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Despite advances in next generation sequencing (NGS), genetic diagnoses remain elusive for many patients with neurologic syndromes. Long‐read sequencing (LRS) and optical genome mapping (OGM) technologies improve upon existing capabilities in the detection and interpretation of structural variation in repetitive DNA, on a single haplotype, while also providing enhanced breakpoint resolution. We performed LRS and OGM on two patients with known chromosomal rearrangements and inconclusive Sanger or NGS. The first patient, who had epilepsy and developmental delay, had a complex translocation between two chromosomes that included insertion and inversion events. The second patient, who had a movement disorder, had an inversion on a single chromosome disrupted by multiple smaller inversions and insertions. Sequence level resolution of the rearrangements identified pathogenic breaks in noncoding sequence in or near known disease‐causing genes with relevant neurologic phenotypes (MBD5, NKX2‐1). These specific variants have not been reported previously, but expected molecular consequences are consistent with previously reported cases. As the use of LRS and OGM technologies for clinical testing increases and data analyses become more standardized, these methods along with multiomic data to validate noncoding variation effects will improve diagnostic yield and increase the proportion of probands with detectable pathogenic variants for known genes implicated in neurogenetic disease. [ABSTRACT FROM AUTHOR]

We report a 17‐year‐old male with supravalvular stenosis, initial failure to thrive and delayed early development, short stature, acromelia, dysmorphic facial features, hypertelorism, macrocephaly, syringomyelia, hypertension, and anxiety disorder. Fluorescent in situ hybridization (FISH), chromosomal microarray analysis (CMA), and exome sequencing (ES) were nondiagnostic. Combined optical genome mapping (OGM) and genome sequencing (GS) showed a complex rearrangement including an X chromosome with a 22.5 kb deletion in band Xq28 replaced by a 61.4 kb insertion of duplicated chromosome 7p22.3 material. The deletion removes the distal 3′ untranslated region (UTR) of FUNDC2, the entire CMC4 and MTCP1, and the first five exons of BRCC3. Transcriptome analysis revealed absent expression of CMC4 and MTCP1 and BRCC3 with normal transcript level of FUNDC2. The inserted duplication includes only one known gene: UNCX. Similar overlapping Xq28 deletions have been reported to be associated with Moyamoya disease (MMD), short stature, hypergonadotropic hypogonadism (HH), and facial dysmorphism. Although he has short stature, our patient does not have signs of Moyamoya arteriopathy or hypogonadism. The structurally abnormal X chromosome was present in his mother, but not in his unaffected brother, maternal uncle, or maternal grandparents. We propose that the combination of his absent Xq28 and duplicated 7p22.3 genomic material is responsible for his phenotype. This case highlights the potential of combined OGM and GS for detecting complex structural variants compared with standard of care genetic testing such as CMA and ES. [ABSTRACT FROM AUTHOR]

Genomic structural variants (SVs) play a pivotal role in driving the evolution of hematologic malignancies, particularly in leukemia, in which genetic abnormalities are crucial features. Detecting SVs is essential for achieving precise diagnosis and prognosis in these cases. Karyotyping, often complemented by fluorescence in situ hybridization and/or chromosomal microarray analysis, provides standard diagnostic outcomes for various types of SVs in front‐line testing for leukemia. Recently, optical genome mapping (OGM) has emerged as a promising technique due to its ability to detect all SVs identified by other cytogenetic methods within one single assay. Furthermore, OGM has revealed additional clinically significant SVs in various clinical laboratories, underscoring its considerable potential for enhancing front‐line testing in cases of leukemia. This review aims to elucidate the principles of conventional cytogenetic techniques and OGM, with a focus on the technical performance of OGM and its applications in diagnosing and prognosticating myelodysplastic syndromes, acute myeloid leukemia, acute lymphoblastic leukemia, and chronic lymphocytic leukemia. [ABSTRACT FROM AUTHOR]

ABSTRACT Genomic repeat sequences are patterns of nucleic acids that exist in multiple copies throughout the genome. More than 60 Mendelian disorders are caused by the expansion or contraction of these repeats. Various specific methods for determining tandem repeat variations have been developed. However, these methods are highly specific to the genomic region being studied and sometimes require specialized tools. In this study, we have investigated the use of Optical Genome Mapping (OGM) as a diagnostic tool for detecting repeat disorders. We evaluated 19 patients with a prediagnosis of repeat disorders and explained the molecular etiology of 9 of them with OGM (5 patients with Facioscapulohumeral Muscular Dystrophy (FSHD), 2 patients with Friedreich's Ataxia (FA), 1 patient with Fragile X Syndrome (FXS), and 1 patient with Progressive Myoclonic Epilepsy 1A (EPM1A)). We confirmed OGM results with more widely used fragment analysis techniques. This study highlights the utility of OGM as a diagnostic tool for repeat expansion and contraction diseases such as FA, FXS, EPM1A, and FSHD. [ABSTRACT FROM AUTHOR]

Background: Certain structural variants (SVs) including large-scale genetic copy number variants, as well as copy number-neutral inversions and translocations may not all be resolved by chromosome karyotype studies. The identification of genetic risk factors for Parkinson's disease (PD) has been primarily focused on the gene-disruptive single nucleotide variants. In contrast, larger SVs, which may significantly influence human phenotypes, have been largely underexplored. Optical genomic mapping (OGM) represents a novel approach that offers greater sensitivity and resolution for detecting SVs. In this study, we used induced pluripotent stem cell (iPSC) lines of patients with PD-linked SNCA and PRKN variants as a proof of concept to (i) show the detection of pathogenic SVs in PD with OGM and (ii) provide a comprehensive screening of genetic abnormalities in iPSCs. Results: OGM detected SNCA gene triplication and duplication in patient-derived iPSC lines, which were not identified by long-read sequencing. Additionally, various exon deletions were confirmed by OGM in the PRKN gene of iPSCs, of which exon 3–5 and exon 2 deletions were unable to phase with conventional multiplex-ligation-dependent probe amplification. In terms of chromosomal abnormalities in iPSCs, no gene fusions, no aneuploidy but two balanced inter-chromosomal translocations were detected in one line that were absent in the parental fibroblasts and not identified by routine single nucleotide variant karyotyping. Conclusions: In summary, OGM can detect pathogenic SVs in PD-linked genes as well as reveal genomic abnormalities for iPSCs that were not identified by other techniques, which is supportive for OGM's future use in gene discovery and iPSC line screening. [ABSTRACT FROM AUTHOR]

Abstract Structural variants (SVs) are important contributors to human disease. Their characterization remains however difficult due to their size and association with repetitive regions. Long-read sequencing (LRS) and optical genome mapping (OGM) can aid as their molecules span multiple kilobases and capture SVs in full. In this study, we selected six individuals who presented with unresolved SVs. We applied LRS onto all individuals and OGM to a subset of three complex cases. LRS detected and fully resolved the interrogated SV in all samples. This enabled a precise molecular diagnosis in two individuals. Overall, LRS identified 100% of the junctions at single-basepair level, providing valuable insights into their formation mechanisms without need for additional data sources. Application of OGM added straightforward variant phasing, aiding in the unravelment of complex rearrangements. These results highlight the potential of LRS and OGM as follow-up molecular tests for complete SV characterization. We show that they can assess clinically relevant structural variation at unprecedented resolution. Additionally, they detect (complex) cryptic rearrangements missed by conventional methods. This ultimately leads to an increased diagnostic yield, emphasizing their added benefit in a diagnostic setting. To aid their rapid adoption, we provide detailed laboratory and bioinformatics workflows in this manuscript.

