Airway wall thickening and emphysema show independent familial aggregation in chronic obstructive pulmonary disease

Airway imaging in disease: gimmick or useful tool?

Airway remodeling is an important pathophysiological mechanism in a variety of chronic airway diseases. Historically investigators have had to use invasive techniques such as histological examination of excised tissue to study airway wall structure. The last several years has seen a proliferation of relatively noninvasive techniques to assess the airway branching pattern, wall thickness, and more recently, airway wall tissue components. These methods include computed tomography, magnetic resonance imaging, and optical coherence tomography. These new imaging technologies have become popular because to understand the physiology of lung disease it is important we understand the underlying anatomy. However, these new approaches are not standardized or available in all centers so a review of their validity and clinical utility is appropriate. This review documents how investigators are working hard to correct for inconsistencies between techniques so that they become more accepted and utilized in clinical settings. These new imaging techniques are very likely to play a frontline role in the study of lung disease and will, hopefully, allow clinicians and investigators to better understand disease pathogenesis and to design and assess new therapeutic interventions.

Pathobiologic mechanisms of chronic obstructive pulmonary disease

COPD is a worldwide public health problem that reduces the quality of life. The exact pathways by which CS and other environmental toxins produce COPD are not known. Currently, the leading candidates are (1) the protease-antiprotease hypothesis, (2) the Dutch hypothesis, (3) the British hypothesis, and the (4) autoimmunity hypothesis. Given the heterogeneity of the disease (and phenotypes), it is probably unrealistic that one pathway will fully explain COPD pathophysiology.

Morphological measurements in computed tomography correlate with airflow obstruction in chronic obstructive pulmonary disease: systematic review and meta-analysis

Objectives

To determine the correlation between CT measurements of emphysema or peripheral airways and airflow obstruction in chronic obstructive pulmonary disease (COPD).

Methods

PubMed, Embase and Web of Knowledge were searched from 1976 to 2011. Two reviewers independently screened 1,763 citations to identify articles that correlated CT measurements to airflow obstruction parameters of the pulmonary function test in COPD patients, rated study quality and extracted information. Three CT measurements were accessed: lung attenuation area percentage < -950 Hounsfield units, mean lung density and airway wall area percentage. Two airflow obstruction parameters were accessed: forced expiratory volume in the first second as percentage from predicted (FEV₁ %pred) and FEV₁ divided by the forced volume vital capacity.

Results

Seventy-nine articles (9,559 participants) were included in the systematic review, demonstrating different methodologies, measurements and CT airflow obstruction correlations. There were 15 high-quality articles (2,095 participants) in the meta-analysis. The absolute pooled correlation coefficients ranged from 0.48 (95 % CI, 0.40 to 0.54) to 0.65 (0.58 to 0.71) for inspiratory CT and 0.64 (0.53 to 0.72) to 0.73 (0.63 to 0.80) for expiratory CT.

Conclusions

CT measurements of emphysema or peripheral airways are significantly related to airflow obstruction in COPD patients. CT provides a morphological method to investigate airway obstruction in COPD.

Key Points

• Computed tomography is widely performed in patients with chronic obstructive pulmonary disease (COPD)

• CT provides quantitative morphological methods to investigate airflow obstruction in COPD

• CT measurements correlate significantly with the degree of airflow obstruction in COPD

• Expiratory CT measurements correlate more strongly with airflow obstruction than inspiratory CT

• Low-dose CT decreases the radiation dose for diagnosis and quantitative emphysema evaluation

Electronic supplementary material

The online version of this article (doi:10.1007/s00330-012-2480-8) contains supplementary material, which is available to authorized users.

Persistent systemic inflammation is associated with poor clinical outcomes in COPD: a novel phenotype

Background

Because chronic obstructive pulmonary disease (COPD) is a heterogeneous condition, the identification of specific clinical phenotypes is key to developing more effective therapies. To explore if the persistence of systemic inflammation is associated with poor clinical outcomes in COPD we assessed patients recruited to the well-characterized ECLIPSE cohort (NCT00292552).

Methods and Findings

Six inflammatory biomarkers in peripheral blood (white blood cells (WBC) count and CRP, IL-6, IL-8, fibrinogen and TNF-α levels) were quantified in 1,755 COPD patients, 297 smokers with normal spirometry and 202 non-smoker controls that were followed-up for three years. We found that, at baseline, 30% of COPD patients did not show evidence of systemic inflammation whereas 16% had persistent systemic inflammation. Even though pulmonary abnormalities were similar in these two groups, persistently inflamed patients during follow-up had significantly increased all-cause mortality (13% vs. 2%, p<0.001) and exacerbation frequency (1.5 (1.5) vs. 0.9 (1.1) per year, p<0.001) compared to non-inflamed ones. As a descriptive study our results show associations but do not prove causality. Besides this, the inflammatory response is complex and we studied only a limited panel of biomarkers, albeit they are those investigated by the majority of previous studies and are often and easily measured in clinical practice.

Conclusions

Overall, these results identify a novel systemic inflammatory COPD phenotype that may be the target of specific research and treatment.

Cigarette smoking behaviors and time since quitting are associated with differential DNA methylation across the human genome

The impact of cigarette smoking can persist for extended periods following smoking cessation and may involve epigenetic reprogramming. Changes in DNA methylation associated with smoking may help to identify molecular pathways that contribute to the latency between exposure and disease onset. Cross-sectional cohort data from subjects in the International COPD Genetics Network (n = 1085) and the Boston Early-Onset COPD study (n = 369) were analyzed as the discovery and replication cohorts, respectively. Genome-wide methylation data on 27 578 CpG sites in 14 475 genes were obtained on DNA from peripheral blood leukocytes using the Illumina HumanMethylation27K Beadchip in both cohorts. We identified 15 sites significantly associated with current smoking, 2 sites associated with cumulative smoke exposure, and, within the subset of former smokers, 3 sites associated with time since quitting cigarettes. Two loci, factor II receptor-like 3 (F2RL3) and G-protein-coupled receptor 15 (GPR15), were significantly associated in all three analyses and were validated by pyrosequencing. These findings (i) identify a novel locus (GPR15) associated with cigarette smoking and (ii) suggest the existence of dynamic, site-specific methylation changes in response to smoking which may contribute to the extended risks associated with cigarette smoking that persist after cessation.

