October 29, 2021  |  

Targeting Clinically Significant Dark Regions of the Human Genome with High-Accuracy, Long-Read Sequencing

There are many clinically important genes in “dark” regions of the human genome. These regions are characterized as dark due to a paucity of NGS coverage as a result of short-read sequencing or mapping difficulties. Low NGS sequencing yield can arise in these regions due to the presence of various repeat elements or biased base composition while inaccurate mapping can result from segmental duplications. Long-read sequencing coupled with an optimized, robust enrichment method has the potential to illuminate these dark regions. 


October 29, 2021  |  

Resolving Complex Pathogenic Alleles using HiFi Long-Range Amplicon Data and a New Clustering Algorithm

Many genetic diseases are mapped to structurally complex loci. These regions contain highly similar paralogous alleles (>99% identity) that span kilobases within the human genome. Comprehensive screening for pathogenic variants is incomplete and labor intensive using short-reads or optical mapping. In contrast, long-range amplification and PacBio HiFi sequencing fully and directly resolve and phase a wide range of pathogenic variants without inference. To capitalize on the accuracy of HiFi data we designed a new amplicon analysis tool, pbAA. pbAA can rapidly deconvolve a mixture of haplotypes, enabling precise diplotyping, and disease allele classification. 


October 28, 2021  |  

HiFiViral SARS-CoV-2: A Kitted Solution for Genome Surveillance that is Robust Across Sample Input Quantities and New Variants

The COVID-19 pandemic continues to be a major global epidemiological challenge with the ongoing emergence of new strain lineages that are more contagious, more virulent, drug resistant and in some cases evade vaccine-induced immunity. In response, the HiFiViral SARS-CoV-2 kit (PacBio; Menlo Park, California) was developed as a scalable solution for the Sequel II and Sequel IIe systems. The HiFiViral SARS-CoV-2 is an easy to perform solution for surveillance of variants to support pandemic response by public health. With 80% of samples yielding complete genome coverage in a 96-plex run, the combination of long read lengths and a differentiated probe design provides highly accurate results and robust genome coverage across a range of Ct values.


September 7, 2021  |  

Full-Length Sequencing of CYP2D6 Locus with HiFi Reads Increasing Genotypes Accuracy 

The highly polymorphic CYP2D6 gene impacts the metabolism of 25% of the mostly prescribed drugs. Thus, accurate identification of variant CYP2D6 alleles in individuals is necessary for personalized medicine. PacBio HiFi sequencing produces long and accurate reads to identify variant regions. Here, we describe an end-to-end workflow for the characterization of full-length CYP2D6 by HiFi sequencing. 


September 7, 2021  |  

Targeting Clinically Significant Dark Regions of the Human Genome with High-Accuracy, Long-Read Sequencing

There are many clinically important genes in “dark” regions of the human genome. These regions are characterized as dark due to a paucity of NGS coverage as a result of short-read sequencing or mapping difficulties. Low NGS sequencing yield can arise in these regions due to the presence of various repeat elements or biased base composition while inaccurate mapping can result from segmental duplications. Long-read sequencing coupled with an optimized, robust enrichment method has the potential to illuminate these dark regions. 


September 7, 2021  |  

Resolving Complex Pathogenic Alleles using HiFi Long-Range Amplicon Data and a New Clustering Algorithm

Many genetic diseases are mapped to structurally complex loci. These regions contain highly similar paralogous alleles (>99% identity) that span kilobases within the human genome. Comprehensive screening for pathogenic variants is incomplete and labor intensive using short-reads or optical mapping. In contrast, long-range amplification and PacBio HiFi sequencing fully and directly resolve and phase a wide range of pathogenic variants without inference. To capitalize on the accuracy of HiFi data we designed a new amplicon analysis tool, pbAA. pbAA can rapidly deconvolve a mixture of haplotypes, enabling precise diplotyping, and disease allele classification. 


June 1, 2021  |  

Sequencing of expanded CGG repeats in the FMR1 gene.

