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Chris Saunders

@ctsa

Rare disease and cancer analysis models for sequencing data. Scientist at PacBio. Art school survivor. Views my own.

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19.08.2023
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Latest posts by Chris Saunders @ctsa

By both improving accuracy and unifying assembly-based and mapping-based inferences, the portello approach has the potential to substantially improve analysis for rare-disease and other WGS applications. See our new preprint here:

doi.org/10.64898/202...

20.02.2026 16:12 πŸ‘ 2 πŸ” 2 πŸ’¬ 0 πŸ“Œ 0
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We also demonstrate the potential for improved CNV inference in a segmental duplication region where assembly-based read mapping substantially clarifies copy number inference compared to a conventional mapping approach. (4/5)

20.02.2026 16:12 πŸ‘ 1 πŸ” 0 πŸ’¬ 1 πŸ“Œ 0
Small variant basepair errors comparison between conventionally mapped reads and portello-mapped reads.

Small variant basepair errors comparison between conventionally mapped reads and portello-mapped reads.

We demonstrate that variant calling shows improved accuracy given these assembly-based read mappings. For instance, given the same set of input reads, DeepVariant calling from portello-mapped reads shows a 47% reduction in errors compared to calls from a conventional mapping process. (3/5)

20.02.2026 16:12 πŸ‘ 1 πŸ” 1 πŸ’¬ 1 πŸ“Œ 0
Portello workflow schematic

Portello workflow schematic

Portello facilitates an assembly-based approach to read mapping, wherein reads mapped to their own diploid assembly contigs are transferred back to a reference genome. This approach allows standard secondary analysis tools and viewers to operate on reads mapped in the context of the diploid assembly

20.02.2026 16:12 πŸ‘ 2 πŸ” 0 πŸ’¬ 1 πŸ“Œ 0
Comparison of read mappings at HG002 chr4:40,294,825-40,295,700, showing conventional (pbmm2) read mappings (above) and portello mappings (below). The same set of unaligned input reads were input into each mapping process.

Comparison of read mappings at HG002 chr4:40,294,825-40,295,700, showing conventional (pbmm2) read mappings (above) and portello mappings (below). The same set of unaligned input reads were input into each mapping process.

What if you could improve small variant accuracy, CNV inference, and interpretability of your HiFi WGS data by taking a different approach to read mapping? Our new preprint describes portello, a method which demonstrates the potential for such improvements. (1/5)

20.02.2026 16:12 πŸ‘ 25 πŸ” 11 πŸ’¬ 1 πŸ“Œ 1
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Dan Portik from #PacBio presents work on strand-specific 5hmC methylated base detection using PacBio HiFi sequencing, highlighting approaches for accurate epigenetic analysis with long reads.

See it today at #PAG33 β€” Poster P051, 3:00–4:30 PM.

12.01.2026 23:18 πŸ‘ 7 πŸ” 2 πŸ’¬ 0 πŸ“Œ 0
Jobs | University of Utah Founded in 1850, The University of Utah is the flagship institution of higher learning in Utah, and offers over 100 undergraduate and more than 90 graduate degree programs to over 30,000 students. Uni...

I am hiring a staff bioinformatician for my new lab at the University of Utah! Please consider applying if you are on the hunt:
employment.utah.edu/salt-lake-ci...

12.01.2026 21:04 πŸ‘ 31 πŸ” 32 πŸ’¬ 1 πŸ“Œ 1
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Absolutely thrilled to share the latest work from my lab focused on the variation and evolution of human centromeres among global populations! We assembled 2,110 human centromeres, identifying 226 new major haplotypes and 1,870 Ξ±-satellite HOR variants. www.biorxiv.org/content/10.6...

16.12.2025 16:05 πŸ‘ 108 πŸ” 46 πŸ’¬ 4 πŸ“Œ 2
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Long-Read Sequencing Workshop The program will involve sessions on Genome Evolution, Genome Regulation, Transcriptomics, Rare Diseases, Common Diseases, and Viral and Microbial Genomes. Committed speakers include Adam Phillipy (NH...

Join us at this exciting Workshop on #LongReads with keynotes from @aphillippy.bsky.social @mydennis.bsky.social
co-organized by @christinebeck.bsky.social and Mark Adams @jacksonlab.bsky.social Register www.jax.org/longread
#RNA #genomics #bioinformatics #cancer #medicine #evolution #neuroscience

14.11.2025 19:56 πŸ‘ 26 πŸ” 9 πŸ’¬ 1 πŸ“Œ 0

Nice to chat at CSHL last week. I missed the chance to tell you in person what a valuable resource these videos have been, I think I've seen every one. Even for well-known topics, the clarity of presentation can really sharpen intuition. Thanks for the great work.