BODE-index, modified BODE-index and ADO-score in chronic obstructive pulmonary disease: relationship with COPD phenotypes and CT lung density changes

COPD is a heterogeneous disorder whose assessment is going to be increasingly multidimensional. Grading systems such as BODE (Body-Mass Index, Obstruction, Dyspnea, Exercise), mBODE (BODE modified in grading of walked distance), ADO (Age, Dyspnea, Obstruction) are proposed to assess COPD severity and outcome. Computed tomography (CT) is deemed to reflect COPD lung pathologic changes. We studied the relationship of multidimensional grading systems (MGS) with clinically determined COPD phenotypes and CT lung density. Seventy-two patients underwent clinical and chest x-ray evaluation, pulmonary function tests (PFT), 6-minute walking test (6MWT) to derive: predominant COPD clinical phenotype, BODE, mBODE, ADO. Inspiratory and expiratory CT was performed to calculate mean lung attenuation (MLA), relative area with density below-950 HU at inspiration (RAI(-950)), and below -910 HU at expiration (RAE(-910)). MGS, PFT, and CT data were compared between bronchial versus emphysematous COPD phenotype. MGS were correlated with CT data. The prediction of CT density by means of MGS was investigated by direct and stepwise multivariate regression. MGS did not differ in clinically determined COPD phenotypes. BODE was more closely related and better predicted CT findings than mBODE and ADO; the better predictive model was obtained for CT expiratory data; stepwise regression models of CT data did not include 6MWT distance; the dyspnea score MRC was included only to predict RA-950 and RA-910 which quantify emphysema extent. BODE reflect COPD severity better than other MGS, but not its clinical heterogeneity. 6MWT does not significantly increase BODE predictivity of CT lung density changes.

Barr RG, Berkowitz EA, Bigazzi F, Bode F, Bon J, Bowler RP, Chiles C, Crapo JD, Criner GJ, Curtis JL, Dass C, Dirksen A, Dransfield MT, Edula G, Erikkson L, Friedlander A, Galperin-Aizenberg M, Gefter WB, Gierada DS, Grenier PA, Goldin J, Han MK, Hanania NA, Hansel NN, Jacobson FL, Kauczor HU, Kinnula VL, Lipson DA, Lynch DA, MacNee W, Make BJ, Mamary AJ, Mann H, Marchetti N, Mascalchi M, McLennan G, Murphy JR, Naidich D, Nath H, Newell JD, Pistolesi M, Regan EA, Reilly JJ, Sandhaus R, Schroeder JD, Sciurba F, Shaker S, Sharafkhaneh A, Silverman EK, Steiner RM, Strange C, Sverzellati N, Tashjian JH, van Beek EJR, Washington L, Washko GR, Westney G, Wood SA, Woodruff PG. A combined pulmonary-radiology workshop for visual evaluation of COPD: study design, chest CT findings and concordance with quantitative evaluation

The purposes of this study were: to describe chest CT findings in normal non-smoking controls and cigarette smokers with and without COPD; to compare the prevalence of CT abnormalities with severity of COPD; and to evaluate concordance between visual and quantitative chest CT (QCT) scoring.

METHODS

Volumetric inspiratory and expiratory CT scans of 294 subjects, including normal non-smokers, smokers without COPD, and smokers with GOLD Stage I-IV COPD, were scored at a multi-reader workshop using a standardized worksheet. There were 58 observers (33 pulmonologists, 25 radiologists); each scan was scored by 9-11 observers. Interobserver agreement was calculated using kappa statistic. Median score of visual observations was compared with QCT measurements.

RESULTS

Interobserver agreement was moderate for the presence or absence of emphysema and for the presence of panlobular emphysema; fair for the presence of centrilobular, paraseptal, and bullous emphysema subtypes and for the presence of bronchial wall thickening; and poor for gas trapping, centrilobular nodularity, mosaic attenuation, and bronchial dilation. Agreement was similar for radiologists and pulmonologists. The prevalence on CT readings of most abnormalities (e.g. emphysema, bronchial wall thickening, mosaic attenuation, expiratory gas trapping) increased significantly with greater COPD severity, while the prevalence of centrilobular nodularity decreased. Concordances between visual scoring and quantitative scoring of emphysema, gas trapping and airway wall thickening were 75%, 87% and 65%, respectively.

CONCLUSIONS

Despite substantial inter-observer variation, visual assessment of chest CT scans in cigarette smokers provides information regarding lung disease severity; visual scoring may be complementary to quantitative evaluation.

Annual change in pulmonary function and clinical phenotype in chronic obstructive pulmonary disease

RATIONALE

Although the rate of annual decline in FEV1 is one of the most important outcome measures in chronic obstructive pulmonary disease (COPD), little is known about intersubject variability based on clinical phenotypes.

OBJECTIVES

To examine the intersubject variability in a 5-year observational cohort study, particularly focusing on emphysema severity.

METHODS

A total of 279 eligible patients with COPD (stages I-IV: 26, 45, 24, and 5%) participated. We conducted a detailed assessment of pulmonary function and computed tomography (CT) at baseline, and performed spirometry every 6 months before and after inhalation of bronchodilator. Smoking status, exacerbation, and pharmacotherapy were carefully monitored. Emphysema severity was evaluated by CT and annual measurements of carbon monoxide transfer coefficient.

MEASUREMENTS AND MAIN RESULTS

Using mixed effects model analysis, the annual decline in post-bronchodilator FEV1 was -32±24 (SD) ml/yr (n=261). We classified the subjects of less than the 25th percentile as Rapid decliners, the 25th to 75th percentile as Slow decliners, and greater than the 75th percentile as Sustainers (-63±2, -31±1, and -2±1 [SE] ml/yr). Emphysema severity, but not %FEV1, showed significant differences among the three groups. Multiple logistic regression analysis demonstrated that the Rapid decliners were independently associated with emphysema severity assessed either by CT or carbon monoxide transfer coefficient. The Sustainers displayed less emphysema and higher levels of circulating eosinophils.

CONCLUSIONS

Emphysema severity is independently associated with a rapid annual decline in FEV1 in COPD. Sustainers and Rapid decliners warrant specific attention in clinical practice.

A genome-wide association study of COPD identifies a susceptibility locus on chromosome 19q13

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 FEV(1) (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.

