Cryptic Chromosomal Rearrangements Research Articles

Identification of a novel cryptic variant chromosomal rearrangement involving 9q34, 22q11.2, and 5q22 resulting in ins(9;22) and t(5;22) in chronic myeloid leukemia: a case report.

Chronic myeloid leukemia (CML) is a malignant clonal disorder of the hematopoietic stem cells characterized by the aberrant production and uncontrolled proliferation of mature granulocytes with normal cell differentiation. The Philadelphia (Ph) chromosome resulting from reciprocal translocation between chromosomes 9 and 22 is the main genetic molecular hallmark of CML seen in more than 90% of the patients. However, about 5-10% of CML patients show a variant genetic rearrangement, involving one or more chromosomes in addition to 9 and 22. Herein, we describe the results of hematological, cytogenetic, fluorescence in situ hybridization (FISH), and high-end molecular analysis in a 77-year-old man diagnosed with CML. The combination of conventional cytogenetic analysis along with metaphase FISH and whole chromosomal paint revealed a novel cryptic variant chromosomal rearrangement involving 9q34, 22q11.2, and 5q22, resulting in ins(9;22) and t(5;22). At the molecular level, using PCR, myeloid NGS panels, and whole transcriptome analyses, we showed that this complex rearrangement indeed resulted in the formation of the BCR::ABL1 e13a2 major fusion transcript. No additional somatic mutations or kinase domain mutations were identified, thereby suggesting that the current case is indeed genetically homogeneous. This study provided strong evidence to support the idea that insertion-derived BCR::ABL1 fusions often involve complex chromosomal abnormalities that are overlooked by conventional cytogenetics but can be identified by a combination of conventional, molecular cytogenetics, and high-end NGS studies.

Characterization of cryptic complex chromosome rearrangements in balanced chromosomal rearrangement carriers and their PGT-SR clinical outcome assessments

Several reports have presented that balanced chromosomal rearrangements (BCRs) carriers with normal phenotypes may be carriers of complex rearrangements. However, the incidence and PGT clinical outcomes of cryptic complex chromosome rearrangements (CCCRs) in individuals with BCRs is remain unknown. We recruited a cohort of 1,264 individuals with BCR carriers from 2016 to 2021 at the Reproductive and Genetic Hospital of CITIC Xiangya. Peripheral blood was collected for karyotyping and genomic DNA extraction and the PGT-SR clinical outcomes of CCCRs carriers were analyzed and compared with those of BCR carriers. Our findings revealed that 3.6% (45/1,264) of BCR carriers had CCCRs, involving 3–25 breakpoints on 1–3 chromosomes. Furthermore, when mate-pair sequencing was employed, 63.3% (19/30) of CCCR carriers were found to have chromosome rearrangements that were different from those identified by the MicroSeq technique. And the transferable embryo rate of CCCR carriers with 3 chromosomes was significantly lower than that of CCCR carriers with only 1–2 chromosomes. In this research, we revealed that some of the BCR carriers were actually CCCR carriers, and the prognosis of PGT in CCCR carriers with one or two chromosomes is better than that of CCCR carriers with three chromosomes.

P-529 Optical Genomic Mapping (OGM) enable cryptic chromosomal rearrangements in a couple with recurrent miscarriages undergoing preimplantation genetic diagnosis

