Daan W. Loth

Genome-Wide Association Studies Identify CHRNA5/3 and HTR4 in the Development of Airflow Obstruction

RATIONALE Genome-wide association studies (GWAS) have identified loci influencing lung function, but fewer genes influencing chronic obstructive pulmonary disease (COPD) are known. OBJECTIVES Perform meta-analyses of GWAS for airflow obstruction, a key pathophysiologic characteristic of COPD assessed by spirometry, in population-based cohorts examining all participants, ever smokers, never smokers, asthma-free participants, and more severe cases. METHODS Fifteen cohorts were studied for discovery (3,368 affected; 29,507 unaffected), and a population-based family study and a meta-analysis of case-control studies were used for replication and regional follow-up (3,837 cases; 4,479 control subjects). Airflow obstruction was defined as FEV(1) and its ratio to FVC (FEV(1)/FVC) both less than their respective lower limits of normal as determined by published reference equations. MEASUREMENTS AND MAIN RESULTS The discovery meta-analyses identified one region on chromosome 15q25.1 meeting genome-wide significance in ever smokers that includes AGPHD1, IREB2, and CHRNA5/CHRNA3 genes. The region was also modestly associated among never smokers. Gene expression studies confirmed the presence of CHRNA5/3 in lung, airway smooth muscle, and bronchial epithelial cells. A single-nucleotide polymorphism in HTR4, a gene previously related to FEV(1)/FVC, achieved genome-wide statistical significance in combined meta-analysis. Top single-nucleotide polymorphisms in ADAM19, RARB, PPAP2B, and ADAMTS19 were nominally replicated in the COPD meta-analysis. CONCLUSIONS These results suggest an important role for the CHRNA5/3 region as a genetic risk factor for airflow obstruction that may be independent of smoking and implicate the HTR4 gene in the etiology of airflow obstruction.

Chronic obstructive pulmonary disease and lipid core carotid artery plaques in the elderly: the Rotterdam Study.

RATIONALE Chronic obstructive pulmonary disease (COPD) is an independent risk factor for ischemic stroke and the risk increases with severity of airflow limitation. Even though vulnerable carotid artery plaque components, such as intraplaque hemorrhage and lipid core, place persons at high risk for ischemic events, the plaque composition in patients with COPD has never been explored. OBJECTIVES To investigate the prevalence of carotid wall thickening, the different carotid artery plaque components, and their relationship with severity of airflow limitation in elderly patients with COPD. METHODS This cross-sectional analysis was part of the Rotterdam Study, a prospective population-based cohort study performed in subjects aged 55 years and older. Diagnosis of COPD was confirmed by spirometry. Participants with carotid wall intima-media thickness greater than or equal to 2.5 mm on ultrasonography underwent high-resolution magnetic resonance imaging for characterization of carotid plaques. Data were analyzed using logistic regression. MEASUREMENTS AND MAIN RESULTS COPD cases (n = 253) had a twofold increased risk (odds ratio, 2.0; 95% confidence interval, 1.44-2.85; P < 0.0001) of presentation with carotid wall thickening on ultrasonography compared with control subjects with a normal lung function (n = 920). Moreover, the risk increased significantly with severity of airflow limitation. On magnetic resonance imaging, vulnerable lipid core plaques were more frequent in COPD cases than in control subjects (odds ratio, 2.1; 95% confidence interval, 1.25-3.69; P = 0.0058). CONCLUSIONS Carotid artery wall thickening is more prevalent in patients with COPD than in control subjects. In elderly subjects with carotid wall thickening, COPD is an independent predictor for the presence of a lipid core, and therefore of vulnerable plaques.

A Genome‐Wide Association Study for Venous Thromboembolism: The Extended Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium

Venous thromboembolism (VTE) is a common, heritable disease resulting in high rates of hospitalization and mortality. Yet few associations between VTE and genetic variants, all in the coagulation pathway, have been established. To identify additional genetic determinants of VTE, we conducted a two‐stage genome‐wide association study (GWAS) among individuals of European ancestry in the extended cohorts for heart and aging research in genomic epidemiology (CHARGE) VTE consortium. The discovery GWAS comprised 1,618 incident VTE cases out of 44,499 participants from six community‐based studies. Genotypes for genome‐wide single‐nucleotide polymorphisms (SNPs) were imputed to approximately 2.5 million SNPs in HapMap and association with VTE assessed using study‐design appropriate regression methods. Meta‐analysis of these results identified two known loci, in F5 and ABO. Top 1,047 tag SNPs (P ≤ 0.0016) from the discovery GWAS were tested for association in an additional 3,231 cases and 3,536 controls from three case‐control studies. In the combined data from these two stages, additional genome‐wide significant associations were observed on 4q35 at F11 (top SNP rs4253399, intronic to F11) and on 4q28 at FGG (rs6536024, 9.7 kb from FGG; P < 5.0 × 10−13 for both). The associations at the FGG locus were not completely explained by previously reported variants. Loci at or near SUSD1 and OTUD7A showed borderline yet novel associations (P < 5.0 × 10−6) and constitute new candidate genes. In conclusion, this large GWAS replicated key genetic associations in F5 and ABO, and confirmed the importance of F11 and FGG loci for VTE. Future studies are warranted to better characterize the associations with F11 and FGG and to replicate the new candidate associations.