10.11.2025 18:00 πŸ‘ 4 πŸ” 0 πŸ’¬ 1 πŸ“Œ 0
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GitHub - PacificBiosciences/Paraviewer Contribute to PacificBiosciences/Paraviewer development by creating an account on GitHub.

My new tool Paraviewer is now available for use at github.com/PacificBiosc...! If you use Paraphase, try this new next-step tool - it automates and greatly simplifies variant visualization from Paraphase variant calling. If you're at #ASHG2025, visit me today at poster 4109W. #pacbio

15.10.2025 14:58 πŸ‘ 7 πŸ” 5 πŸ’¬ 1 πŸ“Œ 0
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Complex structural variant visualization with SVTopo - BMC Genomics Background Structural variants are genomic variants that impact at least 50 nucleotides. Structural variants can play major roles in diversity and human health. Many structural variants are difficult to interpret and understand with existing visualization tools, especially when comprised of inverted sequences or multiple breakend pairs. Results We present SVTopo, a tool to visualize germline structural variants with supporting evidence from high-accuracy long reads in easily understood figures. We include examples of 101 visually complex structural variants from seven unrelated human genomes, manually assigned to ten categories. These demonstrate a broad spectrum of rearrangement and showcase the frequency of complex structural variants in human genomes. Conclusions SVTopo shows breakpoint evidence in ways that aid reasoning about the impact of multi-breakpoint rearrangements. The images created aid human reasoning about the result of structural variation on gene and regulatory regions.

My complex variant visualization tool SVTopo is now officially published in BMC Genomics! link.springer.com/article/10.1.... This tool allows HiFi users to view complex germline structural variation in intuitive and informative plots.

09.10.2025 19:00 πŸ‘ 6 πŸ” 7 πŸ’¬ 2 πŸ“Œ 0
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Megaplasmids associate with Escherichia coli and other Enterobacteriaceae Humans and animals are ubiquitously colonized by Enterobacteriaceae , a bacterial family that contains both commensals and clinically significant pathogens. Here, we report Enterobacteriaceae megaplas...

New pre-print from the Banfield lab, highlighting an interesting case of 1.5Mb megaplasmids found in human gut.

Plasmid genomes were resolved using #PacBio HiFi sequencing with hifiasm-meta for #metagenome assembly. Host association was detected using epigenetic signals.

doi.org/10.1101/2025...

01.10.2025 16:43 πŸ‘ 48 πŸ” 22 πŸ’¬ 1 πŸ“Œ 2

I'm excited to share our pre-print about a new variant benchmarking tool we've been working on for the past few months!

Aardvark: Sifting through differences in a mound of variants
GitHub: github.com/PacificBiosc...

Some highlights in this thread:
1/N

06.10.2025 20:07 πŸ‘ 32 πŸ” 17 πŸ’¬ 1 πŸ“Œ 1
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In Stockholm for work and got a great recommendation to KlΓ€ttercentret Telefonplan for a boulder break last night. Great gym all around and easy hop on the metro from city center.

05.10.2025 06:24 πŸ‘ 0 πŸ” 0 πŸ’¬ 0 πŸ“Œ 0
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Congrats to @dantipov.bsky.social et al. on the publication of Verkko2! The team put a ton of work into this making it the first assembler that deals with the complexity of human acrocentric chromosomes. Lots of interesting discoveries to come! genome.cshlp.org/content/earl...

17.06.2025 13:39 πŸ‘ 32 πŸ” 19 πŸ’¬ 1 πŸ“Œ 1

Now published! Note that since Vikram's original post (quoted here), he's made it easy to dynamically update a set of multi-MUMs (e.g. when more genomes are added to a pangenome) and to find multi-MUMs for huge collections like HPRCv2 genomebiology.biomedcentral.com/articles/10....

17.06.2025 14:02 πŸ‘ 54 πŸ” 23 πŸ’¬ 1 πŸ“Œ 1

Very excited to share I’ll be starting my own group at University of Utah in the Department of Human Genetics in the new year! Reach out if you are interested! vollgerlab.com

05.06.2025 14:15 πŸ‘ 66 πŸ” 13 πŸ’¬ 9 πŸ“Œ 4
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Great keynote talk at #SFAF by Rob Knight, summarizing key innovations in microbiome research over the past decade.

One recent highlight is how long reads have transformed metagenome assembly, particularly #PacBio HiFi reads. The future is complete MAGs!

