To evaluate the clinical value of optical genome mapping (OGM) for prenatal diagnosis in fetuses with structural anomalies.

OGM was performed prospectively in 204 cases of fetuses with structural anomalies. Detection rates of OGM were investigated. Subgroup analysis was then conducted.

Overall, pathogenic or likely pathogenic (P/LP) chromosome aberrations were identified in 28 (13.7%) fetuses with structural anomalies using OGM, including 12 with numerical chromosomal abnormalities, 14 with P/LP copy number variations (CNVs) and two with balanced chromosomal rearrangements. OGM structural variation (SV) algorithm provided the structure and breakpoint information for 17 SVs and revealed six deletions, six tandem direct duplications, one inverted duplication, one paired duplication flanking a cryptic inversion and three balanced chromosomal rearrangements (one likely benign and two with breakpoints disrupting OMIM Morbid gene associated with dominant inheritance disorders). The diagnostic yields of OGM in the cystic hygroma group and multisystem malformation group were both significantly higher than those in other groups (35.7% vs. 10.3%, adjusted p = 0.018; 31.3% vs. 10.3%, adjusted p = 0.04).

Our study suggests that OGM is a reliable, comprehensive and high-resolution technology with an acceptable turnaround time that is a powerful method for prenatal diagnosis in fetuses with structural anomalies.

Triplications involving 5q21.3q23.3 are rare, and a phenotype has not been established. Here, we present a 4-month-old male with dysmorphic facial features and congenital cardiac malformation. Chromosomal microarray identified a pathogenic triplication of 5q21.3q23.3 with chromosome analysis showing the extra 5q material inserted into 16q. Optical genome mapping (OGM) was performed to further characterize the triplication. We compared the clinical features of our proband with previous case reports of individuals with duplications or triplications in the region to identify a phenotype. Common features appear to include short stature, developmental delays, learning difficulties, and cardiac malformations. We discuss genes in the region with a reported role in cardiac development, hypothesize that the triplication may have resulted from microhomology-mediated break-induced replication, and discuss the utility and limitations of OGM in this case. To our knowledge, this is the first reported case of a de novo triplication of 5q21.3q23.3.

Senior-Løken syndrome is a rare ciliopathy characterized by retinal dystrophy and nephronophthisis. This autosomal recessive inherited disease is caused by pathogenic variants in several genes, including IQCB1. We present a Senior-Løken case that remained genetically unexplained after routine genetic testing, including exome and genome sequencing. To identify the genetic cause for this individual, a combination of innovative long-read technologies was employed. Using optical genome mapping, an intronic 6.2-kb insertion in IQCB1 was revealed. Validation by long-read genome sequencing determined that this insertion consisted of a LINE-1/ERV1-mobile element. The variant was found in trans with a pathogenic IQCB1 2-bp deletion previously identified by exome sequencing. To investigate the consequences of the insertion, targeted long-read RNA-sequencing was performed, revealing a complex splice defect causing the introduction of a premature stop codon. This finding suggests that mobile element insertions represent a yet underestimated variant type that is difficult to detect using short-read sequencing.

Short tandem repeats (STRs) are common variations in human genomes that frequently expand or contract, causing genetic disorders, mainly when expanded. Traditional diagnostic methods for identifying these expansions, such as repeat-primed PCR and Southern blotting, are often labor-intensive, locus-specific, and are unable to precisely determine long repeat expansions. Sequencing-based methods, although capable of genome-wide detection, are limited by inaccuracy (short-read technologies) and high associated costs (long-read technologies). This study evaluated optical genome mapping (OGM) as an efficient, accurate approach for measuring STR lengths and assessing somatic stability in 85 samples with known pathogenic repeat expansions in DMPK, CNBP, and RFC1, causing myotonic dystrophy types 1 and 2 and cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS), respectively. Three workflows-manual de novo assembly, local guided assembly (local-GA), and a molecule distance script-were applied, of which the latter two were developed as part of this study to assess the repeat sizes and somatic repeat stability. OGM successfully identified 84/85 (98.8%) of the pathogenic expansions, distinguishing between wild-type and expanded alleles or between two expanded alleles in recessive cases, with greater accuracy than standard of care (SOC) for long repeats and no apparent upper size limit. Notably, OGM detected somatic instability in a subset of DMPK, CNBP, and RFC1 samples. These findings suggest OGM could advance diagnostic accuracy for large repeat expansions, providing a more comprehensive genome-wide assay for repeat expansion disorders by measuring exact repeat lengths and somatic instability across multiple loci simultaneously.