Chronic obstructive pulmonary disease and cerebral Microbleeds the Rotterdam study

RATIONALE Chronic obstructive pulmonary disease (COPD) is a common, complex multisystem disease in the elderly with multiple comorbidities that significantly impact morbidity and mortality. Although cerebral small-vessel disease is an important cause of cognitive decline and age-related disability, it is a poorly investigated potential systemic manifestation of patients with COPD. OBJECTIVES To examine whether COPD relates to the development and location of cerebral microbleeds, a novel marker of cerebral small-vessel disease. METHODS Cross-sectional and longitudinal analyses were part of the Rotterdam Study, a prospective population-based cohort study in subjects aged greater than or equal to 55 years. Diagnosis of COPD was confirmed by spirometry. Cerebral microbleeds were detected using high-resolution magnetic resonance imaging (MRI). MEASUREMENTS AND MAIN RESULTS Subjects with COPD (n = 165) had a higher prevalence of cerebral microbleeds compared with subjects with normal lung function (n = 645) independent of age, sex, smoking status, atherosclerotic macroangiopathy, antithrombotic use, total cholesterol, triglycerides, and serum creatinin (odds ratio [OR], 1.7; 95% confidence interval [CI], 1.15-2.47; P = 0.007). Regarding the specific microbleed location, subjects with COPD had a significantly higher prevalence of microbleeds in deep or infratentorial locations (OR, 3.3; 95% CI, 1.97-5.53; P < 0.001), which increased with severity of airflow limitation and are suggestive of hypertensive or arteriolosclerotic microangiopathy. Furthermore, in longitudinal analysis restricted to subjects without microbleed at baseline, COPD was an independent predictor of incident cerebral microbleeds in deep or infratentorial locations (OR, 7.1; 95% CI, 2.1-24.5; P = 0.002). CONCLUSIONS Our findings are compatible with COPD causing an increased risk of the development of cerebral microbleeds in deep or infratentorial locations.

Large-Scale Genome-Wide Association Studies and Meta-Analyses of Longitudinal Change in Adult Lung Function

Background Genome-wide association studies (GWAS) have identified numerous loci influencing cross-sectional lung function, but less is known about genes influencing longitudinal change in lung function. Methods We performed GWAS of the rate of change in forced expiratory volume in the first second (FEV1) in 14 longitudinal, population-based cohort studies comprising 27,249 adults of European ancestry using linear mixed effects model and combined cohort-specific results using fixed effect meta-analysis to identify novel genetic loci associated with longitudinal change in lung function. Gene expression analyses were subsequently performed for identified genetic loci. As a secondary aim, we estimated the mean rate of decline in FEV1 by smoking pattern, irrespective of genotypes, across these 14 studies using meta-analysis. Results The overall meta-analysis produced suggestive evidence for association at the novel IL16/STARD5/TMC3 locus on chromosome 15 (P  =  5.71 × 10-7). In addition, meta-analysis using the five cohorts with ≥3 FEV1 measurements per participant identified the novel ME3 locus on chromosome 11 (P  =  2.18 × 10-8) at genome-wide significance. Neither locus was associated with FEV1 decline in two additional cohort studies. We confirmed gene expression of IL16, STARD5, and ME3 in multiple lung tissues. Publicly available microarray data confirmed differential expression of all three genes in lung samples from COPD patients compared with controls. Irrespective of genotypes, the combined estimate for FEV1 decline was 26.9, 29.2 and 35.7 mL/year in never, former, and persistent smokers, respectively. Conclusions In this large-scale GWAS, we identified two novel genetic loci in association with the rate of change in FEV1 that harbor candidate genes with biologically plausible functional links to lung function.

