpoints are common although duplications, insertions and inversions have also been detected. We report a patient with two simultaneous reciprocal translocations, t(3;4) and t(2;14;18), involving five chromosomes and six breakpoints. He showed dysmorphic features, preaxial polydactyly in the left hand, brachydactyly, postnatal growth retardation and developmental delay. The rearrangement was characterized by FISH analysis which detected an interstitial segment from chromosome 14 inserted in the derivative chromosome 2, and by whole genome array which revealed an interstitial deletion of approximately 4.5 Mb at the breakpoint site on chromosome 3. To our knowledge this microdeletion has not been previously reported and includes ~12 genes. The haploinsufficiency of one or several of these genes is likely to have contributed to the clinical phenotype of the patient.

Characterization of a de novo complex chromosome rearrangement (CCR) involving chromosomes 2 and 12, associated with mental retardation and impaired speech development

We report on a currently six-year-old patient with a de novo complex chromosome rearrangement (CCR) involving chromosomes 2 and 12. A translocation 2;12 that appeared to be reciprocal after standard banding turned out to be a complex event with seven breaks after molecular cytogenetic analyses. Array CGH analysis showed no imbalances at the breakpoints but revealed an additional microdeletion of about 80 kb on chromosome 11. The same deletion was also present in the phenotypically normal father. The patient showed relatively mild mental retardation, defined mainly as impaired speech development (orofacial dyspraxia) and psychomotor retardation. In addition, mild dysmorphic facial features like hypertelorism, a prominent philtrum and down-turned corners of the mouth were observed. We narrowed down all breakpoint regions to about 100 kb, using a panel of mapped bacterial artificial chromosome (BAC) clones for fluorescence in situ hybridization (FISH). BACs spanning or flanking all seven breakpoints were identified and no chromosomal imbalances were found consistent with the array CGH results. Our investigations resulted in the following karyotype: 46,XY,t(2;12)(2pter-->2p25.3::2p23.3-->2p25.2::2p23.3-->2p14::2q14.3-->2p14::2q14.3-->2q14.3::12q 12-->12qter;12pter-->12q12::2p25.3-->2p25.2::2q14.3-->2qter).

Prenatal diagnosis of ade novo complex chromosome rearrangement (CCR) mediated by six breakpoints, and a review of 20 prenatally ascertained CCRs

OBJECTIVES

To describe the cytogenetic and FISH characterization of a prenatally diagnosed de novo complex chromosome rearrangement (CCR), showing the involvement of four chromosomes and six breakpoints, and review the literature concerning prenatally detected CCRs in order to obtain insights into addressing karyotype-phenotype correlations in prenatal genetic counseling.

METHODS

Conventional protocols were used to set up cultures and chromosome preparations. Commercial and homemade probes were used for the FISH analyses.

RESULTS

An apparently balanced de novo t(4;10;20) was prenatally identified by means of cytogenetic analysis. FISH revealed a rearrangement mediated by six breakpoints and the insertion of chromosome 8 material within the 4q region. The pregnancy was interrupted. The fetus showed malformations and anomalous cortical neuron migration. The assembled list of 20 prenatally detected CCRs points to the preferential involvement of chromosomes 4, 6 and 14. The involvement of chromosome 20 is described here for the first time.

CONCLUSIONS

FISH analysis is essential for the accurate definition of a complex rearrangement. Phenotype description of fetuses carrying CCRs investigated by means of molecular cytogenetic techniques may contribute to improving and personalizing genetic counseling in prenatal diagnosis.