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?

Robertsonian Translocation between Human Chromosomes 21 and 22, Inherited across Three Generations, without Any Phenotypic Effect.

Chromosomal translocations can result in phenotypic effects of varying severity, depending on the position of the breakpoints and the rearrangement of genes within the interphase nucleus of the translocated chromosome regions. Balanced translocations are often asymptomatic phenotypically and are typically detected due to a decrease in fertility resulting from issues during meiosis. Robertsonian translocations are among the most common chromosomal abnormalities, often asymptomatic, and can persist in the population as a normal polymorphism. We serendipitously discovered a Robertsonian translocation between chromosome 21 and chromosome 22, which is inherited across three generations without any phenotypic effect, notably only in females. In situ hybridization with alpha-satellite DNAs revealed the presence of both centromeric sequences in the translocated chromosome. The reciprocal translocation resulted in a partial deletion of the short arm of both chromosomes 21, and 22, with the ribosomal RNA genes remaining present in the middle part of the new metacentric chromosome. The rearrangement did not cause alterations to the long arm. The spread of an asymptomatic heterozygous chromosomal polymorphism in a population can lead to mating between heterozygous individuals, potentially resulting in offspring with a homozygous chromosomal configuration for the anomaly they carry. This new karyotype may not produce phenotypic effects in the individual who presents it. The frequency of karyotypes with chromosomal rearrangements in asymptomatic heterozygous form in human populations is likely underestimated, and molecular karyotype by array Comparative Genomic Hybridization (array-CGH) analysis does not allow for the identification of this type of chromosomal anomaly, making classical cytogenetic analysis the preferred method for obtaining clear results on a karyotype carrying a balanced rearrangement.

A multiomic characterization of the leukemia cell line REH using short- and long-read sequencing.

The B-cell acute lymphoblastic leukemia (ALL) cell line REH, with the t(12;21) ETV6::RUNX1 translocation, is known to have a complex karyotype defined by a series of large-scale chromosomal rearrangements. Taken from a 15-yr-old at relapse, the cell line offers a practical model for the study of pediatric B-ALL. In recent years, short- and long-read DNA and RNA sequencing have emerged as a complement to karyotyping techniques in the resolution of structural variants in an oncological context. Here, we explore the integration of long-read PacBio and Oxford Nanopore whole-genome sequencing, IsoSeq RNA sequencing, and short-read Illumina sequencing to create a detailed genomic and transcriptomic characterization of the REH cell line. Whole-genome sequencing clarified the molecular traits of disrupted ALL-associated genes including CDKN2A, PAX5, BTG1, VPREB1, and TBL1XR1, as well as the glucocorticoid receptor NR3C1 Meanwhile, transcriptome sequencing identified seven fusion genes within the genomic breakpoints. Together, our extensive whole-genome investigation makes high-quality open-source data available to the leukemia genomics community.

Brd4::Nutm1 fusion gene initiates NUT carcinoma in vivo.

NUT carcinoma (NC) is an aggressive cancer with no effective treatment. About 70% of NUT carcinoma is associated with chromosome translocation events that lead to the formation of a BRD4::NUTM1 fusion gene. Because the BRD4::NUTM1 gene is unequivocally cytotoxic when ectopically expressed in cell lines, questions remain on whether the fusion gene can initiate NC. Here, we report the first genetically engineered mouse model for NUT carcinoma that recapitulates the human t(15;19) chromosome translocation in mice. We demonstrated that the mouse t(2;17) syntenic chromosome translocation, forming the Brd4::Nutm1 fusion gene, could induce aggressive carcinomas in mice. The tumors present histopathological and molecular features similar to human NC, with enrichment of undifferentiated cells. Similar to the reports of human NC incidence, Brd4::Nutm1 can induce NC from a broad range of tissues with a strong phenotypical variability. The consistent induction of poorly differentiated carcinoma demonstrated a strong reprogramming activity of BRD4::NUTM1. The new mouse model provided a critical preclinical model for NC that will lead to better understanding and therapy development for NC.

A working model for the formation of Robertsonian chromosomes.