Abstract Study question Could Optical Genomic Mapping (OGM) detect chromosomal structural variations (SVs) below the detection limit of conventional cytogenetic diagnostics in couples with recurrent miscarriages? Summary answer The Next-generation cytogenetics of Optical Genomic Mapping confirmed a cryptic chromosomal translocation in a couple with recurrent miscarriages undergoing preimplantation genetic testing for aneuploidies (PGT-A). What is known already Chromosomal structural variants (SVs) significantly contribute to infertility, recurrent pregnancy losses and congenital defects... Approximately 2-4% of couples facing recurrent miscarriages carry chromosomal abnormalities. Currently, their detection is based on convencional cytogenetic methods (karyotyping, FISH or array-CGH), however cryptic chromosomal rearrangements are difficult to identify. Next-generation cytogenetics such as OGM is able to detect SVs with a resolution of < 500 kb, allowing a better understanding of the cause of patient’s infertility. In our study, we utilized OGM to confirm a cryptic translocation in a couple experiencing recurrent miscarriages, aiming to enhance our understanding of the underlying causes of their infertility. Study design, size, duration Our study focuses on a non-consanguineous couple diagnosed with recurrent pregnancy loss that attended to our private fertility clinic to undergo assisted reproductive treatment (ART) with their autologous semen, oocytes and PGT-A. Conventional cytogenetic technique was performed on both partners by G-banding karyotyping. PGT-A was performed by NGS (Veriseq, Illumina). Optical Genomic Mapping (OGM) served as a diagnostic tool, complemented by lymphocyte FISH analysis to confirm chromosomal structural variations in these infertile patients. Participants/materials, setting, methods Ultra High Molecular Weight genomic DNA (UHMW gDNA) was extracted from frozen human peripheral blood of both partners. UHMW gDNA was quantified using Qubit dsDNA assay BR kit and Qubit 4 Fluorometer (Thermo Fisher Scientific). We used Saphyr system (Bionano Genomics) for cytogenetic diagnosis. The consensus genomic map was constructed by de novo assembly in the Bionano Solve data analysis software. SVs were identified by aligning Optical Genomic Map with the reference genome GRCh38/hg38. Main results and the role of chance The couple had suffered four prior miscarriages and undergoing three PGT-A cycles. Both partners provided a normal karyotype. Among 13 biopsied embryos, four showed CNVs on chromosomes 2(p24.3è25.3, 12Mb) and 6(p24.1è25.3, 11Mb). Following this result we suspected that the couple might has a cryptic chromosomal structural abnormalities. To test our hypothesis, we performed OGM. We analysed UHMW gDNA samples from both partners. OGM generated an average of 823.67Gb. The average N50 molecule length (≥150kb) was 318kb. The average mapping rate was 90.75% and the average labeling rate was 15.30 labels per 100kb. The average effective coverage depth was 242X. OGM successfully identified a cryptic translocation in the male partner ogm[GRch38]t(2;6)(p24.3;24.1), while the female partner showed no abnormalities. Translocation breakpoints identified by OGM were Chr2:12.560.508 and Chr6:11.622.593. The translocated segments were near to the detection limit of conventional cytogenetic analysis and with similar pattern that could be the reason for missed detection by karyotyping. Importantly, we identified one gene disrupted by OGM rearrangement breakpoint: MIR3681HG. A previous study considered that CNV loci of 2p24.3, including MIR3681HG gene, could be associated with spermatogenesis. The lymphocyte FISH analysis finding corroborated the OGM result. Limitations, reasons for caution OGM is a very powerful method for detecting chromosomal structural variants in human genomes and is able to detect cryptic structural variants. However, this is a very new diagnostic application, so there is limited experience with OGM for correlating structural variations results to infertility diagnosis in couples with recurrent miscarriages. Wider implications of the findings A balanced cryptic translocation has been identified in a couple with recurrent miscarriages. Our case report demonstrates the high diagnostic capability of Optical Genomic Mapping for cryptic SVs. OGM technology allows a more accurate cytogenetic diagnosis by detecting cryptic structural variants with high resolution in infertile patients with recurrent miscarriages. Trial registration number not applicable

Optical Genome Mapping for Cryptic Chromosomal Rearrangements Identification in Clinical Practice

Optical Genome Mapping for Cryptic Chromosomal Rearrangements Identification in Clinical Practice

Optical Genome Mapping Allows Detection and Characterization of Cytogenetically Cryptic Oncogenic Fusions in Pediatric Acute Myeloid Leukemia

