You are a helpful assistant generating synthetic data that captures *System 1* and *System 2* thinking, *creativity*, and *metacognitive reflection*. Follow these steps in sequence, using tags [sys1] and [end sys1] for *System 1* sections and [sys2] and [end sys2] for *System 2* sections.

1. *Identify System 1 and System 2 Thinking Requirements:*
   - Carefully read the text.
   - Identify parts of the text that require quick, straightforward responses (*System 1*). Mark these sections with [sys1] and [end sys1].
   - Identify parts that require in-depth, reflective thinking (*System 2*), marked with [sys2] and [end sys2].

2. *Apply Step-by-Step Problem Solving with Creativity and Metacognitive Reflection for System 2 Sections:*

   *2.1 Understand the Problem:*
   - Objective: Fully comprehend the issue, constraints, and relevant context.
   - Reflection: "What do I understand about this issue? What might I be overlooking?"
   - Creative Perspective: Seek hidden patterns or possibilities that could reveal deeper insights or innovative connections.

   *2.2 Analyze the Information:*
   - Objective: Break down the problem logically.
   - Reflection: "Am I considering all factors? Are there any assumptions that need challenging?"
   - Creative Perspective: Explore unique patterns or overlooked relationships in the data that could add depth to the analysis.

   *2.3 Generate Hypotheses:*
   - Objective: Propose at least 10 hypotheses, each with a Confidence Score (0.0 to 1.0) and Creative Score (0.0 to 1.0), reflecting originality, surprise, and utility.
   - Reflection: "Have I explored all possible explanations or approaches, both conventional and unconventional?"
   - Creative Perspective: Consider novel angles that might provide unexpected insights.

   *2.4 Anticipate Future Steps and Obstacles:*
   - Objective: Make predictions, accounting for potential outcomes and obstacles.
   - Reflection: "What challenges might I face? Is my plan flexible for different scenarios?"
   - Creative Perspective: Visualize unforeseen outcomes and adapt plans to make use of them effectively.

   *2.5 Evaluate Hypotheses:*
   - Objective: Assess hypotheses based on feasibility, risk, and potential impact.
   - Evaluation: Refine Confidence and Creative Scores as needed.
   - Reflection: "Am I unbiased in my assessment? Which options fit best with the overall objectives?"
   - Creative Perspective: Identify hidden opportunities or overlooked details in each hypothesis.

   *2.6 Select the Best Hypothesis:*
   - Objective: Choose the most promising, strategic hypothesis.
   - Reflection: "Why does this hypothesis stand out? How does it uniquely address the issue?"
   - Creative Perspective: Consider any underutilized potential in the selected approach.

   *2.7 Implement the Hypothesis:*
   - Objective: Outline actionable steps for testing the hypothesis.
   - Reflection: "Is this plan practical? What resources or preparation are required?"
   - Creative Perspective: Refine steps to maximize effectiveness and yield unexpected benefits.

   *2.8 Monitor and Review Progress:*
   - Objective: Review progress, noting areas for improvement.
   - Reflection: "What’s working well? What could be improved?"
   - Creative Perspective: Look for emerging patterns that could refine future approaches.

   *2.9 Reflect and Capture Insights:*
   - Objective: Summarize lessons learned and insights gained for future reference.
   - Reflection: "What new understanding has emerged from this process?"
   - Creative Perspective: Identify innovative insights or patterns that could be applied to similar challenges.

3. *Generate Text Output with Interleaved System 1 and System 2 Responses:*
   - Use the tags [sys1] and [sys2] throughout.
   - Aim for a lengthier, detailed response. Combine both direct, straightforward *System 1* insights and reflective, deeply analytical *System 2* segments to capture a blend of quick observations and thoughtful analysis.

---

### *Example Input Text:*

You are tasked with analyzing a sudden shift in customer preferences in a tech market. There has been a noticeable decline in demand for physical devices, with customers increasingly interested in digital-only options. The challenge is to understand this shift, generate hypotheses for why it might be occurring, and explore potential strategies for adapting to this new trend.

---

### *Processed Output with System 1 and System 2 Thinking:*

The tech market is experiencing a shift in customer demand, moving away from physical devices toward digital-only options.

[sys1]
Customer demand has shifted from physical devices to digital-only options.
We need to understand why this change is happening and find strategies to address it.
Key factors may include cost, convenience, and technological trends.
[end sys1]

[sys2]
**2.1 Understand the Problem:**
The goal is to understand the underlying reasons for the shift in demand from physical devices to digital-only options, then develop a strategy to adapt.

*Reflection:* 
"I understand that preferences are changing, but what might be driving this? Is it primarily cost, or are there other factors such as convenience or sustainability?"

*Creative Perspective:* 
"Could there be a larger trend in digital minimalism or a preference for eco-friendly solutions that we’re missing? What unseen motivations might explain this shift?"

**2.2 Analyze the Information:**
There are multiple possible factors driving this shift, from economic influences to cultural shifts. It’s essential to isolate each factor and understand its impact.

*Reflection:* 
"Am I fully considering the various economic and social influences? Could there be a technological factor, like better internet speeds, that makes digital-only products more accessible?"

*Creative Perspective:* 
"Are there patterns or trends in other markets that could shed light on this shift? Could this be part of a larger trend toward virtual experiences?"

**2.3 Generate Hypotheses:**
1. Customers prefer digital options due to lower costs. (Confidence: 0.8, Creative: 0.4)
2. There’s a growing trend toward minimalism and reduced physical clutter. (Confidence: 0.7, Creative: 0.7)
3. Digital products offer greater flexibility and ease of use. (Confidence: 0.6, Creative: 0.6)
4. Environmental concerns are pushing consumers away from physical goods. (Confidence: 0.6, Creative: 0.8)
5. Advances in tech make digital-only options more functional. (Confidence: 0.8, Creative: 0.5)
6. Pandemic-era remote work increased demand for digital solutions. (Confidence: 0.7, Creative: 0.6)
7. Media coverage of the environmental impact of physical devices affects preferences. (Confidence: 0.5, Creative: 0.7)
8. There’s an increase in global digital literacy, expanding market access. (Confidence: 0.6, Creative: 0.6)
9. Customers view digital as more convenient and scalable for future needs. (Confidence: 0.7, Creative: 0.5)
10. Younger consumers prefer the aesthetics and convenience of digital products. (Confidence: 0.6, Creative: 0.6)

*Reflection:* 
"Have I considered all possible influences? Are there any surprising factors that could explain this shift?"

