Yohan Bossé

Expression quantitative trait loci (eQTL) mapping studies are the next most important step in genomics to identify susceptibility genes and molecular pathways involved in human diseases following the completion of genome-wide association studies (GWAS). This article reviews the emerging concepts in genetics of gene expression and the empirical value of eQTL mapping to refine GWAS asthma susceptibility loci. eQTL mapping studies were paramount to reveal the cis and trans control of gene expression, the cell type and tissue specificity of eQTLs, and the pleiotropic nature of eQTL single nucleotide polymorphisms. A small number of eQTL studies were recently performed in tissues and cell types that are relevant for asthma and are used to interpret the biology underpinning GWAS loci including the most robust asthma susceptibility locus on 17q21. The full potential of eQTL mapping studies is just starting to be revealed. Imminent progress is expected owing to the accelerating advances in sequencing technologies to map genetic variants and transcriptomes as well as the development of bioinformatics and computational algorithms to exploit integrative genomic approaches. A short-term challenge in the field of asthma is the creation of well powered eQTL datasets testing gene expression and other molecular phenotypes in disease-relevant tissues.

Calcific aortic valve stenosis (AS) affects 2-5% of the population aged > 65 years. Functional DNA variants at the NOTCH1 locus result in bicuspid aortic valve (BAV) and severe valve calcification. The contribution of these variants to AS in the population with tricuspid aortic valve (TAV) remains to be determined. Fourteen genetic variants surrounding the NOTCH1 gene were genotyped, including rare mutations previously reported, and common polymorphisms. The study involved 457 French Canadian patients with severe tricuspid AS. Genotyping was carried out using the Illumina BeadXpress platform. Allele frequencies of common single nucleotide polymorphisms (SNPs) for patients with AS were compared to a shared control group of European ancestry (n = 3,294). In total, 88 ancestry-informative markers were used to correct for population stratification. The mutation R1107X, previously associated with AS and BAV, was identified in a relatively young patient (aged 58 years). The mutations R1279H and V2285I were detected in 18 and 14 heterozygotes, respectively. A common polymorphism (rs13290979) located in intron 2 was significantly associated with AS (p = 0.003), which remained significant after correction for multiple testing. However, this association was no longer significant after accounting for population stratification (p = 0.088). In this study, rare functional variants were found in the NOTCH1 gene in a French Canadian population of patients with severe tricuspid AS. This also suggests, for the first time, the presence of a common polymorphism in this gene conferring susceptibility to AS.

Cigarette smoking is the leading risk factor for lung cancer. To identify genes deregulated by smoking and to distinguish gene expression changes that are reversible and persistent following smoking cessation, we carried out genome-wide gene expression profiling on nontumor lung tissue from 853 patients with lung cancer. Gene expression levels were compared between never and current smokers, and time-dependent changes in gene expression were studied in former smokers. A total of 3,223 transcripts were differentially expressed between smoking groups in the discovery set (n = 344, P < 1.29 × 10⁻⁶). A substantial number of smoking-induced genes also were validated in two replication sets (n = 285 and 224), and a gene expression signature of 599 transcripts consistently segregated never from current smokers across all three sets. The expression of the majority of these genes reverted to never-smoker levels following smoking cessation, although the time course of normalization differed widely among transcripts. Moreover, some genes showed very slow or no reversibility in expression, including SERPIND1, which was found to be the most consistent gene permanently altered by smoking in the three sets. Our findings therefore indicate that smoking deregulates many genes, many of which reverse to normal following smoking cessation. However, a subset of genes remains altered even decades following smoking cessation and may account, at least in part, for the residual risk of lung cancer among former smokers. Cancer Res; 72(15); 3753–63. ©2012 AACR.

