Rationale: Computed tomography (CT) scanning of the lung may reduce phenotypic heterogeneity in defining subjects with chronic obstructive pulmonary disease (COPD), and allow identification of genetic determinants of emphysema severity and distribution.
Objectives: We sought to identify genes associated with CT scan distribution of emphysema in individuals without α1-antitrypsin deficiency but with severe COPD.
Methods: We evaluated baseline CT densitometry phenotypes in 282 individuals with emphysema enrolled in the Genetics Ancillary Study of the National Emphysema Treatment Trial, and used regression models to identify genetic variants associated with emphysema distribution.
Measurements and Main Results: Emphysema distribution was assessed by two methods—assessment by radiologists and by computerized density mask quantitation, using a threshold of −950 Hounsfield units. A total of 77 polymorphisms in 20 candidate genes were analyzed for association with distribution of emphysema. GSTP1, EPHX1, and MMP1 polymorphisms were associated with the densitometric, apical-predominant distribution of emphysema (p value range = 0.001–0.050). When an apical-predominant phenotype was defined by the radiologist scoring method, GSTP1 and EPHX1 single-nucleotide polymorphisms were found to be significantly associated. In a case–control analysis of COPD susceptibility limited to cases with densitometric upper-lobe–predominant cases, the EPHX1 His139Arg single-nucleotide polymorphism was associated with COPD (p = 0.005).
Conclusions: Apical and basal emphysematous destruction appears to be influenced by different genes. Polymorphisms in the xenobiotic enzymes, GSTP1 and EPHX1, are associated with apical-predominant emphysema. Altered detoxification of cigarette smoke metabolites may contribute to emphysema distribution, and these findings may lead to further insight into genetic determinants of emphysema.
COPD; genetics; association analysis; computed tomography; emphysema
Chronic obstructive pulmonary disease (COPD) has been classically divided into blue bloaters and pink puffers. The utility of these clinical subtypes is unclear. However, the broader distinction between airway-predominant and emphysema-predominant COPD may be clinically relevant. The objective was to define clinical features of emphysema-predominant and non-emphysematous COPD patients.
Current and former smokers from the Genetic Epidemiology of COPD Study (COPDGene) had chest computed tomography (CT) scans with quantitative image analysis. Emphysema-predominant COPD was defined by low attenuation area at -950 Hounsfield Units (LAA-950) ≥10%. Non-emphysematous COPD was defined by airflow obstruction with minimal to no emphysema (LAA-950 < 5%).
Out of 4197 COPD subjects, 1687 were classified as emphysema-predominant and 1817 as non-emphysematous; 693 had LAA-950 between 5–10% and were not categorized. Subjects with emphysema-predominant COPD were older (65.6 vs 60.6 years, p < 0.0001) with more severe COPD based on airflow obstruction (FEV1 44.5 vs 68.4%, p < 0.0001), greater exercise limitation (6-minute walk distance 1138 vs 1331 ft, p < 0.0001) and reduced quality of life (St. George’s Respiratory Questionnaire score 43 vs 31, p < 0.0001). Self-reported diabetes was more frequent in non-emphysematous COPD (OR 2.13, p < 0.001), which was also confirmed using a strict definition of diabetes based on medication use. The association between diabetes and non-emphysematous COPD was replicated in the ECLIPSE study.
Non-emphysematous COPD, defined by airflow obstruction with a paucity of emphysema on chest CT scan, is associated with an increased risk of diabetes. COPD patients without emphysema may warrant closer monitoring for diabetes, hypertension, and hyperlipidemia and vice versa.
Clinicaltrials.gov identifiers: COPDGene NCT00608764, ECLIPSE NCT00292552.
Electronic supplementary material
The online version of this article (doi:10.1186/1471-2466-14-164) contains supplementary material, which is available to authorized users.
Airway disease; CT scan; Diabetes mellitus; Emphysema; Spirometry
There is considerable variability in the susceptibility of smokers to develop chronic obstructive pulmonary disease (COPD). The only known genetic risk factor is severe deficiency of α1-antitrypsin, which is present in 1–2% of individuals with COPD. We conducted a genome-wide association study (GWAS) in a homogenous case-control cohort from Bergen, Norway (823 COPD cases and 810 smoking controls) and evaluated the top 100 single nucleotide polymorphisms (SNPs) in the family-based International COPD Genetics Network (ICGN; 1891 Caucasian individuals from 606 pedigrees) study. The polymorphisms that showed replication were further evaluated in 389 subjects from the US National Emphysema Treatment Trial (NETT) and 472 controls from the Normative Aging Study (NAS) and then in a fourth cohort of 949 individuals from 127 extended pedigrees from the Boston Early-Onset COPD population. Logistic regression models with adjustments of covariates were used to analyze the case-control populations. Family-based association analyses were conducted for a diagnosis of COPD and lung function in the family populations. Two SNPs at the α-nicotinic acetylcholine receptor (CHRNA 3/5) locus were identified in the genome-wide association study. They showed unambiguous replication in the ICGN family-based analysis and in the NETT case-control analysis with combined p-values of 1.48×10−10, (rs8034191) and 5.74×10−10 (rs1051730). Furthermore, these SNPs were significantly associated with lung function in both the ICGN and Boston Early-Onset COPD populations. The C allele of the rs8034191 SNP was estimated to have a population attributable risk for COPD of 12.2%. The association of hedgehog interacting protein (HHIP) locus on chromosome 4 was also consistently replicated, but did not reach genome-wide significance levels. Genome-wide significant association of the HHIP locus with lung function was identified in the Framingham Heart study (Wilk et al., companion article in this issue of PLoS Genetics; doi:10.1371/journal.pgen.1000429). The CHRNA 3/5 and the HHIP loci make a significant contribution to the risk of COPD. CHRNA3/5 is the same locus that has been implicated in the risk of lung cancer.