Alleles of the FMR1 gene with more than 200 CGG repeats generally undergo methylation-coupled gene silencing, resulting in fragile X syndrome, the leading heritable form of cognitive impairment. Smaller expansions (55-200 CGG repeats) result in elevated levels of FMR1 mRNA, which is directly responsible for the late-onset neurodegenerative disorder, fragile X-associated tremor/ataxia syndrome (FXTAS). For mechanistic studies and genetic counseling, it is important to know with precision the number of CGG repeats; however, no existing DNA sequencing method is capable of sequencing through more than ~100 CGG repeats, thus limiting the ability to precisely characterize the disease-causing alleles. The recent development of single molecule, real-time sequencing represents a novel approach to DNA sequencing that couples the intrinsic processivity of DNA polymerase with the ability to read polymerase activity on a single-molecule basis. Further, the accuracy of the method is improved through the use of circular templates, such that each molecule can be read multiple times to produce a circular consensus sequence (CCS). We have succeeded in generating CCS reads representing multiple passes through both strands of repeat tracts exceeding 700 CGGs (>2 kb of 100 percent CG) flanked by native FMR1 sequence, with single-molecule readlengths exceeding 12 kb. This sequencing approach thus enables us to fully characterize the previously intractable CGG-repeat sequence, leading to a better understanding of the distinct associated molecular pathologies. Real-time kinetic data also provides insight into the activity of DNA polymerase inside this unique sequence. The methodology should be widely applicable for studies of the molecular pathogenesis of an increasing number of repeat expansion-associated neurodegenerative and neurodevelopmental disorders, and for the efficient identification of such disorders in the clinical setting.


June 1, 2021  |  

Single Molecule Real Time (SMRT) sequencing sensitively detects polyclonal and compound BCR-ABL in patients who relapse on kinase inhibitor therapy.

Secondary kinase domain (KD) mutations are the most well-recognized mechanism of resistance to tyrosine kinase inhibitors (TKIs) in chronic myeloid leukemia (CML) and other cancers. In some cases, multiple drug resistant KD mutations can coexist in an individual patient (“polyclonality”). Alternatively, more than one mutation can occur in tandem on a single allele (“compound mutations”) following response and relapse to sequentially administered TKI therapy. Distinguishing between these two scenarios can inform the clinical choice of subsequent TKI treatment. There is currently no clinically adaptable methodology that offers the ability to distinguish polyclonal from compound mutations. Due to the size of the BCR-ABL KD where TKI-resistant mutations are detected, next-generation platforms are unable to generate reads of sufficient length to determine if two mutations separated by 500 nucleotides reside on the same allele. Pacific Biosciences RS Single Molecule Real-Time (SMRT) circular consensus sequencing technology is a novel third generation deep sequencing technology capable of rapidly and reliably achieving average read lengths of ~1000 bp and frequently beyond 3000 bp, allowing sequencing of the entire ABL KD on single strand of DNA. We sought to address the ability of SMRT sequencing technology to distinguish polyclonal from compound mutations using clinical samples obtained from patients who have relapsed on BCR-ABL TKI treatment.


June 1, 2021  |  

Evaluating the potential of new sequencing technologies for genotyping and variation discovery in human data.

A first look at Pacific Biosciences RS data Pacific Biosciences technology provides a fundamentally new data type that provides the potential to overcome these limitations by providing significantly longer reads (now averaging >1kb), enabling more unique seeds for reference alignment. In addition, the lack of amplification in the library construction step avoids a common source of base composition bias. With these potential advantages in mind, we here evaluate the utility of the Pacific Biosciences RS platform for human medical resequencing projects by assessing the quality of the raw sequencing data, as well as its use for SNP discovery and genotyping using the Genome Analysis Toolkit (GATK).


June 1, 2021  |  

SMRT Sequencing of whole mitochondrial genomes and its utility in association studies of metabolic disease.

In this study we demonstrate the utility of Single-Molecule Real Time SMRT sequencing to detect variants and to recapitulate whole mitochondrial genomes in an association study of Metabolic syndrome using samples from a well-studied cohort from Micronesia. The Micronesian island of Kosrae is a rare genetic isolate that offers significant advantages for genetic studies of human disease. Kosrae suffers from one of the highest rates of MetS (41%), obesity (52%), and diabetes (17%) globally and has a homogeneous environment making this an excellent population in which to study these significant health problems. We are conducting family-based association analyses aimed at identifying specific mitochondrial variants that contribute to obesity and other co-morbid conditions. We sequenced whole mitochondrial genomes from 10 Kosraen individuals who represent greater than 25 % of the mitochondrial genetic diversity for the entire Kosraen population. Using Pacific Biosciences C2 chemistry, SMRTbell libraries were constructed from pooled, full-length, unsheared 5 kb PCR amplicons, tiling the entire 16.6 kb mtDNA genome. Average read lengths for each sample were between 2500-3000 bp, with 5% of reads between 6,000-8,000 bases, depending on movie lengths. The data generated in this study serve as proof of principle that SMRT Sequencing data can be utilized for identification of high-quality variants and complete mitochondrial genome sequences. These data will be leveraged to identify causative variants for Metabolic syndrome and associated disorders.


Talk with an expert

If you have a question, need to check the status of an order, or are interested in purchasing an instrument, we're here to help.