Eric Gamazon
At the intersection of computational biology, statistical genetics, and functional genomics, my research work, as part of Dr. Nancy Cox’s computational lab in Genetic Medicine, focuses on the identification and characterization of genetic variation influencing complex human traits. Our primary interest is in developing and extending methods for elucidating the genetic architecture of complex disorders and pharmacologic phenotypes. An ongoing project involves the genetics of gene expression and the use of expression quantitative trait loci (eQTLs) to expand on genetic association studies.
In addition, as a bioinformatician in the Pharmacogenomics of Anticancer Agents Research (PAAR) Group at the University of Chicago, I apply computational approaches (e.g., genome-wide association studies) to the study of a wide array of functionally diverse chemotherapeutics. Within PAAR, I work with a multidisciplinary team of investigators whose goal is to study the contribution of genetic polymorphisms to the pharmacodynamics and pharmacokinetics of anticancer agents.
Research interests
-
InterestseQTL, Genomics, complex traits, Disease Susceptibility, Pharmacogenetics, Epigenetics, Methylation, Transcriptomics, Genetic Association Studies, RNA Sequencing
Other
-
Scientific MembershipsAmerican Society of Human Genetics, Philosophy of Science Association, International Society for Computational Biology
-
Journal RefereeJournal of Biomedical Informatics, Pharmacogenetics and Genomics, PLoS ONE, Bioinformatics, Personalized Medicine, BMC Genomics
-
Other InterestsThe Notebooks of Malte Laurids Brigge (Rainer Maria Rilke), Gitanjali (Rabindranath Tagore), The Sorrows of Young Werther (Johann Wolfgang von Goethe), The Crisis of European Sciences and Transcendental Philosophy (Edmund Husserl)
Publications
-
12.30Impact points
On Sharing Quantitative Trait GWAS Results in an Era of Multiple-omics Data and the Limits of Genomic Privacy.
American journal of human genetics. 04/2012; 90(4):591-8.
Recent advances in genome-scale, system-level measurements of quantitative phenotypes (transcriptome, metabolome, and proteome) promise to yield unprecedented biological insights. In this environment, broad dissemination of results from genome-wide association studies (GWASs) or deep-sequencing effo... [more] Recent advances in genome-scale, system-level measurements of quantitative phenotypes (transcriptome, metabolome, and proteome) promise to yield unprecedented biological insights. In this environment, broad dissemination of results from genome-wide association studies (GWASs) or deep-sequencing efforts is highly desirable. However, summary results from case-control studies (allele frequencies) have been withdrawn from public access because it has been shown that they can be used for inferring participation in a study if the individual's genotype is available. A natural question that follows is how much private information is contained in summary results from quantitative trait GWAS such as regression coefficients or p values. We show that regression coefficients for many SNPs can reveal the person's participation and for participants his or her phenotype with high accuracy. Our power calculations show that regression coefficients contain as much information on individuals as allele frequencies do, if the person's phenotype is rather extreme or if multiple phenotypes are available as has been increasingly facilitated by the use of multiple-omics data sets. These findings emphasize the need to devise a mechanism that allows data sharing that will facilitate scientific progress without sacrificing privacy protection.
-
3.99Impact points
Whole-genome studies identify solute carrier transporters in cellular susceptibility to paclitaxel.
Pharmacogenetics and genomics. 03/2012;
OBJECTIVE: The clinical use of paclitaxel is limited by variable responses and the potential for significant toxicity. To date, studies of associations between variants in candidate genes and paclitaxel effects have yielded conflicting results. We aimed to evaluate the relationships between global g... [more] OBJECTIVE: The clinical use of paclitaxel is limited by variable responses and the potential for significant toxicity. To date, studies of associations between variants in candidate genes and paclitaxel effects have yielded conflicting results. We aimed to evaluate the relationships between global gene expression and paclitaxel sensitivity. METHODS: We utilized well-genotyped lymphoblastoid cell lines derived from the International HapMap Project to evaluate the relationships between cellular susceptibility to paclitaxel and global gene expression. Cells were exposed to varying concentrations of paclitaxel to evaluate paclitaxel-induced cytotoxicity and apoptosis. Among the top genes, we identified solute carrier (SLC) genes associated with paclitaxel sensitivity and narrowed down the list to those that had single nucleotide polymorphisms associated with both the expression level of the SLC gene and also with paclitaxel sensitivity. We performed an independent validation in an independent set of cell lines and also conducted functional studies using RNA interference. RESULTS: Of all genes associated with paclitaxel-induced cytotoxicity at P less than 0.05 (1713 genes), there was a significant enrichment in SLC genes (31 genes). A subset of SLC genes, namely SLC31A2, SLC43A1, SLC35A5, and SLC41A2, was associated with paclitaxel sensitivity and had regulating single nucleotide polymorphisms that were also associated with paclitaxel-induced cytotoxicity. Multivariate modeling demonstrated that those four SLC genes together explained 20% of the observed variability in paclitaxel susceptibility. Using RNA interference, we demonstrated increased paclitaxel susceptibility with knockdown of three SLC genes, SLC31A2, SLC35A5, and SLC41A2. CONCLUSION: Our findings are novel and lend further support to the role of transporters, specifically solute carriers, in mediating cellular susceptibility to paclitaxel.
