Detecting Structural Variants with Long-Read Sequencing: Methods and Considerations
Structural variants (SVs) are genomic rearrangements involving deletions, insertions, duplications, inversions, and translocations that typically exceed 50 base pairs in size. These variants contribute substantially to human genetic diversity, disease susceptibility, gene expression regulation, and species-level evolutionary differences [6]. Short-read sequencing platforms, while widely used for their high base accuracy and cost efficiency, have limited ability to resolve repetitive and structurally complex genomic regions, which has accelerated adoption of long-read sequencing platforms including Pacific Biosciences (PacBio) and Oxford Nanopore Technologies (ONT) [14]. This article provides an evidence-based overview of SV types, the limitations of short-read approaches, long-read sequencing methods, and practical considerations for researchers and analysts selecting SV detection tools and designing workflows.
The Structural Variant Landscape and Why Size Matters
Structural variants encompass a broad range of genomic alterations that differ in size, mechanism of formation, and functional impact. Common SV classes include deletions, insertions, duplications, inversions, and translocations, as well as more complex rearrangements that combine multiple alteration types [6]. Mobile element insertions and tandem repeat expansions represent additional SV categories that carry clinical significance [11].
The size threshold that distinguishes SVs from smaller indels is not universally standardized, but variants larger than approximately 50 base pairs are generally classified as structural variants in bioinformatics pipelines. This size distinction matters because the detection strategies that work well for small variants often fail for larger rearrangements. Short-read sequencing generates reads of 100 to 300 base pairs, which means that any variant larger than the read length must be inferred from indirect signals such as discordant read pairs, split reads, or coverage anomalies instead of observed directly [6].
Long-read sequencing platforms produce reads ranging from several kilobases to hundreds of kilobases, allowing variants to be spanned by individual reads. This direct observation capability fundamentally changes the detection problem. A deletion of 5 kilobases, for example, can be entirely contained within a single long read, whereas short-read approaches must piece together evidence from multiple fragments that may not uniquely map to the region [14].
The clinical relevance of SVs is well established. In rare disease cohorts, long-read sequencing has identified pathogenic variants that short-read approaches missed, including copy-number variants, inversions, mobile element insertions, and low-complexity repeat expansions [11]. More than half of families with suspected rare monogenic diseases remain unsolved after whole-genome analysis by short-read sequencing, and long-read sequencing can help bridge this diagnostic gap by capturing variants inaccessible to short reads [5].
Short-Read Limitations in Structural Variant Detection
Short-read sequencing achieves high accuracy for single-nucleotide variants and small indels in well-mapped and moderately complex genomic regions, but shows reduced sensitivity and completeness for structural variant detection [14]. Several technical factors explain this limitation.
Repetitive Region Ambiguity
Repetitive sequences pose a fundamental challenge for short-read alignment. When a read of 150 base pairs originates from a region that is repeated elsewhere in the genome, the aligner cannot determine with confidence which copy produced the read. This ambiguity leads to missed variants, incorrect variant sizes, or spurious calls. Long-read sequencing resolves this problem because reads spanning multiple repeat units provide unique anchoring information [12].
The Telomere-to-Telomere CHM13 reference genome, which added nearly 200 million base pairs of sequence compared to its predecessors, demonstrated that improved reference completeness universally improves read mapping and variant calling. This reference eliminated tens of thousands of spurious variants per sample and reduced false positives in 269 medically relevant genes by up to a factor of 12 [12]. The implication for SV detection is clear: both read length and reference quality determine detection accuracy.
Indirect Evidence and Breakpoint Imprecision
Short-read SV callers rely on indirect signals. Discordant read pairs indicate that two reads that should map close together are separated by an unexpected distance or orientation. Split reads show that a single fragment maps to two different genomic locations. Coverage depth changes suggest deletions or duplications. Each of these signals provides partial information, and integrating them into a confident SV call requires sophisticated statistical modeling [6].
Even when short-read approaches detect an SV, the breakpoint resolution is often imprecise. The exact nucleotide position where the rearrangement occurs may be uncertain by hundreds of base pairs. This imprecision matters for clinical interpretation because breakpoint location determines which genes or regulatory elements are disrupted [17].