There is considerable variability in the susceptibility of smokers to develop chronic obstructive pulmonary disease (COPD), which is a heritable multi-factorial trait. Identifying the genetic determinants of COPD risk will have tremendous public health importance. This study describes the first genome-wide association study (GWAS) in COPD. We conducted a GWAS in a homogenous case-control cohort from Norway and evaluated the top 100 single nucleotide polymorphisms in the family-based International COPD Genetics Network. The polymorphisms that showed replication were further evaluated in subjects from the US National Emphysema Treatment Trial and controls from the Normative Aging Study and then in a fourth cohort of extended pedigrees from the Boston Early-Onset COPD population. Two polymorphisms in the α-nicotinic acetylcholine receptor 3/5 locus on chromosome 15 showed unambiguous evidence of association with COPD. This locus has previously been implicated in both smoking behavior and risk of lung cancer, suggesting the possibility of multiple functional polymorphisms in the region or a single polymorphism with wide phenotypic consequences. The hedgehog interacting protein (HHIP) locus on chromosome 4, which is associated with COPD, is also a significant risk locus for COPD.
Chronic obstructive pulmonary disease (COPD) is a heterogeneous syndrome, including emphysema and airway disease. Phenotypes defined on the basis of chest computed tomography (CT) may decrease disease heterogeneity and aid in the identification of candidate genes for COPD subtypes. To identify these genes, we performed genome-wide linkage analysis in extended pedigrees from the Boston Early-Onset COPD Study, stratified by emphysema status (defined by chest CT scans) of the probands, followed by genetic association analysis of positional candidate genes. A region on chromosome 1p showed strong evidence of linkage to lung function traits in families of emphysema-predominant probands in the stratified analysis (LOD score = 2.99 in families of emphysema-predominant probands versus 1.98 in all families). Association analysis in 949 individuals from 127 early-onset COPD pedigrees revealed association for COPD-related traits with an intronic single-nucleotide polymorphism (SNP) in transforming growth factor-β receptor-3 (TGFBR3) (P = 0.005). This SNP was significantly associated with COPD affection status comparing 389 cases from the National Emphysema Treatment Trial to 472 control smokers (P = 0.04), and with FEV1 (P = 0.004) and CT emphysema (P = 0.05) in 3,117 subjects from the International COPD Genetics Network. Gene-level replication of association with lung function was seen in 427 patients with COPD from the Lung Health Study. In conclusion, stratified linkage analysis followed by association testing identified TGFBR3 (betaglycan) as a potential susceptibility gene for COPD. Published human microarray and murine linkage studies have also demonstrated the importance of TGFBR3 in emphysema and lung function, and our group and others have previously found association of COPD-related traits with TGFB1, a ligand for TGFBR3.
betaglycan; chronic obstructive pulmonary disease; computed tomography; linkage; single nucleotide polymorphism
Rationale: Genome-wide association studies have shown significant associations between variants near hedgehog interacting protein HHIP, FAM13A, and cholinergic nicotinic acetylcholine receptor CHRNA3/5 with increased risk of chronic obstructive pulmonary disease (COPD) in smokers; however, the disease mechanisms behind these associations are not well understood.
Objectives: To identify the association between replicated loci and COPD-related phenotypes in well-characterized patient populations.
Methods: The relationship between these three loci and COPD-related phenotypes was assessed in the Evaluation of COPD Longitudinally to Identify Predictive Surrogate End-point (ECLIPSE) cohort. The results were validated in the family-based International COPD Genetics Network (ICGN).
Measurements and Main Results: The CHRNA3/5 locus was significantly associated with pack-years of smoking (P = 0.002 and 3 × 10−4), emphysema assessed by a radiologist using high-resolution computed tomography (P = 2 × 10−4 and 4.8 × 10−5), and airflow obstruction (P = 0.004 and 1.8 × 10−5) in the ECLIPSE and ICGN populations, respectively. However, variants in the IREB2 gene were only significantly associated with FEV1. The HHIP locus was not associated with smoking intensity but was associated with FEV1/FVC (P = 1.9 × 10−4 and 0.004 in the ECLIPSE and ICGN populations). The HHIP locus was also associated with fat-free body mass (P = 0.007) and with both retrospectively (P = 0.015) and prospectively (P = 0.024) collected COPD exacerbations in the ECLIPSE cohort. Single-nucleotide polymorphisms in the FAM13A locus were associated with lung function.
Conclusions: The CHRNA3/5 locus was associated with increased smoking intensity and emphysema in individuals with COPD, whereas the HHIP and FAM13A loci were not associated with smoking intensity. The HHIP locus was associated with the systemic components of COPD and with the frequency of COPD exacerbations. FAM13A locus was associated with lung function.
COPD exacerbations; nicotine addiction; high-resolution CT; genetic association analysis; emphysema
Chronic obstructive pulmonary disease (COPD) is a phenotypically heterogeneous disease. In COPD, the presence of emphysema is associated with increased mortality and risk of lung cancer. High resolution computed tomography (HRCT) scans are useful in quantifying emphysema but are associated with radiation exposure and high incidence of false positive findings (i.e., nodules). Using a comprehensive biomarker panel, we sought to determine if there was a peripheral blood biomarker signature of emphysema.