-
4.31Impact points
Genetic susceptibility to type 2 diabetes and breast cancer risk in women of European and african ancestry.
Cancer epidemiology, biomarkers & prevention : a publication of the American Association for Cancer Research, cosponsored by the American Society of Preventive Oncology. 03/2012; 21(3):552-6.
Epidemiologic studies have reported a positive association between type 2 diabetes (T2D) and breast cancer risk, independent of body weight. We investigated 40 genetic variants known to be associated with T2D in relation to breast cancer risk among 2,651 breast cancer cases and 2,520 controls of Afr... [more] Epidemiologic studies have reported a positive association between type 2 diabetes (T2D) and breast cancer risk, independent of body weight. We investigated 40 genetic variants known to be associated with T2D in relation to breast cancer risk among 2,651 breast cancer cases and 2,520 controls of African or European ancestry that were pooled from seven studies. We found that two T2D risk alleles in Caucasian women (rs5945326-G, rs12518099-C) and one in women of African ancestry (rs7578597-T) were positively associated with breast cancer risk at a nominal significance level of 0.05, whereas two T2D risk alleles were inversely associated with breast cancer risk in Caucasian women (rs1111875-C, rs10923931-T). The composite T2D susceptibility score (the number of risk allele) was not significantly associated with breast cancer risk. The association between established T2D genetic susceptibility variants and breast cancer risk in women of African or European ancestry is likely weak, if it does exist. Impact: The pleiotropic effects of known T2D risk alleles cannot explain the association between T2D and breast cancer risk. Cancer Epidemiol Biomarkers Prev; 21(3); 552-6. ©2012 AACR.
-
On Sharing Quantitative Trait GWAS Results in an Era of Multiple-omics Data and the Limits of Genomic Privacy
American Journal of Human Genetics. 03/2012;
Recent advances in genome-scale, system-level measurements of quantitative phenotypes (transcriptome, metabolome, and proteome) promise to yield unprecedented biological insights. In this environment, broad dissemination of results from genome-wide association studies (GWASs) or deep-sequencing effo... [more] Recent advances in genome-scale, system-level measurements of quantitative phenotypes (transcriptome, metabolome, and proteome) promise to yield unprecedented biological insights. In this environment, broad dissemination of results from genome-wide association studies (GWASs) or deep-sequencing efforts is highly desirable. However, summary results from case-control studies (allele frequencies) have been withdrawn from public access because it has been shown that they can be used for inferring participation in a study if the individual's genotype is available. A natural question that follows is how much private information is contained in summary results from quantitative trait GWAS such as regression coefficients or p values. We show that regression coefficients for many SNPs can reveal the person's participation and for participants his or her phenotype with high accuracy. Our power calculations show that regression coefficients contain as much information on individuals as allele frequencies do, if the person's phenotype is rather extreme or if multiple phenotypes are available as has been increasingly facilitated by the use of multiple-omics data sets. These findings emphasize the need to devise a mechanism that allows data sharing that will facilitate scientific progress without sacrificing privacy protection.
-
3.99Impact points
The limits of genome-wide methods for pharmacogenomic testing.
Pharmacogenetics and genomics. 02/2012; 22(4):261-72.
The goal of pharmacogenomics is the translation of genomic discoveries into individualized patient care. Recent advances in the means to survey human genetic variation are fundamentally transforming our understanding of the genetic basis of interindividual variation in therapeutic response. The goal... [more] The goal of pharmacogenomics is the translation of genomic discoveries into individualized patient care. Recent advances in the means to survey human genetic variation are fundamentally transforming our understanding of the genetic basis of interindividual variation in therapeutic response. The goal of this study was to systematically evaluate high-throughput genotyping technologies for their ability to assay variation in pharmacogenetically important genes (pharmacogenes). These platforms are either being proposed for or are already being widely used for clinical implementation; therefore, knowledge of coverage of pharmacogenes on these platforms would serve to better evaluate current or proposed pharmacogenetic association studies. Among the genes included in our study are drug-metabolizing enzymes, transporters, receptors, and drug targets, of interest to the entire pharmacogenetic community. We considered absolute and linkage disequilibrium (LD)-informed coverage, minor allele frequency spectrum, and functional annotation for a Caucasian population. We also examined the effect of LD, effect size, and cohort size on the power to detect single nucleotide polymorphism associations. In our analysis of 253 pharmacogenes, we found that no platform showed more than 85% coverage of these genes (after accounting for LD). Furthermore, the lack of coverage showed a marked increase at minor allele frequencies of less than 20%. Even after accounting for LD, only 30% of the missense polymorphisms (which are enriched for low-frequency alleles) were covered by HapMap, with still lower coverage on the other platforms. We have conducted the first systematic evaluation of the Axiom Genomic Database, Omni 2.5 M, and the Drug Metabolizing Enzymes and Transporters chip. This study is the first to utilize the 1000 Genomes Project to present a comprehensive evaluative framework. Our results provide a much-needed assessment of microarray-based genotyping and next-generation sequencing technologies' ability to survey fully the variation in genes of particular interest to the pharmacogenetics community. Our findings demonstrate the limitations of genome-wide methods and the challenges of implementing pharmacogenomic tests into the clinical context.