The continued evolution of genomic technologies over the past few decades has revolutionized the field of neurogenetics, offering profound insights into the genetic underpinnings of neurological disorders. Identification of causal genes for numerous monogenic neurological conditions has informed key aspects of disease mechanisms and facilitated research into critical proteins and molecular pathways, laying the groundwork for therapeutic interventions. However, the question remains: has this transformative trend reached its zenith? In this review, we suggest that despite significant strides in genome sequencing and advanced computational analyses, there is still ample room for methodological refinement. We anticipate further major genetic breakthroughs corresponding with the increased use of long-read genomes, variant calling software, AI tools, and data aggregation databases. Genetic progress has historically been driven by technological advancements from the commercial sector, which are developed in response to academic research needs, creating a continuous cycle of innovation and discovery. This review explores the potential of genomic technologies to address the challenges of neurogenetic disorders. By outlining both established and modern resources, we aim to emphasize the importance of genetic technologies as we enter an era poised for discoveries.

Short tandem repeat (STR) sequences are highly variable DNA segments that significantly contribute to human neurodegenerative disorders, highlighting their crucial role in neuropsychiatric conditions. This article examines the pathogenicity of abnormal STRs and classifies tandem repeat expansion disorders(TREDs), emphasizing their genetic characteristics, mechanisms of action, detection methods, and associated animal models. STR expansions exhibit complex genetic patterns that affect the age of onset and symptom severity. These expansions disrupt gene function through mechanisms such as gene silencing, toxic gain-of-function mutations leading to RNA and protein toxicity, and the generation of toxic peptides via repeat-associated non-AUG (RAN) translation. Advances in sequencing technologies-from traditional PCR and Southern blotting to next-generation and long-read sequencing-have enhanced the accuracy of STR variation detection. Research utilizing these technologies has linked STR expansions to a range of neuropsychiatric disorders, including autism spectrum disorders and schizophrenia, highlighting their contribution to disease risk and phenotypic expression through effects on genes involved in neurodevelopment, synaptic function, and neuronal signaling. Therefore, further investigation is essential to elucidate the intricate interplay between STRs and neuropsychiatric diseases, paving the way for improved diagnostic and therapeutic strategies.

Complex chromosomal rearrangements (CCRs) are constitutive structural aberrations involving three or more chromosomal breaks on three or more chromosomes resulting from complex events such as fork stalling and template switching, microhomology-mediated break-induced repair, or breakage-fusion-bridge cycles.

Here we report an 11-year-old female that was referred to our outpatient clinics for learning disability and dysmorphic features. Due to clinical findings, karyotype analysis was done initially, and a CCR involving five chromosomes was detected. Fluorescence in situ hybridization (FISH) analysis and chromosomal microarray analysis were done subsequently. Balanced translocations were observed between chromosomes 1, 5, 7, and 10, a balanced paracentric inversion of chromosome 2, and two interstitial deletions in the long arm of the chromosome 5. Optical genome mapping was done to further investigate this exceptional CCR and a paracentric inversion that was associated with the two interstitial deletions was detected in the long arm of chromosome 5.

Molecular cytogenetic techniques, such as microarray and FISH, are essential for detecting copy number variations at CCRs that appear to be balanced by karyotyping. Nonetheless, optical genome mapping enhances the resolution offering a valuable complement to traditional cytogenetic techniques.

Technological advances such as next-generation sequencing (NGS) have enabled high-throughput assessment of the human genome, supporting the usage of genetic testing as a first-line tool across clinical medicine. Although individually rare, genetic causes account for end-stage renal disease in 10% to 15% of adults and 70% of children, and in many of these individuals, genetic testing can identify a specific etiology and meaningfully impact management. However, with numerous options for genetic testing available, nephrologists may feel uncomfortable integrating genetics into their clinical practice. Here, we aim to demystify the process of genetic test selection and highlight the opportunities for interdisciplinary collaboration between nephrologists and genetics professionals, thereby supporting precision medicine for patients with kidney disease. We first detail the various clinical genetic testing modalities, highlighting their technical advantages and limitations, and then discuss indications for their usage. Next, we provide a generalized workflow for genetic test selection among individuals with kidney disease and illustrate how this workflow can be applied to genetic test selection across diverse clinical contexts. We then discuss key areas related to the usage of genetic testing in clinical nephrology that merit further research and approaches to investigate them.