Clinical phenotypes of COPD: identification, definition and implications for guidelines

The term phenotype in the field of COPD is defined as "a single or combination of disease attributes that describe differences between individuals with COPD as they relate to clinically meaningful outcomes". Among all phenotypes described, there are three that are associated with prognosis and especially are associated with a different response to currently available therapies. There phenotypes are: the exacerbator, the overlap COPD-asthma and the emphysema-hyperinflation. The exacerbator is characterised by the presence of, at least, two exacerbations the previous year, and on top of long-acting bronchodilators, may require the use of antiinflammatory drugs. The overlap phenotype presents symptoms of increased variability of airflow and incompletely reversible airflow obstruction. Due to the underlying inflammatory profile, it uses to have a good therapeutic response to inhaled corticosteroids in addition to bronchodilators. Lastly, the emphysema phenotype presents a poor therapeutic response to the existing antiinflammatory drugs and long-acting bronchodilators together with rehabilitation are the treatments of choice. Identifying the peculiarities of the different phenotypes of COPD will allow us to implement a more personalised treatment, in which the characteristics of the patients, together with their severity will be key to choose the best treatment option.

Quantitative computed tomography in COPD: possibilities and limitations

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease that is characterized by chronic airflow limitation. Unraveling of this heterogeneity is challenging but important, because it might enable more accurate diagnosis and treatment. Because spirometry cannot distinguish between the different contributing pathways of airflow limitation, and visual scoring is time-consuming and prone to observer variability, other techniques are sought to start this phenotyping process. Quantitative computed tomography (CT) is a promising technique, because current CT technology is able to quantify emphysema, air trapping, and large airway wall dimensions. This review focuses on CT quantification techniques of COPD disease components and their current status and role in phenotyping COPD.

Quantitative CT assessment of emphysema and airways in relation to lung cancer risk

PURPOSE

To determine whether quantitative computed tomographic (CT) measurements of emphysema and airway dimensions are associated with lung cancer risk in a screening population.

MATERIALS AND METHODS

Institutional review board approval and informed consent for the use of deidentified images were obtained. In this retrospective study, CT scans were analyzed from 279 participants in the CT screening arm of the National Lung Screening Trial who were diagnosed with lung cancer and 279 participants who were not diagnosed with lung cancer after a median follow-up period of 6.6 years. Quantitative CT measurements of emphysema and right upper lobe apical segmental and subsegmental airway dimensions, and multiple patient history-related variables, were compared between the two groups. Significant variables were tested in multivariate models for association with lung cancer by using multiple logistic regression.

RESULTS

The emphysema index of percentage upper lung volume less than -950 HU had the strongest association with lung cancer (mean, 10.7% [standard deviation, 13.5] in patients vs 7.2% [standard deviation, 10.4] in control subjects; P < .001), but the relationship was weak (R(2) = 0.015, P < .001, c = 0.57). No CT measures of emphysema had an association with lung cancer independent of the patient medical history variables. Airway dimensions were not associated with lung cancer.

CONCLUSION

Quantitative CT measurements of emphysema but not airway dimensions were only weakly associated with lung cancer, demonstrating no potential practical value for clinical risk stratification.

Prediction of cardiovascular events by using non-vascular findings on routine chest CT

Background

Routine computed tomography (CT) examinations contain an abundance of findings unrelated to the diagnostic question. Those with prognostic significance may contribute to early detection and treatment of disease, irrelevant findings can be ignored. We aimed to assess the association between unrequested chest CT findings in lungs, mediastinum and pleura and future cardiovascular events.

Methods

Multi-center case-cohort study in 5 tertiary and 3 secondary care hospitals involving 10410 subjects who underwent routine chest CT for non-cardiovascular reasons. 493 cardiovascular hospitalizations or deaths were recorded during an average follow-up time of 17.8 months. 1191 patients were randomly sampled to serve as a control subcohort. Hazard ratios and annualized event rates were calculated.

Results

Abnormalities in the lung (26–44%), pleura (14–15%) and mediastinum (20%) were common. Hazard ratios after adjustment for age and sex were for airway wall thickening 2.26 (1.59–3.22), ground glass opacities 2.50 (1.72–3.62), consolidations 1.97 (1.12–3.47), pleural effusions 2.77 (1.81–4.25) and lymph-nodes 2.04 (1.40–2.96). Corresponding annual event rates were 5.5%, 6.0%, 3.8%, 10.2% and 4.4%.

Conclusions

We have identified several common chest CT findings that are predictive for future risk of cardiovascular events and found that other findings have little utility for this. The added value of the non-vascular predictors to established vascular calcifications on CT remains to be determined.

Impact of non-linear smoking effects on the identification of gene-by-smoking interactions in COPD genetics studies

BACKGROUND

The identification of gene-by-environment interactions is important for understanding the genetic basis of chronic obstructive pulmonary disease (COPD). Many COPD genetic association analyses assume a linear relationship between pack-years of smoking exposure and forced expiratory volume in 1 s (FEV(1)); however, this assumption has not been evaluated empirically in cohorts with a wide spectrum of COPD severity.

METHODS

The relationship between FEV(1) and pack-years of smoking exposure was examined in four large cohorts assembled for the purpose of identifying genetic associations with COPD. Using data from the Alpha-1 Antitrypsin Genetic Modifiers Study, the accuracy and power of two different approaches to model smoking were compared by performing a simulation study of a genetic variant with a range of gene-by-smoking interaction effects.

RESULTS

Non-linear relationships between smoking and FEV(1) were identified in the four cohorts. It was found that, in most situations where the relationship between pack-years and FEV(1) is non-linear, a piecewise linear approach to model smoking and gene-by-smoking interactions is preferable to the commonly used total pack-years approach. The piecewise linear approach was applied to a genetic association analysis of the PI*Z allele in the Norway Case-Control cohort and a potential PI*Z-by-smoking interaction was identified (p=0.03 for FEV(1) analysis, p=0.01 for COPD susceptibility analysis).

CONCLUSION

In study samples of subjects with a wide range of COPD severity, a non-linear relationship between pack-years of smoking and FEV(1) is likely. In this setting, approaches that account for this non-linearity can be more powerful and less biased than the more common approach of using total pack-years to model the smoking effect.

Involvement of surfactant protein D in emphysema revealed by genetic association study

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.