114 plasma biomarkers were measured using a custom assay in 588 individuals enrolled in the COPDGene study. Quantitative emphysema measurements included percent low lung attenuation (%LAA) ≤ −950 HU, ≤ − 910 HU and mean lung attenuation at the 15th percentile on lung attenuation curve (LP15A). Multiple regression analysis was performed to determine plasma biomarkers associated with emphysema independent of covariates age, gender, smoking status, body mass index and FEV1. The findings were subsequently validated using baseline blood samples from a separate cohort of 388 subjects enrolled in the Treatment of Emphysema with a Selective Retinoid Agonist (TESRA) study.
Regression analysis identified multiple biomarkers associated with CT-assessed emphysema in COPDGene, including advanced glycosylation end-products receptor (AGER or RAGE, p < 0.001), intercellular adhesion molecule 1 (ICAM, p < 0.001), and chemokine ligand 20 (CCL20, p < 0.001). Validation in the TESRA cohort revealed significant associations with RAGE, ICAM1, and CCL20 with radiologic emphysema (p < 0.001 after meta-analysis). Other biomarkers that were associated with emphysema include CDH1, CDH 13 and SERPINA7, but were not available for validation in the TESRA study. Receiver operating characteristics analysis demonstrated a benefit of adding a biomarker panel to clinical covariates for detecting emphysema, especially in those without severe airflow limitation (AUC 0.85).
Our findings, suggest that a panel of blood biomarkers including sRAGE, ICAM1 and CCL20 may serve as a useful surrogate measure of emphysema, and when combined with clinical covariates, may be useful clinically in predicting the presence of emphysema compared to just using covariates alone, especially in those with less severe COPD. Ultimately biomarkers may shed light on disease pathogenesis, providing targets for new treatments.
Electronic supplementary material
The online version of this article (doi:10.1186/s12931-014-0127-9) contains supplementary material, which is available to authorized users.
COPD; Biomarkers; RAGE; ICAM1; CCL20; Emphysema
Superoxide dismutase-3 (SOD3) is a major extracellular antioxidant enzyme, and previous studies have indicated a possible role of this gene in chronic obstructive pulmonary disease (COPD). We hypothesized that polymorphisms in the SOD3 gene would be associated with COPD and COPD-related phenotypes.
We genotyped three SOD3 polymorphisms (rs8192287 (E1), rs8192288 (I1) and rs1799895 (R213G)) in a case-control cohort, with severe COPD cases from the National Emphysema Treatment Trial (NETT, n=389) and smoking controls from the Normative Aging Study (NAS, n=472). We examined whether the SNPs were associated with COPD status, lung function variables, and quantitative CT measurements of emphysema and airway wall thickness. Further, we tried to replicate our initial findings in two family-based studies, the International COPD Genetics Network (ICGN, n=3061) and the Boston Early-Onset COPD Study (EOCOPD, n=949).
In NETT COPD cases, the minor alleles of SNPs E1 and I1 were associated with a higher percentage of emphysema (%LAA950) on chest CT scan (p=0.029 and p=0.0058). The association with E1 was replicated in the ICGN family study, where the minor allele was associated with more emphysema (p=0.048). Airway wall thickness was positively associated with the E1 SNP in ICGN; however, this finding was not confirmed in NETT. Quantitative CT data were not available in EOCOPD. The SNPs were not associated with lung function variables or COPD status in any of the populations.
In conclusion, polymorphisms in the SOD3 gene were associated with CT emphysema but not COPD susceptibility, highlighting the importance of phenotype definition in COPD genetics studies.
Rationale: Pulmonary emphysema overlaps partially with spirometrically defined chronic obstructive pulmonary disease and is heritable, with moderately high familial clustering.
Objectives: To complete a genome-wide association study (GWAS) for the percentage of emphysema-like lung on computed tomography in the Multi-Ethnic Study of Atherosclerosis (MESA) Lung/SNP Health Association Resource (SHARe) Study, a large, population-based cohort in the United States.
Methods: We determined percent emphysema and upper-lower lobe ratio in emphysema defined by lung regions less than −950 HU on cardiac scans. Genetic analyses were reported combined across four race/ethnic groups: non-Hispanic white (n = 2,587), African American (n = 2,510), Hispanic (n = 2,113), and Chinese (n = 704) and stratified by race and ethnicity.
Measurements and Main Results: Among 7,914 participants, we identified regions at genome-wide significance for percent emphysema in or near SNRPF (rs7957346; P = 2.2 × 10−8) and PPT2 (rs10947233; P = 3.2 × 10−8), both of which replicated in an additional 6,023 individuals of European ancestry. Both single-nucleotide polymorphisms were previously implicated as genes influencing lung function, and analyses including lung function revealed independent associations for percent emphysema. Among Hispanics, we identified a genetic locus for upper-lower lobe ratio near the α-mannosidase–related gene MAN2B1 (rs10411619; P = 1.1 × 10−9; minor allele frequency [MAF], 4.4%). Among Chinese, we identified single-nucleotide polymorphisms associated with upper-lower lobe ratio near DHX15 (rs7698250; P = 1.8 × 10−10; MAF, 2.7%) and MGAT5B (rs7221059; P = 2.7 × 10−8; MAF, 2.6%), which acts on α-linked mannose. Among African Americans, a locus near a third α-mannosidase–related gene, MAN1C1 (rs12130495; P = 9.9 × 10−6; MAF, 13.3%) was associated with percent emphysema.