The biological functions of epicardial adipose tissue (EAT) remain largely unknown. However, the proximity of EAT to the coronary arteries suggests a role in the pathogenesis of coronary artery disease (CAD). The objectives of this study were to identify genes differentially regulated among three adipose tissues, namely EAT, mediastinal (MAT) and subcutaneous (SAT) and to study their possible relationships with the development of cardiovascular diseases. Samples were collected from subjects undergoing coronary artery bypass grafting surgeries. Gene expression was evaluated in the three adipose depots of six men using the Illumina® HumanWG-6 v3.0 expression BeadChips. Twenty-three and 73 genes were differentially up-regulated in EAT compared to MAT and SAT, respectively. Ninety-four genes were down-regulated in EAT compared to SAT. However, none were significantly down-regulated in EAT compared to MAT. More specifically, the expression of the adenosine A1 receptor (ADORA1), involved in myocardial ischemia, was significantly up-regulated in EAT. Levels of the prostaglandin D2 synthase (PTGDS) gene, recently associated with the progression of atherosclerosis, were significantly different in the three pairwise comparisons (EAT>MAT>SAT). The results of ADORA1 and PTGDS were confirmed by quantitative real-time PCR in 25 independent subjects. Overall, the transcriptional profiles of EAT and MAT were similar compared to the SAT. Despite this similarity, two genes involved in cardiovascular diseases, ADORA1 and PTGDS, were differentially up-regulated in EAT. These results provide insights about the biology of EAT and its potential implication in CAD.

P73 is a gene that may confer a genetic susceptibility to the development of chronic rhinosinusitis. To verify an association between p73 and chronic rhinosinusitis, identified in a pooling-based genome-wide association study in a human population. Prospective recruitment of 206 patients and 196 postal code-matched controls. DNA extraction, followed by pooling, high-density single nucleotide polymorphism (SNP) genotyping, and individual genotyping, was carried out. Gene sequencing was carried out in 10 patients and 1 control. Statistical analysis of SNP rs3765731 revealed a significant difference in minor allele frequency between the case and control groups. Minor allele A was more frequent in the healthy group, with an odds ratio of 0.6533, whereas G had a higher association with the disease state. Subgroup analysis of allele frequencies showed A to be associated with a lesser likelihood of developing chronic rhinosinusitis. Homozygous AA patients with severe disease had a sevenfold lesser risk of chronic rhinosinusitis compared with GG homozygotes (odds ratio 0.14). Sequencing did not reveal any amino acid changes conferring a change of function in secreted proteins. We have demonstrated an association between rs3765731 and chronic rhinosinusitis. Minor allele A has a protective effect compared with major allele G. Interaction with other signaling proteins and induction of other genes will better explain this mechanism.

Modern methods for the study of genetics offer promising new means of exploring complex diseases such as chronic rhinosinusitis (CRS). Powerful new high-throughput tools extend the capabilities of existing technologies. However, for the inexperienced reader, a lack of familiarity with the techniques used may limit comprehension of the articles and hamper the appreciation of the potential of this area of research. To improve understanding, we present an introduction to research methods in common user language, describing the techniques and applications of each while outlining differences between techniques of study of gene expression and genetic association studies. Online tools for experiment design and data analysis are presented. Practical examples from our work in the genetics of CRS are used to help understand applications for these tools. It is expected that this article will allow physicians to acquire an improved understanding of the uses and limitations of these types of studies as these techniques become increasingly commonplace in our specialty.

Background: Genetic variants at the vitamin D receptor (VDR) locus are associated with asthma and atopy. We hypothesized that polymorphisms in other genes of the vitamin D pathway are associated with asthma or atopy. Methods: Eleven candidate genes were chosen for this study, five of which code for proteins in the vitamin D metabolism pathway (CYP27A1, CYP27B1, CYP2R1, CYP24A1, GC) and six that are known to be transcriptionally regulated by vitamin D (IL10, IL1RL1, CD28, CD86, IL8, SKIIP). For each gene, we selected a maximally informative set of common SNPs (tagSNPs) using the European-derived (CEU) HapMap dataset. A total of 87 SNPs were genotyped in a French-Canadian family sample ascertained through asthmatic probands (388 nuclear families, 1064 individuals) and evaluated using the Family Based Association Test (FBAT) program. We then sought to replicate the positive findings in four independent samples: two from Western Canada, one from Australia and one from the USA (CAMP). Results: A number of SNPs in the IL10, CYP24A1, CYP2R1, IL1RL1 and CD86 genes were modestly associated with asthma and atopy (p < 0.05). Two-gene models testing for both main effects and the interaction were then performed using conditional logistic regression. Two-gene models implicating functional variants in the IL10 and VDR genes as well as in the IL10 and IL1RL1 genes were associated with asthma (p < 0.0002). In the replicate samples, SNPs in the IL10 and CYP24A1 genes were again modestly associated with asthma and atopy (p < 0.05). However, the SNPs or the orientation of the risk alleles were different between populations. A two-gene model involving IL10 and VDR was replicated in CAMP, but not in the other populations. Conclusion: A number of genes involved in the vitamin D pathway demonstrate modest levels of association with asthma and atopy. Multilocus models testing genes in the same pathway are potentially more effective to evaluate the risk of asthma, but the effects are not uniform across populations.