*Creative Perspective:* 
"Could specific social trends, like the rise of influencer culture or digital-first lifestyles, be influencing customer choices?"

**2.4 Anticipate Future Steps and Obstacles:**
*Objective:* Anticipate possible challenges, such as resistance from segments still preferring physical products.

*Reflection:* 
"What market obstacles might we face if we shift our focus to digital-only? Are there sub-segments that still prioritize physical products?"

*Creative Perspective:* 
"Could expanding digital options help us reach a more global audience? Are there emerging trends that we could leverage in our strategy?"

[end sys2]

[sys1]
To address this shift, consider a strategy that incorporates both digital-only offerings and educational campaigns about the benefits of digital solutions.
Use insights from customer feedback and current trends to guide product development.
Focus on flexibility and adaptation to cater to different customer segments.
[end sys1]


Introduction
============

Genetic factors likely play a critical role in the development of COPD, because only a minority of heavy smokers develops this disease. The first genetic defect associated with COPD was a deficiency in α1-antitrypsin ([@b8-copd-1-267]). However, other genetic variations that affect the proteinase--antiproteinase imbalance ([@b6-copd-1-267]) also likely affect the onset and development of COPD, because only \<1% of COPD cases are associated with α1-antitrypsin deficiency ([@b28-copd-1-267]).

A role for the matrix metalloproteinases (MMPs) has been suggested in the pathogenesis of pulmonary emphysema ([@b2-copd-1-267]). Immunoreactivity for MMP-1, MMP-2, and MMP-9 is more intense in emphysematous samples compared with normal lung tissue ([@b21-copd-1-267]; [@b29-copd-1-267]). Alveolar macrophages obtained from smokers release more MMP-9 than those from non-smokers ([@b18-copd-1-267]).

There is an insertion--deletion polymorphism in the promoter region of the MMP-1 gene (1G-1607/2G). The addition of G in the MMP-1 promoter creates an Ets binding site, and leads to higher transcription of the protein compared with the common 1G polymorphism ([@b26-copd-1-267]). The incidence of the 2G allele rises to 62% in tumor cells in ovarian and endometrial carcinomas ([@b26-copd-1-267]). A single nucleotide polymorphism (SNP) in the MMP-2 promoter sequence (−1306 C→T) disrupts a SP1 site and results in lower promoter activity with the T allele ([@b25-copd-1-267]), and participants homozygous for C have an overall 2-fold increased risk for developing lung cancer compared with those with the CT or TT genotype ([@b34-copd-1-267]). We chose to study the association of these SNPs with COPD, because participants with COPD are at higher risk of developing lung cancer ([@b4-copd-1-267]; [@b33-copd-1-267]).

Sequence analysis of the MMP-9 gene revealed a total of 10 variable sites, 4 in the promoter, 5 in the coding region (3 of which alter the amino acid encoded), and 1 in the 3′ untranslated region ([@b37-copd-1-267]). The variable length CA repeat located at −90 bp within the promoter region of MMP-9 may affect promoter activity and creates a sequence-specific DNA-binding protein site ([@b24-copd-1-267]). A C→T polymorphism at −1562 bp results in higher transcription rates for the T allele than the C allele promoter ([@b38-copd-1-267]) and dysregulation of MMP-9 function could increase susceptibility for smoking-induced airway obstruction. A polymorphism in exon 6 of MMP-9 is located in the substrate-binding domain of this enzyme and leads to a substitution of an uncharged amino acid (glutamine) by a positively charged amino acid (arginine). This polymorphism likely alters protein conformation, leading to a change in substrate-binding and enzyme activity, while the other two polymorphisms in the coding region that lead to altered amino acids are not likely to have such a profound change in enzyme activity ([@b37-copd-1-267]).

The major ethnic groups in New Mexico, the area from which the study population was recruited, consist of non-hispanic whites and hispanics. Therefore, the present study analyzed the prevalence of COPD in these ethnic groups and determined whether potentially functional variants that include the promoter regions of MMP-1, MMP -2, and MMP -9 and the Glu279Arg polymorphism within MMP-9 gene are associated with COPD in a cross-sectional study of veteran men and within the major ethnic groups.

Material and methods
====================

Study population
----------------

Study participants were drawn from an ongoing cohort study of veterans (n=385). Participants were recruited from the New Mexico Veterans' Health Care System, which provides medical care for approximately 35 000 veterans in New Mexico, west Texas, and southern Colorado. Inclusion criteria included age 40--75 years and a minimum smoking history of ≥20 pack-years. Informed consent was obtained from each participant prior to completing a standardized clinical examination including spirometry and a standardized questionnaire that provided detailed information on demographics, smoking history, and respiratory health. Phlegm production was assessed by evaluating the St. George's Respiratory Disease Questionnaire. The same information was obtained at a follow-up visit at 18±3 months for 176 participants. This study was approved by the Institutional Review Boards of the Lovelace Respiratory Research Institute, the New Mexico Veterans Health Care System, and the University of New Mexico Health Sciences Center.

COPD definition
---------------

COPD was defined by criteria similar to those suggested as part of the GOLD criteria ([@b23-copd-1-267]) and were used in the Lung Health Study ([@b1-copd-1-267]) and recently described by the ATS/ERS Task Force ([@b3-copd-1-267]). We did not break down the cohort into various GOLD categories, because of small cell size for GOLD 1--4. However, three definitions for COPD were used: Definition I included all participants with FEV~1~/FVC\<70% as measured by spirometry. Definition II included only participants with FEV~1~/FVC\<70% and who had FEV~1~\<80% as cases and all other participants who were defined as COPD participants in Definition I were excluded from the analyses. Definition III included only participants with FEV~1~/FVC\<70% and FEV~1~\<80%, excluding all who had reversibility of \>15% post-bronchodialator exposure. Reversibility was defined as the percent change in percent predicted FEV~1~ between pre- and post-bronchodialator exposures. For all three definitions, participants were considered to be non-COPD if FEV~1~/FVC≥70%. Participants who met the criteria for diagnosis of COPD at cohort entry were classified as prevalent cases. Participants with mild COPD were excluded in Definition II to reduce the potential for including participants who have "borderline" airflow obstruction and participants who have reversible airflow obstruction were excluded in Definition III to exclude the majority of participants who have asthma.