Conclusions: Our results suggest that some genes previously identified as influencing lung function are independently associated with emphysema rather than lung function, and that genes related to α-mannosidase may influence risk of emphysema.
emphysema; computed tomography; multiethnic; cohort study; genetic association
Chronic obstructive pulmonary disease (COPD) is characterized by alveolar destruction and abnormal inflammatory responses to noxious stimuli. Surfactant protein–D (SFTPD) is immunomodulatory and essential to host defense. We hypothesized that polymorphisms in SFTPD could influence the susceptibility to COPD. We genotyped six single-nucleotide polymorphisms (SNPs) in surfactant protein D in 389 patients with COPD in the National Emphysema Treatment Trial (NETT) and 472 smoking control subjects from the Normative Aging Study (NAS). Case-control association analysis was performed using Cochran–Armitage trend tests and multivariate logistic regression. The replication of significant associations was attempted in the Boston Early-Onset COPD Study, the Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints (ECLIPSE) Study, and the Bergen Cohort. We also correlated SFTPD genotypes with serum concentrations of surfactant protein–D (SP-D) in the ECLIPSE Study. In the NETT–NAS case-control analysis, four SFTPD SNPs were associated with susceptibility to COPD: rs2245121 (P = 0.01), rs911887 (P = 0.006), rs6413520 (P = 0.004), and rs721917 (P = 0.006). In the family-based analysis of the Boston Early-Onset COPD Study, rs911887 was associated with prebronchodilator and postbronchodilator FEV1 (P = 0.003 and P = 0.02, respectively). An intronic SNP in SFTPD, rs7078012, was associated with COPD in the ECLIPSE Study and the Bergen Cohort. Multiple SFTPD SNPs were associated with serum SP-D concentrations in the ECLIPSE Study. We demonstrated an association of polymorphisms in SFTPD with COPD in multiple populations. We demonstrated a correlation between SFTPD SNPs and SP-D protein concentrations. The SNPs associated with COPD and SP-D concentrations differed, suggesting distinct genetic influences on susceptibility to COPD and SP-D concentrations.
COPD; surfactant protein–D; single-nucleotide polymorphisms; genetics
The principal determining factors influencing the development of the airway disease and emphysema components of COPD have not been clearly defined. Genetic variability in COPD patients might influence the varying degrees of involvement of airway disease and emphysema. Therefore, we investigated genetic association of SNPs in COPD candidate genes for association with emphysema severity and airway wall thickness phenotypes.
Polymorphisms in six candidate genes were analyzed in 379 subjects of the National Emphysema Treatment Trial (NETT) Genetics Ancillary Study with quantitative chest CT data. Genetic association with percent of lung below −950 hounsfield units (LAA950), airway wall thickness (WT), and derived square root wall area of 10 mm internal perimeter airways (SRWA) were investigated.
Three SNPs in EPHX1, five SNPs in SERPINE2, and one SNP in GSTP1 were significantly associated with LAA950. Five SNPs in TGFB1, two SNPs in EPHX1, one SNP in SERPINE2, and two SNPs in ADRB2 were associated with airway wall phenotypes in NETT.
In conclusion, several COPD candidate genes showed evidence for association with airway wall thickness and emphysema severity using CT in a severe COPD population. Further investigation will be required to replicate these genetic associations for emphysema and airway wall phenotypes.
Airway; chronic obstructive pulmonary disease; computed tomography; emphysema; genetic association
Cachexia, whether assessed by body mass index (BMI) or fat-free mass index (FFMI), affects a significant proportion of patients with chronic obstructive pulmonary disease (COPD), and is an independent risk factor for increased mortality, increased emphysema, and more severe airflow obstruction. The variable development of cachexia among patients with COPD suggests a role for genetic susceptibility. The objective of the present study was to determine genetic susceptibility loci involved in the development of low BMI and FFMI in subjects with COPD. A genome-wide association study (GWAS) of BMI was conducted in three independent cohorts of European descent with Global Initiative for Chronic Obstructive Lung Disease stage II or higher COPD: Evaluation of COPD Longitudinally to Identify Predictive Surrogate End-Points (ECLIPSE; n = 1,734); Norway-Bergen cohort (n = 851); and a subset of subjects from the National Emphysema Treatment Trial (NETT; n = 365). A genome-wide association of FFMI was conducted in two of the cohorts (ECLIPSE and Norway). In the combined analyses, a significant association was found between rs8050136, located in the first intron of the fat mass and obesity–associated (FTO) gene, and BMI (P = 4.97 × 10−7) and FFMI (P = 1.19 × 10−7). We replicated the association in a fourth, independent cohort consisting of 502 subjects with COPD from COPDGene (P = 6 × 10−3). Within the largest contributing cohort of our analysis, lung function, as assessed by forced expiratory volume at 1 second, varied significantly by FTO genotype. Our analysis suggests a potential role for the FTO locus in the determination of anthropomorphic measures associated with COPD.
chronic obstructive pulmonary disease genetics; chronic obstructive pulmonary disease epidemiology; chronic obstructive pulmonary disease metabolism; genome-wide association study
Pulmonary emphysema is divided into three major subtypes at autopsy: centrilobular, paraseptal and panlobular emphysema. These subtypes can be defined by visual assessment on computed tomography (CT); however, clinical characteristics of emphysema subtypes on CT are not well-defined. We developed a reliable approach to visual assessment of emphysema subtypes on CT and examined if emphysema subtypes have distinct characteristics.
The Multi-Ethnic Study of Atherosclerosis COPD Study recruited smokers with COPD and controls age 50–79 years with ≥10 pack-years. Participants underwent CT following a standardized protocol. Definitions of centrilobular, paraseptal and panlobular emphysema were obtained by literature review. Six-minute walk distance and pulmonary function were performed following guidelines.
Twenty-seven percent of 318 smokers had emphysema on CT. Inter-rater reliability of emphysema subtype was substantial (K:0.70). Compared to participants without emphysema, individuals with centrilobular or panlobular emphysema had greater dyspnea, reduced walk distance, greater hyperinflation, and lower diffusing capacity. In contrast, individuals with PSE were similar to controls, except for male predominance. Centrilobular but not panlobular or paraseptal emphysema was associated with greater smoking history (+21 pack-years P<0.001). Panlobular but not other types of emphysema was associated with reduced body mass index (−5 kg/m2;P=0.01). Other than for dyspnea, these findings were independent of the forced expiratory volume in one second. Seventeen percent of smokers without COPD on spirometry had emphysema, which was independently associated with reduced walk distance.