Structural Variant Size and Complexity
Short-read methods struggle with large and complex SVs. Inversions, for example, produce no change in read depth and may produce only subtle alignment signatures. Translocations involving repetitive regions are particularly difficult because the breakpoint sequences may not be unique. Complex SVs that combine deletions with insertions or inversions generate mixed signals that confound short-read callers [6].
A benchmarking study comparing sequencing technologies found that short-read sequencing combined with the DRAGEN pipeline achieved high accuracy for small variants but required more than 60x coverage to approach saturation for structural variant detection, whereas long-read sequencing reached accuracy saturation between 20x and 45x coverage [14]. This coverage difference has direct cost implications for study design.
Long-Read Sequencing Platforms and Their Characteristics
Two long-read sequencing platforms dominate current research and clinical applications: Pacific Biosciences and Oxford Nanopore Technologies. Each platform has distinct characteristics that influence SV detection performance.
Pacific Biosciences HiFi Sequencing
PacBio HiFi sequencing produces reads with high base accuracy, typically exceeding 99% per-read accuracy, through circular consensus sequencing. The reads range from approximately 10 to 25 kilobases in length. HiFi reads combine the length advantages of long-read sequencing with base accuracy approaching that of short reads [11].
In a study of 96 short-read-negative probands with suspected genetic rare diseases, PacBio HiFi sequencing generated hg38-aligned variants and de novo phased genome assemblies. New disease-relevant findings were identified in 16 of 96 probands, with 9 probands harboring pathogenic or likely pathogenic variants. Seven cases included variants that were only correctly interpreted in long-read data, including copy-number variants, an inversion, a mobile element insertion, two low-complexity repeat expansions, and a 1 base pair deletion [11].
Oxford Nanopore Sequencing
Oxford Nanopore Technologies sequencing measures changes in electrical current as DNA passes through a protein nanopore. The platform produces very long reads, with N50 values often exceeding 30 kilobases, and can sequence native DNA without amplification, preserving epigenetic modifications [5].
A rare disease cohort study using nanopore sequencing achieved approximately 36x average coverage and 32-kilobase read N50 from a single flow cell per sample. The analysis pipeline generated assemblies, phased variants, and methylation calls. Long-read sequencing covered coding exons in approximately 280 genes and about 5 known Mendelian disease-associated genes that were not covered by short-read sequencing. Diagnostic variants were established in 11 probands, with diverse underlying genetic causes including de novo and compound heterozygous variants, large-scale SVs, and epigenetic modifications [5].
Nanopore sequencing has also demonstrated utility in resolving balanced translocation breakpoints. In a case of NF2-related schwannomatosis, nanopore long-read sequencing revealed that a cytogenetically balanced translocation disrupted the NF2 gene, information that short-read approaches could not provide [17].
Platform Comparison for SV Detection
Benchmarking studies have compared SV calling performance across platforms. PacBio Revio with DeepVariant achieved the highest single-nucleotide variant and indel accuracy genome-wide, while ONT R10 with DeepVariant performed particularly well in clinically relevant loci. For structural variant detection, SVIM and Sawfish performed best for PacBio data, while Sniffles2 and CuteSV2 performed best for ONT data [14].
The choice between platforms depends on study goals, budget, and infrastructure. PacBio HiFi offers higher per-read accuracy, which simplifies downstream analysis. ONT offers longer reads, real-time data streaming, and lower upfront instrument costs. Both platforms can detect SVs that short-read approaches miss, but the optimal analysis pipeline differs by platform.
Alignment Strategies for Long-Read SV Detection
Accurate read alignment is the foundation of SV detection. Long-read aligners must handle higher error rates than short-read aligners while preserving the ability to detect genuine structural variation. The choice of aligner and alignment parameters directly affects SV calling performance.
Minimap2 and NGMLR
Minimap2 is a widely used long-read aligner that optimizes for speed. It uses minimizer-based indexing and a flexible gap penalty scheme to achieve fast alignment across diverse datasets. NGMLR (Non-Global Linear-time aligner for Long Reads) was designed specifically for SV detection and uses a more accurate but computationally expensive approach [9].
