Browsing by Author "Mahmoud, Medhat"
Now showing 1 - 10 of 10
Results Per Page
Sort Options
Item Characterizing a complex CT-rich haplotype in intron 4 of SNCA using large-scale targeted amplicon long-read sequencing(Springer Nature, 2024) Alvarez Jerez, Pilar; Daida, Kensuke; Grenn, Francis P.; Malik, Laksh; Miano-Burkhardt, Abigail; Makarious, Mary B.; Ding, Jinhui; Gibbs, J. Raphael; Moore, Anni; Reed, Xylena; Nalls, Mike A.; Shah, Syed; Mahmoud, Medhat; Sedlazeck, Fritz J.; Dolzhenko, Egor; Park, Morgan; Iwaki, Hirotaka; Casey, Bradford; Ryten, Mina; Blauwendraat, Cornelis; Singleton, Andrew B.; Billingsley, Kimberley J.Parkinson’s disease (PD) is a common neurodegenerative disorder with a significant risk proportion driven by genetics. While much progress has been made, most of the heritability remains unknown. This is in-part because previous genetic studies have focused on the contribution of single nucleotide variants. More complex forms of variation, such as structural variants and tandem repeats, are already associated with several synucleinopathies. However, because more sophisticated sequencing methods are usually required to detect these regions, little is understood regarding their contribution to PD. One example is a polymorphic CT-rich region in intron 4 of the SNCA gene. This haplotype has been suggested to be associated with risk of Lewy Body (LB) pathology in Alzheimer’s Disease and SNCA gene expression, but is yet to be investigated in PD. Here, we attempt to resolve this CT-rich haplotype and investigate its role in PD. We performed targeted PacBio HiFi sequencing of the region in 1375 PD cases and 959 controls. We replicate the previously reported associations and a novel association between two PD risk SNVs (rs356182 and rs5019538) and haplotype 4, the largest haplotype. Through quantitative trait locus analyzes we identify a significant haplotype 4 association with alternative CAGE transcriptional start site usage, not leading to significant differential SNCA gene expression in post-mortem frontal cortex brain tissue. Therefore, disease association in this locus might not be biologically driven by this CT-rich repeat region. Our data demonstrates the complexity of this SNCA region and highlights that further follow up functional studies are warranted.Item FixItFelix: improving genomic analysis by fixing reference errors(Springer Nature, 2023) Behera, Sairam; LeFaive, Jonathon; Orchard, Peter; Mahmoud, Medhat; Paulin, Luis F.; Farek, Jesse; Soto, Daniela C.; Parker, Stephen C. J.; Smith, Albert V.; Dennis, Megan Y.; Zook, Justin M.; Sedlazeck, Fritz J.The current version of the human reference genome, GRCh38, contains a number of errors including 1.2 Mbp of falsely duplicated and 8.04 Mbp of collapsed regions. These errors impact the variant calling of 33 protein-coding genes, including 12 with medical relevance. Here, we present FixItFelix, an efficient remapping approach, together with a modified version of the GRCh38 reference genome that improves the subsequent analysis across these genes within minutes for an existing alignment file while maintaining the same coordinates. We showcase these improvements over multi-ethnic control samples, demonstrating improvements for population variant calling as well as eQTL studies.Item Genome-Wide Analysis of Structural Variants in Parkinson Disease(Wiley, 2023) Billingsley, Kimberley J.; Ding, Jinhui; Jerez, Pilar Alvarez; Illarionova, Anastasia; Levine, Kristin; Grenn, Francis P.; Makarious, Mary B.; Moore, Anni; Vitale, Daniel; Reed, Xylena; Hernandez, Dena; Torkamani, Ali; Ryten, Mina; Hardy, John; Consortium (UKBEC), UK Brain Expression; Chia, Ruth; Scholz, Sonja W.; Traynor, Bryan J.; Dalgard, Clifton L.; Ehrlich, Debra J.; Tanaka, Toshiko; Ferrucci, Luigi; Beach, Thomas G.; Serrano, Geidy E.; Quinn, John P.; Bubb, Vivien J.; Collins, Ryan L; Zhao, Xuefang; Walker, Mark; Pierce-Hoffman, Emma; Brand, Harrison; Talkowski, Michael E.; Casey, Bradford; Cookson, Mark R; Markham, Androo; Nalls, Mike A.; Mahmoud, Medhat; Sedlazeck, Fritz J; Blauwendraat, Cornelis; Gibbs, J. Raphael; Singleton, Andrew B.Objective Identification