Abstract Background Certain structural variants (SVs) including large-scale genetic copy number variants, as well as copy number-neutral inversions and translocations may not all be resolved by chromosome karyotype studies. The identification of genetic risk factors for Parkinson’s disease (PD) has been primarily focused on the gene-disruptive single nucleotide variants. In contrast, larger SVs, which may significantly influence human phenotypes, have been largely underexplored. Optical genomic mapping (OGM) represents a novel approach that offers greater sensitivity and resolution for detecting SVs. In this study, we used induced pluripotent stem cell (iPSC) lines of patients with PD-linked SNCA and PRKN variants as a proof of concept to (i) show the detection of pathogenic SVs in PD with OGM and (ii) provide a comprehensive screening of genetic abnormalities in iPSCs. Results OGM detected SNCA gene triplication and duplication in patient-derived iPSC lines, which were not identified by long-read sequencing. Additionally, various exon deletions were confirmed by OGM in the PRKN gene of iPSCs, of which exon 3–5 and exon 2 deletions were unable to phase with conventional multiplex-ligation-dependent probe amplification. In terms of chromosomal abnormalities in iPSCs, no gene fusions, no aneuploidy but two balanced inter-chromosomal translocations were detected in one line that were absent in the parental fibroblasts and not identified by routine single nucleotide variant karyotyping. Conclusions In summary, OGM can detect pathogenic SVs in PD-linked genes as well as reveal genomic abnormalities for iPSCs that were not identified by other techniques, which is supportive for OGM’s future use in gene discovery and iPSC line screening.

Abstract Background Deletion or duplication in the DMD gene is one of the most common causes of Duchenne and Becker muscular dystrophy (DMD/BMD). However, the pathogenicity of complex rearrangements involving DMD, especially segmental duplications with unknown breakpoints, is not well understood. This study aimed to evaluate the structure, pattern, and potential impact of rearrangements involving DMD duplication. Methods Two families with DMD segmental duplications exhibiting phenotypical differences were recruited. Optical genome mapping (OGM) was used to explore the cryptic pattern of the rearrangements. Breakpoints were validated using long-range polymerase chain reaction combined with next-generation sequencing and Sanger sequencing. Results A multi-copy duplication involving exons 64–79 of DMD was identified in Family A without obvious clinical symptoms. Family B exhibited typical DMD neuromuscular manifestations and presented a duplication involving exons 10–13 of DMD. The rearrangement in Family A involved complex in-cis tandem repeats shown by OGM but retained a complete copy (reading frame) of DMD inferred from breakpoint validation. A reversed insertion with a segmental repeat was identified in Family B by OGM, which was predicted to disrupt the normal structure and reading frame of DMD after confirming the breakpoints. Conclusions Validating breakpoint and rearrangement pattern is crucial for the functional annotation and pathogenic classification of genomic structural variations. OGM provides valuable insights into etiological analysis of DMD/BMD and enhances our understanding for cryptic effects of complex rearrangements.

Abstract Background Structural variations (SVs) are key genetic contributors to neurodevelopmental disorders (NDDs). Exome sequencing (ES), the current first-line tool for genetic testing of NDDs, falls short in SVs detection. This diagnostic gap is being actively addressed by new methods such as optical genome mapping (OGM). Methods This study evaluated the utility of combining OGM and RNA-seq in the detection and interpretation of SVs in ES-negative NDDs. OGM was performed in 43 patients with NDDs with inconclusive ES results. Candidate SVs were selected based on disease association and pathogenicity evaluation, and further validated or reconstructed by alternative methods, including long-read sequencing for a complex rearrangement event. RNA-Seq was performed on blood samples from patients with candidate SVs to facilitate interpretation of pathogenicity. Results OGM detected four candidate SVs, and RNA-seq confirmed the pathogenicity of three SVs in the patient cohort. This combined approach solved three cases—two cases with de novo SVs in genes associated with autosomal dominant NDDs, including a deletion encompassing the promoter and 5′UTR of MBD5 and an intragenic duplication of PAFAH1B1, and a third case possessing an intragenic duplication in trans with a pathogenic single-nucleotide variant of PLA2G6, associated with autosomal recessive NDDs. The expression alteration of the affected genes and the tandem positioning of two intragenic duplications were confirmed by RNA-seq. In the fourth case, OGM detected a complex rearrangement involving chromosomes 2 and 6, much more complex than the de novo t(2:6)(q13;q15) indicated by conventional cytogenetic analysis. Reconstruction showed that 17 segments of 6q15 spanning 9.3 Mb were disarranged and joined 2q11.2, with four breakpoints detected in the 5′ and 3′ non-coding region of the NDD-associated gene SYNCRIP. RNA-seq revealed largely preserved SYNCRIP expression, leaving the pathogenicity of this complex rearrangement event uncertain. Conclusions SVs in ES-negative NDDs can be identified by OGM, which is particularly useful for SVs in non-coding regions not covered by ES. OGM helps to construct complex SVs and provides information on the location and orientation of duplications, which is crucial for pathogenicity interpretation. The integration of RNA-seq facilitates the interpretation of the functional consequences of SVs at the transcriptional level. These findings demonstrate the utility and feasibility of combining OGM and RNA-seq in ES-negative cases with NDDs.

Background: Structural variations (SVs) are key genetic contributors to neurodevelopmental disorders (NDDs). Exome sequencing (ES), the current first-line tool for genetic testing of NDDs, falls short in SVs detection. This diagnostic gap is being actively addressed by new methods such as optical genome mapping (OGM). Methods: This study evaluated the utility of combining OGM and RNA-seq in the detection and interpretation of SVs in ES-negative NDDs. OGM was performed in 43 patients with NDDs with inconclusive ES results. Candidate SVs were selected based on disease association and pathogenicity evaluation, and further validated or reconstructed by alternative methods, including long-read sequencing for a complex rearrangement event. RNA-Seq was performed on blood samples from patients with candidate SVs to facilitate interpretation of pathogenicity. Results: OGM detected four candidate SVs, and RNA-seq confirmed the pathogenicity of three SVs in the patient cohort. This combined approach solved three cases—two cases with de novo SVs in genes associated with autosomal dominant NDDs, including a deletion encompassing the promoter and 5′UTR of MBD5 and an intragenic duplication of PAFAH1B1, and a third case possessing an intragenic duplication in trans with a pathogenic single-nucleotide variant of PLA2G6, associated with autosomal recessive NDDs. The expression alteration of the affected genes and the tandem positioning of two intragenic duplications were confirmed by RNA-seq. In the fourth case, OGM detected a complex rearrangement involving chromosomes 2 and 6, much more complex than the de novo t(2:6)(q13;q15) indicated by conventional cytogenetic analysis. Reconstruction showed that 17 segments of 6q15 spanning 9.3 Mb were disarranged and joined 2q11.2, with four breakpoints detected in the 5′ and 3′ non-coding region of the NDD-associated gene SYNCRIP. RNA-seq revealed largely preserved SYNCRIP expression, leaving the pathogenicity of this complex rearrangement event uncertain. Conclusions: SVs in ES-negative NDDs can be identified by OGM, which is particularly useful for SVs in non-coding regions not covered by ES. OGM helps to construct complex SVs and provides information on the location and orientation of duplications, which is crucial for pathogenicity interpretation. The integration of RNA-seq facilitates the interpretation of the functional consequences of SVs at the transcriptional level. These findings demonstrate the utility and feasibility of combining OGM and RNA-seq in ES-negative cases with NDDs. [ABSTRACT FROM AUTHOR]