Emphysema subtypes on CT are common in smokers with and without COPD. Centrilobular and panlobular emphysema but not paraseptal emphysema have considerable symptomatic and physiological consequences.
Emphysema; computed tomography; centrilobular; paraseptal; panlobular
The imbalance between proteases and antiproteases has been proposed to participate to the pathogenesis of chronic obstructive pulmonary disease (COPD) and emphysema. Gene level variation in different metalloproteinases, metalloproteinase inhibitors, and cytokines affecting them may contribute to this imbalance and destruction of the lung parenchyma. We investigated whether polymorphisms in selected protease-antiprotease balance pathway genes predispose to different emphysema subtypes (centrilobular, paraseptal, panlobular, and bullae) and airflow limitation among Finnish construction workers.
Eleven single nucleotide polymorphisms (SNPs) from seven genes (GC: rs7041 and rs4588; MMP1: rs1799750; MMP9: rs3918242; MMP12: rs652438; TIMP2: rs2277698; TNF: rs1799724 and rs1800629; TGFB1: rs1800469, rs1800470, and rs2241718) were analyzed from 951 clinically and radiologically characterized construction workers. The genotype and haplotype data was compared to different emphysematous signs confirmed with high resolution computed tomography (HRCT), forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and maximal expiratory flow at 50% of FVC (MEF50) by using linear and logistic regression analyses, adjusted for potential confounders.
The TIMP2 rs2277698 SNP was associated with overall (p = 0.022) and paraseptal (p = 0.010) emphysema, as well as with FEV1/FVC ratio (p = 0.035) and MEF50 (p = 0.008). The TGFB1 rs2241718 and MMP9 rs3918242 SNPs were associated with centrilobular emphysema (p = 0.022 and p = 0.008), and the TNF rs1800629 SNP with paraseptal emphysema (p = 0.017). In stratified analysis, individuals with at least one TIMP2 rs2277698 or TNF rs1800629 variant allele were found to be at around two-fold risk for pathological paraseptal changes (OR 1.94, 95% CI 1.14-3.30; OR 2.10, 95% CI 1.24-3.56). On the contrary, the risk for pathological centrilobular changes was halved for individuals with at least one MMP9 rs3918242 (OR 0.51, 95% CI 0.30-0.86) or TGFB1 rs2241718 (OR 0.53, 95% CI 0.30-0.90) variant allele, or TGFB1 rs1800469-rs1800470 AT-haplotype (OR 0.55, 95% CI 0.33-0.93). MEF50, in turn, was significantly reduced among individuals with at least one TIMP2 rs2277698 variant allele (p = 0.011).
Our findings strengthen the hypothesis of the importance of protease-antiprotease balance in pathogenesis of emphysema and shed light on the aetiology of different emphysema subtypes by associating MMP9 and TGFB1 to centrilobular emphysema, and TIMP2 and TNF to paraseptal emphysema and/or airflow obstruction.
Emphysema; Lung function; Genetics; Protease-antiprotease balance
SERPINE2 (serpin peptidase inhibitor, clade E, member 2) has previously been identified as a positional candidate gene for chronic obstructive pulmonary disease (COPD) and has subsequently been associated to COPD and emphysema in several populations. We aimed to further examine the role of SERPINE2 polymorphisms in the development of pulmonary emphysema and different emphysema subtypes.
Four single nucleotide polymorphisms (SNPs) in SERPINE2 were analyzed from 951 clinically and radiologically examined Finnish construction workers. The genotype and haplotype data was compared to different emphysematous signs confirmed with high-resolution computed tomography (HRCT), forced vital capacity (FVC), forced expiratory volume in one second (FEV1), diffusing capacity (DLCO), and specific diffusing capacity (DLCO/VA).
Three of the studied SERPINE2 SNPs (rs729631, rs975278, and rs6748795) were found to be in tight linkage disequilibrium. Therefore, only one of these SNPs (rs729631) was included in the subsequent analyses, in addition to the rs840088 SNP which was in moderate linkage with the other three studied SNPs. The rs729631 SNP showed a significant association with panlobular emphysema (p = 0.003). In further analysis, the variant allele of the rs729631 SNP was found to pose over two-fold risk (OR 2.22, 95% CI 1.05-4.72) for overall panlobular changes and over four-fold risk (OR 4.37, 95% CI 1.61-11.86) for pathological panlobular changes. A haplotype consisting of variant alleles of both rs729631 and rs840088 SNPs was found to pose an almost four-fold risk for overall panlobular (OR 3.72, 95% CI 1.56-8.90) and subnormal (OR 3.98, 95% CI 1.55-10.20) emphysema.
Our results support the previously found association between SERPINE2 polymorphisms and pulmonary emphysema. As a novel finding, our study suggests that the SERPINE2 gene may in particular be involved in the development of panlobular changes, i.e., the same type of changes that are involved in alpha-1-antitrypsin (AAT) -deficiency.