Genetics of sputum gene expression in chronic obstructive pulmonary disease

Previous expression quantitative trait loci (eQTL) studies have performed genetic association studies for gene expression, but most of these studies examined lymphoblastoid cell lines from non-diseased individuals. We examined the genetics of gene expression in a relevant disease tissue from chronic obstructive pulmonary disease (COPD) patients to identify functional effects of known susceptibility genes and to find novel disease genes. By combining gene expression profiling on induced sputum samples from 131 COPD cases from the ECLIPSE Study with genomewide single nucleotide polymorphism (SNP) data, we found 4315 significant cis-eQTL SNP-probe set associations (3309 unique SNPs). The 3309 SNPs were tested for association with COPD in a genomewide association study (GWAS) dataset, which included 2940 COPD cases and 1380 controls. Adjusting for 3309 tests (p<1.5e-5), the two SNPs which were significantly associated with COPD were located in two separate genes in a known COPD locus on chromosome 15: CHRNA5 and IREB2. Detailed analysis of chromosome 15 demonstrated additional eQTLs for IREB2 mapping to that gene. eQTL SNPs for CHRNA5 mapped to multiple linkage disequilibrium (LD) bins. The eQTLs for IREB2 and CHRNA5 were not in LD. Seventy-four additional eQTL SNPs were associated with COPD at p<0.01. These were genotyped in two COPD populations, finding replicated associations with a SNP in PSORS1C1, in the HLA-C region on chromosome 6. Integrative analysis of GWAS and gene expression data from relevant tissue from diseased subjects has located potential functional variants in two known COPD genes and has identified a novel COPD susceptibility locus.

The role of CT scanning in multidimensional phenotyping of COPD

BACKGROUND

COPD is a heterogeneous disease characterized by airflow obstruction and diagnosed by lung function. CT imaging is emerging as an important, noninvasive tool in phenotyping COPD. However, the use of CT imaging in defining the disease heterogeneity above lung function is not fully known.

METHODS

Seventy-five patients with COPD (58 men, 17 women) were studied with CT imaging and with measures of airway inflammation. Airway physiology and health status were also determined.

RESULTS

The presence of emphysema (EM), bronchiectasis (BE), and bronchial wall thickening (BWT) was found in 67%, 27%, and 27% of subjects, respectively. The presence of EM was associated with lower lung function (mean difference % FEV(1), -20%; 95% CI, -28 to -11; P < .001). There was no difference in airway inflammation, exacerbation frequency, or bacterial load in patients with EM alone or with BE and/or BWT ± EM. The diffusing capacity of the lung for carbon monoxide/alveolar volume ratio was the most sensitive and specific parameter in identifying EM (area under the receiver operator characteristic curve, 0.87; 95% CI, 0.79-0.96). Physiologic cluster analysis identified three clusters, two of which were EM predominant and the third characterized by a heterogeneous combination of EM and BE.

CONCLUSIONS

The application of CT imaging can be useful as a tool in the multidimensional approach to phenotyping patients with COPD.

The chronic bronchitic phenotype of COPD: an analysis of the COPDGene Study

BACKGROUND

Chronic bronchitis (CB) in patients with COPD is associated with an accelerated lung function decline and an increased risk of respiratory infections. Despite its clinical significance, the chronic bronchitic phenotype in COPD remains poorly defined.

METHODS

We analyzed data from subjects enrolled in the Genetic Epidemiology of COPD (COPDGene) Study. A total of 1,061 subjects with GOLD (Global Initiative for Chronic Obstructive Lung Disease) stage II to IV were divided into two groups: CB (CB+) if subjects noted chronic cough and phlegm production for ≥ 3 mo/y for 2 consecutive years, and no CB (CB-) if they did not.

RESULTS

There were 290 and 771 subjects in the CB+ and CB- groups, respectively. Despite similar lung function, the CB+ group was younger (62.8 ± 8.4 vs 64.6 ± 8.4 years, P = .002), smoked more (57 ± 30 vs 52 ± 25 pack-years, P = .006), and had more current smokers (48% vs 27%, P < .0001). A greater percentage of the CB+ group reported nasal and ocular symptoms, wheezing, and nocturnal awakenings secondary to cough and dyspnea. History of exacerbations was higher in the CB+ group (1.21 ± 1.62 vs 0.63 ± 1.12 per patient, P < .027), and more patients in the CB+ group reported a history of severe exacerbations (26.6% vs 20.0%, P = .024). There was no difference in percent emphysema or percent gas trapping, but the CB+ group had a higher mean percent segmental airway wall area (63.2% ± 2.9% vs 62.6% ± 3.1%, P = .013).

CONCLUSIONS

CB in patients with COPD is associated with worse respiratory symptoms and higher risk of exacerbations. This group may need more directed therapy targeting chronic mucus production and smoking cessation not only to improve symptoms but also to reduce risk, improve quality of life, and improve outcomes.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT00608764; URL: www.clinicaltrials.gov.

High-resolution computed tomography quantitation of emphysema is correlated with selected lung function values in stable COPD

BACKGROUND

The literature shows conflicting results when high-resolution computed tomography (HRCT) scores of emphysema were correlated with different indices of airflow obstruction.

OBJECTIVES

We correlated HRCT scores of emphysema with different indices of airflow obstruction.

METHODS

We performed HRCT of the chest in 59 patients, all smokers or ex-smokers, with stable chronic obstructive pulmonary disease of different severity [GOLD stages I-IV; mean age ± SD 67.8 ± 7.3 years; pack/years 51.0 ± 34.6; percent predicted forced expiratory volume in 1 s (FEV(1)% predicted) 52.3 ± 17.6; post-bronchodilator FEV(1)% predicted 56.5 ± 19.1; FEV(1)/forced vital capacity (FVC) ratio 50.8 ± 10.2; post-bronchodilator FEV(1)/FVC ratio 51.6 ± 11.0; percent diffusion lung capacity for carbon monoxide (DLCO%) 59.2 ± 21.1; DLCO/percent alveolar volume (VA%) 54.5 ± 18.2; percent residual volume 163.0 ± 35.6; percent total lung capacity (TLC%) 113.2 ± 15; residual volume/TLC 1.44 ± 0.2]. All patients were in stable phase.