Background: Abnormal gene fusions are predominant oncogenic drivers in pediatric acute myeloid leukemia (AML) and are important diagnostic and prognostic markers. However, several oncogenic fusions specific for or enriched in pediatric AML (like CBFA2T3::GLIS2, NUP98::NSD1, ETV6::MNX1 and others) are not detectable by conventional cytogenetic analysis (cytogenetically cryptic) and may not be included in fluorescence in situ hybridization (FISH) or molecular fusion panels designed for adult patients. Optical genome mapping (OGM) is a powerful new method for genome-wide, high-resolution detection of copy number abnormalities and balanced chromosome rearrangements. This study determined the frequency of cryptic oncogenic fusions in an institutional cohort of pediatric AML cases and evaluated OGM as a method for their detection and characterization. Methods: Retrospective review of genetic testing results was performed for 93 consecutive de novo or relapsed pediatric AML cases tested at the Children's Hospital Los Angeles (CHLA) Center for Personalized Medicine between March 2016 and July 2023. Genetic testing was performed as part of clinical care following standard procedures and consisted of karyotype analysis, FISH testing, chromosomal microarray (CMA) analysis, CHLA custom sequencing panel (OncoKids®) (June 2017 onwards) and RNA-Seq fusion assay (March 2022 onwards). Cases with normal or inconclusive karyotype in which an oncogenic fusion was detected by another clinical assay were selected for OGM testing. High molecular weight DNA from peripheral blood or bone marrow samples was labeled, processed and imaged in a Saphyr System and analyzed in the Bionano Access software following the manufacturer's recommendations (BionanoGenomics, San Diego CA). Results: Out of 93 pediatric AML cases included in the study, a gene fusion was identified as the primary oncogenic driver in 54 (58%) and a DNA sequence variant in 11 (12%). In 28 cases (30%), the primary genetic abnormality remained undetermined after comprehensive genetic testing. In 17/54 (31%) fusion-driven cases [17/93 (18%) overall cases], the oncogenic fusion remained undetected by karyotype analysis (cryptic). OGM was completed in 13/17 fusion positive cases with non-informative karyotype; it could not be performed in 4 cases due to lack of samples (n=2) or poor DNA quality (n=2), and is still in progress for a subset of 28 unknown cases with available material. OGM analysis successfully revealed all cryptic fusions previously detected by FISH, CMA, OncoKids® and/or RNA-Seq, including NUP98::NSD1 (n=3), KMT2A::MLLT10 (n=3), KMT2A::MLLT3 (n=2)and one case each of CBFA2T3::GLIS2, NUP98::KDM5A, DEK::NUP214, MYB::GATA1 and ETV6::MNX1. Chromosomal mechanism and structure of cryptic fusions were resolved by OGM and included: intrinsically cryptic fusions due to chromosome location of partner genes ( NUP98::NSD1, n=4; CBFA2T3::GLIS2, NUP98::KDM5A and ETV6::MNX1, n=1 each); complex rearrangements due to incompatible gene orientation ( KMT2A::MLLT10 n=2; MYB::GATA1, n=1); three-way rearrangements involving an additional chromosome ( KMT2A::MLLT3 n=2) and small insertions ( KMT2A::MLLT10 and DEK::NUP214, n=1 each). OGM also matched the performance of chromosomal microarray (CMA) analysis in detection of copy number variants. Conclusions: We confirm the significant contribution of cryptic chromosome rearrangements to pathogenesis of pediatric AML, and highlight the importance of tailored testing approaches that effectively detect highly heterogeneous fusion drivers. Our preliminary results show potential of OGM to identify clinically significant cryptic fusions in pediatric AML, and to thus markedly increase diagnostic yield compared to karyotype analysis. As a single assay that detects abnormalities currently interrogated by conventional cytogenetics, FISH and CMA, OGM may allow streamlined and more cost-effective genetic evaluation for pediatric AML.

P-736 Balanced cryptic chromosomal rearrangement carriers detection by optical genome mapping (OGM)