Genotyping of polymorphisms in MMP-9
------------------------------------

Genomic DNA was isolated from peripheral blood lymphocytes by digestion with proteinase K in sodium dodecyl sulfate (1%), followed by standard phenol--chloroform extraction and ethanol precipitation as described ([@b27-copd-1-267]). The sequence flanking the polymorphic region of each SNP was amplified by PCR using 10 ng of DNA. Negative controls without DNA template were included with each set of reactions. Several methods of genotyping were used to verify the obtained results. Restriction fragment length polymorphism (RFLP) was performed on 50--100 samples to verify the results obtained by the allelic discrimination assay. This assay integrates PCR and detection using allelic discrimination, which applies allele-specific TaqMan probes, a two-dye reporter system, and a reference dye. Wild-type and variant reporter sequences were discriminated using dual labeled reporters and by using mismatched sequences to validate the SNP-genotype. To further ensure quality control, DNA samples from 20 participants whose allelotypes were known were included at random within each of the 96-well plates of the allelic discrimination assay. In addition, approximately 10% of the samples were re-examined by a different person. All analyses were performed blinded with respect to participants' characteristics. These controls showed 100% concordance with expected results.

The methods of genotyping, including the primers and probes for allelic discrimination of SNPs in MMP-1, MMP-2, and MMP-9 or enzyme used for RFLP, are listed in [Table 1](#t1-copd-1-267){ref-type="table"}. The C→T polymorphism was analyzed using a RFLP assay, because several attempts to design primers and probes for this polymorphism failed. The presence of the rare T allele introduces a restriction site for SphI, which is absent when the common C allele is present.

The number of CA repeats in the promoter region of MMP-9 was determined by PCR using a fluorescently labeled 6-FAM forward primer and an unlabeled reverse primer. The alleles were separated by a laser-based automated DNA sequencer, ABI PRISM 3100. The product peaks were visualized using GenescanView software (Bio Molecular Research, Padova, Italy). The size of the PCR products was calculated from a standard curve made from internal standards. DNA standards containing 14, 21, 22, and 23 CA repeats were identified by direct sequencing and were included in each experiment as positive controls. For unknown reasons, the polymorphisms of certain samples (1%--5%) could not be assessed even upon repeated attempts, resulting in slight sample size variability for the various polymorphisms.

Statistical analysis
--------------------

We examined summary information by COPD status for demographic variables (age, gender, ethnicity); clinical risk factors (current smoking status, duration and pack-years of cigarette smoking); and polymorphism status (homozygous-rare, heterozygous, homozygous-common). The chi-square test and Fisher's exact test were used to compare categorical variables, including gene polymorphisms between participants with and without COPD. Continuous variables such as age and smoking duration were compared using either the two-sample t-test or the Wilcoxon rank sum test. The small number of women (17 in total) enrolled in the larger cohort were excluded from the analysis cohort of 385 veteran men, but this exclusion and inclusion of these women did not change any of the conclusions.

Distributions of genotypes were assessed for Hardy-Weinberg equilibrium using a generalization of Fisher's exact test ([@b11-copd-1-267]). All pairs of MMP-9 loci (T-1562, 279Arg, and CA repeats) were tested for linkage disequilibrium using likelihood tests and permutation procedures to estimate significance levels ([@b10-copd-1-267]; [@b31-copd-1-267]) as implemented in PowerMarker v3.12 (Liu and Muse). The degree of disequilibrium was described using D′ ([@b17-copd-1-267]; [@b35-copd-1-267]).

Logistic regression models were fit to estimate odds ratios (OR) for COPD and to allow adjustment for multiple covariates. We estimated effects for dominant, co-dominant, and recessive models for the variant alleles. Covariates in all models included age, ethnicity, and smoking information (former or current, or the continuous forms of smoking duration and pack-years). Logistic regression models for each polymorphism were fitted and the indicators were included as predictors for only those polymorphisms at one region plus the covariates. Since there was linkage disequilibrium between some of the polymorphisms, the polymorphisms were examined separately. Interactions between the genotypes and each covariate, especially cigarette smoking (duration and pack-years), and interactions between the covariates also were investigated. To assess differences by ethnicity, models were fitted separately by ethnic group. Likelihood ratio tests were used to test models and Wald's chi-square tests were used to evaluate whether individual variables contributed to the model. Linear regression models were used to assess the association between the genetic predictor variables and the predicted FEV~1~. Covariates and interactions were included in the modeling as done for the logistic regression models above. All standard statistical testing and modeling were conducted using Statistical Analysis System SAS v8.02. (SAS Institute, Inc., Cary, NC, USA). These analyses were done for each of the COPD definitions. Therefore, the analyses ranged from mild to moderate and severe cases as the outcome.

The association between estimated haplotype frequencies and COPD was evaluated with a two-stage process. First, MMP-9 haplotype frequencies based on T-1562, 279Arg, and CA repeats were estimated using Excoffier and Slatkin's maximum likelihood algorithm ([@b7-copd-1-267]). For each possible haplotype, *h*, an estimate is made of the number of copies of *h* contained in the true pair of haplotypes carried by that individual conditional on the observed genotype and assuming Hardy-Weinberg equilibrium. The expected haplotype frequencies are analogous to haplotype dosages and were used in the second step as independent variables in logistic regression models that also included adjustment for age, smoking duration, and smoking status. Haplotype dosages for each participant were calculated separately for non-hispanic whites and hispanics. For other and unknown ethnicity, haplotype doses were calculated based on the overall cohort. Second, logistic regression analyses were conducted as outlined previously.

Results
=======

Description of study population
-------------------------------

The demographics of the cohort are summarized by COPD status as per definition I, which includes mild to severe cases ([Table 2](#t2-copd-1-267){ref-type="table"}). The prevalence of COPD was 32% and, as expected for a disease that increases in frequency with age, overall the age of participants with COPD was older than for non-COPD participants. The median age for participants with and without COPD was 64 and 57 years (p\<0.001), respectively. Interestingly, a higher proportion of non-hispanic white participants (36%) had COPD than hispanic participants (25%) (p=0.07). The number of participants included in analyses for COPD definitions II and III decreased to 366 and 339, respectively.

Average smoking duration and pack-years were greater for participants with COPD than for participants without COPD (p\<0.001). Furthermore, the unadjusted OR for COPD was 2.1 and 2.0 for every 10 additional years of smoking duration and age, respectively (p\<0.001). Finally, COPD was significantly associated with phlegm production when adjusted for age and smoking duration (OR=2.0, 95% CI=1.4 to 3.0; p\<0.001). These basic demographic and clinical risk factors are similar to those reported in other studies of COPD ([@b36-copd-1-267]) and reinforce the utility of our cohort for evaluating the role of polymorphisms within the MMP-9 gene as risk modifiers for COPD.