Background— Calcific aortic valve stenosis (AS) is a major societal and economic burden that is rising after the current shift toward an older population. Understanding the pathobiology of AS is crucial to implementing better preventive and therapeutic options. Research conducted during the past decade clearly points to active molecular and cellular processes involved in disease pathogenesis. However, no genomic approaches were used to identify genes and pathways that are differentially regulated in aortic valves of patients with and without AS. Methods and Results— A large-scale quantitative measurements of gene expression was performed on 5 normal and 5 AS valves using Affymetrix GeneChips. A total of 409 and 306 genes were significantly up- and downregulated in AS valves, respectively. The 2 most highly upregulated genes were matrix metalloproteinase 12 and chitinase 3-like 1. The upregulation of these 2 biologically relevant genes in AS was validated by real-time polymerase chain reaction in 38 aortic valves (12 normal and 26 AS). To provide a global biological validation of the whole-genome gene expression analysis, the microarray experiment was repeated in a second set of aortic valves with (n=5) or without (n=5) AS. There was an overrepresentation of small P values among genes claimed significant in the first microarray experiment. A total of 223 genes were replicated ( P 1.2), including matrix metalloproteinase 12 and chitinase 3-like 1. Conclusions— This study reveals many unrecognized genes potentially implicated in the pathogenesis of AS. These new genes were overlaid on known pathological pathways leading to AS to refine our molecular understanding of this disease.

Chronic obstructive pulmonary disease (COPD) is influenced by genetic and environmental factors. A large number of candidate gene-association studies and genome-wide linkage scans have been conducted to elucidate the genetic architecture underlying this disease. The compilation of these studies clearly revealed the complex genetic nature of COPD. Multiple genes acting on specific environmental backgrounds are likely to be the tenet of this multifactorial disorder. Encouragingly, reproducible susceptibility genes, such as SERPINE2, were recently identified. Advances in genomic research offer unprecedented capabilities to interrogate the human genome and are likely to accelerate the discovery of new genes. A comprehensive catalogue of genes implicated in the pathogenesis of COPD has great potential to lead to the development of new therapies and explain interindividual response to treatment.

Factors conferring susceptibility to chronic rhinosinusitis remain unknown. However, advances in genomics offer powerful tools to explore this disorder. Tumour necrosis factor (TNF) is a crucial proinflammatory cytokine that exerts inflammatory and immunomodulatory activities important in host defense. Our objective was to determine whether polymorphisms in genes in the TNF superfamily (TNF, TNF-alpha-induced protein 3, TNF-alpha-induced protein 6) were associated with chronic rhinosinusitis. Deoxyribonucleic acid (DNA) extracted from a population of 206 patients with severe chronic rhinosinusitis and 196 postal code-matched controls was used. Three candidate genes related to the TNF inflammatory pathway were assessed. For each gene, an informative set of single nucleotide polymorphisms was genotyped. Thirty-five single nucleotide polymorphisms were genotyped. Two polymorphisms located within the TNF-alpha-induced protein 3 gene (TNFAIP3) reached the nominal p value threshold (p < .05) for association with chronic rhinosinusitis. However, none of these polymorphisms resist multiple testing adjustments. Our data suggest that two polymorphisms in TNFAIP3 are weakly associated with severe chronic rhinosinusitis but do not support an association with genetic variants in TNF or TNF-alpha-induced protein 6. Although these results do not support correction for multiple testing and have to be validated in a second population, they nevertheless suggest that further studies of the role of TNFAIP3 in the pathogenesis of disease are warranted.