-
9.53Impact points
Mixed effects modeling of proliferation rates in cell-based models: consequence for pharmacogenomics and cancer.
PLoS genetics. 02/2012; 8(2):e1002525.
The International HapMap project has made publicly available extensive genotypic data on a number of lymphoblastoid cell lines (LCLs). Building on this resource, many research groups have generated a large amount of phenotypic data on these cell lines to facilitate genetic studies of disease risk or... [more] The International HapMap project has made publicly available extensive genotypic data on a number of lymphoblastoid cell lines (LCLs). Building on this resource, many research groups have generated a large amount of phenotypic data on these cell lines to facilitate genetic studies of disease risk or drug response. However, one problem that may reduce the usefulness of these resources is the biological noise inherent to cellular phenotypes. We developed a novel method, termed Mixed Effects Model Averaging (MEM), which pools data from multiple sources and generates an intrinsic cellular growth rate phenotype. This intrinsic growth rate was estimated for each of over 500 HapMap cell lines. We then examined the association of this intrinsic growth rate with gene expression levels and found that almost 30% (2,967 out of 10,748) of the genes tested were significant with FDR less than 10%. We probed further to demonstrate evidence of a genetic effect on intrinsic growth rate by determining a significant enrichment in growth-associated genes among genes targeted by top growth-associated SNPs (as eQTLs). The estimated intrinsic growth rate as well as the strength of the association with genetic variants and gene expression traits are made publicly available through a cell-based pharmacogenomics database, PACdb. This resource should enable researchers to explore the mediating effects of proliferation rate on other phenotypes.
-
15.05Impact points
Enrichment of cis-regulatory gene expression SNPs and methylation quantitative trait loci among bipolar disorder susceptibility variants.
Molecular psychiatry. 01/2012;
We conducted a systematic study of top susceptibility variants from a genome-wide association (GWA) study of bipolar disorder to gain insight into the functional consequences of genetic variation influencing disease risk. We report here the results of experiments to explore the effects of these susc... [more] We conducted a systematic study of top susceptibility variants from a genome-wide association (GWA) study of bipolar disorder to gain insight into the functional consequences of genetic variation influencing disease risk. We report here the results of experiments to explore the effects of these susceptibility variants on DNA methylation and mRNA expression in human cerebellum samples. Among the top susceptibility variants, we identified an enrichment of cis regulatory loci on mRNA expression (eQTLs), and a significant excess of quantitative trait loci for DNA CpG methylation, hereafter referred to as methylation quantitative trait loci (mQTLs). Bipolar disorder susceptibility variants that cis regulate both cerebellar expression and methylation of the same gene are a very small proportion of bipolar disorder susceptibility variants. This finding suggests that mQTLs and eQTLs provide orthogonal ways of functionally annotating genetic variation within the context of studies of pathophysiology in brain. No lymphocyte mQTL enrichment was found, suggesting that mQTL enrichment was specific to the cerebellum, in contrast to eQTLs. Separately, we found that using mQTL information to restrict the number of single-nucleotide polymorphisms studied enhances our ability to detect a significant association. With this restriction a priori informed by the observed functional enrichment, we identified a significant association (rs12618769, P(bonferroni)<0.05) from two other GWA studies (TGen+GAIN; 2191 cases and 1434 controls) of bipolar disorder, which we replicated in an independent GWA study (WTCCC). Collectively, our findings highlight the importance of integrating functional annotation of genetic variants for gene expression and DNA methylation to advance the biological understanding of bipolar disorder.Molecular Psychiatry advance online publication, 3 January 2012; doi:10.1038/mp.2011.174.
-
7.39Impact points
An eQTL-based method identifies CTTN and ZMAT3 as pemetrexed susceptibility markers.
