Biology subjects

Deanna M Church

Publications and source records attributed to Deanna M Church.

4 recordsLinked to original sources

bioRxiv2016

Evaluation of GRCh38 and de novo haploid genome assemblies demonstrates the enduring quality of the reference assembly

The human reference genome assembly plays a central role in nearly all aspects of todays basic and clinical research. GRCh38 is the first coordinate-changing assembly update since 2009 and reflects the resolution of roughly 1000 issues and encompasses modifications ranging from thousands of single base changes to megabase-scale path reorganizations, gap closures and localization of previously orphaned sequences. We developed a new approach to sequence generation for targeted base updates and used data from new genome mapping technologies and single haplotype resources to identify and resolve larger assembly issues. For the first time, the reference assembly contains sequence-based representations for the centromeres. We also expanded the number of alternate loci to create a reference that provides a more robust representation of human population variation. We demonstrate that the updates render the reference an improved annotation substrate, alter read alignments in unchanged regions and impact variant interpretation at clinically relevant loci. We additionally evaluated a collection of new de novo long-read haploid assemblies and conclude that while the new assemblies compare favorably to the reference with respect to continuity, error rate, and gene completeness, the reference still provides the best representation for complex genomic regions and coding sequences. We assert that the collected updates in GRCh38 make the newer assembly a more robust substrate for comprehensive analyses that will promote our understanding of human biology and advance our efforts to improve health.

Genomics↗

bioRxiv2016

High-Quality Assembly of an Individual of Yoruban Descent

De novo assembly of human genomes is now a tractable effort due in part to advances in sequencing and mapping technologies. We use PacBio single-molecule, real-time (SMRT) sequencing and BioNano genomic maps to construct the first de novo assembly of NA19240, a Yoruban individual from Africa. This chromosome-scaffolded assembly of 3.08 Gb with a contig N50 of 7.25 Mb and a scaffold N50 of 78.6 Mb represents one of the most contiguous high-quality human genomes. We utilize a BAC library derived from NA19240 DNA and novel haplotype-resolving sequencing technologies and algorithms to characterize regions of complex genomic architecture that are normally lost due to compression to a linear haploid assembly. Our results demonstrate that multiple technologies are still necessary for complete genomic representation, particularly in regions of highly identical segmental duplications. Additionally, we show that diploid assembly has utility in improving the quality of de novo human genome assemblies.

Bioinformatics↗

bioRxiv2016

A variant by any name: quantifying annotation discordance across tools and clinical databases

BackgroundClinical genomic testing is dependent on the robust identification and reporting of variant-level information in relation to disease. With the shift to high-throughput sequencing, a major challenge for clinical diagnostics is the cross-identification of variants called on their genomic position to resources that rely on transcript- or protein-based descriptions.\n\nMethodsWe evaluated the accuracy of three tools (SnpEff, Variant Effect Predictor and Variation Reporter) that generate transcript and protein-based variant nomenclature from genomic coordinates according to guidelines by the Human Genome Variation Society (HGVS). Our evaluation was based on comparisons to a manually curated list of 127 test variants of various types drawn from data sources, each with HGVS-compliant transcript and protein descriptors. We further evaluated the concordance between annotations generated by Snpeff and Variant Effect Predictor with those in major germline and cancer databases: ClinVar and COSMIC, respectively.\n\nResultsWe find that there is substantial discordance between the annotation tools and databases in the description of insertion and/or deletions. Accuracy based on our ground truth set was between 80-90% for coding and 50-70% for protein variants, numbers that are not adequate for clinical reporting. Exact concordance for SNV syntax was over 99.5% between ClinVar and Variant Effect Predictor (VEP) and SnpEff, but less than 90% for non-SNV variants. For COSMIC, exact concordance for coding and protein SNVs were between 65 and 88%, and less than 15% for insertions. Across the tools and datasets, there was a wide range of equivalent expressions describing protein variants.\n\nConclusionOur results reveal significant inconsistency in variant representation across tools and databases. These results highlight the urgent need for the adoption and adherence to uniform standards in variant annotation, with consistent reporting on the genomic reference, to enable accurate and efficient data-driven clinical care.

Genomics↗

bioRxiv2014

Single haplotype assembly of the human genome from a hydatidiform mole

An accurate and complete reference human genome sequence assembly is essential for accurately interpreting individual genomes and associating sequence variation with disease phenotypes. While the current reference genome sequence is of very high quality, gaps and misassemblies remain due to biological and technical complexities. Large repetitive sequences and complex allelic diversity are the two main drivers of assembly error. Although increasing the length of sequence reads and library fragments can help overcome these problems, even the longest available reads do not resolve all regions of the human genome. In order to overcome the issue of allelic diversity, we used genomic DNA from an essentially haploid hydatidiform mole, CHM1. We utilized several resources from this DNA including a set of end-sequenced and indexed BAC clones, an optical map, and 100X whole genome shotgun (WGS) sequence coverage using short (lllumina) read pairs. We used the WGS sequence and the GRCh37 reference assembly to create a sequence assembly of the CHM1 genome. We subsequently incorporated 382 finished CHORI-17 BAC clone sequences to generate a second draft assembly, CHM1_1.1 (NCBI AssemblyDB GCA_000306695.2). Analysis of gene and repeat content show this assembly to be of excellent quality and contiguity, and comparisons to ClinVar and the NHGRI GWAS catalog show that the CHM1 genome does not harbor an excess of deleterious alleles. However, comparison to assembly-independent resources, such as BAC clone end sequences and long reads generated by a different sequencing technology (PacBio), indicate misassembled regions. The great majority of these regions is enriched for structural variation and segmental duplication, and can be resolved in the future by sequencing BAC clone tiling paths. This publicly available first generation assembly will be integrated into the Genome Reference Consortium (GRC) curation framework for further improvement, with the ultimate goal being a completely finished gap-free assembly.

Genomics↗