Background: Deletion or duplication in the DMD gene is one of the most common causes of Duchenne and Becker muscular dystrophy (DMD/BMD). However, the pathogenicity of complex rearrangements involving DMD, especially segmental duplications with unknown breakpoints, is not well understood. This study aimed to evaluate the structure, pattern, and potential impact of rearrangements involving DMD duplication. Methods: Two families with DMD segmental duplications exhibiting phenotypical differences were recruited. Optical genome mapping (OGM) was used to explore the cryptic pattern of the rearrangements. Breakpoints were validated using long-range polymerase chain reaction combined with next-generation sequencing and Sanger sequencing. Results: A multi-copy duplication involving exons 64–79 of DMD was identified in Family A without obvious clinical symptoms. Family B exhibited typical DMD neuromuscular manifestations and presented a duplication involving exons 10–13 of DMD. The rearrangement in Family A involved complex in-cis tandem repeats shown by OGM but retained a complete copy (reading frame) of DMD inferred from breakpoint validation. A reversed insertion with a segmental repeat was identified in Family B by OGM, which was predicted to disrupt the normal structure and reading frame of DMD after confirming the breakpoints. Conclusions: Validating breakpoint and rearrangement pattern is crucial for the functional annotation and pathogenic classification of genomic structural variations. OGM provides valuable insights into etiological analysis of DMD/BMD and enhances our understanding for cryptic effects of complex rearrangements. [ABSTRACT FROM AUTHOR]

Background: X‐linked recessive type 3 Charcot–Marie–Tooth (CMTX3) is a rare subtype of childhood‐onset CMT. To date, all reported CMTX3 patients share a common founder 78 kb insertion from chromosome 8 into the Xq27.1 palindrome region. Methods: We conducted patient–parent trio optical genome mapping (OGM) on a male patient presenting with clinically diagnosed Dejerine–Sottas disease for whom initial standard diagnostic genetic tests, including whole‐genome sequencing (WGS), yielded negative results. Results: OGM analysis revealed a maternally inherited interchromosomal insertion from chromosome region 7q31.1 into Xq27.1. Coupled with manual reassessment of WGS data, this confirmed the molecular diagnosis of atypical CMTX3 and showed that the 122.4 kb inserted fragment contained DLD and partially LAMB1. Subsequent analyses confirmed that the rearrangement had arisen de novo in the proband's mother. Conclusion: We report the second Xq27.1 rearrangement associated with CMTX3, providing novel clinical insights into its phenotypic and genotypic spectrum. Our findings highlight the importance of including genomic rearrangement analysis of Xq27.1 in standard diagnostic pipelines for childhood‐onset CMT. Given the overlap in polyneuropathy phenotypes resulting from insertions from chromosomes 7 and 8 into the same Xq27.1 palindrome region, the pathogenic mechanism underlying peripheral neuropathy in CMTX3 likely involves dysregulation of genes within this region. [ABSTRACT FROM AUTHOR]

We report an index patient with complete insensitivity to pain and a history of painless fractures, joint hypermobility, and behavioral problems. The index patient descends froma familywith notable cases among hismaternal relatives, including his aunt and his mother's first cousin, both of whom suffer from congenital insensitivity to pain. The patient had normal results for prior genetic testing: fragile-X syndrome testing, chromosomal microarray analysis, and exome sequencing. Optical genome mapping detected a homozygous deletion affecting the noncoding 5' untranslated region (UTR) and the first non-coding exon of the SCN9A gene in all affected family members, compatiblewith recessive disease transmission. Pathogenic homozygous loss-of-function variants in the SCN9A gene are associated with impaired pain sensation in humans. Optical genome mapping can thus detect pathogenic structural variants in patients without molecular etiology by standard diagnostic procedures and is a more accessible diagnostic tool than short-read or long-read whole-genome sequencing. [ABSTRACT FROM AUTHOR]

Background: Tuberous sclerosis is a multi-system disorder caused by mutations in either TSC1 or TSC2. The majority of affected patients (85%--90%) have heterozygous variants, and a smaller number (around 5%) have mosaic variants. Despite using various techniques, some patients still have "no mutation identified" (NMI). Methods: We hypothesized that the causal variants of patients with NMI may be structural variants or deep intronic variants. To investigate this, we sequenced the DNA of 26 tuberous sclerosis patients with NMI using targeted long-read sequencing. Results: We identified likely pathogenic/pathogenic variants in 13 of the cases, of which 6 were large deletions, four were InDels, two were deep intronic variants, one had retrotransposon insertion in either TSC1 or TSC2, and one was complex rearrangement. Furthermore, there was a de novo Alu element insertion with a high suspicion of pathogenicity that was classified as a variant of unknown significance. Conclusion: Our findings expand the current knowledge of known pathogenic variants related to tuberous sclerosis, particularly uncovering mosaic complex structural variations and retrotransposon insertions that have not been previously reported in tuberous sclerosis. Our findings suggest a higher prevalence of mosaicism among tuberous sclerosis patients than previously recognized. Our results indicate that long-read sequencing is a valuable approach for tuberous sclerosis cases with no mutation identified (NMI). [ABSTRACT FROM AUTHOR]

A glioma is a solid brain tumor which originates in the brain or brain stem area. The diagnosis of gliomas based on standard-of-care (SOC) techniques includes karyotyping, fluorescence in situ hybridization (FISH), and chromosomal microarray (CMA), for detecting the pathogenic variants and chromosomal abnormalities. But these techniques do not reveal the complete picture of genetic complexity, thus requiring an alternative technology for better characterization of these tumors. The present study aimed to evaluate the clinical performance and feasibility of using optical genome mapping (OGM) for chromosomal characterization of gliomas. Herein, we evaluated 10 cases of gliomas that were previously characterized by CMA. OGM analysis showed concordance with the results of CMA in identifying the characterized Structural Variants (SVs) in these cases. More notably, it also revealed additional clinically relevant aberrations, demonstrating a higher resolution and sensitivity. These clinically relevant SVs included cryptic translocation, and SVs which are beyond the detection capabilities of CMA. Our analysis highlights the unique capability of OGM to detect all classes of SVs within a single assay, thereby unveiling clinically significant data with a shorter turnaround time. Adopting this diagnostic tool as a standard of care for solid tumors like gliomas shows potential for improving therapeutic management, potentially leading to more personalized and timely interventions for patients. [ABSTRACT FROM AUTHOR]

Background: Structural variants (SVs) are currently analyzed using a combination of conventional methods; however, this approach has limitations. Optical genome mapping (OGM), an emerging technology for detecting SVs using a single-molecule strategy, has the potential to replace conventional methods. We compared OGM with conventional diagnostic methods for detecting SVs in various hematologic malignancies. Methods: Residual bone marrow aspirates from 27 patients with hematologic malignancies in whom SVs were observed using conventional methods (chromosomal banding analysis, FISH, an RNA fusion panel, and reverse transcription PCR) were analyzed using OGM. The concordance between the OGM and conventional method results was evaluated. Results: OGM showed concordance in 63% (17/27) and partial concordance in 37% (10/27) of samples. OGM detected 76% (52/68) of the total SVs correctly (concordance rate for each type of SVs: aneuploidies, 83% [15/18]; balanced translocation, 80% [12/15] unbalanced translocation, 54% [7/13] deletions, 81% [13/16]; duplications, 100% [2/2] inversion 100% [1/1]; insertion, 100% [1/1]; marker chromosome, 0% [0/1]; isochromosome, 100% [1/1]). Sixteen discordant results were attributed to the involvement of centromeric/telomeric regions, detection sensitivity, and a low mapping rate and coverage. OGM identified additional SVs, including submicroscopic SVs and novel fusions, in five cases. Conclusions: OGM shows a high level of concordance with conventional diagnostic methods for the detection of SVs and can identify novel variants, suggesting its potential utility in enabling more comprehensive SV analysis in routine diagnostics of hematologic malignancies, although further studies and improvements are required. [ABSTRACT FROM AUTHOR]

