Biomedical subjects

Vikas Bansal

Publications and source records attributed to Vikas Bansal.

6 recordsLinked to original sources

PubMed2026

Likelihood-based optimization enables accurate copy number estimation for paralogous genes using exome data.

MOTIVATION: Exome sequencing is widely used for genetic studies; however, accurate detection of copy number variants (CNV) in paralogous genes is challenging due to short-read mapping ambiguity and extensive copy-number variation. The human genome contains several hundred paralogous genes, many of which are known to harbor disease-associated CNVs. Existing exome CNV callers are primarily designed for rare CNV detection in uniquely mappable regions and are not well-suited for paralogous genes. METHODS: We describe a computational method (EdgeCopy) for copy number profiling of paralogous genes using whole-exome sequence data. EdgeCopy aggregates reads mapped to all copies of paralogous genes and relates observed read depth to copy number for multiple exome samples using an approximate composite likelihood function. The likelihood function is optimized using numerical optimization to obtain gene-level fractional copy number estimates that are discretized and refined using a Hidden Markov Model to obtain exon-level copy number estimates. RESULTS: Benchmarking of Edgecopy using experimental copy number data showed high concordance (mean = 0.973) for six disease-associated paralogous genes. We evaluated performance using whole-exome data from approximately 2400 samples across five continental populations from the 1000 Genomes Project. EdgeCopy shows robust concordance with whole-genome sequencing based estimates (0.974-0.982) across populations and 130 paralogous genes spanning a wide range of copy-number variation. In comparison, copy number analysis using a state-of-the-art exome CNV caller failed to estimate copy number for paralogous genes with very high mapping ambiguity and showed much lower concordance (0.565) for CNV events compared to EdgeCopy (0.908). AVAILABILITY: EdgeCopy is freely available at https://github.com/vibansal-lab/edgecopy.

Humans↗

PubMed2025

Analysis of targeted and whole genome sequencing of PacBio HiFi reads for a comprehensive genotyping of gene-proximal and phenotype-associated Variable Number Tandem Repeats.

Variable Number Tandem repeats (VNTRs) refer to repeating motifs of size greater than five bp. VNTRs are an important source of genetic variation, and have been associated with multiple Mendelian and complex phenotypes. However, the highly repetitive structures require reads to span the region for accurate genotyping. Pacific Biosciences HiFi sequencing spans large regions and is highly accurate but relatively expensive. Therefore, targeted sequencing approaches coupled with long-read sequencing have been proposed to improve efficiency and throughput. In this paper, we systematically explored the trade-off between targeted and whole genome HiFi sequencing for genotyping VNTRs. We curated a set of 10 , 787 gene-proximal (G-)VNTRs, and 48 phenotype-associated (P-)VNTRs of interest. Illumina reads only spanned 46% of the G-VNTRs and 71% of P-VNTRs, motivating the use of HiFi sequencing. We performed targeted sequencing with hybridization by designing custom probes for 9,999 VNTRs and sequenced 8 samples using HiFi and Illumina sequencing, followed by adVNTR genotyping. We compared these results against HiFi whole genome sequencing (WGS) data from 28 samples in the Human Pangenome Reference Consortium (HPRC). With the targeted approach only 4,091 (41%) G-VNTRs and only 4 (8%) of P-VNTRs were spanned with at least 15 reads. A smaller subset of 3,579 (36%) G-VNTRs had higher median coverage of at least 63 spanning reads. The spanning behavior was consistent across all 8 samples. Among 5,638 VNTRs with low-coverage ( < 15), 67% were located within GC-rich regions ( > 60%). In contrast, the 40X WGS HiFi dataset spanned 98% of all VNTRs and 49 (98%) of P-VNTRs with at least 15 spanning reads, albeit with lower coverage. Spanning reads were sufficient for accurate genotyping in both cases. Our findings demonstrate that targeted sequencing provides consistently high coverage for a small subset of low-GC VNTRs, but WGS is more effective for broad and sufficient sampling of a large number of VNTRs.

Minisatellite Repeats↗

PubMed2006

Evidence for large inversion polymorphisms in the human genome from HapMap data.