Decades of genetic association testing in human cohorts have provided important insights into the genetic architecture and biological underpinnings of complex traits and diseases. However, for certain traits, genome-wide association studies (GWAS) for common SNPs are approaching signal saturation, which underscores the need to explore other types of genetic variation to understand the genetic basis of traits and diseases. Copy number variation (CNV) is an important source of heritability that is well known to functionally affect human traits. Recent technological and computational advances enable the large-scale, genome-wide evaluation of CNVs, with implications for downstream applications such as polygenic risk scoring and drug target identification. Here, we review the current state of CNV-GWAS, discuss current limitations in resource infrastructure that need to be overcome to enable the wider uptake of CNV-GWAS results, highlight emerging opportunities and suggest guidelines and standards for future GWAS for genetic variation beyond SNPs at scale.

Here we describe a neonate exhibiting hypotonia, macrocephaly, renal cysts, and respiratory failure requiring tracheostomy and ventilator support. Genetic analysis via rapid genome sequencing (rGS) identified a loss on chromosome 4 encompassing polycystin-2 (PKD2) and a loss on chromosome 22 encompassing SH3 and Multiple Ankyrin Repeat Domains 3 (SHANK3), indicative of Phelan-McDermid syndrome. Further analysis via traditional karyotyping, Optical Genome Mapping (OGM), and PacBio long-read sequencing revealed a more complex landscape of chromosomal rearrangements in this individual, including a balanced 3;12 translocation, and an unbalanced 17;22 translocation. The proband's phenotypic presentation is thought to be the result of Phelan-McDermid syndrome and represents an expansion of the described phenotypes to include significant respiratory failure. This study underscores the challenges and importance of comprehensive genetic testing in elucidating complex presentations and highlights the need for complementary testing methods to overcome limitations in resolution.

The whole genome karyotype refers to the sequence of large chromosomal segments that make up an individual's genotype. karyotype analysis, which includes descriptions of aneuploidies and other rearrangements is crucial for understanding genetic risk factors, for diagnosis, treatment decisions, and genetic counseling linked to constitutional disorders. The current karyotyping standard is based on microscopic examination of chromosomes, a complex process that requires high expertise and offers Mb scale resolution. Optical Genome Mapping (OGM) technology can identify large DNA lesions in a cost-effective manner. In this paper, we developed OMKar, a method that uses OGM data to create a virtual karyotype. OMKar processes Structural (SV) and Copy Number (CN) Variants as inputs and encodes them into a compact breakpoint graph. It recomputes copy numbers using Integer Linear Programming to maintain CN balance and then identifies constrained Eulerian paths representing entire donor chromosomes. In tests using 38 whole genome simulations of constitutional disorders, OMKar reconstructed the karyotype with 88% precision and 95% recall on SV concordance and 95% Jaccard score on CN concordance. We applied OMKar to 50 prenatal, 41 postnatal, and 63 parental samples from ten different sites. OMKar reconstructed the correct karyotype in 144 out of 154 samples, covering 25 of 25 aneuploidies, 32 of 32 balanced translocations, and 72 of 82 unbalanced variations. Detected constitutional disorders included Cri-du-chat, Wolf-Hirschhorn, Prader-Willi deletions, Down, and Turner syndromes. Importantly, it identified a plausible genetic mechanism for five cases of constitutional disorder that were not detected by other technologies. Together, these results demonstrate the robustness of OMKar for OGM-based karyotyping. OMKar is publicly available at https://github.com/siavashre/OMKar .