Human molecular genetics. 12/2011;
Pemetrexed, approved for the treatment of non-small cell lung cancer and malignant mesothelioma, has adverse effects including neutropenia, leucopenia, thrombocytopenia, anemia, fatigue and nausea. The results we report here represent the first genome-wide study aimed at identifying genetic predicto... [more] Pemetrexed, approved for the treatment of non-small cell lung cancer and malignant mesothelioma, has adverse effects including neutropenia, leucopenia, thrombocytopenia, anemia, fatigue and nausea. The results we report here represent the first genome-wide study aimed at identifying genetic predictors of pemetrexed response. We utilized expression quantitative trait loci (eQTLs) mapping combined with drug-induced cytotoxicity data to gain mechanistic insights into the observed genetic associations with pemetrexed susceptibility. We found that CTTN and ZMAT3 expression signature explained >30% of the pemetrexed susceptibility phenotype variation for pemetrexed in the discovery population. Replication using PCR and a semi-high-throughput, scalable assay system confirmed the initial discovery results in an independent set of samples derived from the same ancestry. Furthermore, functional validation in both germline and tumor cells demonstrates a decrease in cell survival following knockdown of CTTN or ZMAT3. In addition to our particular findings on genetic and gene expression predictors of susceptibility phenotype for pemetrexed, the work presented here will be valuable to the robust discovery and validation of genetic determinants and gene expression signatures of various chemotherapeutic susceptibilities.
-
4.40Impact points
Genome-wide meta-analysis identifies variants associated with platinating agent susceptibility across populations.
The pharmacogenomics journal. 08/2011;
Platinating agents are used in the treatment of many cancers, yet they can induce toxicities and resistance that limit their utility. Using previously published and additional world population panels of diverse ancestry totaling 608 lymphoblastoid cell lines (LCLs), we performed meta-analyses of ove... [more] Platinating agents are used in the treatment of many cancers, yet they can induce toxicities and resistance that limit their utility. Using previously published and additional world population panels of diverse ancestry totaling 608 lymphoblastoid cell lines (LCLs), we performed meta-analyses of over 3 million single-nucleotide polymorphisms (SNPs) for both carboplatin- and cisplatin-induced cytotoxicity. The most significant SNP in the carboplatin meta-analysis is located in an intron of NBAS (neuroblastoma amplified sequence; P=5.1 × 10(-7)). The most significant SNP in the cisplatin meta-analysis is upstream of KRT16P2 (P=5.8 × 10(-7)). We also show that cisplatin-susceptibility SNPs are enriched for carboplatin-susceptibility SNPs. Most of the variants that associate with platinum-induced cytotoxicity are polymorphic across multiple world populations; therefore, they could be tested in follow-up studies in diverse clinical populations. Seven genes previously implicated in platinating agent response, including BCL2 (B-cell CLL/lymphoma 2), GSTM1 (glutathione S-transferase mu 1), GSTT1, ERCC2 and ERCC6, were also implicated in our meta-analyses.The Pharmacogenomics Journal advance online publication, 16 August 2011; doi:10.1038/tpj.2011.38.
-
5.56Impact points
Population differences in microRNA expression and biological implications.
RNA biology. 07/2011; 8(4):692-701.
Population differences observed for complex traits may be attributed to the combined effect of socioeconomic, environmental, genetic and epigenetic factors. To better understand population differences in complex traits, genome-wide genetic and gene expression differences among ethnic populations hav... [more] Population differences observed for complex traits may be attributed to the combined effect of socioeconomic, environmental, genetic and epigenetic factors. To better understand population differences in complex traits, genome-wide genetic and gene expression differences among ethnic populations have been studied. Here we set out to evaluate population differences in small non-coding RNAs through an evaluation of microRNA (miRNA) baseline expression in HapMap lymphoblastoid cell lines (LCLs) derived from 53 CEU (Utah residents with northern and western European ancestry) and 54 YRI (African from Ibadan, Nigeria). Using the Exiqon miRCURYTM LNA arrays, we found that 16% of all miRNAs evaluated in our study differ significantly between these 2 ethnic groups (pBonferroni corrected< 0.05). Furthermore, we explored the potential biological function of these observed differentially expressed miRNAs by comprehensively examining their effect on the transcriptome and their relationship with cellular sensitivity drug phenotypes. After multiple testing adjustment (false discovery rate (FDR)< 0.1), we found that 55% and 88% of the differentially expressed miRNAs were significantly and inversely correlated with an mRNA expression phenotype in the CEU and YRI samples, respectively. Interestingly, a substantial proportion (64%) of these miRNAs correlated with cellular sensitivity to chemotherapeutic agents (FDR< 0.05). Lastly, upon performing a genome-wide association study between SNPs and miRNA expression, we identified a large number of SNPs exhibiting different allele frequencies that affect the expression of these differentially expressed miRNAs, suggesting the role of genetic variants in mediating the observed population differences.
-
6.75Impact points
Platinum sensitivity-related germline polymorphism discovered via a cell-based approach and analysis of its association with outcome in ovarian cancer patients.
Clinical cancer research : an official journal of the American Association for Cancer Research. 06/2011; 17(16):5490-500.