22.05.2025 15:55 πŸ‘ 10 πŸ” 3 πŸ’¬ 1 πŸ“Œ 0
GitHub - PacificBiosciences/sawfish: Joint structural variant and copy number variant caller for HiFi sequencing data Joint structural variant and copy number variant caller for HiFi sequencing data - PacificBiosciences/sawfish

In addition to CNV recall and breakpoint accuracy improvements, this update boosts precision for large, unbalanced SVs and simplifies analysis by harmonizing all depth and breakpoint evidence into one consistent call set. The full update is now available in the most recent sawfish2 release on github

20.05.2025 00:52 πŸ‘ 0 πŸ” 0 πŸ’¬ 0 πŸ“Œ 0
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Just released a major update to the sawfish SV caller, which adds CNV calling and integration. Assessment on a set of pathogenic CNVs from Gross et al. shows this integrated-call strategy can substantially improve (single-method) recall, especially at lower HiFi sequencing depths

20.05.2025 00:52 πŸ‘ 6 πŸ” 1 πŸ’¬ 1 πŸ“Œ 0
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Human de novo mutation rates from a four-generation pedigree reference - Nature Analysis of more than 95% of each diploid human genome of a four-generation, twenty-eight-member family using five complementary short-read and long-read sequencing technologies provides a truth set t...

Long-read sequencing of large pedigrees is an ideal way to map all classes of denovo mutations! A collaboration between University of Utah, University of Washington, and PacBio. Glad to be a part of this project πŸ‘

www.nature.com/articles/s41...

23.04.2025 16:11 πŸ‘ 17 πŸ” 9 πŸ’¬ 1 πŸ“Œ 0
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This example is hard to understand from e.g. IGV/Ribbon (see Fig1) but pretty simple in SVTopo: 4 blocks deleted (B,D,F,H), 2 inverted (E,G), 1 re-ordered (C)

22.04.2025 14:22 πŸ‘ 2 πŸ” 1 πŸ’¬ 1 πŸ“Œ 0
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Complex structural variant visualization with SVTopo Structural variants are genomic variants that impact at least 50 nucleotides and can play major roles in diversity and human health. Many structural variants are complex multi-breakpoint rearrangement...

I just released a new preprint! The manuscript describes SVTopo, a software tool that enhances visualization of complex SVs using HiFi data: www.biorxiv.org/content/10.1.... Here’s a summary of the results:

22.04.2025 14:21 πŸ‘ 13 πŸ” 8 πŸ’¬ 1 πŸ“Œ 1

Last day to submit abstracts to #HiTSeq25 @hitseq.bsky.social #ISMB2025 - send us your work for an opportunity to present in the podium or poster.

17.04.2025 16:17 πŸ‘ 1 πŸ” 2 πŸ’¬ 0 πŸ“Œ 0
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Sawfish: Improving long-read structural variant discovery and genotyping with local haplotype modeling academic.oup.com/bioinformati... 🧬πŸ–₯️πŸ§ͺ github.com/PacificBiosc...

11.04.2025 15:30 πŸ‘ 14 πŸ” 6 πŸ’¬ 1 πŸ“Œ 0
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Hello bluesky world! Newbee here! I have a postdoc position immediately available in my lab. It will focus on identifying high-quality transposons in many genomes and finding their impacts in evolution and traits. Most works, including EDTA2 development and annotation of 400+ genomes, are done! 1/n

10.04.2025 18:08 πŸ‘ 25 πŸ” 22 πŸ’¬ 3 πŸ“Œ 2
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GitHub - ACEnglish/truvari: Structural variant toolkit for VCFs Structural variant toolkit for VCFs. Contribute to ACEnglish/truvari development by creating an account on GitHub.

πŸš€ Truvari v5.0 is here! πŸŽ‰
What’s new?
πŸ”Ή Enhanced symbolic variant support for <DEL>, <DUP>, <INV>
πŸ”Ή Robust BND comparison for cross-representation SV matching
πŸ”Ή Improved SV sequence similarity & HUGE SV support
πŸ”Ή Cleaner UI & Revamped API

πŸ‘‰ More: github.com/ACEnglish/tr...
#Genomics #Bioinformatics

10.01.2025 13:43 πŸ‘ 6 πŸ” 5 πŸ’¬ 0 πŸ“Œ 0

Finally, a huge thank-you to all sawfish co-authors and the broader @pacbio.bsky.social team, our anonymous reviewers, SV community members, and users for their contributions, feedback and many helpful suggestions!

10.04.2025 15:41 πŸ‘ 1 πŸ” 0 πŸ’¬ 0 πŸ“Œ 0