Congenital Adrenal Hyperplasia (CAH), one of the most common inherited disorders, is caused by defects in adrenal steroidogenesis. It is potentially lethal if untreated and is associated with multiple comorbidities, including fertility issues, obesity, insulin resistance, and dyslipidemia. CAH can result from variants in multiple genes, but the most frequent cause is deletions and conversions in the segmentally duplicated RCCX module, which contains the CYP21A2 gene and a pseudogene. The molecular genetic test to identify pathogenic alleles is cumbersome, incomplete, and available from a limited number of laboratories. It requires testing parents for accurate interpretation, leading to healthcare inequity. Less severe forms are frequently misdiagnosed, and phenotype/genotype correlations incompletely understood. We explored whether emerging technologies could be leveraged to identify all pathogenic alleles of CAH, including phasing in proband-only cases. We targeted long-read sequencing outputs that would be practical in a clinical laboratory setting. Both HiFi-based and nanopore-based whole-genome long-read sequencing datasets could be mined to accurately identify pathogenic single-nucleotide variants, full gene deletions, fusions creating non-functional hybrids between the gene and pseudogene ("30-kb deletion"), as well as count the number of RCCX modules and phase the resulting multimodular haplotypes. On the Hi-Fi data set of 6 samples, the PacBio Paraphase tool was able to distinguish nine different mono-, bi-, and tri-modular haplotypes, as well as the 30-kb and whole gene deletions. To do the same on the ONT-Nanopore dataset, we designed a tool, Parakit, which creates an enriched local pangenome to represent known haplotype assemblies and map ClinVar pathogenic variants and fusions onto them. With few labels in the region, optical genome mapping was not able to reliably resolve module counts or fusions, although designing a tool to mine the dataset specifically for this region may allow doing so in the future. Both sequencing techniques yielded congruent results, matching clinically identified variants, and offered additional information above the clinical test, including phasing, count of RCCX modules, and status of the other module genes, all of which may be of clinical relevance. Thus long-read sequencing could be used to identify variants causing multiple forms of CAH in a single test.

Current standard-of-care (SOC) methods for genetic testing are capable of resolving deletions and sequence variants, but they mostly fail to provide information on the breakpoints of duplications and balanced structural variants (SV). However, this information may be necessary for their clinical assessment, especially if the carrier's phenotype is difficult to assess and/or carrier analysis of relatives is not viable. A promising approach to solving such challenging cases arises with access to optical genome mapping (OGM) but has not been systematically explored as of yet.

In this retrospective study, we evaluated diagnostic cases from a 1-year period (2023) in which an SV discovery by SOC methods (microarray, karyotyping and whole-exome sequencing) was followed up by OGM, with the objective to unlock clinically relevant information about the SV.

Seven cases were shown by SOC methods to bear potential pathogenic SVs and were consequently followed up by OGM. Of these, six were solved by the additional use of OGM alone. One case required sequencing after OGM analysis to further specify the SV's breakpoints. In all seven cases, OGM was crucial for determining the clinical relevance of the detected SV.

This study describes the use of OGM as a valuable method for characterising duplications and balanced SVs. Often, this additional information does not add to the quality of a clinical report. However, for a subset of patients, these data are critical, especially in the prenatal setting or when no familial analyses are possible.

Optical genome mapping (OGM) offers high consistency in simultaneously detecting structural and copy number variants. This study aimed to retrospectively evaluate the efficacy and potential applications of OGM in preconception genetic counseling. Herein, 74 samples from 37 families were included, and their results of OGM were compared to conventional methods, namely karyotyping (KT) and chromosomal microarray analysis (CMA), which identified 27 variants across 16 positive families. Notably, OGM achieved a concordance rate of 94.7% and 100% with KT and CMA, respectively, presenting an overall concordance of 96.3%, as it missed detecting a centromeric translocation. Additionally, OGM detected two cryptic balanced translocations and a small deletion in three families that were missed by conventional methods, improving the diagnostic rate by 5.4%, along with assisting in the diagnoses of six families (16.2%) by identifying complex rearrangements and confirming cryptic translocations. The combination of KT with OGM yielded the highest diagnostic rate in all families. Overall, the findings of this study present the notable potential of OGM for its application, combined with KT per requirement, in clinical settings to improve the efficiency and accuracy of diagnoses and rapid screening of individuals seeking preconception genetic counseling.

Hearing loss (HL) is the most common sensory disorder, characterized by a wide range of causes, including both environmental and genetic factors. While single-nucleotide variants (SNVs) and small insertions/deletions have been extensively studied, the role of structural variations (SVs) in hearing impairment has gained increasing recognition. This review article aims to provide a comprehensive overview of the importance of SVs in HL, by exploring the SVs associated with HL and their underlying pathogenic mechanisms. Additionally, diagnostic methods of SVs have been briefly evaluated and compared in general. Three major mechanisms by which SVs can lead to HL are gene disruption, gene dosage imbalance, and position effect. Furthermore, to facilitate the detection of SVs in HL, this review presents a table highlighting the key genes and genomic regions implicated in SVs and their diagnostic approaches associated with HL patients. In the next step, indications for the use of SV diagnostic techniques are compiled in another table in this article, which will help experts in choosing the most appropriate technique. At last, the comprehensive review presented here underscores the significant role of SVs in HL. Further research is required to fully elucidate the spectrum of SVs in HL and optimize the clinical use of SV detection methods in routine diagnostic procedures.