The genetic risk factors for chronic obstructive pulmonary disease (COPD) are still largely unknown. To date, genome-wide association studies (GWASs) of limited size have identified several novel risk loci for COPD at CHRNA3/CHRNA5/IREB2, HHIP and FAM13A; additional loci may be identified through larger studies. We performed a GWAS using a total of 3499 cases and 1922 control subjects from four cohorts: the Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints (ECLIPSE); the Normative Aging Study (NAS) and National Emphysema Treatment Trial (NETT); Bergen, Norway (GenKOLS); and the COPDGene study. Genotyping was performed on Illumina platforms with additional markers imputed using 1000 Genomes data; results were summarized using fixed-effect meta-analysis. We identified a new genome-wide significant locus on chromosome 19q13 (rs7937, OR = 0.74, P = 2.9 × 10−9). Genotyping this single nucleotide polymorphism (SNP) and another nearby SNP in linkage disequilibrium (rs2604894) in 2859 subjects from the family-based International COPD Genetics Network study (ICGN) demonstrated supportive evidence for association for COPD (P = 0.28 and 0.11 for rs7937 and rs2604894), pre-bronchodilator FEV1 (P = 0.08 and 0.04) and severe (GOLD 3&4) COPD (P = 0.09 and 0.017). This region includes RAB4B, EGLN2, MIA and CYP2A6, and has previously been identified in association with cigarette smoking behavior.
To investigate the association between emphysema heterogeneity in spatial distribution, pulmonary function and disease severity.
Methods and Materials
We ascertained a dataset of anonymized Computed Tomography (CT) examinations acquired on 565 participants in a COPD study. Subjects with chronic bronchitis (CB) and/or bronchodilator response were excluded resulting in 190 cases without COPD and 160 cases with COPD. Low attenuations areas (LAAs) (≤950 Hounsfield Unit (HU)) were identified and quantified at the level of individual lobes. Emphysema heterogeneity was defined in a manner that ranged in value from −100% to 100%. The association between emphysema heterogeneity and pulmonary function measures (e.g., FEV1% predicted, RV/TLC, and DLco% predicted) adjusted for age, sex, and smoking history (pack-years) was assessed using multiple linear regression analysis.
The majority (128/160) of the subjects with COPD had a heterogeneity greater than zero. After adjusting for age, gender, smoking history, and extent of emphysema, heterogeneity in depicted disease in upper lobe dominant cases was positively associated with pulmonary function measures, such as FEV1 Predicted (p<.001) and FEV1/FVC (p<.001), as well as disease severity (p<0.05). We found a negative association between HI% , RV/TLC (p<0.001), and DLco% (albeit not a statistically significant one, p = 0.06) in this group of patients.
Subjects with more homogeneous distribution of emphysema and/or lower lung dominant emphysema tend to have worse pulmonary function.
CT-diagnosed emphysema is associated with poor prognosis in chronic obstructive pulmonary disease (COPD). Its clinical impacts on prognoses of asthma with chronic airflow obstruction (CAO) are not well known. We sought to compare mortalities and prognostic factors in COPD and asthma with CAO by the presence or absence of CT-diagnosed emphysema.
Retrospective cohort study.
Referral centre hospital for respiratory disease.
1272 patients aged over 40 years with CAO (January 2000 to December 2011). CAO was defined as a forced expiratory volume in 1 s/forced vital capacity <0.7 after bronchodilator use throughout the observation period.
Primary and secondary outcome measurements
Overall mortality served as the primary endpoint. We compared mortalities and prognostic factors of COPD and asthma subgroups with or without emphysema. Secondary endpoints were the prevalence of COPD and asthma in patients with CAO.
Overall, diagnoses included COPD with emphysema in 517 (40.6%) patients, COPD without emphysema in 104 (8.2%) patients, asthma with emphysema in 178 (13.9%) patients, asthma without emphysema in 169 (13.3%) patients, other respiratory diseases (RD) with emphysema in 128 (10.1%) patients, and other RD without emphysema in 176 (13.8%) patients. Patients with asthma without emphysema had the best prognosis followed by those with asthma with emphysema, COPD without emphysema and COPD with emphysema. Each subgroup had distinct prognostic factors. Presence of emphysema was an independent risk factor for de novo lung cancer among patients with CAO.
Patients with asthma with CAO have a better prognosis than patients with COPD. The presence of CT-diagnosed emphysema predicts poor prognosis in COPD and asthma with CAO.
Surfactant protein D (SFTPD) induces emphysema in knockout mice, but the association of SFTPD with chronic obstructive pulmonary disease (COPD) and emphysema in humans is unclear. Therefore, we aimed to determine the association between genetic variations in SFTPD and susceptibility to COPD and emphysema.
Two populations were studied: population A comprised 270 smokers, including 188 COPD and 82 at-risk subjects, and population B comprised 1131 autopsy cases including 160 cases with emphysema. Six single-nucleotide polymorphisms (SNPs) that tagged the linkage disequilibrium blocks on the entire SFTPD gene were genotyped; the associations of the genotypes with COPD, pulmonary function, percentage of the low-attenuation area (LAA%), and percentage of the airway wall area (WA%) were determined in population A. In population B, the associations of the genotypes with emphysema were assessed.
A C allele at SNP rs721917 that results in the replacement of Met with Thr at position 11 in SFTPD was positively correlated with the LAA% in the upper lung (P=1.1 × 10−5) and overall LAA% (P=1.0 × 10−4), and negatively correlated with the serum concentration of SFTPD (P=7 × 10−11) in the population A. The C/C (rs721917/rs10887199) haplotype was associated with emphysema in both the populations.
Subjects with a C allele at rs721917 have a lower serum SFTPD concentration and are more susceptible to emphysema. This suggests a protective effect of SFTPD against COPD and emphysema.
chronic obstructive pulmonary disease; emphysema; genetic variation; pulmonary surfactant-associated protein D
The receptor for advanced glycation end products (RAGE) is a multiligand signal transduction receptor that can initiate and perpetuate inflammation. Its soluble isoform (sRAGE) acts as a decoy receptor for RAGE ligands, and is thought to afford protection against inflammation. With the present study, we aimed at determining whether circulating sRAGE is correlated with emphysema and chronic cor pulmonale in chronic obstructive pulmonary disease (COPD).