Robertsonian chromosomes form by fusion of two chromosomes that have centromeres located near their ends, known as acrocentric or telocentric chromosomes. This fusion creates a new metacentric chromosome and is a major mechanism of karyotype evolution and speciation. Robertsonian chromosomes are common in nature and were first described in grasshoppers by the zoologist W. R. B. Robertson more than 100 years ago. They have since been observed in many species, including catfish, sheep, butterflies, bats, bovids, rodents and humans, and are the most common chromosomal change in mammals. Robertsonian translocations are particularly rampant in the house mouse, Mus musculus domesticus, where they exhibit meiotic drive and create reproductive isolation. Recent progress has been made in understanding how Robertsonian chromosomes form in the human genome, highlighting some of the fundamental principles of how and why these types of fusion events occur so frequently. Consequences of these fusions include infertility and Down's syndrome. In this Hypothesis, I postulate that the conditions that allow these fusions to form are threefold: (1) sequence homology on non-homologous chromosomes, often in the form of repetitive DNA; (2) recombination initiation during meiosis; and (3) physical proximity of the homologous sequences in three-dimensional space. This Hypothesis highlights the latest progress in understanding human Robertsonian translocations within the context of the broader literature on Robertsonian chromosomes.

The first case of six-way complex translocation of t(4;7;9;22;8;14) in a patient with chronic myeloid leukemia.

In chronic myeloid leukemia (CML), patients exhibit the t(9;22)(q34.1;q11.2) translocation, resulting in the formation of a Philadelphia chromosome (Ph). However, a subset of CML patients display variant complex translocations, characterized by three-way, four-way, and five-way translocations, which have been occasionally associated with a poor prognosis. This case report presents the first case of a t(9;22) variant six-way complex translocation in CML. The R banding chromosome karyotyping technique was used to obtain preliminary karyotyping results, and the multi-probe FISH technique was used to assist in the verification of chromosome results. Both FISH and PCR proved the existence of fusion genes. A 45-year-old male patient admitted to our hospital due to elevated WBC and anemia. Bone marrow smears revealed a significant proliferation of mature granulocytes, accompanied by an increase in eosinophils and basophils. Karyotype analysis indicated abnormalities in six chromosomes, including 4, 7, 8, 9, 14, and 22. Further analysis using FISH technology demonstrated the presence of the BCR::ABL1 fusion gene, as well as the mapping of the BCR (22q11), MYC (8q24), IGH (14q32), D4S163 (4q35.1), and D7S486 (7q31) genes to new chromosomes. Ultimately, the karyotype findings were described as t(4;7;9;22;8;14)(q27;q22;q34;q11;q22;q12). PCR showed that BCR::ABL1 was p210. After treatment with imatinib for 4 months, the patient achieved complete cytogenetic response (CCyR) and early molecular response (EMR). This is the first report of complex chromosomal karyotype involving six-way translocation in CML; the combination of chromosome analysis and FISH techniques is an effective strategy in determining the karyotype result.

Optical Genome Mapping as a Potential Routine Clinical Diagnostic Method.

Chromosome analysis (CA) and chromosomal microarray analysis (CMA) have been successfully used to diagnose genetic disorders. However, many conditions remain undiagnosed due to limitations in resolution (CA) and detection of only unbalanced events (CMA). Optical genome mapping (OGM) has the potential to address these limitations by capturing both structural variants (SVs) resulting in copy number changes and balanced rearrangements with high resolution. In this study, we investigated OGM's concordance using 87 SVs previously identified by CA, CMA, or Southern blot. Overall, OGM was 98% concordant with only three discordant cases: (1) uncalled translocation with one breakpoint in a centromere; (2) uncalled duplication with breakpoints in the pseudoautosomal region 1; and (3) uncalled mosaic triplication originating from a marker chromosome. OGM provided diagnosis for three previously unsolved cases: (1) disruption of the SON gene due to a balanced reciprocal translocation; (2) disruption of the NBEA gene due to an inverted insertion; (3) disruption of the TSC2 gene due to a mosaic deletion. We show that OGM is a valid method for the detection of many types of SVs in a single assay and is highly concordant with legacy cytogenomic methods; however, it has limited SV detection capabilities in centromeric and pseudoautosomal regions.

