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Roche is developing a high-throughput low cost sequencer for NGS

Reporter: Stephen J. Williams, PhD

 

Reported from Diagnostic World News

Long-Read Sequencing in the Age of Genomic Medicine

 

 

By Aaron Krol

December 16, 2015 | This September, Pacific Biosciences announced the creation of the Sequel, a DNA sequencer half the cost and seven times as powerful as its previous RS II instrument. PacBio, with its unique long-read sequencing technology, had already secured a place in high-end research labs, producing finished, highly accurate genomes and helping to explore the genetic “dark matter” that other next-generation sequencing (NGS) instruments miss. Now, in partnership with Roche Diagnostics, PacBio is repositioning itself as a company that can serve hospitals as well.

“Pseudogenes, large structural variants, validation, repeat disorders, polymorphic regions of the genome―all those are categories where you practically need PacBio,” says Bobby Sebra, Director of Technology Development at the Icahn School of Medicine at Mount Sinai. “Those are gaps in the system right now for short-read NGS.”

Mount Sinai’s genetic testing lab owns three RS II sequencers, running almost around the clock, and was the first lab to announce it had bought a Sequel just weeks after the new instruments were launched. (It arrived earlier this month and has been successfully tested.) Sebra’s group uses these sequencers to read parts of the genome that, thanks to their structural complexity, can only be assembled from long, continuous DNA reads.

There are a surprising number of these blind spots in the human genome. “HLA is a huge one,” Sebra says, referring to a highly variable region of the genome involved in the immune system. “It impacts everything from immune response, to pharmacogenomics, to transplant medicine. It’s a pretty important and really hard-to-genotype locus.”

Nonetheless, few clinical organizations are studying PacBio or other long-read technologies. PacBio’s instruments, even the Sequel, come with a relatively high price tag, and research on their value in treating patients is still tentative. Mount Sinai’s confidence in the technology is surely at least partly due to the influence of Sebra―an employee of PacBio for five years before coming to New York―and Genetics Department Chair Eric Schadt, at one time PacBio’s Chief Scientific Officer.

Even here, the sequencers typically can’t be used to help treat patients, as the instruments are sold for research use only. Mount Sinai is still working on a limited number of tests to submit as diagnostics to New York State regulators.

Physician Use

Roche Diagnostics, which invested $75 million in the development of the Sequel, wants to change that. The company is planning to release its own, modified version of the instrument in the second half of 2016, specifically for diagnostic use. Roche will initially promote the device for clinical studies, and eventually seek FDA clearance to sell it for routine diagnosis of patients.

In an email to Diagnostics World, Paul Schaffer, Lifecycle Leader for Roche’s sequencing platforms division, wrote that the new device will feature an integrated software pipeline to interpret test results, in support of assays that Roche will design and validate for clinical indications. The instrument will also have at least minor hardware modifications, like near field communication designed to track Roche-branded reagents used during sequencing.

This new version of the Sequel will probably not be the first instrument clinical labs turn to when they decide to start running NGS. Short-read sequencers are sure to outcompete the Roche machine on price, and can offer a pretty useful range of assays, from co-diagnostics in cancer to carrier testing for rare genetic diseases. But Roche can clear away some of the biggest barriers to entry for hospitals that want to pursue long-read sequencing.

Today, institutions like Mount Sinai that use PacBio typically have to write a lot of their own software to interpret the data that comes off the machines. Off-the-shelf analysis, with readable diagnostic reports for doctors, will make it easier for hospitals with less research focus to get on board. To this end, Roche acquired Bina, an NGS analysis company that handles structural variants and other PacBio specialties, in late 2014.

The next question will be whether Roche can design a suite of tests that clinical labs will want to run. Long-read sequencing is beloved by researchers because it can capture nearly complete genomes, finding the correct order and orientation of DNA reads. “The long-read technologies like PacBio’s are going to be, in the future, the showcase that ties it all together,” Sebra says. “You need those long reads as scaffolds to bring it together.”

But that envisions a future in which doctors will want to sequence their patients’ entire genomes. When it comes to specific medical tests, targeting just a small part of the genome connected to disease, Roche will have to content itself with some niche applications where PacBio stands out.

Early Applications

“At this time we are not releasing details regarding the specific assays under development,” Schaffer told Diagnostics World in his email. “However, virology and genetics are a key focus, as they align with other high-priority Roche Diagnostics products.”

Genetic disease is the obvious place to go with any sequencing technology. Rare hereditary disorders are much easier to understand on a genetic level than conditions like diabetes or heart disease; typically, the pathology can be traced back to a single mutation, making it easy to interpret test results.