Disease-causing copy-number variants (CNVs) often encompass contiguous genes and can be detected using chromosomal microarray analysis (CMA). Conversely, CNVs affecting single disease-causing genes have historically been challenging to detect due to their small sizes.

A custom comprehensive CMA (Baylor College of Medicine - BCM v11.2) containing 400k probes and featuring exonic coverage for >4200 known or candidate disease-causing genes was utilized for the detection of CNVs at single-exon resolution. CMA results across a consecutive clinical cohort of more than 13 000 patients referred for genetic investigation at Baylor Genetics were examined. The genomic characteristics of CNVs impacting single protein-coding genes were investigated.

Pathogenic or likely pathogenic (P/LP) CNVs (n = 190) affecting single protein-coding genes were detected in 188 patients, accounting for 9.9% (188/1894) of patients with P/LP CMA findings. The P/LP monogenic CNVs accounted for 9.2% (190/2058) of all P/LP nuclear CNVs detected by CMA. A total of 57.9% (110/190) of P/LP monogenic CNVs were smaller than 50 kb in size. Single exons were affected by 26.3% (50/190) of P/LP monogenic CNVs while 13.2% (25/190) affected 2 exons. CNVs were detected across 107 unique genes associated with predominantly autosomal dominant (AD) and X-linked (XL) conditions but also contributed to autosomal recessive (AR) conditions.

CMA with exon-targeted coverage of disease-associated genes facilitated the detection of small CNVs affecting single protein-coding genes, adding substantial clinical sensitivity to comprehensive CNV investigation. This approach resolved monogenic CNVs associated with autosomal and X-linked monogenic etiologies and yielded multiple significant findings. Monogenic CNVs represent an underrecognized subset of disease-causing alleles for Mendelian disorders.

Approximately 7% of individuals with dystrophinopathy remain undiagnosed at the genetic level using conventional genetic tests like multiplex ligation-dependent probe amplification (MLPA) and next-generation sequencing (NGS). We used the optical genome mapping (OGM) technology to detect and analyze uncommon mutations or structural variations (SVs) within the DMD gene, thus contributing to more precise clinical diagnoses.

We herein included eight patients with dystrophinopathy (six males and two females) in whom pathogenic variants of the DMD gene could not be accurately identified using MLPA and NGS. Clinical data were collected for all patients and genetic testing was performed using OGM.

Conventional methods (MLPA and NGS) failed to detect pathogenic mutations in six out of eight individuals (four males and two females). OGM testing uncovered rare mutations in the DMD gene in four patients, including a pericentric inversion in chromosome X (one male), a complex rearrangement (one male), and two X-autosome translocations (two females). No mutations were detected in the remaining two male patients. OGM also accurately mapped balanced X-autosome translocations in female patients, defining chromosomal breakpoints. In the other two male patients in whom MLPA suggested non-contiguous exon duplications or deletions in the DMD gene, OGM characterized one case as a complex rearrangement and the other as a deletion within the DMD gene.

OGM is a valuable diagnostic tool for dystrophinopathy patients with negative results from conventional genetic tests. It can effectively elucidate complex SVs and pinpoint breakpoints in X-autosomal translocations in female patients, facilitating prompt and appropriate interventions.

Maple syrup urine disease (MSUD) is a rare inherited metabolic disorder characterized by deficient activity of the branched-chain alpha-ketoacid dehydrogenase (BCKDH) complex, required to metabolize the amino acids leucine, isoleucine, and valine. Despite its profound metabolic implications, the molecular alterations underlying this metabolic impairment had not yet been completely elucidated. We performed a comprehensive multi-omics integration analysis, including genomic, epigenomic, and transcriptomic data from fibroblasts derived from a cohort of MSUD patients and unaffected controls to genetically characterize an MSUD case and to unravel the MSUD pathophysiology. MSUD patients exhibit a defined episignature that reshapes the global DNA methylation landscape, resulting in the stimulation of HOX cluster genes and the restriction of cell cycle gene-related signatures. Subsequent data integration revealed the impact of AP1-related and CEBPB transcription factors on the observed molecular reorganization, with MEIS1 emerging as a potential downstream candidate affected by robust epigenetic repression in MSUD patients. Furthermore, the integration of multi-omics layers facilitated the identification of a strong epigenetic repression in the DBT promoter in a patient wherein no BCKDH pathogenic variants had been detected. A Circular Chromatin Conformation Capture assay indicated a disturbance of the interactions of DBT promoter, thereby unveiling alternative modes of disease inheritance. Integration of multi-omics data unveiled underlying molecular networks rewired in MSUD patients and represents a powerful approach with diagnostic potential for rare genetic disorders with unknown genetic bases.