Abstract Study question To evaluate diagnosis value of optical genome mapping (OGM) for potential preimplantation genetic testing in chromosomal structural rearrangement (PGT-SR) patients with cryptic chromosomal rearrangement. Summary answer OGM is an efficient method for cryptic chromosomal rearrangement detection. However, SVs near telomere and centromere regions could hardly be reported with this method. What is known already About 5∼10% infertility or sterility people carry balanced chromosomal structural variations (SVs) with high risks of miscarriage and birth defects resulting from imbalanced gametes when producing fetus. However, some balanced cryptic SVs with specific location or small fragments cannot be detected by traditional cytogenetic techniques like G-banding testing or CNV-seq. Currently, several optimized techniques are able to detect typically cryptic structural abnormality. OGM, the molecular genetic detection technique relying on new principle in recent years, have overcome the shortcomings of former techniques and are potentially capable to detect both routine and cryptic SVs well. Study design, size, duration From 2019 to 2022, 12 couples in The First Affiliated Hospital of Sun Yat-sen University and The First People’s Hospital of Yunnan Province with history of offspring birth defect, recurrent unexplained recurrent miscarriage or unexpected copy number variation in embryos from previous PGT cycles were included for diagnosis or re-analysis. Participants/materials, setting, methods Peripheral blood lymphocytes from these patients were collected and detected by OGM or traditional karyotype analysis(G-400 banding), FISH, CNV-seq, third generation sequencing(Nanopore). The results of traditional genetic test and OGM were compared to evaluate the accuracy of OGM detection of chromosomal structure vatiation. Main results and the role of chance In the 11 couples bearing adverse pregnancy or childbirth defect with normal karyotype by G-banding, OGM discovered novel chromosome translocations or inversion in 9 couples (81.81%). In 1 couple with t(4:17)(q12;p13) diagnosed by G-banding, OGM detect an additional chromosomal translocation of t(17;19)(q12;p13), which produced the repeated CNVs in chromosome19 observed in embryos from two previous PGT cycles. For small fragment translocation, terminal translocation and inversion, OGM is able to detected balanced structure abnormal of 500kbs. The OGM diagnosis were confirmed by FISH or third generation sequencing (Nanopore) or embryo mutation. The breaking position reported by OGM and Nanopore were comparable. In sum, OGM reported further information of balanced SVs in 83.33% (10/12) potential patients with duplication and depletion in embryos or abortus. Limitations, reasons for caution Due to the limitation of principle, the structural abnormalities of some special locations (centromere, secondary constriction, etc.) cannot be detected. OGM has high sensitivity and many mutations, which requires examiners to have strong ability to analyze results and genetic counseling. The price of OGM also limits the promotion and application. Wider implications of the findings OGM can provide more precious result for SVs, and PGT-SR can definitely improve the outcome of certain population with cryptic chromosomal rearrangements. The shortcoming of OGM has not been overcame yet, so it is suggested as auxiliary method beside conventional G-binding in certain circumstances in ART population. Trial registration number Not applicable

Identification of complex and cryptic chromosomal rearrangements by optical genome mapping

BackgroundOptical genome mapping (OGM) has developed into a highly promising method for detecting structural variants (SVs) in human genomes. Complex chromosomal rearrangements (CCRs) and cryptic translocations are rare events that are considered difficult to detect by routine cytogenetic methods. In this study, OGM was applied to delineate the precise chromosomal rearrangements in three cases with uncertain or unconfirmed CCRs detected by conventional karyotyping and one case with a cryptic translocation suggested by fetal chromosomal microarray analysis (CMA).ResultsIn the three cases with CCRs, OGM not only confirmed or revised the original karyotyping results but also refined the precise chromosomal structures. In the case with a suspected translocation not detected by karyotyping, OGM efficiently identified the cryptic translocation and defined the genomic breakpoints with relatively high accuracy.ConclusionsOur study confirmed OGM as a robust alternative approach to karyotyping for the detection of chromosomal structural rearrangements, including CCRs and cryptic translocations.

Practical Applications of Chromosomal Microarray in Prenatal Diagnosis

AbstractG-banded karyotyping is the most common approach for the detection of genomic alterations. However, this is unable to detect genomic changes of less than 5 Mb. The ability of fluorescence in situ hybridization (FISH) to detect cryptic chromosomal rearrangements exceeds the resolution of routine karyotype. However, conventional FISH is for targeted regions only, whereas the chromosomal microarray is a whole-genome copy number evaluation technique with a resolution of 10 to 20 kb. In this article, we discuss the application of chromosomal microarray 750 K to 384 consecutive prenatal diagnosis cases. Overall diagnostic yield is 15.36%, and chromosomal microarray accounts for a 3.6% additional detection rate. We suggest applying this technique in routine prenatal diagnosis as a first-tier test in prenatal diagnosis along with a backup culture in all cases.