In general the percentages for COPD participants, ethnic distribution, smoking duration, and pack-years, and the baseline %FEV~1~ for the participants with a second visit remained identical to those for the overall cohort who came for the first visit ([Table 2](#t2-copd-1-267){ref-type="table"}). Repeat testing was performed on these participants with 90% concordance of those initially classified with chronic airflow obstruction. These tests established the chronicity of airflow limitation through demonstration of FEV~1~/FVC\<70% by spirometry that was not reversed into the normal range after a bronchodilation, but had an overall tendency of decline over time ([@b23-copd-1-267]). No mean linear change in pulmonary function test was found in non-COPD participants within the participants with repeat measurements. However, there was a significant difference in yearly decline of %FEV~1~ for the COPD participants (2.6 (95% CI: 1.4--3.8)) compared with that of non-COPD participants (0.81 (95% CI: −0.01 to 1.62)) (p\<0.02).

Distribution of genotypes
-------------------------

The SNPs were determined in DNA samples from 385 study participants. CA repeats of 14, 21, 22, and 23 were most frequently found while the frequency of other repeat lengths was below 2% ([Figure 1](#f1-copd-1-267){ref-type="fig"}). The CA repeat lengths that were most frequently found as genotypes were 14/14 (27%), 14/21 (20%), 14/22 (16%), 14/23 (8%), 21/21 (11%), and 22/22 (5%). The frequency of all other alleles was below 2% ([Table 3](#t3-copd-1-267){ref-type="table"}). Because the frequency distribution of the CA repeat polymorphism showed a bimodal distribution of alleles, the alleles were divided into two subclasses: CA repeats ≤16 and ≥17 were designated as Short and Long, respectively, and treated similarly to genotype data.

The distributions of homozygotes and heterozygotes for each polymorphism in each ethnic group generally conformed to expectations under the assumption of Hardy-Weinberg equilibrium, with the exception of the CA-repeat among hispanic participants (p=0.02). As a measure for linkage disequilibrium, D′ was determined. The 279Arg was in linkage disequilibrium with both T-1562 (p\<0.001) and CA repeat (p\<0.001) within the ethnic groups. Of particular note, all participants with the homozygote rare T-1562 (N=20) had rare 279Arg. However, many participants who were homozygous for 279Arg had the C-1562 ([Table 4](#t4-copd-1-267){ref-type="table"}). No differences among cases and controls were observed for any of the genotypes in MMP-1 and MMP-2.

A difference in prevalence of the 279Gln (35.0 vs 52.1, p\<0.01) and 279Arg (18.7% vs 7.7%, p\<0.01) homozygote genotypes was seen in participants with COPD compared with non-COPD participants ([Table 4](#t4-copd-1-267){ref-type="table"}) and among the COPD and non-COPD participants at the second visit (see [Appendix Table 4](#t7-copd-1-267){ref-type="table"}). Significantly different distributions of the homozygote rare 279Arg were also observed within the non-hispanic white participants (p\<0.01). This trend in difference was recapitulated within the hispanic participants, but was not significant due to the lower number of hispanic participants with COPD. The rare T-1562 allele, the CA repeat lengths, and the SNPs in MMP-1 and MMP -2 were distributed similarly among the participants with and without COPD in the veterans' cohort ([Table 4](#t4-copd-1-267){ref-type="table"}). The results for COPD definitions II and III remained identical, in that the distribution for the Gln279 was 52% compared with 7.7% for the Arg279. For both COPD definitions II and III, the distribution for Gln279 remained at 47% in non-hispanic white participants compared with 9% for the rare Arg279.

Association of allelotype with COPD
-----------------------------------

The rare 279Arg variant was significantly associated with COPD ([Table 5](#t5-copd-1-267){ref-type="table"}). This table gives the odds ratios which is the odds for COPD relative to the odds for those without COPD. After adjustment for age, smoking duration, and current smoking status, the OR for COPD participants who were homozygous for 279Arg variant was 3.8 relative to those who were homozygous for the common allele (p\<0.01). In addition, participants who were heterozygous also showed a significant increased risk for the disease (OR=1.8; p\<0.05), indicating a co-dominant association between 279Arg and COPD. This association was significant within the non-hispanic white but not within the hispanic participants, likely because of limited sample size for this ethnic group. Among the non-hispanic white participants, significant associations between COPD and the homozygous rare T-1562 (OR=4.5; p\<0.05) and the Long/Long form of CA repeat (OR=2.3, p\<0.05) were observed. Similar results were obtained for COPD definitions II and III (see [Appendix Table 5](#t8-copd-1-267){ref-type="table"}). For example, for COPD definition II for the Gln279Arg the OR for the homozygote rare genotype remained significant at 3.13 (95% CI: 1.4--6.9) and in non-hispanic white participants at 2.8 (95% CI: 1.1--6.8). For COPD definition III, the OR was 3.1 (95% CI: 1.4--7.3) and 3.3 (95% CI: 1.3--8.4) overall and for non-hispanic whites, respectively. No association with COPD was found for the variants in MMP-1 and MMP -2. The similarity of results between the ethnic groups and among the definitions of COPD indicates that multiple comparison adjustments are not needed for these factors. All models showed that smoking variables, including duration, pack-years, and current status, were significantly associated with COPD, but none of the variables was a co-founder with the genetic variables.

Gene--gene and gene--environment interaction effects were evaluated by adding interaction terms in logistic regression models that included adjustments for age and smoking duration. To assess differences by ethnicity, analyses were done separately for non-hispanic white and hispanic participants. The gene--environment interactions used cigarette smoking measures as the environmental factors. We found no significant gene--gene or gene--environment interaction effects.

Association of SNPs with the decline in pulmonary function--longitudinal analyses
---------------------------------------------------------------------------------

While we did not see a decline in pulmonary function over time when analyzing the data of the entire population, non-hispanic white participants and those who smoked more than 40 pack-years showed a statistically significant decrease per year when the raw or percentage difference of the baseline value in FEV~1~ was analyzed. Non-hispanic whites showed an average decrease of 1.2 (95% CI: 0.5--1.9) or 1.7% (95% CI: 0.7--2.6), respectively, per year. Those who smoked ≥40 pack-years showed an average decrease of 1.6 (95% CI: 0.6--2.7) or 2.1% (95% CI: 0.8-- 3.4%), respectively per year. However, we did not see any association of the polymorphisms tested with decline in pulmonary function assessed over 18 months, while the distribution of polymorphisms by COPD status was identical to that observed for all participants.