The performance of these aligners varies across genomic regions and for specific SV types. A key limitation is that constraining read mapping to a single gap penalty across distinct mutational hotspots reduces read alignment accuracy and impedes SV detection. Different genomic regions may require different gap penalties to achieve optimal alignment [9].
Dual-Mode Alignment Approaches
The Vulcan pipeline addresses the single-gap-penalty limitation by implementing dual-mode alignment. Vulcan first maps reads with minimap2, computes the normalized edit distance of the mapped reads, and identifies poorly aligned reads. These problematic reads are then realigned using NGMLR, which uses a more accurate but computationally expensive alignment strategy. This approach improves alignments for Oxford Nanopore reads and leads to improved SV calling accuracy compared to either mapping method alone [9].
The dual-mode strategy recognizes that most reads align well with fast methods, but a subset of reads spanning SV breakpoints or repetitive regions requires more careful alignment. By targeting the expensive aligner to only the reads that need it, Vulcan achieves a balance between speed and accuracy [9].
Non-Linear Mapping for Complex Rearrangements
Recent developments in alignment algorithms have introduced non-linear mapping approaches. VACmap, for example, enhances detection and representation of all genetic variation types. In the Challenging Medically-Relevant Genes benchmark, VACmap improved duplication detection from 20% to 90% and improved characterization of complex inversions in repetitive regions and gene conversion events. It resolved clinically significant loci including the LPA gene, GBA1, and STRC, which are affected by pseudogene recombination [16].
Non-linear mapping approaches are particularly valuable for complex SVs that produce non-linear alignment signatures. Standard linear aligners assume that the reference and query sequences have a collinear relationship, which breaks down for inversions, duplications, and gene conversions [16].
Structural Variant Calling Tools for Long Reads
Multiple SV calling tools have been developed for long-read data, each with distinct algorithmic strategies, strengths, and limitations. Tool selection should be guided by the specific SV classes of interest, sequencing platform, and computational resources.
SVIM
SVIM (Structural Variant Identification using Mapped Long Reads) is an alignment-based SV detection approach that identifies deletions, insertions, duplications, and inversions from long-read alignments. It clusters aligned reads based on their alignment signatures and uses the clustered information to determine variant boundaries and genotypes [14].
Benchmarking studies have shown that SVIM performs particularly well for PacBio data, achieving high accuracy across variant classes and sizes [14]. SVIM is appropriate for germline SV detection in diploid genomes and has been widely adopted in research pipelines.
cuteSV
cuteSV is a sensitive, fast, and scalable alignment-based SV detection approach designed for comprehensive discovery of diverse SV types. It uses a clustering-based strategy to collect SV signals from long-read alignments and then refines the candidate variants. Benchmarking results indicate that cuteSV is suitable for large-scale genome projects due to its excellent SV yields and ultra-fast speed [7].
The cuteSV framework is available at https://github.com/tjiangHIT/cuteSV and includes documentation for applying the tool correctly and comprehensively [7]. The tool handles the high sequencing error rates characteristic of long-read platforms and the complexity of SV structures.
Sniffles2 and CuteSV2 for ONT Data
For Oxford Nanopore data, Sniffles2 and CuteSV2 have demonstrated the best performance in benchmarking studies [14]. These tools are optimized for the error profile of nanopore sequencing and can detect SVs across a wide range of sizes and types.
Dysgu
Dysgu is a structural variant caller that works with both paired-end short reads and long reads. It detects signals from alignment gaps, discordant and supplementary mappings, and generates consensus contigs before classifying events using machine learning. Additional SVs are identified by remapping of anomalous sequences. Dysgu outperforms existing state-of-the-art tools using paired-end or long reads, offering high sensitivity and precision while being among the fastest tools to run [8].
An interesting finding from the dysgu study is that combining low-coverage paired-end and long-read data is competitive in performance with long-read data at higher coverage values [8]. This finding has practical implications for study design, suggesting that hybrid approaches may offer cost-effective alternatives to high-coverage long-read sequencing alone.
VolcanoSV
VolcanoSV is a hybrid SV detection pipeline that utilizes both a reference genome and local de novo assembly to generate a phased diploid assembly. It uses phased SNPs and unique k-mer similarity analysis to enable precise haplotype-resolved SV discovery. VolcanoSV constructs comprehensive genetic maps encompassing SNPs, small indels, and all types of SVs [19].