In 200 COPD patients and 201 age- and sex-matched controls, we measured lung function by spirometry, and sRAGE by ELISA method. We also measured the plasma levels of two RAGE ligands, N-epsilon-carboxymethyl lysine and S100A12, by ELISA method. In the COPD patients, we assessed the prevalence and severity of emphysema by computed tomography (CT), and the prevalence of chronic cor pulmonale by echocardiography. Multiple quantile regression was used to assess the effects of emphysema, chronic cor pulmonale, smoking history, and comorbid conditions on the three quartiles of sRAGE.
sRAGE was significantly lower (p = 0.007) in COPD patients (median 652 pg/mL, interquartile range 484 to 1076 pg/mL) than in controls (median 869 pg/mL, interquartile range 601 to 1240 pg/mL), and was correlated with the severity of emphysema (p < 0.001), the lower the level of sRAGE the greater the degree of emphysema on CT. The relationship remained statistically significant after adjusting for smoking history and comorbid conditions. In addition, sRAGE was significantly lower in COPD patients with chronic cor pulmonale than in those without (p = 0.002). Such difference remained statistically significant after adjusting for smoking history, comorbidities, and emphysema severity. There was no significant difference in the plasma levels of the two RAGE ligands between cases and controls.
sRAGE is significantly lower in patients with COPD than in age- and sex-matched individuals without airflow obstruction. Emphysema and chronic cor pulmonale are independent predictors of reduced sRAGE in COPD.
Rationale: Chronic obstructive pulmonary disease (COPD) is a heterogeneous disorder associated with systemic manifestations that contribute to its morbidity and mortality. Recent work suggests that biomarker signatures in the blood may be useful in evaluating COPD phenotypes and may provide insight into the pathophysiology of systemic manifestations. Adiponectin, primarily produced by fat cells, has been implicated in the pathophysiology of emphysema.
Objectives: To investigate the association of adiponectin with clinical and radiologic COPD phenotypes.
Methods: Adiponectin levels were determined in 633 individuals, including 432 individuals with COPD from a cohort of former or current smokers enrolled in the COPDGene study. Univariate and multiple regression analysis were used to examine the association of adiponectin with clinical and physiologic data together with quantitative high-resolution computed tomography parameters.
Measurements and Main Results: Multiple regression analysis confirmed that higher plasma adiponectin levels were independently associated with emphysema, decreasing body mass index, female sex, older age, and lower percentage change in prebronchodilator/post-bronchodilator FEV1.
Conclusions: The association between plasma adiponectin and computed tomography–assessed emphysema suggests a contribution of adiponectin to the development of emphysema and highlights a role for metabolic derangements in the pathophysiology of emphysema.
phenotypes; adiponectin; chronic obstructive pulmonary disease
Spirometric parameters are the mainstay for diagnosis of COPD, but cannot distinguish airway obstruction from emphysema. We aimed to develop a computer model that quantifies airway collapse on forced expiratory flow–volume loops. We then explored and validated the relationship of airway collapse with computed tomography (CT) diagnosed emphysema in two large independent cohorts.
A computer model was developed in 513 Caucasian individuals with ≥15 pack-years who performed spirometry, diffusion capacity and CT scans to quantify emphysema presence. The model computed the two best fitting regression lines on the expiratory phase of the flow-volume loop and calculated the angle between them. The collapse was expressed as an Angle of collapse (AC) which was then correlated with the presence of emphysema. Findings were validated in an independent group of 340 individuals.
AC in emphysema subjects (N = 251) was significantly lower (131° ± 14°) compared to AC in subjects without emphysema (N = 223), (152° ± 10°) (p < 0.0001). Multivariate regression analysis revealed AC as best indicator of visually scored emphysema (R2 = 0.505, p < 0.0001) with little significant contribution of KCO, %predicted and FEV1, %predicted to the total model (total R2 = 0.626, p < 0.0001). Similar associations were obtained when using CT-automated density scores for emphysema assessment. Receiver operating characteristic (ROC) curves pointed to 131° as the best cut-off for emphysema (95.5% positive predictive value, 97% specificity and 51% sensitivity). Validation in a second group confirmed the significant difference in mean AC between emphysema and non-emphysema subjects. When applying the 131° cut-off, a positive predictive value of 95.6%, a specificity of 96% and a sensitivity of 59% were demonstrated.
Airway collapse on forced expiration quantified by a computer model correlates with emphysema. An AC below 131° can be considered as a specific cut-off for predicting the presence of emphysema in heavy smokers.
Spirometry; Pulmonary emphysema; Flow-volume loops; Chronic obstructive pulmonary disease; Lung collapse
Rationale: Basic research implicates alveolar endothelial cell apoptosis in the pathogenesis of chronic obstructive pulmonary disease (COPD) and emphysema. However, information on endothelial microparticles (EMPs) in mild COPD and emphysema is lacking.
Objectives: We hypothesized that levels of CD31+ EMPs phenotypic for endothelial cell apoptosis would be elevated in COPD and associated with percent emphysema on computed tomography (CT). Associations with pulmonary microvascular blood flow (PMBF), diffusing capacity, and hyperinflation were also examined.
Methods: The Multi-Ethnic Study of Atherosclerosis COPD Study recruited participants with COPD and control subjects age 50–79 years with greater than or equal to 10 pack-years without clinical cardiovascular disease. CD31+ EMPs were measured using flow cytometry in 180 participants who also underwent CTs and spirometry. CD62E+ EMPs phenotypic for endothelial cell activation were also measured. COPD was defined by standard criteria. Percent emphysema was defined as regions less than −950 Hounsfield units on full-lung scans. PMBF was assessed on gadolinium-enhanced magnetic resonance imaging. Hyperinflation was defined as residual volume/total lung capacity. Linear regression was used to adjust for potential confounding factors.