RESULTS

The mean ± SD visual emphysema score in all patients was 25.6 ± 25.4%. There was a weak but significant correlation between the percentage of pulmonary emphysema and numbers of pack/years (R = +0.31, p = 0.024). The percentage of emphysema was inversely correlated with the FEV(1)/FVC ratio before and after bronchodilator use (R = -0.44, p = 0.002, and R = -0.39, p = 0.005), DLCO% (R = -0.64, p = 0.0003) and DLCO/VA% (R = -0.68, p < 0.0001). A weak positive correlation was also found with TLC% (R = +0.28, p = 0.048). When patients with documented emphysema were considered separately, the best significant correlation observed was between DLCO/VA% and HRCT scan score (p = 0.007).

CONCLUSIONS

These data suggest that in patients with stable chronic obstructive pulmonary disease of varying severity, the presence of pulmonary emphysema is best represented by the impaired gas exchange capability of the respiratory system.

Pathogenic triad in COPD: oxidative stress, protease-antiprotease imbalance, and inflammation

Patients with chronic obstructive pulmonary disease (COPD) exhibit dominant features of chronic bronchitis, emphysema, and/or asthma, with a common phenotype of airflow obstruction. COPD pulmonary physiology reflects the sum of pathological changes in COPD, which can occur in large central airways, small peripheral airways, and the lung parenchyma. Quantitative or high-resolution computed tomography is used as a surrogate measure for assessment of disease progression. Different biological or molecular markers have been reported that reflect the mechanistic or pathogenic triad of inflammation, proteases, and oxidants and correspond to the different aspects of COPD histopathology. Similar to the pathogenic triad markers, genetic variations or polymorphisms have also been linked to COPD-associated inflammation, protease–antiprotease imbalance, and oxidative stress. Furthermore, in recent years, there have been reports identifying aging-associated mechanistic markers as downstream consequences of the pathogenic triad in the lungs from COPD patients. For this review, the authors have limited their discussion to a review of mechanistic markers and genetic variations and their association with COPD histopathology and disease status.

Family history is a risk factor for COPD

BACKGROUND

Studies have shown that family history is a risk factor for COPD, but have not accounted for family history of smoking. Therefore, we sought to identify the effects of family history of smoking and family history of COPD on COPD susceptibility.

METHODS

We compared 821 patients with COPD to 776 control smokers from the Genetic Epidemiology of COPD (COPDGene) Study. Questionnaires captured parental histories of smoking and COPD, as well as childhood environmental tobacco smoke (ETS) exposure. Socioeconomic status was defined by educational achievement.

RESULTS

Parental history of smoking (85.5% case patients, 82.9% control subjects) was more common than parental history of COPD (43.0% case patients, 30.8% control subjects). In a logistic regression model, parental history of COPD (OR, 1.73; P < .0001) and educational level (OR, 0.48 for some college vs no college; P < .0001) were significant predictors of COPD, but parental history of smoking and childhood ETS exposure were not significant. The population-attributable risk from COPD family history was 18.6%. Patients with COPD with a parental history had more severe disease, with lower lung function, worse quality of life, and more frequent exacerbations. There were nonsignificant trends for more severe emphysema and airway disease on quantitative chest CT scans.

CONCLUSIONS

Family history of COPD is a strong risk factor for COPD, independent of family history of smoking, personal lifetime smoking, or childhood ETS exposure. Although further studies are required to identify genetic variants that influence COPD susceptibility, clinicians should question all smokers, especially those with known or suspected COPD, regarding COPD family history.

Gender differences of airway dimensions in anatomically matched sites on CT in smokers

RATIONALE AND OBJECTIVES

There are limited data on, and controversies regarding gender differences in the airway dimensions of smokers. Multi-detector CT (MDCT) images were analyzed to examine whether gender could explain differences in airway dimensions of anatomically matched airways in smokers.

MATERIALS AND METHODS

We used VIDA imaging software to analyze MDCT scans from 2047 smokers (M:F, 1021:1026) from the COPDGene® cohort. The airway dimensions were analyzed from segmental to subsubsegmental bronchi. We compared the differences of luminal area, inner diameter, wall thickness, wall area percentage (WA%) for each airway between men and women, and multiple linear regression including covariates (age, gender, body sizes, and other relevant confounding factors) was used to determine the predictors of each airway dimensions.

RESULTS

Lumen area, internal diameter and wall thickness were smaller for women than men in all measured airway (18.4 vs 22.5 mm(2) for segmental bronchial lumen area, 10.4 vs 12.5 mm(2) for subsegmental bronchi, 6.5 vs 7.7 mm(2) for subsubsegmental bronchi, respectively p < 0.001). However, women had greater WA% in subsegmental and subsubsegmental bronchi. In multivariate regression, gender remained one of the most significant predictors of WA%, lumen area, inner diameter and wall thickness.

CONCLUSION

Women smokers have higher WA%, but lower luminal area, internal diameter and airway thickness in anatomically matched airways as measured by CT scan than do male smokers. This difference may explain, in part, gender differences in the prevalence of COPD and airflow limitation.

Dissimilarity-based classification of anatomical tree structures

A novel method for classification of abnormality in anatomical tree structures is presented. A tree is classified based on direct comparisons with other trees in a dissimilarity-based classification scheme. The pair-wise dissimilarity measure between two trees is based on a linear assignment between the branch feature vectors representing those trees. Hereby, localized information in the branches is collectively used in classification and variations in feature values across the tree are taken into account. An approximate anatomical correspondence between matched branches can be achieved by including anatomical features in the branch feature vectors. The proposed approach is applied to classify airway trees in computed tomography images of subjects with and without chronic obstructive pulmonary disease (COPD). Using the wall area percentage (WA%), a common measure of airway abnormality in COPD, as well as anatomical features to characterize each branch, an area under the receiver operating characteristic curve of 0.912 is achieved. This is significantly better than computing the average WA%.

SOX5 is a candidate gene for chronic obstructive pulmonary disease susceptibility and is necessary for lung development

RATIONALE

Chromosome 12p has been linked to chronic obstructive pulmonary disease (COPD) in the Boston Early-Onset COPD Study (BEOCOPD), but a susceptibility gene in that region has not been identified.

OBJECTIVES

We used high-density single-nucleotide polymorphism (SNP) mapping to implicate a COPD susceptibility gene and an animal model to determine the potential role of SOX5 in lung development and COPD.

METHODS

On chromosome 12p, we genotyped 1,387 SNPs in 386 COPD cases from the National Emphysema Treatment Trial and 424 control smokers from the Normative Aging Study. SNPs with significant associations were then tested in the BEOCOPD study and the International COPD Genetics Network. Based on the human results, we assessed histology and gene expression in the lungs of Sox5(-/-) mice.