Some of these mutations are simply intractable for short-read sequencers. A whole class of diseases, the PolyQ disorders and other repeat disorders, develop when a patient has too many copies of a single, repetitive sequence in a gene region. The gene Huntingtin, for example, contains a long stretch of the DNA code CAG; people born with 40 or more CAG repeats in a row will develop Huntington’s disease as they reach early adulthood.

These disorders would be a prime target for Roche’s sequencer. The Sequel’s long reads, spanning thousands of DNA letters at a stretch, can capture the entire repeat region of Huntingtin at a stretch, unlike short-read sequencers that would tend to produce a garbled mess of CAG reads impossible to count or put in order.

Nonetheless, the length of reads is not the only obstacle to understanding these very obstinate diseases. “The entire category of PolyQ disorders, and Fragile X and Huntington’s, is really important,” says Sebra. “But to be frank, they’re the most challenging even with PacBio.” He suggests that, even without venturing into the darkest realms of the genome, a long-read sequencer might actually be useful for diagnosing many of the same genetic diseases routinely covered by other instruments.

That’s because, even when the gene region involved in a disease is well known, there’s rarely only one way for it to go awry. “An example of that is Gaucher’s disease, in a gene called GBA,” Sebra says. “In that gene, there are hundreds of known mutations, some of which you can absolutely genotype using short reads. But others, you would need to phase the entire block to really understand.” Long-read sequencing, which is better at distinguishing maternal from paternal DNA and highlighting complex rearrangements within a gene, can offer a more thorough look at diseases with many genetic permutations, especially when tracking inheritance through a family.

“You can think of long-read sequencing as a really nice way to supplement some of the inherited panels or carrier screening panels,” Sebra says. “You can also use PacBio to verify variants that are called with short-read sequencing.”

Virology is, perhaps, a more surprising focus for Roche. Diagnosing a viral (or bacterial, or fungal) infection with NGS only requires finding a DNA read unique to a particular species or strain, something short-read sequencers are perfectly capable of.

But Mount Sinai, which has used PacBio in pathogen surveillance projects, has seen advantages to getting the full, completely assembled genomes of the organisms it’s tracking. With bacteria, for instance, key genes that confer resistance to antibiotics might be found either in the native genome, or inside plasmids, small packets of DNA that different species of bacteria freely pass between each other. If your sequencer can assemble these plasmids in one piece, it’s easier to tell when there’s a risk of antibiotic resistance spreading through the hospital, jumping from one infectious species to another.

Viruses don’t share their genetic material so freely, but a similar logic can still apply to viral infections, even in a single person. “A virus is really a mixture of different quasi-species,” says Sebra, so a patient with HIV or influenza likely has a whole constellation of subtly different viruses circulating in their body. A test that assembles whole viral genomes—which, given their tiny size, PacBio can often do in a single read—could give physicians a more comprehensive view of what they’re dealing with, and highlight any quasi-species that affect the course of treatment or how the virus is likely to spread.

The Broader View

These applications are well suited to the diagnostic instrument Roche is building. A test panel for rare genetic diseases can offer clear-cut answers, pointing physicians to any specific variants linked to a disorder, and offering follow-up information on the evidence that backs up that call.

That kind of report fits well into the workflows of smaller hospital labs, and is relatively painless to submit to the FDA for approval. It doesn’t require geneticists to puzzle over ambiguous results. As Schaffer says of his company’s overall NGS efforts, “In the past two years, Roche has been actively engaged in more than 25 partnerships, collaborations and acquisitions with the goal of enabling us to achieve our vision of sample in to results out.”

But some of the biggest ways medicine could benefit from long-read sequencing will continue to require the personal touch of labs like Mount Sinai’s.

Take cancer, for example, a field in which complex gene fusions and genetic rearrangements have been studied for decades. Tumors contain multitudes of cells with unique patchworks of mutations, and while long-read sequencing can pick up structural variants that may play a role in prognosis and treatment, many of these variants are rarely seen, little documented, and hard to boil down into a physician-friendly answer.

An ideal way to unravel a unique cancer case would be to sequence the RNA molecules produced in the tumor, creating an atlas of the “transcriptome” that shows which genes are hyperactive, which are being silenced, and which have been fused together. “When you run something like IsoSeq on PacBio and you can see truly the whole transcriptome, you’re going to figure out all possible fusions, all possible splicing events, and the true atlas of reads,” says Sebra. “Cancer is so diverse that it’s important to do that on an individual level.”

Occasionally, looking at the whole transcriptome, and seeing how a mutation in one gene affects an entire network of related genes, can reveal an unexpected treatment option―repurposing a drug usually reserved for other cancer types. But that takes a level of attention and expertise that is hard to condense into a mass-market assay.

And, Sebra suggests, there’s another reason for medical centers not to lean too heavily on off-the-shelf tests from vendors like Roche.