Extensive experiments demonstrate that VolcanoSV surpasses state-of-the-art assembly-based tools in detection of insertion and deletion SVs, exhibiting superior recall, precision, F1 scores, and genotype accuracy across diverse datasets, including low-coverage 10x datasets. It also outperforms assembly-based tools in identification of complex SVs, including translocations, duplications, and inversions, in both simulated and real cancer data [19].
Assembly-Based Approaches
Assembly-based SV detection constructs a genome assembly from sequencing reads and then compares the assembly to a reference genome to identify structural differences. This approach can detect SVs that read-based methods miss, particularly complex and nested variants.
Phased-assembly-driven pangenome graphs represent an emerging approach for SV detection and genotyping. A Holstein breed-specific pangenome graph built using Minigraph-Cactus and 40 phased haploid assemblies from 20 cows outperformed both assembly-based and read-based long-read callers, identifying over 10,000 additional structural variants per sample. The pangenome graph approach significantly improved SV detection and genotyping relative to graphs built across breeds or from fewer or unphased assemblies, with particular advantages in complex regions [15].
At a Glance: Tool Selection Guide
| Analysis Scenario | Recommended Approach | Key Considerations |
|---|---|---|
| PacBio HiFi germline SV detection | SVIM or Sawfish with minimap2 alignment | High base accuracy simplifies filtering, SVIM performs well across variant classes [14] |
| ONT germline SV detection | Sniffles2 or CuteSV2 with minimap2 or NGMLR alignment | Higher error rates require error-aware callers, dual-mode alignment may improve accuracy [9][14] |
| Complex SVs in medically relevant genes | VACmap or VolcanoSV | Non-linear mapping improves duplication and inversion detection, hybrid assembly approaches resolve complex breakpoints [16][19] |
| Somatic SV detection in cancer | Multiple callers with VCF merging | Combining tools and testing different combinations enhances validation of somatic alterations [18] |
| Low-coverage or hybrid data | Dysgu with combined short and long reads | Combining low-coverage paired-end and long reads is competitive with higher-coverage long reads alone [8] |
| Large-scale population studies | cuteSV | Ultra-fast speed and scalability for large genome projects [7] |
Practical Workflow for Long-Read SV Detection
A robust SV detection workflow requires careful attention to data quality, alignment parameters, variant filtering, and validation. The following steps outline a practical approach.
Step 1: Assess Input Data Quality
Before running SV detection, evaluate the sequencing data quality. Key metrics include read length distribution, read N50, estimated coverage, and base quality scores. For ONT data, check the quality score distribution and consider whether the data was generated with the latest pore and chemistry versions. For PacBio HiFi data, verify that the circular consensus sequencing produced adequate per-read accuracy.
Coverage requirements depend on the SV detection approach. Long-read sequencing reaches accuracy saturation for SV detection between 20x and 45x coverage, whereas short-read sequencing requires more than 60x coverage [14]. Low-coverage datasets may still be useful for certain applications, particularly when combined with assembly-based approaches [19].
Step 2: Select and Configure the Aligner
Choose an aligner based on the sequencing platform and downstream analysis goals. Minimap2 provides a good default choice for speed and general applicability. For challenging regions or when maximum accuracy is needed, consider NGMLR or a dual-mode approach like Vulcan [9].
Alignment parameters should be configured based on the expected SV types. Gap penalties influence the ability to detect insertions and deletions. Reads spanning large deletions may require permissive gap penalties to align correctly. The dual-mode alignment strategy implemented in Vulcan addresses this by using different gap penalties for different read subsets [9].
Step 3: Run SV Calling
Select an SV caller appropriate for the platform and variant classes of interest. For PacBio data, SVIM and Sawfish have demonstrated strong performance. For ONT data, Sniffles2 and CuteSV2 are recommended [14]. Consider running multiple callers and merging results to improve sensitivity, particularly for somatic SV detection in cancer samples [18].
Step 4: Filter and Annotate Variants
Raw SV calls typically include false positives that must be filtered. Filtering criteria may include read support, variant size, genotype quality, and allele frequency. Population frequency databases can help distinguish common polymorphisms from rare disease-causing variants.