MEASUREMENTS AND MAIN RESULTS

In the case-control analysis, 27 SNPs were significant at P ≤ 0.01. The most significant SNP in the BEOCOPD replication was rs11046966 (National Emphysema Treatment Trial-Normative Aging Study P = 6.0 × 10(-4), BEOCOPD P = 1.5 × 10(-5), combined P = 1.7 × 10(-7)), located 3' to the gene SOX5. Association with rs11046966 was not replicated in the International COPD Genetics Network. Sox5(-/-) mice showed abnormal lung development, with a delay in maturation before the saccular stage, as early as E16.5. Lung pathology in Sox5(-/-) lungs was associated with a decrease in fibronectin expression, an extracellular matrix component critical for branching morphogenesis.

CONCLUSIONS

Genetic variation in the transcription factor SOX5 is associated with COPD susceptibility. A mouse model suggests that the effect may be due, in part, to its effects on lung development and/or repair processes.

Quantifying the extent of emphysema: factors associated with radiologists' estimations and quantitative indices of emphysema severity using the ECLIPSE cohort

RATIONALE AND OBJECTIVES

This study investigated what factors radiologists take into account when estimating emphysema severity and assessed quantitative computed tomography (CT) measurements of low attenuation areas.

MATERIALS AND METHODS

CT scans and spirometry were obtained on 1519 chronic obstructive pulmonary disease (COPD) subjects, 269 smoker controls, and 184 nonsmoker controls from the Evaluation of COPD Longitudinally to Indentify Surrogate Endpoints (ECLIPSE) study. CT scans were analyzed using the threshold technique (%<-950HU) and a low attenuation cluster analysis. Two radiologists scored emphysema severity (0 to 5 scale), described the predominant type and distribution of emphysema, and the presence of suspected small airways disease.

RESULTS

The percent low attenuation area (%LAA) and visual scores of emphysema severity correlated well (r = 0.77, P < .001). %LAA, low attenuation cluster analysis, and absence of radiologist described gas trapping, distribution, and predominant type of emphysema were predictors of visual scores of emphysema severity (all P < .001). CT scans scored as showing regions of gas trapping had smaller lesions for a similar %LAA than those without (P < .001).

CONCLUSIONS

Visual estimates of emphysema are not only determined by the extent of LAA, but also by lesion size, predominant type, and distribution of emphysema and presence/absence of areas of small airways disease. A computer analysis of low attenuation cluster size helps quantitative algorithms discriminate low attenuation areas from gas trapping, image noise, and emphysema.

Cross-sectional analysis of the utility of pulmonary function tests in predicting emphysema in ever-smokers

Emphysema is largely an under-diagnosed medical condition that can exist in smokers in the absence of airway obstruction. We aimed to determine the sensitivity and specificity of pulmonary function tests (PFTs) in assessing emphysema using quantitative CT scans as the reference standard. We enrolled 224 ever-smokers (current or former) over the age of 40. CT of thorax was used to quantify the low attenuation area (% emphysema), and to measure the standardized airway wall thickness. PFTs were used individually and in combination to predict their ability to discriminate radiographic emphysema. Significant emphysema (>7%) was detected in 122 (54%) subjects. Twenty six (21%) emphysema subjects had no evidence of airflow obstruction (FEV(1)/FVC ratio <70%), while all subjects with >23% emphysema showed airflow obstruction. The sensitivity and specificity of spirometry for detecting radiographic emphysema were 79% and 75%, respectively. Standardized airway wall thickness was increased in subjects with airflow obstruction, but did not correlate with emphysema severity. In this cohort of lifetime ever-smokers, PFTs alone were inadequate for diagnosing emphysema. Airway wall thickness quantified by CT morphometry was associated with airflow limitation, but not with emphysema indicating that the heterogeneous nature of lung disease in smokers may represent distinct phenotypes.

Chronic obstructive pulmonary disease and lung cancer: new molecular insights

Both chronic obstructive pulmonary disease (COPD) and lung cancer are major causes of death worldwide. In most cases this reflects cigarette smoke exposure which is able to induce an inflammatory response in the airways of smokers. Indeed, COPD is characterized by lower airway inflammation, and importantly, the presence of COPD is by far the greatest risk factor for lung cancer amongst smokers. Cigarette smoke induces the release of many inflammatory mediators and growth factors including TGF-β, EGFR, IL-1, IL-8 and G-CSF through oxidative stress pathways and this inflammation may persist for decades after smoking cessation. Mucus production is also increased by these inflammatory mediators, further linking airway inflammation to an important mechanism of lung cancer. A greater understanding of the molecular and cellular pathobiology that distinguishes smokers with lung cancer from smokers with and without COPD is needed to unravel the complex molecular interactions between COPD and lung cancer. By understanding the common signalling pathways involved in COPD and lung cancer the hope is that treatments will be developed that not only treat the underlying disease process in COPD, but also reduce the currently high risk of developing lung cancer in these patients.

[COPD and inflammation: statement from a French expert group. Phenotypes related to inflammation]

INTRODUCTION

The objective of the present article is to review available data on possible links between phenotypes and inflammatory profiles in patients with chronic obstructive pulmonary disease (COPD).

BACKGROUND

Chronic bronchitis is associated with proximal bronchial inflammation and small airway inflammation with remodeling at the site of obstruction. CT scanning enables patients to be phenotyped according to the predominantly bronchial or emphysematous nature of the morphological abnormality. Exacerbations, in a context of persistently elevated baseline inflammation, are associated with increased inflammation and a poor prognosis. Long-term studies have correlated inflammatory markers (and anti-inflammatory drug effects) with dynamic hyperinflation, possibly confirming that inflammation promotes hyperinflation. The inflammatory cell count in the pulmonary arterial walls correlates with the severity of endothelial dysfunction. The risk of developing pulmonary hypertension would seem to increase with low-grade systemic inflammation. The role of low-grade systemic inflammation in COPD co-morbidities, and in nutritional and muscular involvement in particular, remains a matter of debate. Regular physical exercise may help reduce this inflammation.

CONCLUSIONS

In COPD, many aspects of the clinical phenotype are related to inflammation. Better knowledge of these relationships could help optimize current and future treatments.