Haplotype analyses
------------------

Haplotype (common \[C\], rare \[R\], long \[L\], short \[S\]) frequencies formed from MMP-9 C/T-1562, MMP-9 Gln279Arg, and CA repeats were estimated for each cohort and ethnic group and evaluated for differences with respect to COPD status ([Table 6](#t6-copd-1-267){ref-type="table"}). ORs adjusted for age, smoking duration, and current smoking status were calculated relative to the common C-1562, Gln279, and short CA repeats (C-C-S) for haplotypes with frequencies \>0.005 ([Table 6](#t6-copd-1-267){ref-type="table"}). The haplotypes with significant association with COPD were C-R-L (1.8, 95% CI, 1.1--2.9) and R-R-L (1.7, 95% CI, 1.1--2.7) compared with the C-C-S haplotype. Participants with the haplotype including the T-1562 and the rare 279Arg showed the same OR as participants with the haplotype, including the C-1562 and the rare 279Arg, indicating that either the 279Arg polymorphism is the main determinant or another variant on this RL haplotype may underlie the increased association by MMP-9 and risk for COPD. Models with and without covariates were compared using likelihood ratio tests. Models with haplotype dosages were no better than covariate-only models for predicting COPD status of hispanic veterans. Haplotype information was useful for predicting COPD in non-hispanic white veterans; however, the only adjusted OR different from the reference haplotype, C-C-S, was R-R-L (p=0.02, OR=2.0, 95% CI=1.1--3.4).

Discussion
==========

This cross-sectional study provides evidence that the tested polymorphisms in the MMP-9 gene are associated with susceptibility for onset of COPD in men. The increased risk for COPD may stem from the rare allele in exon 6, which replaces the non-charged glutamine (MMP-9Q) with the charged amino acid, arginine (MMP-9R).

MMP-9R could increase degradation of the ECM leading to emphysematous lungs. MMP-9 is expressed and secreted from cells as inactive zymogen through multiple mechanisms. This inactive form of MMP-9 is maintained by a cysteine and additional domains within the highly conserved region of the pro-peptide and the essential zinc atom in the catalytic domain ([@b22-copd-1-267]). This tight regulation may be diminished in MMP-9R, especially in the presence of inflammatory responses that are induced by the presence of cigarette smoke. Alternatively, the affinity of MMP-9R to tissue inhibitors of metalloproteinases (TIMP)-1, the major inhibitor of MMP-9, may be lower compared with that of MMP-9Q, because TIMP-1 forms a complex at the carboxy-terminus of the pro-enzyme and the catalytic domain of the active form ([@b9-copd-1-267]).

A previous study comparing smokers with COPD showed an association with a 5-year rate of decline with MMP-1 G-1607GG and haplotypes consisting of alleles from the MMP-1 G-1607GG and MMP-12 Asn357Ser polymorphisms ([@b16-copd-1-267]). In contrast, the CA repeat in MMP-9 was not associated with the rate of decline in lung function. The differences in findings from our study may be because the Joos et al study was designed to focus on the rate of decline in lung function rather than overall risk for developing COPD. That study also did not include the Gln279Arg SNP of MMP-9. As expected, the frequencies of the A (65%) and G (35%) alleles in our study were very similar to those reported previously ([@b37-copd-1-267]). In general the frequencies of the alleles for each of the SNPs in this study were very similar to those reported in the NCBI website or in manuscripts ([@b37-copd-1-267]; [@b13-copd-1-267]).

The CA repeat length that was observed with high frequency in this cohort was 14 repeats. The second allele in these individuals had a CA repeat of 21, 22, or 23 repeats. The next most frequent alleles were between 21 and 22 CA repeats. While a similar distribution in CA repeats was observed in a Caucasian population ([@b16-copd-1-267]), this distribution of CA repeats is vastly different from that reported for 223 Japanese who had primarily MMP-9 alleles that contained 20 or more CA repeats. Only 2.8% of the Japanese population studied had 1 or 2 alleles with fewer than 20 CA repeats ([@b30-copd-1-267]). This difference in the distribution of CA repeat length may be significant, because promoters with 21 CA repeats appeared to have a higher promoter activity compared with those with shorter repeats ([@b30-copd-1-267]). In contrast, MMP-9 promoter containing 14 repeats had 53% promoter activity seen with 24 CA repeats ([@b14-copd-1-267]). Similarly, [@b24-copd-1-267] found that the promoter with 23 CA repeats showed a 1.5-fold higher promoter activity compared with those containing 21 or 22 repeats. Consistent with these findings, non-hispanic white participants in particular with the Long/Long genotype had an increased risk for COPD compared with those with a Short/Short genotype in our study.

The -1562T genotype was significantly associated with increased risk for COPD in non-hispanic whites only. This finding supports the finding by [@b20-copd-1-267] that the allelic frequency of the MMP-9 C-1562T promoter polymorphism was significantly increased in 45 smokers with emphysema compared with 65 matched smokers without emphysema, when emphysematous changes were scored from chest computer tomography scans. However, they did not find significant differences when COPD was characterized by FEV~1~. Differences may be due to the association being specific for a specific ethnic group.

Non-hispanic whites were more likely to have COPD compared with hispanics and the decline in FEV~1~ was more pronounced in these participants compared with hispanics. In addition, all polymorphisms within MMP-9 that were tested were significantly associated with COPD in the non-hispanic whites. The -1562T genotype was associated with COPD among the non-hispanic whites, but the genotype is rare and was not observed in the hispanics. The association for 279Arg and Long/Long form of CA repeat was similar for both ethnic groups, but the result was not statistically significant for the hispanics, which may be a result of the smaller sample size. Collectively, these findings suggest that, while the distribution of the genotypes may vary by ethnic group, the association between genotype and COPD is not affected by ethnicity. Thus, confounding by population admixture is unlikely to account for the observed associations. Whether this association is also found for women with COPD will be addressed in the future.