Annotation of SV calls with gene and regulatory element information is essential for clinical interpretation. Determine whether the SV disrupts coding sequences, regulatory regions, or other functional elements. For clinical applications, follow established variant interpretation standards.
Step 5: Validate and Confirm
Validation of SV calls is important, particularly for clinical applications. Validation approaches include PCR amplification across breakpoints, orthogonal sequencing methods, or visual inspection of read alignments. For somatic SVs in cancer, comparing tumor and matched normal samples is essential to distinguish somatic from germline events [18].
Records and Measurements for SV Detection Projects
Maintaining detailed records is essential for reproducibility and quality control in SV detection projects. The following records should be documented for each sample and analysis run.
Sequencing Metrics
Record the sequencing platform, instrument model, chemistry version, flow cell type, and base calling software version. Document the raw read count, total bases, read N50, mean read length, and estimated coverage. For ONT data, record the pore version and whether adaptive sampling was used. For PacBio data, record the polymerase version and sequencing mode.
Alignment Metrics
Document the aligner software version, reference genome version, and alignment parameters. Record the percentage of reads mapped, the mapping quality distribution, and the median insert size for paired-end data. For dual-mode alignment approaches, record the proportion of reads that required realignment [9].
Variant Calling Metrics
Record the SV caller software version, parameters, and the reference genome version. Document the number of raw calls, the number of calls passing filters, and the distribution of variant types and sizes. For multi-caller approaches, record the intersection and union of calls across tools [18].
Quality Control Records
Maintain records of quality control metrics at each pipeline stage. These records enable troubleshooting when results are unexpected and provide evidence of data quality for publications or clinical reports. The FAIR Guiding Principles provide a framework for making data findable, accessible, interoperable, and reusable [4].
Common Failure Patterns in Long-Read SV Detection
Understanding common failure modes helps analysts troubleshoot and interpret results appropriately.
Failure Pattern 1: Overcalling in Repetitive Regions
Long-read SV callers can generate false positive calls in repetitive regions where alignment is ambiguous. This problem persists even with long reads, particularly for tandem repeats and segmental duplications. Mitigation strategies include requiring higher read support, filtering calls in known problematic regions, and using assembly-based approaches for confirmation [12].
Failure Pattern 2: Undercalling Large Deletions
Very large deletions may be missed if reads spanning the deletion are filtered out during alignment or if the SV caller requires a minimum number of supporting reads that is not met. Low coverage in the deleted region can also reduce detection sensitivity. Increasing coverage or using assembly-based approaches can improve detection [14].
Failure Pattern 3: Breakpoint Imprecision
Even when an SV is detected, the reported breakpoints may be imprecise. This imprecision can affect clinical interpretation and downstream functional analysis. Tools that perform local assembly around breakpoints, such as VolcanoSV, can improve breakpoint resolution [19].
Failure Pattern 4: Platform-Specific Artifacts
Each sequencing platform has specific error modes that can generate false SV calls. ONT data may produce false deletions in homopolymer regions due to base calling errors. PacBio data may produce false insertions or deletions at specific sequence motifs. Understanding platform-specific artifacts helps analysts distinguish genuine variants from technical noise [14].
Failure Pattern 5: Somatic and Germline Confusion
In cancer samples, distinguishing somatic SVs from germline SVs requires matched normal samples. Without a matched normal, somatic variants cannot be reliably identified. The subtraction method, where variants detected in both tumor and normal are removed from the tumor call set, is a common approach [18].
Limitations and Interpretation Boundaries
Long-read SV detection has made substantial progress, but important limitations remain.
Sequencing Error Rates
Long-read platforms have higher per-read error rates than short-read platforms, particularly for ONT data. While HiFi sequencing achieves high accuracy, the error profile differs from short-read data and requires error-aware analysis tools. Indel-prone sequence contexts remain challenging for all platforms [14].
Coverage Requirements
Long-read sequencing requires substantial coverage for comprehensive SV detection. While accuracy saturation occurs between 20x and 45x coverage, lower coverage datasets may miss variants, particularly in complex regions. The cost of achieving adequate coverage must be weighed against the diagnostic or research value of the results [14].