Devoted as he is to his onetime employer, Sebra is also a fan of other technologies now emerging to capture some of the same long-range, structural information on the genome. “You’ve now got 10X Genomics, BioNano, and Oxford Nanopore,” he says. “Often, any two or even three of those technologies, when you merge them together, can get you a much more comprehensive story, sometimes faster and sometimes cheaper.” At Mount Sinai, for example, combining BioNano and PacBio data has produced a whole human genome much more comprehensive than either platform can achieve on its own.

The same is almost certainly true of complex cases like cancer. Yet, while companies like Roche might succeed in bringing NGS diagnostics to a much larger number of patients, they have few incentives to make their assays work with competing technologies the way a research-heavy institute like Mount Sinai does.

“It actually drives the commercialization of software packages against the ability to integrate the data,” Sebra says.

Still, he’s hopeful that the Sequel can lead the industry to pay more attention to long-read sequencing in the clinic. “The RS II does a great job of long-read sequencing, but the throughput for the Sequel is so much higher that you can start to achieve large genomes faster,” he says. “It makes it more accessible for people who don’t own the RS II to get going.” And while the need for highly specialized genetics labs won’t be falling off anytime soon, most patients don’t have the luxury of being treated in a hospital with the resources of Mount Sinai. NGS companies increasingly see physicians as some of their most important customers, and as our doctors start checking into the health of our genomes, it would be a shame if ubiquitous short-read sequencing left them with blind spots.

Source: http://diagnosticsworldnews.com/2015/12/16/long-read-sequencing-age-genomic-medicine.aspx

 

 

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Author and Reporter: Ritu Saxena, Ph.D.

On 5th of July, I  discussed a general overview of varied mitochondrial functions, diseases, diagnosis and the current research focused on treatment of mitochondrial diseases in a post titled “Mitochondria: More than just the powerhouse of the cell”. https://pharmaceuticalintelligence.com/2012/07/09/mitochondria-more-than-just-the-powerhouse-of-the-cell/

Current post talks about a new technique that has been introduced by the authors as a ‘Comprehensive 1-Step Molecular Analyses of Mitochondrial Genome by Massively Parallel Sequencing’. The technique was recently published in the Clinical Chemistry journal (2012) by Zhang et al.

One mitochondria may have multiple copies of mtDNA  and an interesting feature observed in mitochondria is the heteroplasmy, a phenomenon where mutant and wild-type mtDNA can co-exist. During cell division, the mutant and wild-type copies are distributed randomly in daughter cells. The impact is in the heterogeneity with respect to penetrance and expressivity along that has diverse manifestations in terms of organs being affected, age of onset and the rate of progression. With such variability, the diagnosis becomes even more challenging. Therefore, mutational analysis along with accurate heteroplasmy detection in the mtDNA is an important part of the diagnosis. Thus, there is need for accurate and faster mutation detection methods for patients that are suspected to carry a mitochondrial disease.

The current molecular diagnostic methods for the detection of mtDNA mutations involves several different and complimentary methods. The detection of mutations is approached by first screening for a panel of point mutations that have been commonly associated with the mitochondrial diseases, followed by the quantification of the mutant load. In case none of the point mutations show up in the screening, the whole genome sequencing of mtDNA is performed to identify rare or novel mutations that might be associated with the disease. Also, in order to analyze large deletions within the genome, a an additional step of Southern blotting needs to be performed. Zhang et al, however, developed a novel approach to analyze the mtDNA in “single” step.

The method employed for the 1-step technique is to first enrich the entire mtDNA using amplification by PCR followed by massively parallel sequencing to detect point mutations as well as large heteroplasmic deletions simultaneously. A total of 45 samples were analyzed for the evaluation of analytic sensitivity and specificity. As stated by the authors “Our analysis demonstrated 100% diagnostic sensitivity and specificity of base calls compared to the results from Sanger sequencing” and added ” the method also detected large deletions with the breakpoints mapped”. Apart from the fact that the 1-step technique is less complex, the detection of point mutations has been found to be more accurate compared to Sanger sequencing that doesn’t provide any quantitative information and falls short of detecting heteroplasmy lying below 15%.

Thus,  the 1-step technique developed by Zhang et al has been demonstrated to be better than the combination of methods currently utilized for the detection of mtDNA mutations in terms of simplicity, cost effectiveness and accuracy.

Sources:

http://www.ncbi.nlm.nih.gov/pubmed?term=Comprehensive%201-Step%20Molecular%20Analyses%20of%20Mitochondrial%20Genome%20by%20Massively%20Parallel%20Sequencing

https://pharmaceuticalintelligence.com/2012/07/09/mitochondria-more-than-just-the-powerhouse-of-the-cell/

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