Summary: Background: Fuchs endothelial corneal dystrophy (FECD) is the most common repeat-mediated disease in humans. It exclusively affects corneal endothelial cells (CECs), with ≤81% of cases associated with an intronic TCF4 triplet repeat (CTG18.1). Here, we utilise optical genome mapping (OGM) to investigate CTG18.1 tissue-specific instability to gain mechanistic insights. Methods: We applied OGM to a diverse range of genomic DNAs (gDNAs) from patients with FECD and controls (n = 43); CECs, leukocytes and fibroblasts. A bioinformatics pipeline was developed to robustly interrogate CTG18.1-spanning DNA molecules. All results were compared with conventional polymerase chain reaction-based fragment analysis. Findings: Analysis of bio-samples revealed that expanded CTG18.1 alleles behave dynamically, regardless of cell-type origin. However, clusters of CTG18.1 molecules, encompassing ∼1800–11,900 repeats, were exclusively detected in diseased CECs from expansion-positive cases. Additionally, both progenitor allele size and age were found to influence the level of leukocyte-specific CTG18.1 instability. Interpretation: OGM is a powerful tool for analysing somatic instability of repeat loci and reveals here the extreme levels of CTG18.1 instability occurring within diseased CECs underpinning FECD pathophysiology, opening up new therapeutic avenues for FECD. Furthermore, these findings highlight the broader translational utility of FECD as a model for developing therapeutic strategies for rarer diseases similarly attributed to somatically unstable repeats. Funding: UK Research and Innovation, Moorfields Eye Charity, Fight for Sight, Medical Research Council, NIHR BRC at Moorfields Eye Hospital and UCL Institute of Ophthalmology, Grantová Agentura České Republiky, Univerzita Karlova v Praze, the National Brain Appeal’s Innovation Fund and Rosetrees Trust.

The article in the Annals of Hematology discusses a case study of a 77-year-old man diagnosed with acute monocytic leukemia. The patient had a complex karyotype with various chromosomal abnormalities, including a KMT2A:ARHGEF12 fusion gene. Optical Genome Mapping (OGM) was used to identify the fusion gene, which was missed by traditional cytogenetic and molecular analyses. The rare KMT2A:ARHGEF12 fusion is associated with poor prognosis in hematological malignancies, highlighting the importance of advanced genetic technologies for accurate diagnosis and potential targeted therapies. [Extracted from the article]

Ying Wang, Shaohua Bi, Xiaoqing Shi, Liying Dai Division of Neonatology, Anhui Provincial Children’s Hospital, Hefei, Anhui, 230051, People’s Republic of ChinaCorrespondence: Liying Dai, Division of Neonatology, Anhui Province Children’s Hospital, No. 39, Wangjiang East Road, Baohe District, Hefei, Anhui, 230051, People’s Republic of China, Email dailiying1101@163.comAbstract: Optical Genome Mapping (OGM) technology has garnered growing interest for the identification of chromosomal structural variations (SVs), particularly complex ones that are implicated in genetic diseases in humans. In this study, we performed genetic diagnostics on a neonatal patient who presented with feeding difficulties, hypotonia, and an atrial septal defect. We utilized a combination of trio-whole exome sequencing and OGM for our analysis. The results revealed an unbalanced translocation between maternal chromosomes 4 and 6 in the proband, ogm[GRch38]t(4:6)(q35.2;q25.3), resulting in a 2.8 Mb deletion at the 4q35 terminal and a 10.2 Mb duplication at the 6q25 terminal. In summary, this study highlights how OGM, in conjunction with other genetic approaches, can unveil the genetic etiology of complex clinical syndromes. Neonatal patients often exhibit low specific phenotypes, underlining the significance of SV detection.Keywords: optical genome mapping, unbalanced translocation, copy number variations, neonatal diseases

Abstract While short-read sequencing currently dominates genetic research and diagnostics, it frequently falls short of capturing certain structural variants (SVs), which are often implicated in the etiology of neurodevelopmental disorders (NDDs). Optical genome mapping (OGM) is an innovative technique capable of capturing SVs that are undetectable or challenging-to-detect via short-read methods. This study aimed to investigate NDDs using OGM, specifically focusing on cases that remained unsolved after standard exome sequencing. OGM was performed in 47 families using ultra-high molecular weight DNA. Single-molecule maps were assembled de novo, followed by SV and copy number variant calling. We identified 7 variants of interest, of which 5 (10.6%) were classified as likely pathogenic or pathogenic, located in BCL11A, OPHN1, PHF8, SON, and NFIA. We also identified an inversion disrupting NAALADL2, a gene which previously was found to harbor complex rearrangements in two NDD cases. Variants in known NDD genes or candidate variants of interest missed by exome sequencing mainly consisted of larger insertions (> 1kbp), inversions, and deletions/duplications of a low number of exons (1–4 exons). In conclusion, in addition to improving molecular diagnosis in NDDs, this technique may also reveal novel NDD genes which may harbor complex SVs often missed by standard sequencing techniques.

While balanced reciprocal translocations are relatively common, they often remain clinically silent unless they lead to the disruption of functional genes. In this study, we present the case of a boy exhibiting developmental delay and mild intellectual disability. Initial karyotyping revealed a translocation t(5;6)(q13;q23) between chromosomes 5 and 6 with limited resolution. Optical genome mapping (OGM) enabled a more precise depiction of the breakpoint regions involved in the reciprocal translocation. While the breakpoint region on chromosome 6 did not encompass any known gene, OGM revealed the disruption of the RASGRF2 (Ras protein-specific guanine nucleotide releasing factor 2) gene on chromosome 5, implicating RASGRF2 as a potential candidate gene contributing to the observed developmental delay in the patient. Variations in RASGRF2 have so far not been reported in developmental delay, but research on the RASGRF2 gene underscores its significance in various aspects of neurodevelopment, including synaptic plasticity, signaling pathways, and behavioral responses. This study highlights the utility of OGM in identifying breakpoint regions, providing possible insights into the understanding of neurodevelopmental disorders. It also helps affected individuals in gaining more knowledge about potential causes of their conditions. [ABSTRACT FROM AUTHOR]

While short-read sequencing currently dominates genetic research and diagnostics, it frequently falls short of capturing certain structural variants (SVs), which are often implicated in the etiology of neurodevelopmental disorders (NDDs). Optical genome mapping (OGM) is an innovative technique capable of capturing SVs that are undetectable or challenging-to-detect via short-read methods. This study aimed to investigate NDDs using OGM, specifically focusing on cases that remained unsolved after standard exome sequencing. OGM was performed in 47 families using ultra-high molecular weight DNA. Single-molecule maps were assembled de novo, followed by SV and copy number variant calling. We identified 7 variants of interest, of which 5 (10.6%) were classified as likely pathogenic or pathogenic, located in BCL11A, OPHN1, PHF8, SON, and NFIA. We also identified an inversion disrupting NAALADL2, a gene which previously was found to harbor complex rearrangements in two NDD cases. Variants in known NDD genes or candidate variants of interest missed by exome sequencing mainly consisted of larger insertions (> 1kbp), inversions, and deletions/duplications of a low number of exons (1–4 exons). In conclusion, in addition to improving molecular diagnosis in NDDs, this technique may also reveal novel NDD genes which may harbor complex SVs often missed by standard sequencing techniques. [ABSTRACT FROM AUTHOR]