Cell-based approaches were used to identify genetic markers predictive of patients' risk for poor response prior to chemotherapy. We conducted genome-wide association studies (GWAS) to identify single-nucleotide polymorphisms (SNP) associated with cellular sensitivity to carboplatin through thei... [more] Cell-based approaches were used to identify genetic markers predictive of patients' risk for poor response prior to chemotherapy. We conducted genome-wide association studies (GWAS) to identify single-nucleotide polymorphisms (SNP) associated with cellular sensitivity to carboplatin through their effects on mRNA expression using International HapMap lymphoblastoid cell lines (LCL) and replicated them in additional LCLs. SNPs passing both stages of the cell-based study were tested for association with progression-free survival (PFS) in patients. Phase 1 validation was based on 377 ovarian cancer patients receiving at least four cycles of carboplatin and paclitaxel from the Australian Ovarian Cancer Study (AOCS). Positive associations were then assessed in phase 2 validation analysis of 1,326 patients from the Ovarian Cancer Association Consortium and The Cancer Genome Atlas. In the initial GWAS, 342 SNPs were associated with carboplatin-induced cytotoxicity, of which 18 unique SNPs were retained after assessing their association with gene expression. One SNP (rs1649942) was replicated in an independent LCL set (Bonferroni adjusted P < 0.05). It was found to be significantly associated with decreased PFS in phase 1 AOCS patients (P(per-allele) = 2 × 10(-2)), with a stronger effect in the subset of women with optimally debulked tumors (P(per-allele) = 4 × 10(-3)). rs1649942 was also associated with poorer overall survival in women with optimally debulked tumors (P(per-allele) = 9 × 10(-3)). However, this SNP was not significant in phase 2 validation analysis with patients from numerous cohorts. This study shows the potential of cell-based, genome-wide approaches to identify germline predictors of treatment outcome and highlights the need for extensive validation in patients to assess their clinical effect.
-
6.55Impact points
Genome-wide association and meta-analysis in populations from Starr County, Texas, and Mexico City identify type 2 diabetes susceptibility loci and enrichment for expression quantitative trait loci in top signals.
Diabetologia. 06/2011; 54(8):2047-55.
We conducted genome-wide association studies (GWASs) and expression quantitative trait loci (eQTL) analyses to identify and characterise risk loci for type 2 diabetes in Mexican-Americans from Starr County, TX, USA. Using 1.8 million directly interrogated and imputed genotypes in 837 unrelated type ... [more] We conducted genome-wide association studies (GWASs) and expression quantitative trait loci (eQTL) analyses to identify and characterise risk loci for type 2 diabetes in Mexican-Americans from Starr County, TX, USA. Using 1.8 million directly interrogated and imputed genotypes in 837 unrelated type 2 diabetes cases and 436 normoglycaemic controls, we conducted Armitage trend tests. To improve power in this population with high disease rates, we also performed ordinal regression including an intermediate class with impaired fasting glucose and/or glucose tolerance. These analyses were followed by meta-analysis with a study of 967 type 2 diabetes cases and 343 normoglycaemic controls from Mexico City, Mexico. The top signals (unadjusted p value <1 × 10(-5)) included 49 single nucleotide polymorphisms (SNPs) in eight gene regions (PER3, PARD3B, EPHA4, TOMM7, PTPRD, HNT [also known as RREB1], LOC729993 and IL34) and six intergenic regions. Among these was a missense polymorphism (rs10462020; Gly639Val) in the clock gene PER3, a system recently implicated in diabetes. We also report a second signal (minimum p value 1.52 × 10(-6)) within PTPRD, independent of the previously implicated SNP, in a population of Han Chinese. Top meta-analysis signals included known regions HNF1A and KCNQ1. Annotation of top association signals in both studies revealed a marked excess of trans-acting eQTL in both adipose and muscle tissues. In the largest study of type 2 diabetes in Mexican populations to date, we identified modest associations of novel and previously reported SNPs. In addition, in our top signals we report significant excess of SNPs that predict transcript levels in muscle and adipose tissues.
-
6.63Impact points
Copy number polymorphisms and anticancer pharmacogenomics.
Genome biology. 05/2011; 12(5):R46.