of genetic risk factors for Parkinson disease (PD) has to date been primarily limited to the study of single nucleotide variants, which only represent a small fraction of the genetic variation in the human genome. Consequently, causal variants for most PD risk are not known. Here we focused on structural variants (SVs), which represent a major source of genetic variation in the human genome. We aimed to discover SVs associated with PD risk by performing the first large-scale characterization of SVs in PD. Methods We leveraged a recently developed computational pipeline to detect and genotype SVs from 7,772 Illumina short-read whole genome sequencing samples. Using this set of SV variants, we performed a genome-wide association study using 2,585 cases and 2,779 controls and identified SVs associated with PD risk. Furthermore, to validate the presence of these variants, we generated a subset of matched whole-genome long-read sequencing data. Results We genotyped and tested 3,154 common SVs, representing over 412 million nucleotides of previously uncatalogued genetic variation. Using long-read sequencing data, we validated the presence of three novel deletion SVs that are associated with risk of PD from our initial association analysis, including a 2 kb intronic deletion within the gene LRRN4. Interpretation We identified three SVs associated with genetic risk of PD. This study represents the most comprehensive assessment of the contribution of SVs to the genetic risk of PD to date. ANN NEUROL 2023;93:1012–1022Item Genomic variant benchmark: if you cannot measure it, you cannot improve it(Springer Nature, 2023) Majidian, Sina; Agustinho, Daniel Paiva; Chin, Chen-Shan; Sedlazeck, Fritz J.; Mahmoud, MedhatGenomic benchmark datasets are essential to driving the field of genomics and bioinformatics. They provide a snapshot of the performances of sequencing technologies and analytical methods and highlight future challenges. However, they depend on sequencing technology, reference genome, and available benchmarking methods. Thus, creating a genomic benchmark dataset is laborious and highly challenging, often involving multiple sequencing technologies, different variant calling tools, and laborious manual curation. In this review, we discuss the available benchmark datasets and their utility. Additionally, we focus on the most recent benchmark of genes with medical relevance and challenging genomic complexity.Item Intratumoral Heterogeneity and Clonal Evolution Induced by HPV Integration(AACR, 2023) Akagi, Keiko; Symer, David E.; Mahmoud, Medhat; Jiang, Bo; Goodwin, Sara; Wangsa, Darawalee; Li, Zhengke; Xiao, Weihong; Dan Dunn, Joe; Ried, Thomas; Coombes, Kevin R.; Sedlazeck, Fritz J.; Gillison, Maura L.The human papillomavirus (HPV) genome is integrated into host DNA in most HPV-positive cancers, but the consequences for chromosomal integrity are unknown. Continuous long-read sequencing of oropharyngeal cancers and cancer cell lines identified a previously undescribed form of structural variation, “heterocateny,” characterized by diverse, interrelated, and repetitive patterns of concatemerized virus and host DNA segments within a cancer. Unique breakpoints shared across structural variants facilitated stepwise reconstruction of their evolution from a common molecular ancestor. This analysis revealed that virus and virus–host concatemers are unstable and, upon insertion into and excision from chromosomes, facilitate capture, amplification, and recombination of host DNA and chromosomal rearrangements. Evidence of heterocateny was detected in extrachromosomal and intrachromosomal DNA. These findings indicate that heterocateny is driven by the dynamic, aberrant replication and recombination of an oncogenic DNA virus, thereby extending known consequences of HPV integration to include promotion of intratumoral heterogeneity and clonal evolution.Long-read sequencing of HPV-positive cancers revealed “heterocateny,” a previously unreported form of genomic structural variation characterized by heterogeneous, interrelated, and repetitive genomic rearrangements within a tumor. Heterocateny is driven by unstable