Delineating the mechanism of fragility at BCL6 breakpoint region associated with translocations in diffuse large B cell lymphoma.

BCL6 translocation is one of the most common chromosomal translocations in cancer and results in its enhanced expression in germinal center B cells. It involves the fusion of BCL6 with any of its twenty-six Ig and non-Ig translocation partners associated with diffuse large B cell lymphoma (DLBCL). Despite being discovered long back, the mechanism of BCL6 fragility is largely unknown. Analysis of the translocation breakpoints in 5' UTR of BCL6 reveals the clustering of most of the breakpoints around a region termed Cluster II. In silico analysis of the breakpoint cluster sequence identified sequence motifs that could potentially fold into non-B DNA. Results revealed that the Cluster II sequence folded into overlapping hairpin structures and identified sequences that undergo base pairing at the stem region. Further, the formation of cruciform DNA blocked DNA replication. The sodium bisulfite modification assay revealed the single-strandedness of the region corresponding to hairpin DNA in both strands of the genome. Further, we report the formation of intramolecular parallel G4 and triplex DNA, at Cluster II. Taken together, our studies reveal that multiple non-canonical DNA structures exist at the BCL6 cluster II breakpoint region and contribute to the fragility leading to BCL6 translocation in DLBCL patients.

Non-Invasive Prenatal Test Analysis Opens a Pandora's Box: Identification of Very Rare Cases of SRY-Positive Healthy Females, Segregating for Three Generations Thanks to Preferential Inactivation of the XqYp Translocated Chromosome.

The translocation of the testis-determining factor, the SRY gene, from the Y to the X chromosome is a rare event that causes abnormalities in gonadal development. In all cases of males and females carrying this translocation, disorder of sex development is reported. In our study, we described a peculiar pedigree with the first evidence of four healthy females from three generations who are carriers of the newly identified t(X;Y)(q28;p11.2)(SRY+) translocation with no evidence of ambiguous genitalia or other SRY-dependent alterations. Our study was a consequence of a Non-Invasive Prenatal Test (NIPT) showing a sexual chromosomal abnormality (XXY) followed by a chorionic villus analysis suggesting a normal karyotype 46,XX and t(X;Y) translocation detected by FISH. Here, we (i) demonstrated the inheritance of the translocation in the maternal lineage via karyotyping and FISH analysis; (ii) characterised the structural rearrangement via chromosomal microarray; and (iii) demonstrated, via Click-iT® EdU Imaging assay, that there was an absolute preferential inactivation of the der(X) chromosome responsible for the lack of SRY expression. Overall, our study provides valuable genetic and molecular information that may lead personal and medical decisions.

Evaluation of genetic risk of apparently balanced chromosomal rearrangement carriers by breakpoint characterization.

PURPOSE: To report genetic characteristics and associated risk of chromosomal breaks due to chromosomal rearrangements in large samples. METHODS: MicroSeq, a technique that combines chromosome microdissection and next-generation sequencing, was used to identify chromosomal breakpoints. Long-range PCR and Sanger sequencing were used to precisely characterize 100 breakpoints in 50 ABCR carriers. RESULTS: In addition to the recurrent regions of balanced rearrangement breaks in 8q24.13, 11q11.23, and 22q11.21 that had been documented, we have discovered a 10-Mb region of 12q24.13-q24.3 that could potentially be a sparse region of balanced rearrangement breaks. We found that 898 breakpoints caused gene disruption and a total of 188 breakpoints interrupted genes recorded in OMIM. The percentage of breakpoints that disrupted autosomal dominant genes recorded in OMIM was 25.53% (48/188). Fifty-four of the precisely characterized breakpoints had 1-8-bp microhomologous sequences. CONCLUSION: Our findings provide a reference for the evaluation of the pathogenicity of mutations in related genes that cause protein truncation in clinical practice. According to the characteristics of breakpoints, non-homologous end joining and microhomology-mediated break-induced replication may be the main mechanism for ABCRs formation.