Molecular mechanisms underlying variations in lung function: a systems genetics analysis

BACKGROUND Lung function measures reflect the physiological state of the lung, and are essential to the diagnosis of chronic obstructive pulmonary disease (COPD). The SpiroMeta-CHARGE consortium undertook the largest genome-wide association study (GWAS) so far (n=48,201) for forced expiratory volume in 1 s (FEV1) and the ratio of FEV1 to forced vital capacity (FEV1/FVC) in the general population. The lung expression quantitative trait loci (eQTLs) study mapped the genetic architecture of gene expression in lung tissue from 1111 individuals. We used a systems genetics approach to identify single nucleotide polymorphisms (SNPs) associated with lung function that act as eQTLs and change the level of expression of their target genes in lung tissue; termed eSNPs. METHODS The SpiroMeta-CHARGE GWAS results were integrated with lung eQTLs to map eSNPs and the genes and pathways underlying the associations in lung tissue. For comparison, a similar analysis was done in peripheral blood. The lung mRNA expression levels of the eSNP-regulated genes were tested for associations with lung function measures in 727 individuals. Additional analyses identified the pleiotropic effects of eSNPs from the published GWAS catalogue, and mapped enrichment in regulatory regions from the ENCODE project. Finally, the Connectivity Map database was used to identify potential therapeutics in silico that could reverse the COPD lung tissue gene signature. FINDINGS SNPs associated with lung function measures were more likely to be eQTLs and vice versa. The integration mapped the specific genes underlying the GWAS signals in lung tissue. The eSNP-regulated genes were enriched for developmental and inflammatory pathways; by comparison, SNPs associated with lung function that were eQTLs in blood, but not in lung, were only involved in inflammatory pathways. Lung function eSNPs were enriched for regulatory elements and were over-represented among genes showing differential expression during fetal lung development. An mRNA gene expression signature for COPD was identified in lung tissue and compared with the Connectivity Map. This in-silico drug repurposing approach suggested several compounds that reverse the COPD gene expression signature, including a nicotine receptor antagonist. These findings represent novel therapeutic pathways for COPD. INTERPRETATION The system genetics approach identified lung tissue genes driving the variation in lung function and susceptibility to COPD. The identification of these genes and the pathways in which they are enriched is essential to understand the pathophysiology of airway obstruction and to identify novel therapeutic targets and biomarkers for COPD, including drugs that reverse the COPD gene signature in silico. FUNDING The research reported in this article was not specifically funded by any agency. See Acknowledgments for a full list of funders of the lung eQTL study and the Spiro-Meta CHARGE GWAS.

Common genes underlying asthma and COPD? Genome-wide analysis on the Dutch hypothesis

Asthma and chronic obstructive pulmonary disease (COPD) are thought to share a genetic background (“Dutch hypothesis”). We investigated whether asthma and COPD have common underlying genetic factors, performing genome-wide association studies for both asthma and COPD and combining the results in meta-analyses. Three loci showed potential involvement in both diseases: chr2p24.3, chr5q23.1 and chr13q14.2, containing DDX1, COMMD10 (both participating in the nuclear factor (NF) &kgr;&bgr; pathway) and GNG5P5, respectively. Single nucleotide polymorphisms (SNPs) rs9534578 in GNG5P5 reached genome-wide significance after first replication phase (p=9.96×10−9). The second replication phase, in seven independent cohorts, provided no significant replication. Expression quantitative trait loci (eQTL) analysis in blood cells and lung tissue on the top 20 associated SNPs identified two SNPs in COMMD10 that influenced gene expression. Inflammatory processes differ in asthma and COPD and are mediated by NF-&kgr;&bgr;, which could be driven by the same underlying genes, COMMD10 and DDX1. None of the SNPs reached genome-wide significance. Our eQTL studies support a functional role for two COMMD10 SNPs, since they influence gene expression in both blood cells and lung tissue. Our findings suggest that there is either no common genetic component in asthma and COPD or, alternatively, different environmental factors, e.g. lifestyle and occupation in different countries and continents, which may have obscured the genetic common contribution. This article provides suggestive evidence, but not firm evidence that there is overlap in genetics of asthma and COPD http://ow.ly/we9yE

β-Adrenoceptor blockers and pulmonary function in the general population: the Rotterdam Study.