Recent studies have investigated the contribution of copy number variants (CNVs) to disease susceptibility in a multitude of complex disorders, including systemic lupus erythematosus, Crohn's disease, and various neurodevelopmental disorders. Relatively few CNV studies, however, have been conduc... [more] Recent studies have investigated the contribution of copy number variants (CNVs) to disease susceptibility in a multitude of complex disorders, including systemic lupus erythematosus, Crohn's disease, and various neurodevelopmental disorders. Relatively few CNV studies, however, have been conducted on pharmacologic phenotypes even though these structural variants are likely to play an important role. We developed a genome-wide method to identify CNVs that contribute to heterogeneity in drug response, focusing on drugs that are widely used in anticancer treatment regimens. We conducted a comprehensive genome-wide study of CNVs from population-scale array-based and sequencing-based surveys by analyzing their effect on cellular sensitivity to platinating agents and topoisomerase II inhibitors. We identified extensive CNV regions associated with cellular sensitivity to functionally diverse chemotherapeutics, supporting the hypothesis that variation in copy number contributes to variation in drug response. Interestingly, although single nucleotide polymorphisms (SNPs) tag some of the CNVs associated with drug sensitivity, several of the most significant CNV-drug associations are independent of SNPs; consequently, they represent genetic variations that have not been previously interrogated by SNP studies of pharmacologic phenotypes. Our findings demonstrate that pharmacogenomic studies may greatly benefit from the study of CNVs as expression quantitative trait loci, thus contributing broadly to our understanding of the complex traits genetics of CNVs. We also extend our PACdb resource, a database that makes available to the scientific community relationships between genetic variation, gene expression, and sensitivity to various drugs in cell-based models.
-
Germline polymorphisms discovered via a cell-based, genome-wide approach predict platinum response in head and neck cancers.
Translational research : the journal of laboratory and clinical medicine. 05/2011; 157(5):265-72.
Identifying patients prior to treatment who are more likely to benefit from chemotherapeutic agents or more likely to experience adverse events is an aim of personalized medicine. Pharmacogenomics offers a potential means of achieving this goal through the discovery of predictive germline genetic bi... [more] Identifying patients prior to treatment who are more likely to benefit from chemotherapeutic agents or more likely to experience adverse events is an aim of personalized medicine. Pharmacogenomics offers a potential means of achieving this goal through the discovery of predictive germline genetic biomarkers. When applied particularly to the treatment of head and neck cancers, such information could offer significant benefit to patients as a means of potentially reducing morbidity associated with platinum-based chemotherapy. We developed a genome-wide, cell-based approach to identify single nucleotide polymorphisms (SNPs) associated with platinum susceptibility and then evaluated these SNPs as predictors for response and toxicity in head and neck cancer patients treated with platinum-based therapy as part of a phase II clinical trial. Sixty head and neck cancer patients were evaluated. Of 45 genome-wide SNPs examined, we found that 2 SNPs, rs6870861 (P=0.004; false discovery rate [FDR] <0.05) and rs2551038 (P=0.005; FDR <0.05), were associated significantly with overall response to carboplatin-based induction chemotherapy when incorporated into a model along with total carboplatin exposure. Interestingly, these 2 SNPs are associated strongly with the baseline expression of >20 genes (all P ≤10(-4)), and that 2 genes (SLC22A5 and SLCO4C1) are important organic cation/anion transporters known to affect platinum uptake and clearance. Several other SNPs were associated nominally with carboplatin-related hematologic toxicities. These findings demonstrate importantly that a genome-wide, cell-based model can identify novel germline genetic biomarkers of platinum susceptibility, which are replicable in a clinical setting with treated cancer patients and seem clinically meaningful for potentially enabling future personalization of care in such patients.
-
9.53Impact points
Identification, replication, and functional fine-mapping of expression quantitative trait loci in primary human liver tissue.
PLoS genetics. 05/2011; 7(5):e1002078.
The discovery of expression quantitative trait loci ("eQTLs") can help to unravel genetic contributions to complex traits. We identified genetic determinants of human liver gene expression variation using two independent collections of primary tissue profiled with Agilent (n = 206) and Ill... [more] The discovery of expression quantitative trait loci ("eQTLs") can help to unravel genetic contributions to complex traits. We identified genetic determinants of human liver gene expression variation using two independent collections of primary tissue profiled with Agilent (n = 206) and Illumina (n = 60) expression arrays and Illumina SNP genotyping (550K), and we also incorporated data from a published study (n = 266). We found that ∼30% of SNP-expression correlations in one study failed to replicate in either of the others, even at thresholds yielding high reproducibility in simulations, and we quantified numerous factors affecting reproducibility. Our data suggest that drug exposure, clinical descriptors, and unknown factors associated with tissue ascertainment and analysis have substantial effects on gene expression and that controlling for hidden confounding variables significantly increases replication rate. Furthermore, we found that reproducible eQTL SNPs were heavily enriched near gene starts and ends, and subsequently resequenced the promoters and 3'UTRs for 14 genes and tested the identified haplotypes using luciferase assays. For three genes, significant haplotype-specific in vitro functional differences correlated directly with expression levels, suggesting that many bona fide eQTLs result from functional variants that can be mechanistically isolated in a high-throughput fashion. Finally, given our study design, we were able to discover and validate hundreds of liver eQTLs. Many of these relate directly to complex traits for which liver-specific analyses are likely to be relevant, and we identified dozens of potential connections with disease-associated loci. These included previously characterized eQTL contributors to diabetes, drug response, and lipid levels, and they suggest novel candidates such as a role for NOD2 expression in leprosy risk and C2orf43 in prostate cancer. In general, the work presented here will be valuable for future efforts to precisely identify and functionally characterize genetic contributions to a variety of complex traits.