Candidate genes for COPD in two large data sets

Lack of reproducibility of findings has been a criticism of genetic association studies on complex diseases, such as chronic obstructive pulmonary disease (COPD). We selected 257 polymorphisms of 16 genes with reported or potential relationships to COPD and genotyped these variants in a case-control study that included 953 COPD cases and 956 control subjects. We explored the association of these polymorphisms to three COPD phenotypes: a COPD binary phenotype and two quantitative traits (post-bronchodilator forced expiratory volume in 1 s (FEV₁) % predicted and FEV₁/forced vital capacity (FVC)). The polymorphisms significantly associated to these phenotypes in this first study were tested in a second, family-based study that included 635 pedigrees with 1,910 individuals. Significant associations to the binary COPD phenotype in both populations were seen for STAT1 (rs13010343) and NFKBIB/SIRT2 (rs2241704) (p<0.05). Single-nucleotide polymorphisms rs17467825 and rs1155563 of the GC gene were significantly associated with FEV₁ % predicted and FEV₁/FVC, respectively, in both populations (p<0.05). This study has replicated associations to COPD phenotypes in the STAT1, NFKBIB/SIRT2 and GC genes in two independent populations, the associations of the former two genes representing novel findings.

Quantitative CT: Associations between Emphysema, Airway Wall Thickness and Body Composition in COPD

The objective of the present study was to determine the association between CT phenotypes-emphysema by low attenuation area and bronchitis by airway wall thickness-and body composition parameters in a large cohort of subjects with and without COPD. In 452 COPD subjects and 459 subjects without COPD, CT scans were performed to determine emphysema (%LAA), airway wall thickness (AWT-Pi10), and lung mass. Muscle wasting based on FFMI was assessed by bioelectrical impedance. In both the men and women with COPD, FFMI was negatively associated with %LAA. FMI was positively associated with AWT-Pi10 in both subjects with and without COPD. Among the subjects with muscle wasting, the percentage emphysema was high, but the predictive value was moderate. In conclusion, the present study strengthens the hypothesis that the subgroup of COPD cases with muscle wasting have emphysema. Airway wall thickness is positively associated with fat mass index in both subjects with and without COPD.

Epidemiology, radiology, and genetics of nicotine dependence in COPD

BACKGROUND

Cigarette smoking is the principal environmental risk factor for developing COPD, and nicotine dependence strongly influences smoking behavior. This study was performed to elucidate the relationship between nicotine dependence, genetic susceptibility to nicotine dependence, and volumetric CT findings in smokers.

METHODS

Current smokers with COPD (GOLD stage ≥ 2) or normal spirometry were analyzed from the COPDGene Study, a prospective observational study. Nicotine dependence was determined by the Fagerstrom test for nicotine dependence (FTND). Volumetric CT acquisitions measuring the percent of emphysema on inspiratory CT (% of lung <-950 HU) and gas trapping on expiratory CT (% of lung <-856 HU) were obtained. Genotypes for two SNPs in the CHRNA3/5 region (rs8034191, rs1051730) previously associated with nicotine dependence and COPD were analyzed for association to COPD and nicotine dependence phenotypes.

RESULTS

Among 842 currently smoking subjects (335 COPD cases and 507 controls), 329 subjects (39.1%) showed high nicotine dependence. Subjects with high nicotine dependence had greater cumulative and current amounts of smoking. However, emphysema severity was negatively correlated with the FTND score in controls (ρ = -0.19, p < .0001) as well as in COPD cases (ρ = -0.18, p = 0.0008). Lower FTND score, male gender, lower body mass index, and lower FEV1 were independent risk factors for emphysema severity in COPD cases. Both CHRNA3/5 SNPs were associated with FTND in current smokers. An association of genetic variants in CHRNA3/5 with severity of emphysema was only found in former smokers, but not in current smokers.

CONCLUSIONS

Nicotine dependence was a negative predictor for emphysema on CT in COPD and control smokers. Increased inflammation in more highly addicted current smokers could influence the CT lung density distribution, which may influence genetic association studies of emphysema phenotypes.

Association of COPD candidate genes with computed tomography emphysema and airway phenotypes in severe COPD

The principal determining factors influencing the development of the airway disease and emphysema components of chronic obstructive pulmonary disease (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 the genetic association of single nucleotide polymorphisms (SNPs) in COPD candidate genes for association with emphysema severity and airway wall thickness phenotypes. Polymorphisms in six candidate genes were analysed in 379 subjects of the National Emphysema Treatment Trial (NETT) Genetics Ancillary Study with quantitative chest computed tomography (CT) data. Genetic association with per cent of lung area below -950 HU (LAA950), airway wall thickness, and derived square root wall area (SRWA) of 10-mm internal perimeter airways 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.

Genome-wide association study identifies BICD1 as a susceptibility gene for emphysema

RATIONALE

chronic obstructive pulmonary disease (COPD), characterized by airflow limitation, is a disorder with high phenotypic and genetic heterogeneity. Pulmonary emphysema is a major but variable component of COPD; familial data suggest that different components of COPD, such as emphysema, may be influenced by specific genetic factors.

OBJECTIVES

to identify genetic determinants of emphysema assessed through high-resolution chest computed tomography in individuals with COPD.

METHODS

we performed a genome-wide association study (GWAS) of emphysema determined from chest computed tomography scans with a total of 2,380 individuals with COPD in three independent cohorts of white individuals from (1) a cohort from Bergen, Norway, (2) the Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints (ECLIPSE) Study, and (3) the National Emphysema Treatment Trial (NETT). We tested single-nucleotide polymorphism associations with the presence or absence of emphysema determined by radiologist assessment in two of the three cohorts and a quantitative emphysema trait (percentage of lung voxels less than -950 Hounsfield units) in all three cohorts.

MEASUREMENTS AND MAIN RESULTS

we identified association of a single-nucleotide polymorphism in BICD1 with the presence or absence of emphysema (P = 5.2 × 10(-7) with at least mild emphysema vs. control subjects; P = 4.8 × 10(-8) with moderate and more severe emphysema vs. control subjects).

CONCLUSIONS

our study suggests that genetic variants in BICD1 are associated with qualitative emphysema in COPD. Variants in BICD1 are associated with length of telomeres, which suggests that a mechanism linked to accelerated aging may be involved in the pathogenesis of emphysema. Clinical trial registered with www.clinicaltrials.gov (NCT00292552).

Loci identified by genome-wide association studies influence different disease-related phenotypes in chronic obstructive pulmonary disease

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.