DETECT CRYPTIC CHROMOSOMAL REARRANGEMENT BY OPTICAL GENOME MAPPING (OGM) IN INFERTILE POPULATION

To evaluate diagnosis value of optical genome mapping (OGM) for potential PGT-SR patient with cryptic chromosomal rearrangement.

Detection of cryptic balanced chromosomal rearrangements using high-resolution optical genome mapping

BackgroundChromosomal rearrangements have profound consequences in diverse human genetic diseases. Currently, the detection of balanced chromosomal rearrangements (BCRs) mainly relies on routine cytogenetic G-banded karyotyping. However, cryptic BCRs are hard...

FISH Diagnostics of Chromosomal Translocation with the Technology of Synthesis of Locus-Specific DNA Probes Based on Long-Range PCR

Detection of translocations in subtelomeric regions of chromosomes is a serious diagnostic problem, because they are difficult to determine by conventional cytogenetics with G banding. The aim of this work was the development of the technology of DNA probe synthesis for unique sequences of subtelomeric chromosome regions based on long-range PCR using the clinical case of determining the parental origin of unbalanced translocation between chromosomes 5 and 8. The unbalanced translocation der(5)t(5;8)(р15.33;q24.22) in a proband with physical, motor, intellectual, and speech development delay and in his sibling with speech and intellectual development delay as well, which was previously identified by array comparative genomic hybridization (aCGH), was confirmed by FISH. A balanced translocation 46,XX,t(5;8)(p15.33;q24.22) was detected in the mother’s karyotype using the created locus-specific DNA probe. This chromosome aberration was not detected by G banding of metaphase chromosomes. The father’s karyotype was normal according to FISH results. The method presented here makes it possible to create locus-specific DNA probes in a molecular cytogenetic laboratory using long-range PCR for the rapid diagnosis of cryptic chromosomal rearrangements.

Breakpoint mapping uncovering about 1.32% of apparent balanced reciprocal translocation (ABRT) carriers existing cryptic complex chromosomal structural variations in preimplantation genetic testing (PGT)

To identify precise breakpoints, evaluate the reproduction-related risks and guide the following PGT treatment, high resolution breakpoint mapping was performed in ABRT carriers indicated by G-banding. A single-center, descriptive research. A large sample of 833 cases with ABRT who planned to accept PGT treatment were recruited in this study. For these patients, the approach of the next-generation sequencing following microdissection (MiroSeq) of the junction region in the derivative chromosomes, and linkage analysis of the adjacent single nucleotide polymorphisms (SNPs) were performed to distinguish the carriers from noncarriers in balanced embryos. For some cases with unbalanced chromosome rearrangement in the breakpoint region, SNP-array and fluorescence in situ hybridization (FISH) techniques were further used to determine the accurate karyotype. In the 833 cases with ABRT, we found 11 cases (1.32%) carried cryptic complex chromosomal structural variation, including 3 unbalanced chromosome rearrangements and 8 balanced ones in which 2 cases carried both inversion and translocation. In these 11 cases, 5 cases related to 3 chromosomes with 4 to 21 breakpoints and 6 cases involved 2 chromosomes with 3 to 6 breakpoints. It is noteworthy that there were two cases exhibited rare chromoanagenesis, including chromothripsis and chromoplexy. Fortunately, two couples have been both successfully transplanted a normal embryo and given birth to a healthy child, and the remaining nine cases are undergoing PGT treatment. In this large-scale analysis of ABRT, high resolution breakpoint mapping precisely characterized these breakpoints and uncovered 1.32% of the ABRT carriers existed cryptic complex chromosomal structural rearrangement. These data suggests that high resolution breakpoint mapping used in PGT can improve the accuracy of evaluating the reproduction-related risks and avoid genetic risks for the ABRT carriers.