-
6.96Impact points
The missing association: sequencing-based discovery of novel SNPs in VKORC1 and CYP2C9 that affect warfarin dose in African Americans.
Clinical pharmacology and therapeutics. 03/2011; 89(3):408-15.
It is well recognized that the genetic variants VKORC1-1639, CYP2C9*2, and CYP2C9*3 contribute to warfarin dose response. This has led to warfarin dosing algorithms that include these polymorphisms and explains between 47% and 56% of variability in dose in Caucasians. However, these polymorphisms ex... [more] It is well recognized that the genetic variants VKORC1-1639, CYP2C9*2, and CYP2C9*3 contribute to warfarin dose response. This has led to warfarin dosing algorithms that include these polymorphisms and explains between 47% and 56% of variability in dose in Caucasians. However, these polymorphisms explain significantly less of the variance in dose among African Americans. In order to identify novel variations that affect warfarin dose in African Americans, we used a targeted resequencing strategy that examined evolutionarily conserved sequences and regions of putative transcriptional binding. Through ethnicity-specific warfarin dose model building in 330 African Americans, we identified two novel genetic associations with higher warfarin dose, namely, VKORC1-8191 (rs61162043, P = 0.0041) and 18786 in CYP2C9 (rs7089580, P = 0.035). These novel finds are independent of the previous associations with these genes. Our regression model, encompassing both genetic and clinical variables, explained 40% of the variability in warfarin dose in African-American subjects, significantly more than any model thus far.
-
9.53Impact points
A study of CNVs as trait-associated polymorphisms and as expression quantitative trait loci.
PLoS genetics. 01/2011; 7(2):e1001292.
We conducted a comprehensive study of copy number variants (CNVs) well-tagged by SNPs (r(2)≥ 0.8) by analyzing their effect on gene expression and their association with disease susceptibility and other complex human traits. We tested whether these CNVs were more likely to be functional than frequen... [more] We conducted a comprehensive study of copy number variants (CNVs) well-tagged by SNPs (r(2)≥ 0.8) by analyzing their effect on gene expression and their association with disease susceptibility and other complex human traits. We tested whether these CNVs were more likely to be functional than frequency-matched SNPs as trait-associated loci or as expression quantitative trait loci (eQTLs) influencing phenotype by altering gene regulation. Our study found that CNV-tagging SNPs are significantly enriched for cis eQTLs; furthermore, we observed that trait associations from the NHGRI catalog show an overrepresentation of SNPs tagging CNVs relative to frequency-matched SNPs. We found that these SNPs tagging CNVs are more likely to affect multiple expression traits than frequency-matched variants. Given these findings on the functional relevance of CNVs, we created an online resource of expression-associated CNVs (eCNVs) using the most comprehensive population-based map of CNVs to inform future studies of complex traits. Although previous studies of common CNVs that can be typed on existing platforms and/or interrogated by SNPs in genome-wide association studies concluded that such CNVs appear unlikely to have a major role in the genetic basis of several complex diseases examined, our findings indicate that it would be premature to dismiss the possibility that even common CNVs may contribute to complex phenotypes and at least some common diseases.
-
4.95Impact points
Comprehensive evaluation of the contribution of X chromosome genes to platinum sensitivity.
Molecular cancer therapeutics. 01/2011; 10(3):472-80.
Using a genome-wide gene expression data set generated from Affymetrix GeneChip Human Exon 1.0ST array, we comprehensively surveyed the role of 322 X chromosome gene expression traits on cellular sensitivity to cisplatin and carboplatin. We identified 31 and 17 X chromosome genes whose expression le... [more] Using a genome-wide gene expression data set generated from Affymetrix GeneChip Human Exon 1.0ST array, we comprehensively surveyed the role of 322 X chromosome gene expression traits on cellular sensitivity to cisplatin and carboplatin. We identified 31 and 17 X chromosome genes whose expression levels are significantly correlated (after multiple testing correction) with sensitivity to carboplatin and cisplatin, respectively, in the combined HapMap CEU (Utah residents with ancestry from northern and western Europe) and YRI (Yoruba in Ibahan, Nigeria) populations (false discovery rate, FDR < 0.05). Of those, 14 overlap for both cisplatin and carboplatin. Using an independent gene expression quantification method, the Illumina Sentrix Human-6 Expression BeadChip, measured on the same HapMap cell lines, we found that 4 and 2 of these genes are significantly associated with carboplatin and cisplatin sensitivity, respectively, in both analyses. Two genes, CTPS2 and DLG3, were identified by both genome-wide gene expression analyses as correlated with cellular sensitivity to both platinating agents. The expression of DLG3 gene was also found to correlate with cellular sensitivity to platinating agents in NCI-60 cancer cell lines. In addition, we evaluated whether the expression of X chromosome genes contributed to the observed differences in sensitivity to the platinums between CEU and YRI-derived cell lines. Of the 34 distinct genes significantly correlated with either carboplatin or cisplatin sensitivity, 14 are differentially expressed (defined as P < 0.05) between CEU and YRI. Thus, sex chromosome genes play a role in cellular sensitivity to platinating agents and differences in the expression level of these genes are an important source of variation that should be included in comprehensive pharmacogenomic studies.