Delineation of structural variants (SVs) at sequence resolution in highly repetitive genomic regions has long been intractable. The sequence properties, origins, and functional effects of classes of genomic rearrangements such as ring chromosomes and Robertsonian translocations thus remain unknown. To resolve these complex structures, we leveraged several recent milestones in the field, including (1) the emergence of long-read sequencing, (2) the gapless telomere-to-telomere (T2T) assembly, and (3) a tool (BigClipper) to discover chromosomal rearrangements from long reads. We applied these technologies across 13 cases with ring chromosomes, Robertsonian translocations, and complex SVs that were unresolved by short reads, followed by validation using optical genome mapping (OGM). Our analyses resolved 10 of 13 cases, including a Robertsonian translocation and all ring chromosomes. Multiple breakpoints were localized to genomic regions previously recalcitrant to sequencing such as acrocentric p-arms, ribosomal DNA arrays, and telomeric repeats, and involved complex structures such as a deletion-inversion and interchromosomal dispersed duplications. We further performed methylation profiling from long-read data to discover phased differential methylation in a gene promoter proximal to a ring fusion, suggesting a long-range position effect (LRPE) with heterochromatin spreading. Breakpoint sequences suggested mechanisms of SV formation such as microhomology-mediated and non-homologous end-joining, as well as non-allelic homologous recombination. These methods provide some of the first glimpses into the sequence resolution of Robertsonian translocations and illuminate the structural diversity of ring chromosomes and complex chromosomal rearrangements with implications for genome biology, prediction of LRPEs from integrated multi-omics technologies, and molecular diagnostics in rare disease cases.

Optical genome mapping (OGM) is a novel method enabling the detection of structural genomic variants. The method is based on the laser image acquisition of single, labeled, high-molecular-weight DNA molecules and can detect structural genomic variants such as translocations, inversions, insertions, deletions, duplications, and complex structural rearrangements. We aim to present our experience with OGM at the Clinical Institute of Genomic Medicine, University Medical Centre Ljubljana, Slovenia. Since its introduction in 2021, we have used OGM for the testing of facioscapulohumeral muscular dystrophy 1, characterization and resolution of variants identified by other technologies such as microarrays, exome and genome next-generation sequencing, karyotyping, as well as testing of rare disease patients in whom no genetic cause could be identified using these methods. We present an example family case of two previously undiagnosed male siblings with an overlapping clinical presentation of thrombocytopenia, obesity, and presacral teratoma. After karyotyping, microarray analysis and next-generation sequencing, by using OGM, a maternally inherited cryptic translocation t(X;18)(q27.1;q12.2) was identified in both brothers. Despite an extended segregation analysis, based on strictly applied ACMG criteria and ClinGen guidelines, the identified translocation remains a variant of unknown significance. Despite the remaining limitations of OGM, which will hopefully be resolved by improvements in databases of known benign SV variation and the establishment of official guidelines on the clinical interpretation of OGM variants, our work highlights the complexity of the diagnostic journey, including this novel method, in rare disease cases.

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.

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.

X-linked hypophosphatemia (XLH) is a rare metabolic bone disease caused by inactivation mutations in the PHEX gene. Despite the extensive number of reported PHEX variants, only a few cases of chromosomal abnormalities have been documented.

We aimed to identify the pathogenic variants in 6 unrelated families with a clinical diagnosis of XLH and to propose a genetic workflow for hypophosphatemia patients suspected of having XLH.

Multiple genetic testing assays were used to analyze the 6 families' genetic profiles, including whole exome sequencing, multiplex ligation-dependent probe amplification, whole genome sequencing, reverse transcript polymerase chain reaction, Sanger sequencing, and karyotyping.