Prenatal microarray comparative genomic hybridization: Experience from the two first years of activity at the Lyon university-hospital

ObjectivesThis study aims to describe how microarray comparative genomic hybridization (aCGH) has shifted to become a prenatal diagnosis tool at the Lyon university-hospital. Materials and methodsThis retrospective study included all patients who were referred in the 3 pluridisciplinary centers for prenatal diagnosis of the Lyon university-hospital and who received a prenatal aCGH between June 2013 and June 2015. aCGH was systematically performed in parallel with a karyotype, using the PréCytoNEM array design. ResultsA total of 260 microarrays were performed for the following indications: 249 abnormal ultrasounds (95.8%), 7 characterizations of chromosomal rearrangements (2.7%), and 4 twins with no abnormal ultrasounds (1.5%). With a resolution of 1 mega base, we found 235 normal results (90.4%), 23 abnormal results (8.8%) and 2 non-returns (0.8%). For the chromosomal rearrangements visible on the karyotype, aCGH identified all of the 12 unbalanced rearrangements and did not identify the 2 balanced rearrangements. Among the fetuses with normal karyotypes, 11 showed abnormal microarray results, corresponding to unbalanced cryptic chromosomal rearrangements (4.2%). ConclusionTransferring aCGH to a prenatal diagnosis at the Lyon university-hospital has increased the detection rate of chromosomal abnormalities by 4.2% compared to the single karyotype.

Interstitial Telomeric Motifs in Squamate Reptiles: When the Exceptions Outnumber the Rule.

Telomeres are nucleoprotein complexes protecting the physical ends of linear eukaryotic chromosomes and therefore helping to ensure their stability and integrity. Additionally, telomeric sequences can be localized in non-terminal regions of chromosomes, forming so-called interstitial telomeric sequences (ITSs). ITSs are traditionally considered to be relics of chromosomal rearrangements and thus very informative in the reconstruction of the evolutionary history of karyotype formation. We examined the distribution of the telomeric motifs (TTAGGG)n using fluorescence in situ hybridization (FISH) in 30 species, representing 17 families of squamate reptiles, and compared them with the collected data from another 38 species from literature. Out of the 68 squamate species analyzed, 35 possess ITSs in pericentromeric regions, centromeric regions and/or within chromosome arms. We conclude that the occurrence of ITSs is rather common in squamates, despite their generally conserved karyotypes, suggesting frequent and independent cryptic chromosomal rearrangements in this vertebrate group.

High frequency of cryptic chromosomal rearrangements involving the LMO2 gene in T-cell acute lymphoblastic leukemia

High frequency of cryptic chromosomal rearrangements involving the LMO2 gene in T-cell acute lymphoblastic leukemia

Using Cytogenetic Rearrangements for Cancer Prognosis and Treatment (Pharmacogenetics)

Chromosomal rearrangements including translocations, deletions, inversions, and insertions are common genetic alterations in cancer. Over 1,000 recurrent chromosome rearrangements have been reported so far in different human tumors ( http://cgap.nci.nih.gov/Chromosomes/Mitelman ). Most of these chromosome rearrangements are associated with specific tumor types and bear distinctive diagnostic and prognostic significance. Molecular characterization of these rearrangements has revealed numerous cancer genes, including novel fusion genes, and their normal and aberrant interactions involved in tumorigenesis, and has identified myriad therapeutic targets. With the help of advanced high-throughput technologies, many cryptic chromosome rearrangements undetectable by conventional cytogenetics have recently been discovered and delineated. The understanding of the mechanisms responsible for the formation of recurrent chromosome rearrangements and their biological functions has led to novel treatment regimens that target tumor cells specifically, with minimal impact to normal cells. Here, we review common recurrent chromosome rearrangements in both hematopoietic malignancies and solid tumors, and their clinical significance, with a focus on acquired fusion genes and their therapeutic implications (i.e., pharmacogenetics).

Cryptic Chromosome Rearrangements in Five Patients, with Normal and/or Abnormal Karyotypes, Associated with Mental Retardation, Autism and/or Epilepsy, Detected by BAC Genome Array-CGH

This report describes the usefulness of the BAC genome array-CGH platform in the detection of cryptic rearrangements. We examined ten patients with normal and/or abnormal karyotypes and dysmorphic features, associated with mental retardation, autism and/or epilepsy. This approach led us to discover further cryptic chromosomal rearrangements, not previously detected by conventional cytogenetic procedures, and allowed us to better delineate genotype/phenotype correlation. Our experience shows the validity of the BAC platform as a reliable method for genome-wide screening of chromosomal aberrations in patient with idiopathic mental retardation and/or in association with autism and epilepsy.