concatemerized HPV genomes, which facilitate capture, rearrangement, and amplification of host DNA, and promotes intratumoral heterogeneity and clonal evolution.See related commentary by McBride and White, p. 814.This article is highlighted in the In This Issue feature, p. 799Item Inverted triplications formed by iterative template switches generate structural variant diversity at genomic disorder loci(Elsevier, 2024) Grochowski, Christopher M.; Bengtsson, Jesse D.; Du, Haowei; Gandhi, Mira; Lun, Ming Yin; Mehaffey, Michele G.; Park, KyungHee; Höps, Wolfram; Benito, Eva; Hasenfeld, Patrick; Korbel, Jan O.; Mahmoud, Medhat; Paulin, Luis F.; Jhangiani, Shalini N.; Hwang, James Paul; Bhamidipati, Sravya V.; Muzny, Donna M.; Fatih, Jawid M.; Gibbs, Richard A.; Pendleton, Matthew; Harrington, Eoghan; Juul, Sissel; Lindstrand, Anna; Sedlazeck, Fritz J.; Pehlivan, Davut; Lupski, James R.; Carvalho, Claudia M. B.The duplication-triplication/inverted-duplication (DUP-TRP/INV-DUP) structure is a complex genomic rearrangement (CGR). Although it has been identified as an important pathogenic DNA mutation signature in genomic disorders and cancer genomes, its architecture remains unresolved. Here, we studied the genomic architecture of DUP-TRP/INV-DUP by investigating the DNA of 24 patients identified by array comparative genomic hybridization (aCGH) on whom we found evidence for the existence of 4 out of 4 predicted structural variant (SV) haplotypes. Using a combination of short-read genome sequencing (GS), long-read GS, optical genome mapping, and single-cell DNA template strand sequencing (strand-seq), the haplotype structure was resolved in 18 samples. The point of template switching in 4 samples was shown to be a segment of ∼2.2–5.5 kb of 100% nucleotide similarity within inverted repeat pairs. These data provide experimental evidence that inverted low-copy repeats act as recombinant substrates. This type of CGR can result in multiple conformers generating diverse SV haplotypes in susceptible dosage-sensitive loci.Item MethPhaser: methylation-based long-read haplotype phasing of human genomes(Springer Nature, 2024) Fu, Yilei; Aganezov, Sergey; Mahmoud, Medhat; Beaulaurier, John; Juul, Sissel; Treangen, Todd J.; Sedlazeck, Fritz J.The assignment of variants across haplotypes, phasing, is crucial for predicting the consequences, interaction, and inheritance of mutations and is a key step in improving our understanding of phenotype and disease. However, phasing is limited by read length and stretches of homozygosity along the genome. To overcome this limitation, we designed MethPhaser, a method that utilizes methylation signals from Oxford Nanopore Technologies to extend Single Nucleotide Variation (SNV)-based phasing. We demonstrate that haplotype-specific methylations extensively exist in Human genomes and the advent of long-read technologies enabled direct report of methylation signals. For ONT R9 and R10 cell line data, we increase the phase length N50 by 78%-151% at a phasing accuracy of 83.4-98.7% To assess the impact of tissue purity and random methylation signals due to inactivation, we also applied MethPhaser on blood samples from 4 patients, still showing improvements over SNV-only phasing. MethPhaser further improves phasing across HLA and multiple other medically relevant genes, improving our understanding of how mutations interact across multiple phenotypes. The concept of MethPhaser can also be extended to non-human diploid genomes. MethPhaser is available at https://github.com/treangenlab/methphaser.Item Rescuing low frequency variants within intra-host viral populations directly from Oxford Nanopore sequencing data(Springer Nature, 2022) Liu, Yunxi; Kearney, Joshua; Mahmoud, Medhat; Kille, Bryce; Sedlazeck, Fritz J.; Treangen, Todd J.Infectious disease monitoring on Oxford Nanopore Technologies (ONT) platforms offers rapid turnaround times and low cost. Tracking low frequency intra-host variants provides important insights with respect to elucidating within-host viral population dynamics and transmission. However, given the higher error rate of ONT, accurate identification of intra-host