AIM β-Adrenoceptor blockers have been used with caution in patients with obstructive lung diseases such as asthma or chronic obstructive pulmonary disease (COPD), due to the potentially increased airway reactivity and risk of bronchial obstruction. Cardioselective β-adrenoceptor blockers have a more beneficial profile than non-cardioselective β-adrenoceptor blockers and can be safely prescribed to patients with both cardiovascular disease and COPD. We hypothesized that cardioselective β-adrenoceptor blockers also affect pulmonary function. METHODS This study was performed within the Rotterdam Study, a prospective population-based cohort study. Effects of cardioselective and non-cardioselective β-adrenoceptor blockers on pulmonary function were analysed using regression techniques with multivariable adjustment for potential confounders. RESULTS Current use of non-cardioselective β-adrenoceptor blockers was significantly associated with a lower forced expiratory volume in 1 s (FEV1) of -198 ml (95% CI -301, -96), with a lower forced vital capacity (FVC) of -223 ml (95% CI -367, -79) and with a decreased FEV1  : FVC of -1.38% (95% CI -2.74, -0.13%). Current use of cardioselective β-adrenoceptor blockers was significantly associated with a lower FEV1 of -118 ml (95% CI -157, -78) and with a lower FVC of -167 ml (95% CI -222, -111), but did not affect FEV1: FVC. After exclusion of patients with COPD, asthma and heart failure the effects of cardioselective β-adrenoceptor blockers remained significant for FEV1 (-142 ml [95% CI -189, -96]) and for FVC (-176 ml [95% CI -236, -117]). CONCLUSION In our study both non-cardioselective and cardioselective β-adrenoceptor blockers had a clinically relevant effect on both FEV1 and FVC. In contrast to cardioselective β-adrenoceptor blockers, use of non-cardioselective β-adrenoceptor blockers was associated with a significantly lower FEV1: FVC.

Mendelian randomization study of interleukin-6 in chronic obstructive pulmonary disease

Background: Cross-sectional studies have demonstrated that increased levels of interleukin-6 (IL6) are present in the airways and blood samples of patients with chronic obstructive pulmonary disease (COPD). Objectives: To investigate the association between IL6 and the risk of COPD using a Mendelian randomization approach. Methods: Eight common single-nucleotide polymorphisms (SNPs) in the region of the IL6 gene were genotyped using both TaqMan and Illumina in the Rotterdam Study, a prospective population-based cohort study consisting of 7,983 participants aged 55 years or older, including 928 COPD patients. At baseline, blood was drawn in a random sample of 714 subjects to measure the IL6 plasma level. Analysis of variance, logistic regression, and Cox proportional hazard models – adjusted for age, gender, pack years, and BMI – were used for analyses. Results: High levels of IL6 (>2.4 pg/ml, the highest tertile) were associated with a three-fold increased risk of developing COPD, in comparison to low levels (<1.4 pg/ml, the lowest tertile). The rs2056576 SNP was associated with a 10% increase in the risk of COPD per additional T allele. However, the association was no longer significant after adjustment. No association was found with other common SNPs in the IL6 gene and COPD. Conclusions: Although increased IL6 plasma levels at baseline are associated with the risk of developing COPD during follow-up, there was no strong evidence for an association between common variation in the IL6 gene and the risk of COPD.

Clopidogrel Use Is Associated With an Increased Prevalence of Cerebral Microbleeds in a Stroke-Free Population: The Rotterdam Study

Background Although clopidogrel reduces the incidence of atherothrombotic events, its use is associated with an increased risk of major bleeding. Cerebral microbleeds (CMBs) are indicative of subclinical microangiopathy in the brain and may prelude symptomatic intracerebral hemorrhage. We examined the association between use of clopidogrel and CMBs in persons without a history of stroke. Methods and Results We performed a cross‐sectional analysis using data from the Rotterdam Study, a prospective population‐based cohort of persons aged 45 years and older. Among 4408 stroke‐free individuals who underwent brain magnetic resonance imaging for the detection of CMBs, we identified 121 ever‐users and 4287 never‐users of clopidogrel before magnetic resonance imaging. We used multiple logistic regression to analyze the association between clopidogrel and CMBs with adjustment for age, sex, cardiovascular risk factors, and common cardiovascular medication. Users of clopidogrel had a higher prevalence of CMBs (odd ratio 1.55, 95% CI 1.01 to 2.37) than nonusers and more often had a high number (>4) of CMBs (odds ratio 3.19, 95% CI 1.52 to 6.72). Clopidogrel use was associated with a significantly higher prevalence of deep or infratentorial CMBs (odd ratio 1.90, 95% CI 1.05 to 3.45). Among clopidogrel users, we were unable to demonstrate differences in the prevalence of CMBs by indication of prescription, history of coronary heart disease, or common genetic variants in CYP2C19. Conclusions In stroke‐free individuals, clopidogrel use was associated with a higher prevalence and higher number of CMBs. Whether this association is causal requires confirmation in prospective studies, especially given the small number of participants taking clopidogrel and the possibility of residual confounding in this study.