This article discusses a case study of a 57-year-old Han Chinese male with dopa-responsive dystonia (DRD) caused by a large inversion affecting the GCH1 gene. The patient experienced abnormal head posturing and gait disturbance following a head injury at age 10. Despite not having an identifiable disease-causing variant through conventional gene sequencing, the patient responded well to low-dose levodopa treatment. The study highlights the importance of using whole genome sequencing, nanopore long-read sequencing, and optical genome mapping to detect and confirm complex structural variants in patients with DRD. [Extracted from the article]

Cytogenetic studies are essential in the diagnosis and follow up of patients with bone marrow failure syndromes (BMFSs), but obtaining good quality results is often challenging due to hypocellularity. Optical Genome Mapping (OGM), a novel technology capable of detecting most types chromosomal structural variants (SVs) at high resolution, is being increasingly used in many settings, including hematologic malignancies. Herein, we compared conventional cytogenetic techniques to OGM in 20 patients with diverse BMFSs. Twenty metaphases for the karyotype were only obtained in three subjects (15%), and no SVs were found in any of the samples. One patient with culture failure showed a gain in chromosome 1q by fluorescence in situ hybridization, which was confirmed by OGM. In contrast, OGM provided good quality results in all subjects, and SVs were detected in 14 of them (70%), mostly corresponding to cryptic submicroscopic alterations not observed by standard techniques. Therefore, OGM emerges as a powerful tool that provides complete and evaluable results in hypocellular BMFSs, reducing multiple tests into a single assay and overcoming some of the main limitations of conventional techniques. Furthermore, in addition to confirming the abnormalities detected by conventional techniques, OGM found new alterations beyond their detection limits. [ABSTRACT FROM AUTHOR]

During the last five decades, chromosome analysis identified recurring translocations and inversions in leukemias and lymphomas, which led to cloning of genes at the breakpoints that contribute to oncogenesis. Such molecular cytogenetic methods as fluorescence in situ hybridization (FISH), copy number (CN) arrays or optical genome mapping (OGM) have augmented standard chromosome analysis. The use of both cytogenetic and molecular methods, such as reverse transcription-polymerase chain reaction (RT-PCR) and next generation sequencing (NGS), including whole-genome sequencing (WGS), discloses alterations that not only delineate separate WHO disease entities but also constitute independent prognostic factors, whose use in the clinic improves management of patients with hematologic neoplasms. [ABSTRACT FROM AUTHOR]

Background: Despite recent advances in prenatal genetic diagnosis, medical geneticists still face considerable difficulty in interpreting the clinical outcome of copy‐number‐variant duplications and defining the mechanisms underlying the formation of certain chromosomal rearrangements. Optical genome mapping (OGM) is an emerging cytogenomic tool with proved ability to identify the full spectrum of cytogenetic aberrations. Methods: Here, we report on the use of OGM in a prenatal diagnosis setting. Detailed breakpoint mapping was used to determine the relative orientations of triplicated and duplicated segments in two unrelated foetuses harbouring chromosomal aberrations: a de novo 15q23q24.2 triplication and a paternally inherited 13q14.2 duplication that overlapped partially with the RB1 gene. Results: OGM enabled us to suggest a plausible mechanism for the triplication and confirmed that the RB1 duplication was direct oriented and in tandem. This enabled us to predict the pathogenic consequences, refine the prognosis and adapt the follow‐up and familial screening appropriately. Conclusion: Along with an increase in diagnostic rates, OGM can rapidly highlight genotype–phenotype correlations, improve genetic counselling and significantly influence prenatal management. [ABSTRACT FROM AUTHOR]

ABSTRACT Background X‐linked recessive type 3 Charcot–Marie–Tooth (CMTX3) is a rare subtype of childhood‐onset CMT. To date, all reported CMTX3 patients share a common founder 78 kb insertion from chromosome 8 into the Xq27.1 palindrome region. Methods We conducted patient–parent trio optical genome mapping (OGM) on a male patient presenting with clinically diagnosed Dejerine–Sottas disease for whom initial standard diagnostic genetic tests, including whole‐genome sequencing (WGS), yielded negative results. Results OGM analysis revealed a maternally inherited interchromosomal insertion from chromosome region 7q31.1 into Xq27.1. Coupled with manual reassessment of WGS data, this confirmed the molecular diagnosis of atypical CMTX3 and showed that the 122.4 kb inserted fragment contained DLD and partially LAMB1. Subsequent analyses confirmed that the rearrangement had arisen de novo in the proband's mother. Conclusion We report the second Xq27.1 rearrangement associated with CMTX3, providing novel clinical insights into its phenotypic and genotypic spectrum. Our findings highlight the importance of including genomic rearrangement analysis of Xq27.1 in standard diagnostic pipelines for childhood‐onset CMT. Given the overlap in polyneuropathy phenotypes resulting from insertions from chromosomes 7 and 8 into the same Xq27.1 palindrome region, the pathogenic mechanism underlying peripheral neuropathy in CMTX3 likely involves dysregulation of genes within this region.

We report an index patient with complete insensitivity to pain and a history of painless fractures, joint hypermobility, and behavioral problems. The index patient descends from a family with notable cases among his maternal relatives, including his aunt and his mother’s first cousin, both of whom suffer from congenital insensitivity to pain. The patient had normal results for prior genetic testing: fragile-X syndrome testing, chromosomal microarray analysis, and exome sequencing. Optical genome mapping detected a homozygous deletion affecting the noncoding 5′ untranslated region (UTR) and the first non-coding exon of the SCN9A gene in all affected family members, compatible with recessive disease transmission. Pathogenic homozygous loss-of-function variants in the SCN9A gene are associated with impaired pain sensation in humans. Optical genome mapping can thus detect pathogenic structural variants in patients without molecular etiology by standard diagnostic procedures and is a more accessible diagnostic tool than short-read or long-read whole-genome sequencing.

Abstract Chromosomal structural rearrangements consist of anomalies in genomic architecture that may or may not be associated with genetic material gain and loss. Evaluating the precise breakpoint is crucial from a diagnostic point of view, highlighting possible gene disruption and addressing to appropriate genotype–phenotype association. Structural rearrangements can either occur randomly within the genome or present with a recurrence, mainly due to peculiar genomic features of the surrounding regions. We report about three non-related individuals, harboring chromosomal structural rearrangements interrupting SETBP1, leading to gene haploinsufficiency. Two out of them resulted negative to Chromosomal Microarray Analysis (CMA), being the rearrangement balanced at a microarray resolution. The third one, presenting with a complex three-chromosome rearrangement, had been previously diagnosed with SETBP1 haploinsufficiency due to a partial gene deletion at one of the chromosomal breakpoints. We thoroughly characterized the rearrangements by means of Optical Genome Mapping (OGM) and Whole Genome Sequencing (WGS), providing details about the involved sequences and the underlying mechanisms. We propose structural variants as a recurrent event in SETBP1 haploinsufficiency, which may be overlooked by laboratory routine genomic analyses (CMA and Whole Exome Sequencing) or only partially determined when associated with genomic losses at breakpoints. We finally introduce a possible role of SETBP1 in a Noonan-like phenotype.

