Until recently, most population-scale genome sequencing studies have focused on identifying single nucleotide variants (SNVs) to explore genetic differences between individuals. Like so many SNV-based genome-wide association studies, however, these efforts have had difficulty identifying causative genetic mechanisms underlying most complex functions. More and more, the genomics community has realised that structural variation is likely responsible for many of the traits and phenotypes that scientists have not been able to attribute to SNVs. This class of variants, defined as genetic differences of 50 bp or larger, accounts for most of the DNA sequence differences between any two people. Structural variants…
PurposeCurrent clinical genomics assays primarily utilize short-read sequencing (SRS), but SRS has limited ability to evaluate repetitive regions and structural variants. Long-read sequencing (LRS) has complementary strengths, and we aimed to determine whether LRS could offer a means to identify overlooked genetic variation in patients undiagnosed by SRS.MethodsWe performed low-coverage genome LRS to identify structural variants in a patient who presented with multiple neoplasia and cardiac myxomata, in whom the results of targeted clinical testing and genome SRS were negative.ResultsThis LRS approach yielded 6,971 deletions and 6,821 insertions?>?50?bp. Filtering for variants that are absent in an unrelated control and overlap…
At AGBT 2017, Mike Schatz from Johns Hopkins University and Cold Spring Harbor Laboratory presented data from sequencing, assembling, and analyzing personalized, phased diploid genomes with either Illumina, 10x Genomics, and PacBio SMRT Sequencing. Compared to the short-read-based methods, PacBio data assembled in large, complete contigs and contained the broadest range of structural variants with the best resolution. Plus: unexpected translocation findings with SMRT Sequencing, validated in follow-up studies.
Several new high-quality human genome assemblies produce ethnicity-specific reference sequences and show how scientists can use this genetic information to improve precision medicine studies in Asian sub- populations. These projects demonstrate how long- read SMRT Sequencing provides robust detection of polymorphic structural variants in clinically relevant gene coding regions and phases variants into haplotypes.
Euan Ashley from Stanford University started with the premise that while current efforts in the field of genomics medicine address 30% of patient cases, there’s a need for new approaches to make sense of the remaining 70%. Toward that end, he said that accurately calling structural variants is a major need. In one translational research example, Ashley said that SMRT Sequencing with the Sequel System allowed his team to identify six potentially causative genes in an individual with complex and varied symptoms; one gene was associated with Carney syndrome, which was a match for the person’s physiology and was later…
Melissa Laird Smith discussed how the Icahn School of Medicine at Mount Sinai uses long-read sequencing for translational research. She gave several examples of targeted sequencing projects run on the Sequel System including CYP2D6, phased mutations of GLA in Fabry's disease, structural variation breakpoint validation in glioblastoma, and full-length immune profiling of TCR sequences.
There is great potential for genome sequencing to enhance patient care through improved diagnostic sensitivity and more precise therapeutic targeting. To maximize this potential, genomics strategies that have been developed for genetic discovery - including DNA-sequencing technologies and analysis algorithms - need to be adapted to fit clinical needs. This will require the optimization of alignment algorithms, attention to quality-coverage metrics, tailored solutions for paralogous or low-complexity areas of the genome, and the adoption of consensus standards for variant calling and interpretation. Global sharing of this more accurate genotypic and phenotypic data will accelerate the determination of causality for novel…
Even though each of us shares more than 99% of the DNA sequences in our genome, there are millions of sequence codes or structure in small regions that differ between individuals, giving us different characteristics of appearance or responsiveness to medical treatments. Currently, genetic variants in diseased tissues, such as tumors, are uncovered by exploring the differences between the reference genome and the sequences detected in the diseased tissue. However, the public reference genome was derived with the DNA from multiple individuals. As a result of this, the reference genome is incomplete and may misrepresent the sequence variants of the…
Euan Ashley speaks about precision medicine and said clinical-grade analysis has been limited by complex regions in the human genome. His key theme,"Precision medicine needs to be accurate medicine," was illustrated with several examples where short-read sequencing or traditional clinical sequencing methods failed to be accurate. Also included: targeted RNA sequencing and gene phasing with long-read sequencing.
Interindividual variability in drug metabolism and drug toxicity persists as a major problem for drug development and treatment. Increased or decreased capacity for drug elimination or drug action reduces drug efficacy and places substantial economic burdens on society (e.g., due to treatment of adverse drug reactions) [1]. To a great extent this variation is based on genetic differences, and indeed many drugs now carry pharmacogenomic labels regarding mandatory or informative genetic tests that have to/can be performed before prescription (http://www.fda.gov/drugs/ scienceresearch/researchareas/pharmacogenetics/ucm083378.htm).Theselabelsarebasedonthe most common allelic variants in germline or somatic genes with importance for drug metabolism that encode phase I or…
Development of HIV-1 drug resistance mutations (HDRMs) is one of the major reasons for the clinical failure of antiretroviral therapy. Treatment success rates can be improved by applying personalized anti-HIV regimens based on a patient's HDRM profile. However, the sensitivity and specificity of the HDRM profile is limited by the methods used for detection. Sanger-based sequencing technology has traditionally been used for determining HDRM profiles at the single nucleotide variant (SNV) level, but with a sensitivity of only = 20% in the HIV population of a patient. Next Generation Sequencing (NGS) technologies offer greater detection sensitivity (~ 1%) and larger…
Characterizing large genomic variants is essential to expanding the research and clinical applications of genome sequencing. While multiple data types and methods are available to detect these structural variants (SVs), they remain less characterized than smaller variants because of SV diversity, complexity, and size. These challenges are exacerbated by the experimental and computational demands of SV analysis. Here, we characterize the SV content of a personal genome with Parliament, a publicly available consensus SV-calling infrastructure that merges multiple data types and SV detection methods.We demonstrate Parliament's efficacy via integrated analyses of data from whole-genome array comparative genomic hybridization, short-read next-generation…
In his talk from the AGBT 2015 PacBio workshop, Craig Venter detailed plans to sequence 1 million genomes and gather extensive phenotypic data to make sense of them. Included: generating 30 reference genomes to represent ethnogeographic diversity; the need for long-range continuity in sequencing; and truly predictive genomics.
Anne Deslattes Mays from Georgetown University describes how long-read sequencing provided important biological answers after three years of short-read sequencing failed to generate enough information for her gene discovery project. She says long reads are essential for understanding alternative splicing, RNA editing, and genome rearrangements.
Personal transcriptomes in which all of an individual's genetic variants (e.g., single nucleotide variants) and transcript isoforms (transcription start sites, splice sites, and polyA sites) are defined and quantified for full-length transcripts are expected to be important for understanding individual biology and disease, but have not been described previously. To obtain such transcriptomes, we sequenced the lymphoblastoid transcriptomes of three family members (GM12878 and the parents GM12891 and GM12892) by using a Pacific Biosciences long-read approach complemented with Illumina 101-bp sequencing and made the following observations. First, we found that reads representing all splice sites of a transcript are evident…