Reference Genome Limitations
SV detection depends on the reference genome used for alignment. The Telomere-to-Telomere CHM13 reference has demonstrated improvements in variant calling compared to GRCh38, particularly in previously unresolved regions [12]. However, reference genomes are not available for all species, and reference bias can affect SV detection in populations that diverge from the reference.
Complex Variant Resolution
Despite advances, some complex SVs remain difficult to resolve. Gene conversions, complex rearrangements involving multiple breakpoints, and variants in highly repetitive regions may require specialized approaches. Non-linear mapping methods like VACmap have improved detection of these variants but do not solve all cases [16].
Computational Requirements
Long-read SV detection requires substantial computational resources, particularly for assembly-based approaches. The computational cost of running multiple callers and merging results can be significant. Researchers should plan computational resources accordingly and consider the tradeoffs between sensitivity and computational cost [18].
Safety and Regulatory Context for Clinical Applications
When long-read SV detection is used for clinical diagnosis, regulatory and ethical considerations apply.
Data Sharing and Privacy
Genomic data sharing must comply with applicable policies and regulations. The NIH Genomic Data Sharing Policy establishes expectations for data sharing, including protections for participant privacy and confidentiality [3]. Researchers should review and follow institutional and funder requirements for genomic data management and sharing.
Data Management Standards
The FAIR Guiding Principles provide a framework for data management and stewardship. These principles emphasize that data should be findable, accessible, interoperable, and reusable [4]. Applying FAIR principles to SV detection data supports reproducibility and enables secondary analysis.
Clinical Validation Requirements
Clinical use of long-read SV detection requires validation according to established standards. Variants identified by research pipelines should be confirmed using orthogonal methods before clinical action. The diagnostic yield of long-read sequencing has been demonstrated in research cohorts, but clinical implementation requires careful validation [5][11].
Professional Escalation Criteria
Analysts should escalate findings to clinical professionals when variants with potential clinical significance are identified. The threshold for escalation depends on the clinical context and the strength of evidence. In research settings, findings that meet criteria for clinically actionable variants should be reviewed by qualified professionals before disclosure to participants.
Frequently Asked Questions
What is the minimum coverage needed for long-read SV detection?
Long-read sequencing reaches accuracy saturation for SV detection between 20x and 45x coverage, whereas short-read sequencing requires more than 60x coverage to approach similar performance [14]. Lower coverage may still detect large or high-confidence SVs, but sensitivity decreases. For clinical applications where comprehensive detection is required, coverage of at least 30x is commonly used. The optimal coverage depends on the specific SV classes of interest and the tolerance for false negatives.
How do PacBio and ONT compare for structural variant detection?
Both platforms detect SVs that short-read approaches miss, but they have different strengths. PacBio HiFi offers higher per-read accuracy, which simplifies analysis and improves small variant calling. ONT offers longer reads and real-time data streaming. Benchmarking studies show that SVIM and Sawfish perform best for PacBio data, while Sniffles2 and CuteSV2 perform best for ONT data [14]. The choice between platforms depends on study goals, budget, and existing infrastructure.
Why do short reads miss structural variants that long reads detect?
Short reads cannot span large variants, so SV detection relies on indirect signals such as discordant read pairs, split reads, and coverage changes [6]. These signals are ambiguous in repetitive regions and often produce imprecise breakpoints. Long reads can span entire variants, providing direct evidence of the rearrangement. In a study of short-read-negative probands, long-read sequencing identified variants that were either not called in short-read data, represented by calls with incorrect sizes or structures, or failed quality control and filtration [11].
Should I run multiple SV callers and merge results?
Running multiple callers and merging results can improve sensitivity and validation of somatic alterations, particularly in cancer samples [18]. Different callers use different algorithmic strategies and may detect different variant subsets. However, multi-caller approaches increase computational cost and require careful handling of conflicting calls. For germline SV detection, a single well-validated caller may be sufficient, while somatic SV detection in cancer may benefit from combining tools.
What is the role of assembly in SV detection?
Assembly-based approaches construct a genome assembly from sequencing reads and compare it to a reference genome to identify structural differences. These approaches can detect SVs that read-based methods miss, particularly complex and nested variants. VolcanoSV uses local de novo assembly to generate a phased diploid assembly and outperforms assembly-based tools in detection of insertions, deletions, and complex SVs [19]. Pangenome graphs built from phased assemblies can further improve SV detection and genotyping [15].