Genome editing, notably CRISPR (cluster regularly interspaced short palindromic repeats)/Cas9 (CRISPR-associated protein 9), has revolutionized genetic engineering allowing for precise targeted modifications. This technique's combination with human induced pluripotent stem cells (hiPSCs) is a particularly valuable tool in cerebral organoid (CO) research. In this study, CRISPR/Cas9-generated fluorescently labeled hiPSCs exhibited no significant morphological or growth rate differences compared with unedited controls. However, genomic aberrations during gene editing necessitate efficient genome integrity assessment methods. Optical genome mapping, a high-resolution genome-wide technique, revealed genomic alterations, including chromosomal copy number gain and losses affecting numerous genes. Despite these genomic alterations, hiPSCs retain their pluripotency and capacity to generate COs without major phenotypic changes but one edited cell line showed potential neuroectodermal differentiation impairment. Thus, this study highlights optical genome mapping in assessing genome integrity in CRISPR/Cas9-edited hiPSCs emphasizing the need for comprehensive integration of genomic and morphological analysis to ensure the robustness of hiPSC-based models in cerebral organoid research. [ABSTRACT FROM AUTHOR]

Structural variants drive tumorigenesis by disrupting normal gene function through insertions, inversions, translocations, and copy number changes, including deletions and duplications. Detecting structural variants is crucial for revealing their roles in tumor development, clinical outcomes, and personalized therapy. Presently, most studies rely on short-read data from next-generation sequencing that aligns back to a reference genome to determine if and, if so, where a structural variant occurs. However, structural variant discovery by short-read sequencing is challenging, primarily because of the difficulty in mapping regions of repetitive sequences. Optical genome mapping (OGM) is a recent technology used for imaging and assembling long DNA strands to detect structural variations. To capture the structural variant landscape more thoroughly in the human genome, we developed an integrated pipeline that combines Bionano OGM and Illumina whole-genome sequencing and applied it to samples from 29 pediatric B-ALL patients. The addition of OGM allowed us to identify 511 deletions, 506 insertions, 93 duplications/gains, and 145 translocations that were otherwise missed in the short-read data. Moreover, we identified several novel gene fusions, the expression of which was confirmed by RNA sequencing. Our results highlight the benefit of integrating OGM and short-read detection methods to obtain a comprehensive analysis of genetic variation that can aid in clinical diagnosis, provide new therapeutic targets, and improve personalized medicine in cancers driven by structural variation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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Genetic predisposition is one of the major risk factors for pediatric cancer, with ~10% of children being carriers of a predisposing germline alteration. It is likely that this is the tip of the iceberg and many children are underdiagnosed, as most of the analysis focuses on single or short nucleotide variants, not considering the full spectrum of DNA alterations. Hence, we applied optical genome mapping (OGM) to our cohort of 34 pediatric cancer patients to perform an unbiased germline screening and analyze the frequency of structural variants (SVs) and their impact on cancer predisposition. All children were clinically highly suspicious for germline alterations (concomitant conditions or congenital anomalies, positive family cancer history, particular cancer type, synchronous or metachronous tumors), but whole exome sequencing (WES) had failed to detect pathogenic variants in cancer predisposing genes. OGM detected a median of 49 rare SVs (range 27‐149) per patient. By analysis of 18 patient‐parent trios, we identified three de novo SVs. Moreover, we discovered a likely pathogenic deletion of exon 3 in the known cancer predisposition gene BRCA2, and identified a duplication in RPA1, which might represent a new cancer predisposition gene. We conclude that optical genome mapping is a suitable tool for detecting potentially predisposing SVs in addition to WES in pediatric cancer patients. [ABSTRACT FROM AUTHOR]

Objective: Facioscapulohumeral muscular dystrophy type 1 (FSHD1) is one of the most common forms of autosomal-dominant muscular dystrophies characterized by variable disease penetrance due to shortened D4Z4 repeat units on 4q35. Themolecular diagnosis of FSHD1 is usuallymade by Southern blotting, which is complex, time-consuming, and lacks clinical practicality. Therefore, in this study, optical genome mapping (OGM) is employed for the genetic diagnosis of FSHD1. Furthermore, epigenetic heterogeneity is determined from methylation analysis. Methods: Genomic DNA samples from four members of the same family were subjected to whole-exome sequencing. OGM was used to identify structural variations in D4Z4, while sodium bisulfite sequencing helped identify the methylation levels of CpG sites in a region located distally to the D4Z4 array. A multidisciplinary team collected the clinical data, and comprehensive family analyses aided in the assessment of phenotypes and genotypes. Results: Whole-exome sequencing did not reveal variants related to clinical phenotypes in the patients. OGM showed that the proband was a compound heterozygote for the 4qA allele with four and eight D4Z4 repeat units, whereas the affected younger brother had only one 4qA allele with four D4Z4 repeat units. Both the proband and her younger brother were found to display asymmetric weakness predominantly involving the facial, shoulder girdle, and upper arm muscles, whereas the younger brother had more severe clinical symptoms. The proband's father, who was found to be normal after a neurological examination, also carried the 4qA allele with eight D4Z4 repeat units. The unaffected mother exhibited 49 D4Z4 repeat units of the 4qA allele and a minor mosaic pattern with four D4Z4 repeat units of the 4qA allele. Consequently, the presence of the 4qA allele in the four D4Z4 repeat units strongly pointed to the occurrence of maternal germline mosaicism. The CpG6 methylation levels were lower in symptomatic patients compared to those in the asymptomatic parents. The older sister had lower clinical scores and ACSS and higher CpG6 methylation levels than that of her younger brother. Conclusions: In this study, two siblings with FSHD1 with phenotypically normal parents were identified by OGM. Our findings suggest that the 4qA allele of four D4Z4 repeats was inherited through maternal germline mosaicism. The clinical phenotype heterogeneity is influenced by the CpG6 methylation levels. The results of this study greatly aid in the molecular diagnosis of FSHD1 and in also understanding the clinical phenotypic variability underlying the disease. [ABSTRACT FROM AUTHOR]

Marfan syndrome (MFS) is an autosomal dominant connective tissue disorder due to pathogenic variants in Fibrillin‐1 (FBN1) affecting nearly one in every 10,000 individuals. We report a 16‐month‐old female with early‐onset MFS heterozygous for an 11.2 kb de novo duplication within the FBN1 gene. Tandem location of the duplication was further confirmed by optical genome mapping in addition to genetic sequencing and chromosomal microarray. This is the third reported case of a large multi‐exon duplication in FBN1, and the only one confirmed to be in tandem. As the vast majority of pathogenic variants associated with MFS are point mutations, this expands the landscape of known FBN1 pathogenic variants and supports consistent use of genetic testing strategies that can detect large, indel‐type variants. [ABSTRACT FROM AUTHOR]

Simple Summary: Whilst association of genetic mutations with targeted therapies is common in leukemia, to our knowledge, no one has associated genomic structural variants with drug sensitivities. Here we use optical genome mapping as an unbiased, genome-wide detection method for structural variants and show that some of these events are associated with sensitivity or resistance to clinically relevant anti-cancer drugs. Acute leukemia is a particularly problematic collection of hematological cancers, and, while somewhat rare, the survival rate of patients is typically abysmal without bone marrow transplantation. Furthermore, traditional chemotherapies used as standard-of-care for patients cause significant side effects. Understanding the evolution of leukemia to identify novel targets and, therefore, drug treatment regimens is a significant medical need. Genomic rearrangements and other structural variations (SVs) have long been known to be causative and pathogenic in multiple types of cancer, including leukemia. These SVs may be involved in cancer initiation, progression, clonal evolution, and drug resistance, and a better understanding of SVs from individual patients may help guide therapeutic options. Here, we show the utilization of optical genome mapping (OGM) to detect known and novel SVs in the samples of patients with leukemia. Importantly, this technology provides an unprecedented level of granularity and quantitation unavailable to other current techniques and allows for the unbiased detection of novel SVs, which may be relevant to disease pathogenesis and/or drug resistance. Coupled with the chemosensitivities of these samples to FDA-approved oncology drugs, we show how an impartial integrative analysis of these diverse datasets can be used to associate the detected genomic rearrangements with multiple drug sensitivity profiles. Indeed, an insertion in the gene MUSK is shown to be associated with increased sensitivity to the clinically relevant agent Idarubicin, while partial tandem duplication events in the KMT2A gene are related to the efficacy of another frontline treatment, Cytarabine. [ABSTRACT FROM AUTHOR]