Prenatal Diagnosis of a Satellited Chromosome 8p Results from a de novo Cryptic Translocation between Chromosomes 8 and 22

The authors of the present study report the prenatal detection of a chromosomal abnormality with additional satellites on the distal short arm of chromosome 8. A 35-year-old woman was referred for amniocentesis because of her advanced maternal age and positive result for maternal serum screening test. Cytogenetic analysis of cultured amniocytes showed a satellite 8p chromosome. The satellite 8p chromosome was positive for nucleolus organizer region (NOR) staining. The parents karyotypes were normal. Fluorescence ’ in situ hybridization (FISH) study for metaphases of fetal amniocytes revealed a cryptic translocation of chromosomes 8p and 22p. The fetal karyotype was described as 46,XY,8ps.ish t(8;22)(p23.3;p11.2) (D8S504-;D8S504+)dn. The parents decided to continue the pregnancy and a phenotypically normal boy was born at 38 weeks of gestation. In case of de novo terminal NORs detected prenatally, more accurate cytogenetic and molecular analysis should be performed in order to rule out cryptic chromosomal rearrangement among other chromosomes.

Fluorescence in situ hybridization study of acute myeloid leukemia with cryptic chromosome rearrangements

To detect specific chromosome rearrangements in acute myeloid leukemia (AML) using interphase-fluorescence in situ hybridization (FISH). All cases were studied by R-band karyotypic analysis using direct method and/or short-term culture for chromosomes preparation. Interphase-FISH was performed in 108 cases of AML with M5, M4, M2, M3 subtypes including 103 cases with normal karyotypes, 4 cases with chromosomal abnormalities other than specific chromosomal rearrangements using chromosome translocation probe such as AML1/ETO, PML/RARα, CBFβ/MYH11 and MLL. Of 38 cases of M2-AML without t(8;21) on conventional cytogenetics(CC) analysis, 4 cases showed positivity for AML1/ETO fusion transcript, which included 2 cases with typical signal model and 2 with insertion. Of 9 cases of M3-AML without t(15;17) on CC analysis, 6 showed positivity for PML/RARα fusion transcript including 2 with typical signal model, 3 with insertion, one without PML/RARα rearrangement on reverse transcription-PCR and FISH assay using PML/RARα probe. FISH assay using the RARα dual color, break-apart rearrangement probe indicated a partial deletion of RARα. Of 23 cases with M4 or M4EO-AML without inv(16) on CC analysis, 3 showed positivity for CBFβ/MYH11 fusion transcript. Of 38 cases without 11q23 translocation on CC analysis, all cases were negative for MLL rearrangement. Interphase-FISH can detect specific chromosome rearrangements such as AML1/ETO, PML/RARα or CBFβ/MYH11 in some AML cases with normal karyotype, though it seemed less useful for the detection of MLL rearrangement.

Interphase fluorescence in situ hybridization analysis detects a much higher rate of thyroid tumors with clonal cytogenetic deviations of the main cytogenetic subgroups than conventional cytogenetics

In benign thyroid lesions, three main cytogenetic subgroups, characterized by trisomy 7 or structural aberrations involving either chromosomal region 19q13.4 or 2p21, can be distinguished by conventional cytogenetics (CC). As a rule, these aberrations seem to be mutually exclusive. Interphase fluorescence in situ hybridization (I-FISH) analysis on benign as well as malignant thyroid neoplasias has been performed in the past, but rarely in combination with CC. In the present paper, we have analyzed 161 benign thyroid lesions both with CC and I-FISH on touch preparations by using a multi-target, triple-color FISH assay as well as dual-color break-apart probes for detection of the main cytogenetic subgroups. Within the samples, I-FISH detected tumors belonging to either of the subgroups more frequently than CC (23 vs. 11.4%), either due to small subpopulations of aberrant cells or to cryptic chromosomal rearrangements (three cases). Thus, I-FISH seems to be more sensitive than CC, particularly in the detection of subpopulations of cells harboring cytogenetic aberrations that may be overlooked by CC. In summary, I-FISH on touch preparations of benign thyroid lesions seems to be a favorable method for cytogenetic subtyping of thyroid lesions.