How do I validate structural variant calls?
Validation approaches include PCR amplification across breakpoints, orthogonal sequencing methods, and visual inspection of read alignments. For somatic SVs in cancer, comparing tumor and matched normal samples is essential to distinguish somatic from germline events [18]. The choice of validation method depends on the variant type, the availability of additional samples, and the intended use of the results.
What are the main challenges in detecting somatic SVs in cancer?
Cancer genomes have a complicated landscape of mutations, including large-scale rearrangements. Accurate identification of somatic SVs remains a significant bottleneck in cancer genomics. Challenges include distinguishing somatic from germline variants, detecting variants in heterogeneous tumor samples, and validating low-frequency events. Combining multiple tools and testing different combinations can significantly enhance validation of somatic alterations [18].
How does the reference genome affect SV detection?
The reference genome version affects read mapping and variant calling. The Telomere-to-Telomere CHM13 reference added nearly 200 million base pairs of sequence compared to its predecessors and improved read mapping and variant calling for both short and long reads. It also eliminated tens of thousands of spurious variants per sample [12]. Researchers should use the most complete reference available for their species and be aware that reference choice affects SV detection results.
Related Bioinformatics Guides
- From Raw Reads to Variants: A Diagnostic Blueprint for Next-Generation Sequencing (NGS) Workflows
- Long-Read Sequencing Technologies: PacBio and Oxford Nanopore
- Variant Calling GATK: Structural Analysis and Computational Methodologies in Bioinformatics
- Variant Calling Pipelines: GATK Best Practices, FreeBayes, and DeepVariant Comparison
- Long Read Metagenomic Assembly: Structural Analysis and Computational Methodologies in Bioinformatics
References and Further Reading
- EMBL-EBI Training. European Bioinformatics Institute.
- NCBI Data Resources. National Center for Biotechnology Information.
- Genomic Data Sharing Policy. National Institutes of Health.
- The FAIR Guiding Principles. Scientific Data.
- Advancing long-read nanopore genome assembly and accurate variant calling for rare disease detection.. American journal of human genetics, 2025.
- Structural variant calling: the long and the short of it.. Genome biology, 2019.
- Structural Variant Detection from Long-Read Sequencing Data with cuteSV.. Methods in molecular biology (Clifton, N.J.), 2022.
- Dysgu: efficient structural variant calling using short or long reads.. Nucleic acids research, 2022.
- Vulcan: Improved long-read mapping and structural variant calling via dual-mode alignment.. GigaScience, 2021.
- Single-cell long-read targeted sequencing reveals transcriptional variation in ovarian cancer.. Nature communications, 2024.
- Long-read genome sequencing and variant reanalysis increase diagnostic yield in neurodevelopmental disorders.. Genome research, 2024.
- A complete reference genome improves analysis of human genetic variation.. Science (New York, N.Y.), 2022.
- CMSV: Long-Read-Based Structural Variation Detection Through a CNN-Mamba Model. 2026.
- Benchmarking of sequencing technologies defines optimal strategies for genetic variants detection in a human genome.. 2026.
- Phased-assembly-driven pangenome graphs for structural variant genotyping and complex trait mapping in dairy cattle.. 2026.
- VACmap: an accurate long-read aligner for unraveling complex genomic rearrangements.. 2026.
- Long-read genome sequencing resolves the breakpoints of a chromosome 8,22 balanced translocation in NF2-related schwannomatosis.. 2025.
- Benchmarking long-read structural variant calling tools and combinations for detecting somatic variants in cancer genomes. Scientific Reports, 2025.
- VolcanoSV enables accurate and robust structural variant calling in diploid genomes from single-molecule long read sequencing. Nature Communications, 2024.
- Benchmarking long-read variant calling in diploid and polyploid genomes: insights from human and plants. BMC Genomics, 2026.
- A novel and accelerated method for integrated alignment and variant calling from short and long reads. Frontiers in Bioinformatics, 2026.
This article is educational and does not replace validated analysis plans, institutional policy, clinical interpretation, or specialist review.