Optical genome mapping (OGM) has been known as an all-in-one technology for chromosomal aberration detection. However, there are also aberrations beyond the detection range of OGM. This study aimed to report the aberrations missed by OGM and analyze the contributing factors. OGM was performed by taking both GRCh37 and GRCh38 as reference genomes. The OGM results were analyzed in blinded fashion and compared to standard assays. Quality control (QC) metrics, sample types, reference genome, effective coverage and classes and locations of aberrations were then analyzed. In total, 154 clinically reported variations from 123 samples were investigated. OGM failed to detect 10 (6.5%, 10/154) aberrations with GRCh37 assembly, including five copy number variations (CNVs), two submicroscopic balanced translocations, two pericentric inversion and one isochromosome (mosaicism). All the samples passed pre-analytical and analytical QC. With GRCh38 assembly, the false-negative rate of OGM fell to 4.5% (7/154). The breakpoints of the CNVs, balanced translocations and inversions undetected by OGM were located in segmental duplication (SD) regions or regions with no DLE-1 label. In conclusion, besides variations with centromeric breakpoints, structural variations (SVs) with breakpoints located in large repetitive sequences may also be missed by OGM. GRCh38 is recommended as the reference genome when OGM is performed. Our results highlight the necessity of fully understanding the detection range and limitation of OGM in clinical practice. [ABSTRACT FROM AUTHOR]

Background: Identifying cytogenetic changes in tumors can aid in diagnosis/prognosis and disease management. Complete cytogenetic characterization has historically required a multimethod/time‐consuming approach. Optical genome mapping (OGM) offers a potential solution to this challenge by detecting both balanced and unbalanced abnormalities in a single assay. Methods: Genetic changes acquired with tumor‐forming potential in a prostate xenograft subline [M2205] (derived from a Black male) that were detected using cytogenetic versus OGM analyses were compared to assess the utility of OGM for analyzing solid tumors. Results: Cytogenetic/OGM concordance was noted for (a) copy number gains (16, 1p, 3q, 5q, 7p, 8q, 9q, 11p, 11q, 15q, 20q), (b) copy number losses (Y, 3p, 4p, 6p, 7p, 9p, 11q), and (c) structural changes, including multibreak rearrangements. Discordance was noted for two structural findings, both of which had breakpoints localized to repetitive sequences. The OGM studies identified new findings and confirmed/further characterized 8q24 structural abnormalities. It also detected genes gained/disrupted in the 8q24 region (e.g., MYC, DEPTOR, and EXT1); but recognizing a jumping translocation required cytogenetic analyses. Conclusion: These results support using OGM as a tool to analyze solid tumors in clinical/research settings. Moreover, this OGM analysis expanded the characterization of cytogenetic changes present in the M2205 subline, including alterations associated with tumors from Black males diagnosed with prostate cancer. [ABSTRACT FROM AUTHOR]

Abstract Background Despite recent advances in prenatal genetic diagnosis, medical geneticists still face considerable difficulty in interpreting the clinical outcome of copy‐number‐variant duplications and defining the mechanisms underlying the formation of certain chromosomal rearrangements. Optical genome mapping (OGM) is an emerging cytogenomic tool with proved ability to identify the full spectrum of cytogenetic aberrations. Methods Here, we report on the use of OGM in a prenatal diagnosis setting. Detailed breakpoint mapping was used to determine the relative orientations of triplicated and duplicated segments in two unrelated foetuses harbouring chromosomal aberrations: a de novo 15q23q24.2 triplication and a paternally inherited 13q14.2 duplication that overlapped partially with the RB1 gene. Results OGM enabled us to suggest a plausible mechanism for the triplication and confirmed that the RB1 duplication was direct oriented and in tandem. This enabled us to predict the pathogenic consequences, refine the prognosis and adapt the follow‐up and familial screening appropriately. Conclusion Along with an increase in diagnostic rates, OGM can rapidly highlight genotype–phenotype correlations, improve genetic counselling and significantly influence prenatal management.

A glioma is a solid brain tumor which originates in the brain or brain stem area. The diagnosis of gliomas based on standard-of-care (SOC) techniques includes karyotyping, fluorescence in situ hybridization (FISH), and chromosomal microarray (CMA), for detecting the pathogenic variants and chromosomal abnormalities. But these techniques do not reveal the complete picture of genetic complexity, thus requiring an alternative technology for better characterization of these tumors. The present study aimed to evaluate the clinical performance and feasibility of using optical genome mapping (OGM) for chromosomal characterization of gliomas. Herein, we evaluated 10 cases of gliomas that were previously characterized by CMA. OGM analysis showed concordance with the results of CMA in identifying the characterized Structural Variants (SVs) in these cases. More notably, it also revealed additional clinically relevant aberrations, demonstrating a higher resolution and sensitivity. These clinically relevant SVs included cryptic translocation, and SVs which are beyond the detection capabilities of CMA. Our analysis highlights the unique capability of OGM to detect all classes of SVs within a single assay, thereby unveiling clinically significant data with a shorter turnaround time. Adopting this diagnostic tool as a standard of care for solid tumors like gliomas shows potential for improving therapeutic management, potentially leading to more personalized and timely interventions for patients.

Purpose: Although chromosome 21 is the smallest human chromosome, it is highly relevant in the pathogenicity of both cancer and congenital diseases, including Alzheimer disease and trisomy 21 (Down syndrome). In addition, cases with rare structural variants (SVs) of chromosome 21 have been reported. These events vary in size and include large chromosomal events, such as ring chromosomes and small partial aneuploidies. The p-arm of the acrocentric chromosome 21 was devoid of reference genomic sequence in GRCh37 and GRCh38, which hampered our ability to solve genomic rearrangements and find the mechanism of formation of disease-causing SVs. We hypothesize that conserved satellite structures and segmental duplications located on the p-arm play an important role in the formation of complex SVs involving chromosome 21. Methods: Three cases with complex chromosome 21 rearrangements were studied with a combination of short-read and long-read genome sequencing, as well as optical genome mapping. The data were aligned to the T2T-CHM13 assembly. Results: We were able to resolve all 3 complex chromosome 21 rearrangements in which 15, 8, and 26 breakpoints were identified, respectively. By comparing the identified SV breakpoints, we were able to pinpoint a region between 21p13 and 21p12 that appears to be frequently involved in chromosome 21 rearrangements. Importantly, we observed acrocentric satellite DNA at several breakpoint junctions suggesting an important role for those elements in the formation of complex SVs. Conclusion: Taken together, our results provide further insights into the architecture and underlying mechanisms of complex rearrangements on acrocentric chromosomes.