The study identified 6 novel pathogenic variants, including 1 mosaic variant (exon 16-22 deletion), 3 chromosomal abnormalities (46, XN, inv[X][pter→p22.11::q21.31→p22.11::q21.31 →qter], 46, XN, inv[X][p22.11p22.11], and XXY), a nonclassical intron variant (NM_000444.6, c.1701_31A > G), and a deletion variant (NM_000444.6, c.64_5464-186 del5215) of PHEX. Additionally, a genetic testing workflow was proposed to aid in diagnosing patients suspected of XLH.

Our research expands the mutation spectrum of PHEX and highlights the significance of using multiple genetic testing methods to diagnose XLH.

In clinical practice, timely and accurate diagnosis can effectively reduce unnecessary treatment, avoid high medical costs, and prevent adverse prognoses. However, some patients with malignant tumors and those with infection often exhibit similar symptoms, which are difficult to distinguish, posing challenges in accurate clinical diagnosis. Metagenomic next-generation sequencing (mNGS) technology has been widely applied to confirm the source of infection. Recent studies have shown that for pathogen detection, mNGS technology can be used to perform chromosomal copy number variations (CNVs) analysis in two different analytical pipelines using the same wet test. mNGS technology has further demonstrated its utility in not only the determination of pathogenic microorganisms but also of CNVs, thereby facilitating early differential diagnosis for malignant tumors. In this review, we aim to analyze the diagnostic performance of mNGS technology in the simultaneous detection of pathogenic microorganisms and CNVs in current clinical practice and discuss the advantages and limitations of mNGS-CNV dual-omics detection technology. Our review highlights the need for more large-scale prospective research data on current mNGS-CNV dual-omics detection technology to provide more evidence-based results for researchers and clinicians and to promote the greater role of this technology in future clinical practice.

Structural variants (SVs) of unknown significance are great challenges for prenatal risk assessment, especially when involving dose-sensitive genes such as DMD The pathogenicities of 5'-terminal DMD duplications in the database remain controversial. Four prenatal cases with Xp21.1 duplications were identified by routine prenatal genomic testing, encompassing the 5'-UTR to exons 1-2 in family 1 and family 2, and to exons 1-9 in family 3. The duplication in family 4 was non-contiguous covering the 5'-UTR to exon 1 and exons 3-7. All were traced to unaffected males in the family pedigrees. A new genome-wide approach of optical genome mapping was performed in families 1, 2, and 3 to delineate the breakpoints and orientation of the duplicated fragments. The extra copies were tandemly inserted into the upstream of DMD, preserving the integrity of ORF from the second copy. The pathogenicities were thus reclassified as likely benign. Our data highlight the importance of structural delineation by optical genome mapping in prenatal risk assessment of incidentally identified SVs involving DMD and other similar large dose-sensitive genes.

Pre-implantation genetic testing (PGT) is a crucial process for selecting embryos created through assisted reproductive technology (ART). Couples with chromosomal rearrangements, infertility, recurrent miscarriages, advanced maternal age, known single-gene disorders, a family history of genetic conditions, previously affected pregnancies, poor embryo quality, or congenital anomalies may be candidates for PGT. Preimplantation genetic testing for aneuploidies (PGT-A) enables the selection and transfer of euploid embryos, significantly enhancing implantation rates in assisted reproduction. Fluorescence in situ hybridization (FISH) is the preferred method for analyzing biopsied cells to identify these abnormalities. While FISH is a well-established method for identifying sperm aneuploidy, NGS offers a more comprehensive assessment of genetic material, potentially enhancing our understanding of male infertility. Chromosomal abnormalities, arising during meiosis, can lead to aneuploid sperm, which may hinder embryo implantation and increase miscarriage rates. This review provides a comparative analysis of fluorescence in situ hybridization (FISH) and next-generation sequencing (NGS) in sperm evaluations, focusing on their implications for preimplantation genetic testing. This analysis explores the strengths and limitations of FISH and NGS, aiming to elucidate their roles in improving ART outcomes and reducing the risk of genetic disorders in offspring. Ultimately, the findings will inform best practices in sperm evaluations and preimplantation genetic testing strategies.