Knowledge about structural variation in the human genome has grown tremendously in the past few years. However, inversions represent a class of structural variation that remains difficult to detect. We present a statistical method to identify large inversion polymorphisms using unusual Linkage Disequilibrium (LD) patterns from high-density SNP data. The method is designed to detect chromosomal segments that are inverted (in a majority of the chromosomes) in a population with respect to the reference human genome sequence. We demonstrate the power of this method to detect such inversion polymorphisms through simulations done using the HapMap data. Application of this method to the data from the first phase of the International HapMap project resulted in 176 candidate inversions ranging from 200 kb to several megabases in length. Our predicted inversions include an 800-kb polymorphic inversion at 7p22, a 1.1-Mb inversion at 16p12, and a novel 1.2-Mb inversion on chromosome 10 that is supported by the presence of two discordant fosmids. Analysis of the genomic sequence around inversion breakpoints showed that 11 predicted inversions are flanked by pairs of highly homologous repeats in the inverted orientation. In addition, for three candidate inversions, the inverted orientation is represented in the Celera genome assembly. Although the power of our method to detect inversions is restricted because of inherently noisy LD patterns in population data, inversions predicted by our method represent strong candidates for experimental validation and analysis.

Biometry↗

PubMed2006

Inference about recombination from haplotype data: lower bounds and recombination hotspots.

Recombination is an important evolutionary mechanism responsible for creating the patterns of haplotype variation observable in human populations. Recently, there has been extensive research on understanding the fine-scale variation in recombination across the human genome using DNA polymorphism data. Historical recombination events leave signature patterns in haplotype data. A nonparametric approach for estimating the number of historical recombination events is to compute the minimum number of recombination events in the history of a set of haplotypes. In this paper, we provide new and improved methods for computing lower bounds on the minimum number of recombination events. These methods are shown to detect a higher number of recombination events for a haplotype dataset from a region in the lipoprotein lipase gene than previous lower bounds. We apply our methods to two datasets for which recombination hotspots have been experimentally determined and demonstrate a high density of detectable recombination events in the regions annotated as recombination hotspots. The programs implementing the methods in this paper are available at www.cs.ucsd.edu/users/vibansal/RecBounds/.

Chromosomes, Human↗

PubMed2005

Review of awakening agents.

Brain injuries are a serious burden of illness to Canada and the US. Advances in managing head trauma have allowed more patients to emerge from decreased levels of consciousness and helped them cope with neurocognitive, neurobehavioural, and neuropsychiatric deficits. In this article, we review the current (1986-2002) evidence surrounding the pharmacological management of arousal states and the aforementioned neurological sequelae of head injury in either acute or chronic conditions. This article will review the evidence for the use of psychostimulants (methylphenidate), antidepressants (amitriptyline, selective serotonin reuptake inhibitors, and buproprion), Parkinson's medications (amantadine, bromocriptine, carbidopa/levodopa), anticonvulsants (valproic acid), modafinil (Provigil), lactate, hyperbaric oxygen chamber, electroconvulsive therapy, and transmagnetic stimulation, in patients following a head injury. The review did not include all anticonvulsants, neuroleptics, beta-blockers, benzodiazepines, azospirones or cognitive enhancers. Unfortunately, the quality of the evidence is generally poor, and sometimes conflicting, which in turn results in indecisive guidelines for treating patients. Accepting the inherent flaws in the evidence we feel that this paper may serve as a stepping-stone for future researchers to improve data gathering that targets neurocognitive, neurobehavioural and neuropsychiatric symptoms following a head injury.

Brain Injuries↗

PubMedDate not supplied

The number of recombination events in a sample history: conflict graph and lower bounds.

We consider the following problem: Given a set of binary sequences, determine lower bounds on the minimum number of recombinations required to explain the history of the sample, under the infinite-sites model of mutation. The problem has implications for finding recombination hotspots and for the Ancestral Recombination Graph reconstruction problem. Hudson and Kaplan gave a lower bound based on the four-gamete test. In practice, their bound Rm often greatly underestimates the minimum number of recombinations. The problem was recently revisited by Myers and Griffiths, who introduced two new lower bounds Rh and Rs which are provably better, and also yield good bounds in practice. However, the worst-case complexities of their procedures for computing Rh and Rs are exponential and super-exponential, respectively. In this paper, we show that the number of nontrivial connected components, Rc, in the conflict graph for a given set of sequences, computable in time O(nm2), is also a lower bound on the minimum number of recombination events. We show that in many cases, Rc is a better bound than Rh. The conflict graph was used by Gusfield et al. to obtain a polynomial time algorithm for the galled tree problem, which is a special case of the Ancestral Recombination Graph (ARG) reconstruction problem. Our results also offer some insight into the structural properties of this graph and are of interest for the general Ancestral Recombination Graph reconstruction problem.

Alcohol Dehydrogenase↗