Measurements and Main Results: CD31+ EMPs were elevated in COPD compared with control subjects (P = 0.03) and were notably increased in mild COPD (P = 0.03). CD31+ EMPs were positively related to percent emphysema (P = 0.045) and were inversely associated with PMBF (P = 0.047) and diffusing capacity (P = 0.01). In contrast, CD62E+ EMPs were elevated in severe COPD (P = 0.003) and hyperinflation (P = 0.001).
Conclusions: CD31+ EMPs, suggestive of endothelial cell apoptosis, were elevated in mild COPD and emphysema. In contrast, CD62E+ EMPs indicative of endothelial activation were elevated in severe COPD and hyperinflation.
chronic obstructive pulmonary disease; emphysema; antigens, CD31; endothelium; pulmonary disease
Rare loss-of-function folliculin (FLCN) mutations are the genetic cause of Birt-Hogg-Dubé syndrome, a monogenic disorder characterized by spontaneous pneumothorax, fibrofolliculomas, and kidney tumors. Loss-of-function folliculin mutations have also been described in pedigrees with familial spontaneous pneumothorax. Because the majority of patients with folliculin mutations have radiographic evidence of pulmonary cysts, folliculin has been hypothesized to contribute to the development of emphysema.
To determine whether folliculin sequence variants are risk factors for severe COPD, we genotyped seven previously reported Birt-Hogg-Dubé or familial spontaneous pneumothorax associated folliculin mutations in 152 severe COPD probands participating in the Boston Early-Onset COPD Study. We performed bidirectional resequencing of all 14 folliculin exons in a subset of 41 probands and subsequently genotyped four identified variants in an independent sample of345 COPD subjects from the National Emphysema Treatment Trial (cases) and 420 male smokers with normal lung function from the Normative Aging Study (controls).
None of the seven previously reported Birt-Hogg-Dubé or familial spontaneous pneumothorax mutations were observed in the 152 severe, early-onset COPD probands. Exon resequencing identified 31 variants, including two non-synonymous polymorphisms and two common non-coding polymorphisms. No significant association was observed for any of these four variants with presence of COPD or emphysema-related phenotypes.
Genetic variation in folliculin does not appear to be a major risk factor for severe COPD. These data suggest that familial spontaneous pneumothorax and COPD have distinct genetic causes, despite some overlap in radiographic characteristics.
Hypoxemia, hypercarbia, and pulmonary arterial hypertension are known complications of advanced COPD. We sought to identify genetic polymorphisms associated with these traits in a population of patients with severe COPD from the National Emphysema Treatment Trial (NETT).
In 389 participants from the NETT Genetics Ancillary Study, single-nucleotide polymorphisms (SNPs) were genotyped in five candidate genes previously associated with COPD susceptibility (EPHX1, SERPINE2, SFTPB, TGFB1, and GSTP1). Linear regression models were used to test for associations among these SNPs and three quantitative COPD-related traits (Pao2, Paco2, and pulmonary artery systolic pressure). Genes associated with hypoxemia were tested for replication in probands from the Boston Early-Onset COPD Study.
In the NETT Genetics Ancillary Study population, SNPs in microsomal epoxide hydrolase (EPHX1) [p = 0.01 to 0.04] and serpin peptidase inhibitor, clade E, member 2 (SERPINE2) [p = 0.04 to 0.008] were associated with hypoxemia. One SNP within surfactant protein B (SFTPB) was associated with pulmonary artery systolic pressure (p = 0.01). In probands from the Boston Early-Onset COPD Study, SNPs in EPHX1 and in SERPINE2 were associated with the requirement for supplemental oxygen.
In participants with severe COPD, SNPs in EPHX1 and SERPINE2 were associated with hypoxemia in two separate study populations, and SNPs from SFTPB were associated with pulmonary artery pressure in the NETT participants.
case-control studies; COPD; genetics; phenotype; single-nucleotide polymorphism
Rationale: Previous studies of chronic obstructive pulmonary disease (COPD) have suggested that genetic factors play an important role in the development of disease. However, single-nucleotide polymorphisms that are associated with COPD in genome-wide association studies have been shown to account for only a small percentage of the genetic variance in phenotypes of COPD, such as spirometry and imaging variables. These phenotypes are highly predictive of disease, and family studies have shown that spirometric phenotypes are heritable.
Objectives: To assess the heritability and coheritability of four major COPD-related phenotypes (measurements of FEV1, FEV1/FVC, percent emphysema, and percent gas trapping), and COPD affection status in smokers of non-Hispanic white and African American descent using a population design.
Methods: Single-nucleotide polymorphisms from genome-wide association studies chips were used to calculate the relatedness of pairs of individuals and a mixed model was adopted to estimate genetic variance and covariance.
Measurements and Main Results: In the non-Hispanic whites, estimated heritabilities of FEV1 and FEV1/FVC were both about 37%, consistent with estimates in the literature from family-based studies. For chest computed tomography scan phenotypes, estimated heritabilities were both close to 25%. Heritability of COPD affection status was estimated as 37.7% in both populations.
Conclusions: This study suggests that a large portion of the genetic risk of COPD is yet to be discovered and gives rationale for additional genetic studies of COPD. The estimates of coheritability (genetic covariance) for pairs of the phenotypes suggest considerable overlap of causal genetic loci.
missing heritability; pleiotropy; pulmonary function; imaging phenotypes; chromosomal partition