Quantitative CT measures of emphysema and airway wall thickness are related to D(L)CO

There is limited knowledge on the relationship between diffusing capacity of the lung for carbon monoxide (D(L)CO) and quantitative computed tomography (CT) measures of emphysema and airway wall thickness.

STUDY QUESTION

What is the relationship between D(L)CO and the quantitative CT measures of emphysema and airway wall thickness in subjects with and without COPD?

METHODS

We included 288 COPD subjects (70% men) and 425 non-COPD subjects (54% men). All subjects were current or ex-smokers older than 40 years and all subjects underwent spirometry, diffusing capacity tests and CT examination. Quantitative CT measures included % low attenuation areas < -950 HU (%LAA) and standardized airway wall thickness (AWT-Pi10).

RESULTS

Multiple linear regression analyses showed significant associations between D(L)CO and both %LAA and AWT-Pi10 in the COPD group. The adjusted regression coefficients (SE) for D(L)CO (mmol min(-1) kPa(-1)) were -1.15 (0.11) per 10% increase in %LAA and 0.08 (0.03) per 0.1 mm increase in AWT-Pi10, and the models' adjusted R(2) was 0.65 and 0.49, respectively.

CONCLUSIONS

CT measured emphysema explains a large fraction of the variation of D(L)CO among COPD subjects, and more so in men. Airway wall thickness is also significantly associated with D(L)CO, but explains a much smaller fraction of the variation.

α₁-Antitrypsin protease inhibitor MZ heterozygosity is associated with airflow obstruction in two large cohorts

BACKGROUND

Severe α₁-antitrypsin deficiency is a known genetic risk factor for COPD. Heterozygous (protease inhibitor [PI] MZ) individuals have moderately reduced serum levels of α₁-antitrypsin, but whether they have an increased risk of COPD is uncertain.

METHODS

We compared PI MZ and PI MM individuals in two large populations: a case-control study from Norway (n = 1,669) and a multicenter family-based study from Europe and North America (n = 2,707). We sought to determine whether PI MZ was associated with the specific COPD-related phenotypes of lung function and quantitative CT scan measurements of emphysema and airway disease.

RESULTS

PI MZ was associated with a 3.5% lower FEV₁/FVC ratio in the case-control study (P = .035) and 3.9% lower FEV₁/vital capacity (VC) ratio in the family study (P = .009). In the case-control study, PI MZ also was associated with 3.7% more emphysema on quantitative analysis of chest CT scans (P = .003). The emphysema result was not replicated in the family study. PI MZ was not associated with airway wall thickness or COPD status in either population. Among subjects with low smoking exposure (< 20 pack-years), PI MZ individuals had more severe emphysema on chest CT scan than PI MM individuals in both studies.

CONCLUSIONS

Compared with PI MM individuals, PI MZ heterozygotes had lower FEV₁/(F)VC ratio in two independent studies. Our results suggest that PI MZ individuals may be slightly more susceptible to the development of airflow obstruction than PI MM individuals.

Characterisation of COPD heterogeneity in the ECLIPSE cohort

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a complex condition with pulmonary and extra-pulmonary manifestations. This study describes the heterogeneity of COPD in a large and well characterised and controlled COPD cohort (ECLIPSE).

METHODS

We studied 2164 clinically stable COPD patients, 337 smokers with normal lung function and 245 never smokers. In these individuals, we measured clinical parameters, nutritional status, spirometry, exercise tolerance, and amount of emphysema by computed tomography.

RESULTS

COPD patients were slightly older than controls and had more pack years of smoking than smokers with normal lung function. Co-morbidities were more prevalent in COPD patients than in controls, and occurred to the same extent irrespective of the GOLD stage. The severity of airflow limitation in COPD patients was poorly related to the degree of breathlessness, health status, presence of co-morbidity, exercise capacity and number of exacerbations reported in the year before the study. The distribution of these variables within each GOLD stage was wide. Even in subjects with severe airflow obstruction, a substantial proportion did not report symptoms, exacerbations or exercise limitation. The amount of emphysema increased with GOLD severity. The prevalence of bronchiectasis was low (4%) but also increased with GOLD stage. Some gender differences were also identified.

CONCLUSIONS

The clinical manifestations of COPD are highly variable and the degree of airflow limitation does not capture the heterogeneity of the disease.

Multistudy fine mapping of chromosome 2q identifies XRCC5 as a chronic obstructive pulmonary disease susceptibility gene

RATIONALE

Several family-based studies have identified genetic linkage for lung function and airflow obstruction to chromosome 2q.

OBJECTIVES

We hypothesized that merging results of high-resolution single nucleotide polymorphism (SNP) mapping in four separate populations would lead to the identification of chronic obstructive pulmonary disease (COPD) susceptibility genes on chromosome 2q.

METHODS

Within the chromosome 2q linkage region, 2,843 SNPs were genotyped in 806 COPD cases and 779 control subjects from Norway, and 2,484 SNPs were genotyped in 309 patients with severe COPD from the National Emphysema Treatment Trial and 330 community control subjects. Significant associations from the combined results across the two case-control studies were followed up in 1,839 individuals from 603 families from the International COPD Genetics Network (ICGN) and in 949 individuals from 127 families in the Boston Early-Onset COPD Study.

MEASUREMENTS AND MAIN RESULTS

Merging the results of the two case-control analyses, 14 of the 790 overlapping SNPs had a combined P < 0.01. Two of these 14 SNPs were consistently associated with COPD in the ICGN families. The association with one SNP, located in the gene XRCC5, was replicated in the Boston Early-Onset COPD Study, with a combined P = 2.51 x 10(-5) across the four studies, which remains significant when adjusted for multiple testing (P = 0.02). Genotype imputation confirmed the association with SNPs in XRCC5.

CONCLUSIONS

By combining data from COPD genetic association studies conducted in four independent patient samples, we have identified XRCC5, an ATP-dependent DNA helicase, as a potential COPD susceptibility gene.

Polymorphisms in the superoxide dismutase-3 gene are associated with emphysema in COPD

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 single nucleotide polymorphisms (SNPs) were associated with COPD status, lung function variables, and quantitative computed tomography (CT) measurements of emphysema and airway wall thickness. Furthermore, 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 = .029 and p = .0058). The association with E1 was replicated in the ICGN family study, where the minor allele was associated with more emphysema (p = .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.