High-resolution PGT-A results in incidental identification of patients with small pathogenic copy number variants.

PURPOSE: This study aimed to evaluate whether a high-throughput high-resolution PGT-A method can detect copy number variants (CNVs) that could have clinical implications for patients and their embryos. METHODS: A prospective analysis of PGT-A cases was conducted using a high-resolution SNP microarray platform with over 820,000 probes. Cases where multiple embryos possessed the same segmental imbalance were identified, and preliminary PGT-A reports were issued recommending either parental microarray or conventional karyotyping to identify CNVs or translocations. RESULTS: Analysis of 6080 sequential PGT-A cases led to identification of 41 cases in which incidental findings were observed (0.7%) and parental testing was recommended. All cases, in which parental studies were completed, confirmed the original PGT-A incidental findings. In 2 of the cases, parental studies indicated a pathogenic variant with clinical implications for the associated embryos. In one of these cases, the patient was identified as a carrier of a duplication in chromosome 15q11.2:q11.2 (SNRPN + +), which is associated with autism spectrum disorder. In the second case, the patient was heterozygous positive for an interstitial deletion of 3p26.1:p26.3, which is associated with 3p deletion syndrome and had clinical implications for the patient and associated embryos. In each case, parental studies were concordant with PGT-A findings and revealed the presence of an otherwise unknown CNV. CONCLUSION: High-throughput high-resolution SNP array-based PGT-A has the ability to detect previously unknown and clinically significant parental deletions, duplications, and translocations. The use of cost-effective SNP array-based PGT-A methods may improve the effectiveness of PGT by identifying and preventing previously unknown pathogenic CNVs in children born to patients seeking in vitro fertilization.

Identification of cryptic balanced translocations in couples with unexplained recurrent pregnancy loss based upon embryonic PGT-A results.

PURPOSE: The goal of this study is to determine whether any balanced translocation (BT) had been missed by previous karyotyping in patients with unexplained recurrent pregnancy loss (uRPL). METHODS: This case series included 48 uRPL-affected couples with normal karyotypes. The embryos from these couples have all undergone preimplantation testing for aneuploidies (PGT-A). Based on the PGT-A's results, 48 couples could be categorized into two groups: 17 couples whose multiple embryos were detected with similar structural variations (SVs, segmental/complete) and 31 couples without such findings but who did not develop any euploid embryo despite at least three high-quality blastocysts being tested. The peripheral blood sample of each partner was then collected for mate-pair sequencing (MPseq) to determine whether any of them were BT carriers. RESULTS: MPseq analyses identified 13 BTs in the 17 couples whose multiple embryos had similar SVs detected (13/17, 76.47%) and three BTs in the 31 couples without euploid embryo obtained (3/31, 9.7%). Among the 16 MPseq-identified BTs, six were missed due to the limited resolution of G-banding karyotyping analysis, and the rest were mostly owing to the similar banding patterns and/or comparable sizes shared by the two segments exchanged. CONCLUSION: A normal karyotype does not eliminate the possibility of carrying BT for couples with uRPL. The use of PGT-A allows us to perceive the "carrier couples" missed by karyotyping analysis, providing an increased risk of finding cryptic BTs if similar SVs are always detected on two chromosomes among multiple embryos. Nonetheless, certain carriers with translocated segments of sub-resolution may still go unnoticed.

Olfactory receptor genes and chromosome 11 structural aberrations: Players or spectators?

The largest multi-gene family in metazoans is the family of olfactory receptor (OR) genes. Human ORs are organized in clusters over most chromosomes and seem to include >0.1% the human genome. Because 369 out of 856 OR genes are mapped on chromosome 11 (HSA11), we sought to determine whether they mediate structural rearrangements involving this chromosome. To this aim, we analyzed 220 specimens collected during diagnostic procedures involving structural rearrangements of chromosome 11. A total of 222 chromosomal abnormalities were included, consisting of inversions, deletions, translocations, duplications, and one insertion, detected by conventional chromosome analysis and/or fluorescence in situ hybridization (FISH) and array comparative genomic hybridization (array-CGH). We verified by bioinformatics and statistical approaches the occurrence of breakpoints in cytobands with or without OR genes. We found that OR genes are not involved in chromosome 11 reciprocal translocations, suggesting that different DNA motifs and mechanisms based on homology or non-homology recombination can cause chromosome 11 structural alterations. We also considered the proximity between the chromosomal territories of chromosome 11 and its partner chromosomes involved in the translocations by using the deposited Hi-C data concerning the possible occurrence of chromosome interactions. Interestingly, most of the breakpoints are located in regions highly involved in chromosome interactions. Further studies should be carried out to confirm the potential role of chromosome territories' proximity in promoting genome structural variation, so fundamental in our understanding of the molecular basis of medical genetics and evolutionary genetics.