Optical genome mapping (OGM) is an alternative to classical cytogenetic techniques to improve the detection rate of clinically significant genomic abnormalities. The isolation of high-molecular-weight (HMW) DNA is critical for a successful OGM analysis. HMW DNA quality depends on tissue type, sample size, and storage conditions. We assessed the feasibility of OGM analysis of DNA from nine umbilical cord (UC) and six chorionic villus (CV) samples collected after the spontaneous or therapeutic termination of pregnancy. We analyzed quality control metrics provided by the Saphyr system (Bionano Genomics) and assessed the length of extracted DNA molecules using pulsed-field capillary electrophoresis. OMG data were successfully analyzed for all six CV samples. Five of the UC samples did not meet the Saphyr quality criteria, mainly due to poor DNA quality. In this regard, we found that DNA quality assessment with pulsed-field capillary electrophoresis can predict a successful OGM analysis. OGM data were fully concordant with the results of standard cytogenetic methods. Moreover, OGM detected an average of 14 additional structural variants involving OMIM genes per sample. On the basis of our results, we established the optimal conditions for sample storage and preparation required for a successful OGM analysis. We recommend checking DNA quality before analysis with pulsed-field capillary electrophoresis if the storage conditions were not ideal or if the quality of the sample is poor. OGM can therefore be performed on fetal tissue harvested after the termination of pregnancy, which opens up the perspective for improved diagnostic yield. [ABSTRACT FROM AUTHOR]

Standard cytogenetic techniques (chromosomal banding analysis—CBA, and fluorescence in situ hybridization—FISH) show limits in characterizing complex chromosomal rearrangements and structural variants arising from two or more chromosomal breaks. In this study, we applied optical genome mapping (OGM) to fully characterize two cases of complex chromosomal rearrangements at high resolution. In case 1, an acute myeloid leukemia (AML) patient showing chromothripsis, OGM analysis was fully concordant with classic cytogenetic techniques and helped to better refine chromosomal breakpoints. The OGM results of case 2, a patient with non-Hodgkin lymphoma, were only partially in agreement with previous cytogenetic analyses and helped to better define clonal heterogeneity, overcoming the bias related to clonal selection due to cell culture of cytogenetic techniques. In both cases, OGM analysis led to the identification of molecular markers, helping to define the pathogenesis, classification, and prognosis of the analyzed patients. Despite extensive efforts to study hematologic diseases, standard cytogenetic methods display unsurmountable limits, while OGM is a tool that has the power to overcome these limitations and provide a cytogenetic analysis at higher resolution. As OGM also shows limits in defining regions of a repetitive nature, combining OGM with CBA to obtain a complete cytogenetic characterization would be desirable. [ABSTRACT FROM AUTHOR]

Facioscapulohumeral muscular dystrophy (FSHD) is the third most common hereditary muscular dystrophy, caused by the contraction of the D4Z4 repeats on the permissive 4qA haplotype on chromosome 4, resulting in the faulty expression of the DUX4 gene. Traditional diagnostics are based on Southern blotting, a time- and effort-intensive method that can be affected by single nucleotide variants (SNV) and copy number variants (CNV), as well as by the similarity of the D4Z4 repeats located on chromosome 10. We aimed to evaluate optical genome mapping (OGM) as an alternative molecular diagnostic method for the detection of FSHD. We first performed optical genome mapping with EnFocus™ FSHD analysis using DLE-1 labeling and the Saphyr instrument in patients with inconclusive diagnostic Southern blot results, negative FSHD2 results, and clinically evident FSHD. Second, we performed OGM in parallel with the classical Southern blot analysis for our prospectively collected new FSHD cases. Finally, panel exome sequencing was performed to confirm the presence of FSHD2. In two patients with diagnostically inconclusive Southern blot results, OGM was able to identify shortened D4Z4 repeats on the permissive 4qA alleles, consistent with the clinical presentation. The results of the prospectively collected patients tested in parallel using Southern blotting and OGM showed full concordance, indicating that OGM is a useful alternative to the classical Southern blotting method for detecting FSHD1. In a patient showing clinical FSHD but no shortened D4Z4 repeats in the 4qA allele using OGM or Southern blotting, a likely pathogenic variant in SMCHD1 was detected using exome sequencing, confirming FSHD2. OGM and panel exome sequencing can be used consecutively to detect FSHD2. [ABSTRACT FROM AUTHOR]

Purpose of Review: The length of telomeres, protective structures at the chromosome ends, is a well-established biomarker for pathological conditions including multisystemic syndromes called telomere biology disorders. Approaches to measure telomere length (TL) differ on whether they estimate average, distribution, or chromosome-specific TL, and each presents their own advantages and limitations. Recent Findings: The development of long-read sequencing and publication of the telomere-to-telomere human genome reference has allowed for scalable and high-resolution TL estimation in pre-existing sequencing datasets but is still impractical as a dedicated TL test. As sequencing costs continue to fall and strategies for selectively enriching telomere regions prior to sequencing improve, these approaches may become a promising alternative to classic methods. Summary: Measurement methods rely on probe hybridization, qPCR or more recently, computational methods using sequencing data. Refinements of existing techniques and new approaches have been recently developed but a test that is accurate, simple, and scalable is still lacking. [ABSTRACT FROM AUTHOR]

Facioscapulohumeral muscular dystrophy (FSHD) is the second most common muscular dystrophy in adults, and it is associated with local D4Z4 chromatin relaxation, mostly via the contraction of the D4Z4 macrosatellite repeat array on chromosome 4q35. In this study, we aimed to investigate the use of Optical Genome Mapping (OGM) as a diagnostic tool for testing FSHD cases from the UK and India and to compare OGM performance with that of traditional techniques such as linear gel (LGE) and Pulsed-field gel electrophoresis (PFGE) Southern blotting (SB). A total of 6 confirmed and 19 suspected FSHD samples were processed with LGE and PFGE, respectively. The same samples were run using a Saphyr Genome-Imaging Instrument (1-color), and the data were analysed using custom EnFocus FSHD analysis. OGM was able to confirm the diagnosis of FSHD1 in all FSHD1 cases positive for SB (n = 17), and D4Z4 sizing highly correlated with PFGE-SB (p < 0.001). OGM correctly identified cases with mosaicism for the repeat array contraction (n = 2) and with a duplication of the D4Z4 repeat array. OGM is a promising new technology able to unravel structural variants in the genome and seems to be a valid tool for diagnosing FSHD1. [ABSTRACT FROM AUTHOR]

Simple Summary: Copy number abnormalities (CNAs) are frequent in neuroblastoma and used to determine treatments. Little is known about the role of structural variants (SVs) in disease progression. Optical genome mapping (OGM) uses label patterns to scan the genome which can be used to identify SVs in cancer. Currently, the detection of SVs still relies on standard cytogenetic techniques. We investigated the utility of OGM to detect SVs in neuroblastoma cell lines and tumours and compared it with standard cytogenetic techniques. OGM confirmed known CNAs and identified novel SVs of potential clinical significance. Background: Neuroblastoma is the most common extracranial solid tumour in children, accounting for 15% of paediatric cancer deaths. Multiple genetic abnormalities have been identified as prognostically significant in neuroblastoma patients. Optical genome mapping (OGM) is a novel cytogenetic technique used to detect structural variants, which has not previously been tested in neuroblastoma. We used OGM to identify copy number and structural variants (SVs) in neuroblastoma which may have been missed by standard cytogenetic techniques. Methods: Five neuroblastoma cell lines (SH-SY5Y, NBLW, GI-ME-N, NB1691 and SK-N-BE2(C)) and two neuroblastoma tumours were analysed using OGM with the Bionano Saphyr® instrument. The results were analysed using Bionano Access software and compared to previous genetic analyses including G-band karyotyping, FISH (fluorescent in situ hybridisation), single-nucleotide polymorphism (SNP) array and RNA fusion panels for cell lines, and SNP arrays and whole genome sequencing (WGS) for tumours. Results: OGM detected copy number abnormalities found using previous methods and provided estimates for absolute copy numbers of amplified genes. OGM identified novel SVs, including fusion genes in two cell lines of potential clinical significance. Conclusions: OGM can reliably detect clinically significant structural and copy number variations in a single test. OGM may prove to be more time- and cost-effective than current standard cytogenetic techniques for neuroblastoma. [ABSTRACT FROM AUTHOR]