variants with low allele frequencies remains an open challenge with no viable computational solutions available. In response to this need, we present Variabel, a novel approach and first method designed for rescuing low frequency intra-host variants from ONT data alone. We evaluate Variabel on both synthetic data (SARS-CoV-2) and patient derived datasets (Ebola virus, norovirus, SARS-CoV-2); our results show that Variabel can accurately identify low frequency variants below 0.5 allele frequency, outperforming existing state-of-the-art ONT variant callers for this task. Variabel is open-source and available for download at: www.gitlab.com/treangenlab/variabel.Item SARS-CoV-2 genomic diversity and the implications for qRT-PCR diagnostics and transmission(Cold Spring Harbor Laboratory Press, 2021) Sapoval, Nicolae; Mahmoud, Medhat; Jochum, Michael D.; Liu, Yunxi; Elworth, R. A. Leo; Wang, Qi; Albin, Dreycey; Ogilvie, Huw A.; Lee, Michael D.; Villapol, Sonia; Hernandez, Kyle M.; Berry, Irina Maljkovic; Foox, Jonathan; Beheshti, Afshin; Ternus, Krista; Aagaard, Kjersti M.; Posada, David; Mason, Christopher E.; Sedlazeck, Fritz J.; Treangen, Todd J.The COVID-19 pandemic has sparked an urgent need to uncover the underlying biology of this devastating disease. Though RNA viruses mutate more rapidly than DNA viruses, there are a relatively small number of single nucleotide polymorphisms (SNPs) that differentiate the main SARS-CoV-2 lineages that have spread throughout the world. In this study, we investigated 129 RNA-seq data sets and 6928 consensus genomes to contrast the intra-host and inter-host diversity of SARS-CoV-2. Our analyses yielded three major observations. First, the mutational profile of SARS-CoV-2 highlights intra-host single nucleotide variant (iSNV) and SNP similarity, albeit with differences in C > U changes. Second, iSNV and SNP patterns in SARS-CoV-2 are more similar to MERS-CoV than SARS-CoV-1. Third, a significant fraction of insertions and deletions contribute to the genetic diversity of SARS-CoV-2. Altogether, our findings provide insight into SARS-CoV-2 genomic diversity, inform the design of detection tests, and highlight the potential of iSNVs for tracking the transmission of SARS-CoV-2.Item Vulcan: Improved long-read mapping and structural variant calling via dual-mode alignment(Oxford University Press, 2021) Fu, Yilei; Mahmoud, Medhat; Muraliraman, Viginesh Vaibhav; Sedlazeck, Fritz J; Treangen, Todd JLong-read sequencing has enabled unprecedented surveys of structural variation across the entire human genome. To maximize the potential of long-read sequencing in this context, novel mapping methods have emerged that have primarily focused on either speed or accuracy. Various heuristics and scoring schemas have been implemented in widely used read mappers (minimap2 and NGMLR) to optimize for speed or accuracy, which have variable performance across different genomic regions and for specific structural variants. Our hypothesis is that constraining read mapping to the use of a single gap penalty across distinct mutational hot spots reduces read alignment accuracy and impedes structural variant detection.We tested our hypothesis by implementing a read-mapping pipeline called Vulcan that uses two distinct gap penalty modes, which we refer to as dual-mode alignment. The high-level idea is that Vulcan leverages the computed normalized edit distance of the mapped reads via minimap2 to identify poorly aligned reads and realigns them using the more accurate yet computationally more expensive long-read mapper (NGMLR). In support of our hypothesis, we show that Vulcan improves the alignments for Oxford Nanopore Technology long reads for both simulated and real datasets. These improvements, in turn, lead to improved accuracy for structural variant calling performance on human genome datasets compared to either of the read-mapping methods alone.Vulcan is the first long-read mapping framework that combines two distinct gap penalty modes for improved structural variant recall and precision. Vulcan is open-source and available under the MIT License at https://gitlab.com/treangenlab/vulcan.