Noncoding mutations cause super-enhancer retargeting resulting in protein synthesis dysregulation during B cell lymphoma progression.

Whole-genome sequencing of longitudinal tumor pairs representing transformation of follicular lymphoma to high-grade B cell lymphoma with MYC and BCL2 rearrangements (double-hit lymphoma) identified coding and noncoding genomic alterations acquired during lymphoma progression. Many of these transformation-associated alterations recurrently and focally occur at topologically associating domain resident regulatory DNA elements, including H3K4me3 promoter marks located within H3K27ac super-enhancer clusters in B cell non-Hodgkin lymphoma. One region found to undergo recurrent alteration upon transformation overlaps a super-enhancer affecting the expression of the PAX5/ZCCHC7 gene pair. ZCCHC7 encodes a subunit of the Trf4/5-Air1/2-Mtr4 polyadenylation-like complex and demonstrated copy number gain, chromosomal translocation and enhancer retargeting-mediated transcriptional upregulation upon lymphoma transformation. Consequently, lymphoma cells demonstrate nucleolar dysregulation via altered noncoding 5.8S ribosomal RNA processing. We find that a noncoding mutation acquired during lymphoma progression affects noncoding rRNA processing, thereby rewiring protein synthesis leading to oncogenic changes in the lymphoma proteome.

[CD23 positive, BCL2 rearrangement-negative germinal centre lymphomas]. / CD23-positive, BCL2-Rearrangement-negative Keimzentrumslymphome.

Acknowledgeing that the group of follicular lymphomas is to be regarded as very heterogeneous, a group of follicular lymphomas has been delineated in recent years that was characterised by an often diffuse growth (without formation of evident follicular structures) as well as expression of CD23 in the lymphoma cells and the absence of the classic BCL2 translocation. Further characteristics are a preferred inguinal localisation of the lymphomas and a localised stage with a good prognosis. Genetically, this lymphoma group is characterised by a high rate of either STAT6 or SOCS1 mutations.The ICC classification took this development into account by introducing the provisional entity CD23 positive, BCL2 rearrangement-negative germinal centre lymphoma. Further studies must now show how exactly this entity can be defined (combination of morphology, immunohistochemical phenotype, focus on genetic alterations) in order to pave the way towards a uniform classification and a better clinical characterisation of these cases - especially with regard to possible new therapeutic treatment options.

Secretory Carcinoma with ETV6-NTRK3 Gene Fusion and Lymph Node Metastasis in Maxillary Gingiva: A Case Report with Pathological and Molecular Correlative Studies.

Secretory carcinoma (SC), also known as mammary analogue secretory carcinoma (MASC), is a rare salivary gland neoplasm with distinctive morphology that harbors a diagnostic ETV6 gene rearrangement. MASC was first described as a type of salivary gland neoplasm in 2010 and resembles breast secretory carcinoma. It is often mistaken for other neoplasms. It usually acts as an indolent tumor but can occasionally behave in an aggressive manner. We present a rare case of a patient with an aggressive SC/MASC of maxillary gingivobuccal sulcus with microcystic, solid and papillary patterns that showed ETV6 gene rearrangement by fluorescence in situ hybridization. Next-generation sequencing revealed t(12;15)(p13;q25) ETV6-NTRK3 translocation. Because SC/MASCs harbor the ETV6-NTRK3 translocation, molecular studies and immunostains are crucial to confirm the diagnosis and direct therapy.