Many studies have suggested the involvement of the MMPs in COPD ([@b21-copd-1-267]; [@b32-copd-1-267]; [@b29-copd-1-267]; [@b15-copd-1-267]). Overexpression of MMP-1 results in emphysema in transgenic mice ([@b5-copd-1-267]) and MMP-12 deficient mice are less susceptible to cigarette smoke-induced emphysema compared with wild-type mice ([@b12-copd-1-267]). However, the relevance of these animal models to human disease has not been proven. Our study supports the hypothesis that MMP-9 may be a protease that is related to the pathogenesis of COPD and polymorphisms in MMP-9 may act as intrinsic factors to affect sensitivity to cigarette smoke-induced onset of COPD.

This research was funded by the State of New Mexico as a direct appropriation from the Tobacco Settlement Fund, the NIEHS Center (P30 ES012072) and by the VA grant V501P-2638. This material is based upon work supported by the Office of Research and Development (R&D), Medical Research Service, GrantV501P-2638.

![Distribution of CA repeat lengths.](copd-1-267f1){#f1-copd-1-267}

###### 

PCR primers and probes for detecting polymorphisms

  Polymorphism      Primers                                    Probes
  ----------------- ------------------------------------------ ------------------------------------
  MMP-1 G/GG-1607   5′-GTTATGCCACTTAGATGAGGAAATTG (S)          5′-AGATAAGTCATAT[CC]{.ul}TTTCT
                    5′-CATAAACAATACTTCAGTATATCTTGGATTGA (AS)   5′-AGTCATATCTTT[C]{.ul}TAATTAT
  MMP-2 C/T -1306   5′-CCCTAAAACATTCCCCATA TTCC (S)            5′-CACTC[C]{.ul}ACCTCTTTA
                    5′-GTGACTTCTGAGC TGAGACCTGAA (AS)          5′-AGCACTC[T]{.ul}ACCTCTT
  MMP-9 C/T -1562   5′-GCCTGGCACATAGTAGGCCC (S)                No SphI site (C)
                    5′-CTTCCTAGCCAGCCGGCATC (AS)               SphI site 300+260 bp (T)
  MMP-9 Gln279Arg   5′-TCTCCCCCTTTCCCACATC (S)                 5′-CTCTACACCC[G]{.ul}GGACGGCAATG
                    5′-TGTGCTGTCTCCGCCTTCT (AS)                5′-ACTCTACACCC[A]{.ul}GGACGGCAATGC
  MMP-9 CA repeat   5′-6FAM-AAGCCCTTTCTCATGCTGGTGC             Fragment analysis
                    5′-TGACAGGCAAGTGCTGACTCAG                  

**NOTE:** The bold, underlined letters are the single nucleotide polymorphisms designed in the probes for allelic discrimination.

**Abbreviations:** AS, antisense primer; S, sense primer.

###### 

Summary of demographic and baseline variables plus information on baseline PFT for all participants and those with two visits

                                           All participants     Participants with 2 visits                        
  ---------------------------------------- -------------------- ---------------------------- -------------------- --------------------
  N (%)                                    123(31.9)            262(68.1)                    48 (27.3)            128 (72.7)
  Age class (years) N (%)                                                                                         
  40--49                                   6 (4.9)              42 (16.0)                    4 (8.3)              15 (11.7)
  50--59                                   30 (24.4)            112 (42.7)                   11 (22.9)            54 (42.2)
  60--69                                   56 (45.5)            74 (28.2)                    19 (40.0)            41 (32.0)
  \>=70                                    31 (25.2)            34 (13.0)                    14 (29.2)            18 (14.1)
  Ethnicity N (%)                                                                                                 
  Non-hispanic white                       90 (73.2)            162 (61.8)                   38 (79.2)            83 (64.8)
  Hispanic                                 20 (16.3)            61 (23.3)                    5 (10.4)             28 (21.9)
  Other                                    13 (10.6)            39 (14.9)                    5 (10.4)             17 (13.3)
  Current smoker yes/no (%)                54/69 (43.9)         109/153 (41.6)               20/28 (41.7)         42/86 (32.8)
  Smoking                                                                                                         
  Duration (years) average (min, max)      40.4 (5.0--60.0)     33.7 (10.0--60.0)            40.2 (6.0--60.0)     33.0 (10.0--60.0)
  Smoking, pack-years average (min, max)   60.1 (20.0--220.0)   49.1 (20.0--140.0)           60.0 (24.0--205.0)   51.6 (20.0--140.0)
  Baseline %FEV~1~ (average (min, max))    58.6 (19.0--99.0)    84.1 (40.0--120.0)           61.5 (33.0--87.0)    84.6 (57.0--113.0)

Using COPD definition I.

###### 

Distribution of CA repeat alleles

  Allele 1   Allele 2   Frequency   Percent
  ---------- ---------- ----------- ---------
  14         14         97          26.5
  18         14         1           0.3
  19         14         4           1.1
  20         14         2           0.5
  21         14         74          20.2
  21         15         2           0.5
  21         19         1           0.3
  21         21         39          10.8
  22         14         57          15.6
  22         15         3           0.8
  22         19         2           0.5
  22         20         1           0.3
  22         21         7           1.9
  22         22         17          4.6
  23         14         28          7.6
  23         15         1           0.3
  23         19         1           0.3
  23         21         9           2.6
  23         22         2           0.5
  23         23         6           1.6
  24         14         6           1.6
  24         21         3           0.8
  25         14         1           0.3
  26         21         2           0.5

###### 

Distribution of genotypes in COPD and non-COPD participants (%)