Inherited peripheral neuropathies (IPNs) encompass a clinically and genetically heterogeneous group of disorders causing length-dependent degeneration of peripheral autonomic, motor and/or sensory nerves. Despite gold-standard diagnostic testing for pathogenic variants in over 100 known associated genes, many patients with IPN remain genetically unsolved. Providing patients with a diagnosis is critical for reducing their 'diagnostic odyssey', improving clinical care, and for informed genetic counselling. The last decade of massively parallel sequencing technologies has seen a rapid increase in the number of newly described IPN-associated gene variants contributing to IPN pathogenesis. However, the scarcity of additional families and functional data supporting variants in potential novel genes is prolonging patient diagnostic uncertainty and contributing to the missing heritability of IPNs. We review the last decade of IPN disease gene discovery to highlight novel genes, structural variation and short tandem repeat expansions contributing to IPN pathogenesis. From the lessons learnt, we provide our vision for IPN research as we anticipate the future, providing examples of emerging technologies, resources and tools that we propose that will expedite the genetic diagnosis of unsolved IPN families.

Structural variants (SVs) of the nebulin gene (NEB), including intragenic duplications, deletions, and copy number variation of the triplicate region, are an established cause of recessively inherited nemaline myopathies and related neuromuscular disorders. Large deletions have been shown to cause dominantly inherited distal myopathies. Here we provide an overview of 35 families with muscle disorders caused by such SVs in NEB.

Using custom Comparative Genomic Hybridization arrays, exome sequencing, short-read genome sequencing, custom Droplet Digital PCR, or Sanger sequencing, we identified pathogenic SVs in 35 families with NEB-related myopathies.

In 23 families, recessive intragenic deletions and duplications or pathogenic gains of the triplicate region segregating with the disease in compound heterozygous form, together with a small variant in trans, were identified. In two families the SV was, however, homozygous. Eight families have not been described previously. In 12 families with a distal myopathy phenotype, eight unique, large deletions encompassing 52 to 97 exons in either heterozygous (n = 10) or mosaic (n = 2) state were identified.In the families where inheritance was recessive, no correlation could be made between the types of variants and the severity of the disease. In contrast, all patients with large dominant deletions in NEB had milder, predominantly distal muscle weakness.

For the first time, we establish a clear and statistically significant association between large NEB deletions and a form of distal myopathy. In addition, we provide the hitherto largest overview of the spectrum of SVs in NEB.

Prenatal diagnostic testing of amniotic fluid, chorionic villi, or more rarely, fetal cord blood is recommended following a positive or unreportable noninvasive cell-free fetal DNA test, abnormal maternal biochemical serum screen, abnormal ultrasound, or increased genetic risk for a cytogenomic abnormality based on family history. Although chromosomal microarray is recommended as the first-tier prenatal diagnostic test, in practice, multiple assays are often assessed in concert to achieve a final diagnostic result. The use of multiple methodologies is costly, time consuming, and labor intensive. Optical genome mapping (OGM) is an emerging technique with application for prenatal diagnosis because of its ability to detect and resolve, in a single assay, all classes of pathogenic cytogenomic aberrations. In an effort to characterize the potential of OGM as a novel alternative to traditional standard of care (SOC) testing of prenatal samples, OGM was performed on a total of 200 samples representing 123 unique cases, which were previously tested with SOC methods (92/123 = 74.7% cases tested with at least two SOCs). OGM demonstrated an overall accuracy of 99.6% when compared with SOC methods, a positive predictive value of 100%, and 100% reproducibility between sites, operators, and instruments. The standardized workflow, cost-effectiveness, and high-resolution cytogenomic analysis demonstrate the potential of OGM to serve as a first-tier test for prenatal diagnosis.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

Technologies for detecting structural variation (SV) have advanced with the advent of long-read sequencing, which enables the validation of SV at a nucleotide level. Optical genome mapping (OGM), a technology based on physical mapping, can also provide comprehensive SVs analysis. We applied long-read whole genome sequencing (LRWGS) to accurately reconstruct breakpoint (BP) segments in a patient with complex chromosome 6q rearrangements that remained elusive by conventional karyotyping. Although all BPs were precisely identified by LRWGS, there were two possible ways to construct the BP segments in terms of their orders and orientations. Thus, we also used OGM analysis. Notably, OGM recognized entire inversions exceeding 500 kb in size, which LRWGS could not characterize. Consequently, here we successfully unveil the full genomic structure of this complex chromosomal 6q rearrangement and cryptic SVs through combined long-molecule genomic analyses, showcasing how LRWGS and OGM can complement each other in SV analysis.

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.

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.

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.

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.