-
4.41Impact points
Genome-wide local ancestry approach identifies genes and variants associated with chemotherapeutic susceptibility in African Americans.
PloS one. 01/2011; 6(7):e21920.
Chemotherapeutic agents are used in the treatment of many cancers, yet variable resistance and toxicities among individuals limit successful outcomes. Several studies have indicated outcome differences associated with ancestry among patients with various cancer types. Using both traditional SNP-base... [more] Chemotherapeutic agents are used in the treatment of many cancers, yet variable resistance and toxicities among individuals limit successful outcomes. Several studies have indicated outcome differences associated with ancestry among patients with various cancer types. Using both traditional SNP-based and newly developed gene-based genome-wide approaches, we investigated the genetics of chemotherapeutic susceptibility in lymphoblastoid cell lines derived from 83 African Americans, a population for which there is a disparity in the number of genome-wide studies performed. To account for population structure in this admixed population, we incorporated local ancestry information into our association model. We tested over 2 million SNPs and identified 325, 176, 240, and 190 SNPs that were suggestively associated with cytarabine-, 5'-deoxyfluorouridine (5'-DFUR)-, carboplatin-, and cisplatin-induced cytotoxicity, respectively (p≤10(-4)). Importantly, some of these variants are found only in populations of African descent. We also show that cisplatin-susceptibility SNPs are enriched for carboplatin-susceptibility SNPs. Using a gene-based genome-wide association approach, we identified 26, 11, 20, and 41 suggestive candidate genes for association with cytarabine-, 5'-DFUR-, carboplatin-, and cisplatin-induced cytotoxicity, respectively (p≤10(-3)). Fourteen of these genes showed evidence of association with their respective chemotherapeutic phenotypes in the Yoruba from Ibadan, Nigeria (p<0.05), including TP53I11, COPS5 and GAS8, which are known to be involved in tumorigenesis. Although our results require further study, we have identified variants and genes associated with chemotherapeutic susceptibility in African Americans by using an approach that incorporates local ancestry information.
-
3.99Impact points
Population differences in platinum toxicity as a means to identify novel genetic susceptibility variants.
Pharmacogenetics and genomics. 05/2010; 20(5):327-37.
Clinical studies show that Asians (ASN) are more susceptible to toxicities associated with platinum-containing regimens. We hypothesized that studying ASN as an 'enriched phenotype' population could enable the discovery of novel genetic determinants of platinum susceptibility. Using well-gen... [more] Clinical studies show that Asians (ASN) are more susceptible to toxicities associated with platinum-containing regimens. We hypothesized that studying ASN as an 'enriched phenotype' population could enable the discovery of novel genetic determinants of platinum susceptibility. Using well-genotyped lymphoblastoid cell lines from the HapMap, we determined cisplatin and carboplatin cytotoxicity phenotypes (IC50s) for ASN, Caucasians (CEU), and Africans (YRI). IC50s were used in genome-wide association studies. ASN were most sensitive to platinums, corroborating clinical findings. ASN genome-wide association studies produced 479 single-nucleotide polymorphisms (SNPs) associating with cisplatin susceptibility and 199 with carboplatin susceptibility (P<10). Considering only the most significant variants (P<9.99x10), backwards elimination was then used to identify reduced-model SNPs, which robustly described the drug phenotypes within ASN. These SNPs comprised highly descriptive genetic signatures of susceptibility, with 12 SNPs explaining more than 95% of the susceptibility phenotype variation for cisplatin, and eight SNPs approximately 75% for carboplatin. To determine the possible function of these variants in ASN, the SNPs were tested for association with differential expression of target genes. SNPs were highly associated with the expression of multiple target genes, and notably, the histone H3 family was implicated for both drugs, suggesting a platinum-class mechanism. Histone H3 has repeatedly been described as regulating the formation of platinum-DNA adducts, but this is the first evidence that specific genetic variants might mediate these interactions in a pharmacogenetic manner. Finally, to determine whether any ASN-identified SNPs might also be important in other human populations, we interrogated all 479/199 SNPs for association with platinum susceptibility in an independent combined CEU/YRI population. Three unique SNPs for cisplatin and 10 for carboplatin replicated in CEU/YRI. Enriched 'platinum susceptible' populations can be used to discover novel genetic determinants governing interindividual platinum chemotherapy susceptibility.