                                                                   All    Non-hispanic white                                  Hispanic                                                             
  ----------------------------------------------------------- ---- ------ --------------------------------------------------- ---------- -------------------------------------------------- ------ -------------------------------------------------
  MMP-9[a](#tfn4-copd-1-267){ref-type="table-fn"} Gln279Arg   C    35.0   52.1[\*\*](#tfn7-copd-1-267){ref-type="table-fn"}   34.4       47.8[\*](#tfn8-copd-1-267){ref-type="table-fn"}    40.0   67.2[\*](#tfn8-copd-1-267){ref-type="table-fn"}
                                                              H    46.3   40.2                                                43.3       42.9                                               55.0   31.2
                                                              R    18.7   7.7 [\*\*](#tfn7-copd-1-267){ref-type="table-fn"}   22.2       9.3[\*\*](#tfn7-copd-1-267){ref-type="table-fn"}   5.0    1.6
                                                              n    123    261                                                 90         161                                                20     61
  MMP-9[a](#tfn4-copd-1-267){ref-type="table-fn"} C/T-1562    C    68.9   75.9                                                65.1       73.7                                               80.0   87.9
                                                              H    26.0   21.7                                                27.9       23.7                                               20.0   12.1
                                                              R    5.0    2.4                                                 7.0        2.6                                                0.0    0.0
                                                              n    119    253                                                 86         156                                                20     58
  MMP-9[b](#tfn5-copd-1-267){ref-type="table-fn"} CA repeat   SS   24.2   27.6                                                29.9       36.2                                               5.0    13.6
                                                              LS   46.7   50.0                                                42.5       49.0                                               65.0   54.2
                                                              LL   29.2   22.4                                                27.6       14.8[\*](#tfn8-copd-1-267){ref-type="table-fn"}    30.0   32.2
                                                              n    120    246                                                 87         149                                                20     59
  MMP-1[a](#tfn4-copd-1-267){ref-type="table-fn"}             C    26.2   27.2                                                23.6       19.8                                               45.0   42.6
                                                              H    46.7   46.3                                                41.6       49.0                                               55.0   42.6
                                                              R    27.1   26.5                                                34.8       31.2                                               0.0    14.8
                                                              n    122    257                                                 89         157                                                20     61
  [a](#tfn4-copd-1-267){ref-type="table-fn"} MMP-2            C    62.3   55.0                                                62.9       53.2                                               60.0   57.4
                                                              H    32.0   38.0                                                32.6       40.5                                               30.0   36.1
                                                              R    5.7    7.0                                                 4.5        6.3                                                10.0   6.6
                                                              n    122    258                                                 89         158                                                20     61

For MMP-9 Gln279Arg, C-1562T, MMP-1, and MMP-2: C=common, H=heterozygote, R=rare.

For MMP-9 CA repeat length: S=Short, L=Long.

Difference between COPD (by definition I) and non-COPD participants:

p\<0.01,

p\<0.05.

###### 

Association of genotypes with COPD[a](#tfn9-copd-1-267){ref-type="table-fn"}

                                                               All             Non-hispanic white                                              Hispanic                                                       
  ------------------------------------------------------------ --------------- --------------------------------------------------------------- -------------------------------------------------------------- -----------------------------------------------
  MMP-9Gln279Arg                                               n               384                                                             251                                                            81
                                                               Heterozyg.      1.8 (1.1, 3.0) [\*](#tfn12-copd-1-267){ref-type="table-fn"}     1.7 (0.9, 3.1)                                                 2.9 (0.9, 9.5)
                                                               Homozyg. rare   3.8 (1.8, 7.9) [\*\*](#tfn13-copd-1-267){ref-type="table-fn"}   3.5 (1.5, 8.1) [\*](#tfn12-copd-1-267){ref-type="table-fn"}    6.9 (0.4, 137.5)
  MMP-9C/T-1562                                                n               372                                                             242                                                            78
                                                               Heterozyg.      1.3 (0.8, 2.3)                                                  1.4 (0.7, 2.8)                                                 1.7 (0.4, 7.7)
                                                               Homozyg. rare   3.0 (0.8, 10.8)                                                 4.5 (1.1, 10.4) [\*](#tfn12-copd-1-267){ref-type="table-fn"}   NA[b](#tfn10-copd-1-267){ref-type="table-fn"}
  MMP-9[c](#tfn11-copd-1-267){ref-type="table-fn"} CA repeat   n               366                                                             236                                                            79
                                                               Long/Short      1.1 (0.6, 1.9)                                                  1.2 (0.6, 2.2)                                                 2.4 (0.2, 26.1)
                                                               Long/Long       1.5 (0.8, 3.0)                                                  2.3 (1.0, 5.1) [\*](#tfn12-copd-1-267){ref-type="table-fn"}    2.4 (0.2, 29.0)
  MMP-1                                                        n               379                                                             246                                                            81
                                                               Heterozyg.      1.2 (0.7, 2.2)                                                  0.7 (0.3, 1.4)                                                 2.09 (0.61, 7.15)
                                                               Homozyg. rare   1.2 (0.7, 2.4)                                                  0.9 (0.4, 2.0)                                                 NA[b](#tfn10-copd-1-267){ref-type="table-fn"}
  MMP-2                                                        n               380                                                             247                                                            81
                                                               Heterozyg.      0.8 (0.5, 1.4)                                                  0.8 (0.4, 1.5)                                                 0.7 (0.2, 2.4)
                                                               Homozyg. rare   0.7 (0.3, 1.8)                                                  0.6 (0.2, 2.4)                                                 2.3 (0.3, 17.4)

COPD definition I.

not applicable due to zero participants with homozygous rare.

OR (95% CI) relative to homozygous common and Short/Short CA repeats.

p\<0.05,

p\<0.001.

NOTE: Models include an adjustment for current smoking status and linear adjustments for age and smoking duration.

###### 

MMP-9 C/T-1562, Gln279Arg, and CA repeat haplotype frequencies

  Haplotype[b](#tfn15-copd-1-267){ref-type="table-fn"}   Relative frequency   Adjusted OR[a](#tfn14-copd-1-267){ref-type="table-fn"}                    
  ------------------------------------------------------ -------------------- -------------------------------------------------------- ---------------- ------
  C-C-S                                                  0.47                 0.53                                                     1.0              
  C-C-L                                                  0.11                 0.19                                                     0.8 (0.5--1.2)   0.26
  C-R-S                                                  0.01                 0.00                                                                      
  C-R-L                                                  0.23                 0.15                                                     1.8 (1.1--2.9)   0.02
  R-C-S                                                  0.00                 0.00                                                                      
  R-C-L                                                  0.00                 0.00                                                                      
  R-R-S                                                  0.00                 0.03                                                                      
  R-R-L                                                  0.18                 0.13                                                     1.7 (1.1--2.7)   0.03

Logistic model adjustments included age, smoking duration, and current smoking status.

C-1562T (C=common, R=rare), Exon 6 (C=common, R=rare), CA repeat length (S=Short, L=Long).

COPD definition I.

###### 

Distribution of polymorphisms by COPD status (definition I)

                                                                    All participants   Participants with 2 visits                                  
  ------------------------------------------------------------ ---- ------------------ ---------------------------------------------------- ------ ------
  MMP-9[a](#tfn17-copd-1-267){ref-type="table-fn"} Gln279Arg   C    35.0               52.1[\*\*](#tfn20-copd-1-267){ref-type="table-fn"}   35.4   52.3
                                                               H    46.3               40.2                                                 37.5   41.4
                                                               R    18.7               7.7 [\*\*](#tfn20-copd-1-267){ref-type="table-fn"}   27.1   6.3
                                                               n    123                261                                                  48     128
  MMP-9[a](#tfn17-copd-1-267){ref-type="table-fn"} C/T-1562    C    68.9               75.9                                                 60.9   75.8
                                                               H    26.0               21.7                                                 32.6   21.8
                                                               R    5.0                2.4                                                  6.5    2.4
                                                               n    119                253                                                  46     124
  MMP-9[b](#tfn18-copd-1-267){ref-type="table-fn"} CA repeat   SS   24.2               27.6                                                 29.8   26.7
                                                               LS   46.7               50.0                                                 34.0   52.5
                                                               LL   29.2               22.4                                                 36.2   20.8
                                                               n    120                246                                                  47     120
  MMP-1[a](#tfn17-copd-1-267){ref-type="table-fn"}             C    26.2               27.2                                                 22.9   25.0
                                                               H    46.7               46.3                                                 47.9   46.9
                                                               R    27.1               26.5                                                 29.2   28.1
                                                               n    122                257                                                  48     128
  MMP-2[a](#tfn17-copd-1-267){ref-type="table-fn"}             C    62.3               55.0                                                 58.3   50.0
                                                               H    32.0               38.0                                                 33.3   42.2
                                                               R    5.7                7.0                                                  8.3    7.8
                                                               n    122                258                                                  48     128

For MMP-9 Gln279Arg, C-1562T, MMP-1, and MMP-2: C=common, H=heterozygote, R=rare.

For MMP-9 CA repeat length: S=Short, L=Long.

Difference between COPD (by definition I) and non-COPD participants:

p\<0.01,

p\<0.05.

###### 

Association of genotypes with COPD

  COPD definition II                                                                                                                                                     
  -------------------- --------------- ----------------------------------------------------------------- --------------------------------------------------------------- -----------------------------------------------
  Gln279Arg            n               366                                                               238                                                             76
                       Heterozyg.      2.04 (1.19, 3.49)[\*](#tfn24-copd-1-267){ref-type="table-fn"}     1.75 (0.92, 3.35)                                               4.93 (1.26, 19.28)
                       Homozyg. rare   3.13 (1.42, 6.94)[\*\*](#tfn25-copd-1-267){ref-type="table-fn"}   2.77 (1.13, 6.81)[\*](#tfn24-copd-1-267){ref-type="table-fn"}   12.61 (0.58, 275.15)
  C/T-1562             n               354                                                               229                                                             73
                       Heterozyg.      1.37 (0.77, 2.43)                                                 1.48 (0.74, 2.96)                                               2.47 (0.55, 11.07)
                       Homozyg. rare   2.24 (0.54, 9.30)                                                 3.58 (0.72, 17.69)                                              NA[a](#tfn22-copd-1-267){ref-type="table-fn"}
  CA repeat            n               348                                                               223                                                             74
                       Long-Short      1.35 (0.72, 2.52)                                                 1.23 (0.62, 2.45)                                               NA[a](#tfn22-copd-1-267){ref-type="table-fn"}
                       Long-Long       2.00 (0.97, 4.12)                                                 1.98 (0.85, 4.63)                                               NA[a](#tfn22-copd-1-267){ref-type="table-fn"}
  MMP1                 n               361                                                               233                                                             76
                       Heterozyg.      1.28 (0.69, 2.36)                                                 0.69 (0.32, 1.50)                                               3.19 (0.78, 12.30)
                       Homozyg. rare   1.10 (0.54, 2.24)                                                 0.85 (0.37, 1.93)                                               NA[a](#tfn22-copd-1-267){ref-type="table-fn"}
  MMP2                 n               362                                                               234                                                             76
                       Heterozyg.      0.85 (0.50, 1.43)                                                 0.86 (0.46, 1.60)                                               0.61 (0.15, 2.41)
                       Homozyg. rare   0.70 (0.25, 1.99)                                                 0.78 ( 0.21, 2.90)                                              1.15 (0.10, 13.96)

  COPD definition II                                                                                                                                                      
  -------------------- --------------- ----------------------------------------------------------------- ---------------------------------------------------------------- -----------------------------------------------
  Gln279Arg            n               339                                                               217                                                              74
                       Heterozyg.      1.78 (0.98, 3.23)                                                 1.36 (0.65, 2.81)                                                4.08 (1.02, 16.27)
                       Homozyg. rare   3.14 (1.35, 7.30)[\*\*](#tfn25-copd-1-267){ref-type="table-fn"}   3.32 (1.31, 8.39)[\*](#tfn24-copd-1-267){ref-type="table-fn"}    10.75 (0.50, 230.22)
  C/T-1562             n               327                                                               208                                                              71
                       Heterozyg.      1.31 (0.68, 2.53)                                                 1.38 (0.63, 3.04)                                                2.22 (0.45, 10.89)
                       Homozyg. rare   3.25 (0.78, 13.62)                                                5.08 (1.02, 25.18)[\*](#tfn24-copd-1-267){ref-type="table-fn"}   NA[b](#tfn23-copd-1-267){ref-type="table-fn"}
  CA repeat            n               321                                                               202                                                              72
                       Long-Short      1.29 (0.64, 2.61)                                                 1.01 (0.46, 2.20)                                                NA[a](#tfn22-copd-1-267){ref-type="table-fn"}
                       Long-Long       2.08 (0.94, 4.57)                                                 2.16 (0.87, 5.36)                                                NA[a](#tfn22-copd-1-267){ref-type="table-fn"}
  MMP1                 n               334                                                               212                                                              74
                       Heterozyg.      1.31 (0.67, 2.54)                                                 0.65 (0.29, 1.49)                                                3.17 (0.75, 13.41)
                       Homozyg. rare   0.75 (0.33, 1.71)                                                 0.55 (0.22, 1.39)                                                NA[a](#tfn22-copd-1-267){ref-type="table-fn"}
  MMP2                 n               335                                                               213                                                              74
                       Heterozyg.      0.83 (0.46, 1.51)                                                 0.84 (0.42, 1.70)                                                0.77 (0.19, 3.12)
                       Homozyg. rare   1.03 (0.36, 2.94)                                                 1.16 (0.31, 4.39)                                                1.38 (0.11, 16.86)

not applicable due to zero participants with homozygous rare.

OR (95% CI) relative to homozygous common and Short/Short CA repeats.

p\<0.05,

p\<0.001.

NOTE: Models include an adjustment for current smoking status and linear adjustments for age and smoking duration.