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Published ahead of print on November 17, 2005, doi:10.1164/rccm.200509-1412OC
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American Journal of Respiratory and Critical Care Medicine Vol 173. pp. 379-385, (2006)
© 2006 American Thoracic Society
doi: 10.1164/rccm.200509-1412OC

Original Article

Influence of Leukotriene Pathway Polymorphisms on Response to Montelukast in Asthma

John J. Lima, Shu Zhang, Audrey Grant, Lianhe Shao, Kelan G. Tantisira, Hooman Allayee, Jianwei Wang, James Sylvester, Janet Holbrook, Robert Wise, Scott T. Weiss and Kathleen Barnes

The American Lung Association Asthma Clinical Research Centers; Pharmacogenetics Center, Nemours Children's Clinic, Jacksonville, Florida; Division of Allergy and Clinical Immunology; Center for Clinical Trials, Johns Hopkins University, Baltimore, Maryland; Channing Laboratory, Brigham and Women's Hospital, Boston, Massachusetts; and Department of Preventive Medicine, and Institute for Genetic Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California

Correspondence and requests for reprints should be addressed to John J. Lima, Pharm.D., Centers for Clinical Pediatric Pharmacology and Pharmacogenetics, Nemours Children's Clinic, 807 Children's Way, Jacksonville, FL 32207. E-mail: jlima{at}nemours.org


   ABSTRACT
TOP
 ABSTRACT
METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Rationale: Interpatient variability in montelukast response may be related to variation in leukotriene pathway candidate genes.

Objective: To determine associations between polymorphisms in leukotriene pathway candidate genes with outcomes in patients with asthma receiving montelukast for 6 mo who participated in a clinical trial.

Methods: Polymorphisms were typed using Sequenom matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass array spectrometry and published methods; haplotypes were imputed using single nucleotide polymorphism–expectation maximization (SNP-EM). Analysis of variance and logistic regression models were used to test for changes in outcomes by genotype. In addition, {chi}2 and likelihood ratio tests were used to test for differences between groups. Case-control comparisons were analyzed using the SNP-EM Omnibus likelihood ratio test.

Measurements: Outcomes were asthma exacerbation rate and changes in FEV1 compared with baseline.

Results: DNA was collected from 252 participants: 69% were white, 26% were African American. Twenty-eight SNPs in the ALOX5, LTA4H, LTC4S, MRP1, and cysLT1R genes, and an ALOX5 repeat polymorphism were successfully typed. There were racial disparities in allele frequencies in 17 SNPs and in the repeat polymorphism. Association analyses were performed in 61 whites. Associations were found between genotypes of SNPs in the ALOX5 (rs2115819) and MRP1 (rs119774) genes and changes in FEV1 (p < 0.05), and between two SNPs in LTC4S (rs730012) and in LTA4H (rs2660845) genes for exacerbation rates. Mutant ALOX5 repeat polymorphism was associated with decreased exacerbation rates. There was strong linkage disequilibrium between ALOX5 SNPs. Associations between ALOX5 haplotypes and risk of exacerbations were found.

Conclusions: Genetic variation in leukotriene pathway candidate genes contributes to variability in montelukast response.

Key Words: antiinflammatory • montelukast • pharmacodynamic • pharmacogenetic

Montelukast is a selective cysteinyl leukotriene 1 (cysLT1) receptor antagonist (1). Montelukast is recommended as an alternative to low-dose inhaled corticosteroids for patients with mild persistent asthma and recommended as alternative add-on (to inhaled corticosteroids) treatment in patients with moderate persistent (step 3) and severe persistent (step 4) asthma (2). Numerous clinical trials in adults and children with asthma have established the efficacy and safety of montelukast (3, 4). However, interpatient variability in response to montelukast in both children and adults with asthma is significant, with 35 to 78% of patients receiving montelukast being classified as nonresponders (5–7). The mechanisms underlying interpatient variability in response are not clear but are believed to be due, in part, to genetic variability (8–11). Indeed, several studies have reported that promoter polymorphisms in the ALOX5 (12) and the LTC4 synthase (LTC4S) genes contribute to variability in response to LT modifiers and LT selective antagonists (13–16).

CysLTs are potent mediators of asthma inflammation and are synthesized from arachidonic acid located in membrane-phospholipids by cytosolic phospholipase A2 in response to stimulation (17, 18). Arachidonic acid is converted to 5-hydroperoxyeicosatetraenoic acid and LTA4 by membrane-bound 5-lipoxygenase (ALOX5) and 5-lipoxygenase activating protein (19). In human mast cells, basophils, eosinophils, and macrophages, LTA4 is converted to LTB4 by LTA4 hydrolase (LTA4H), or is conjugated with reduced glutathione by LTC4 synthase to form LTC4 (20, 21). LTC4 is transported to the extracellular space mainly by the multidrug resistance protein 1 (MRP1) (22). LTC4 is converted to LTD4 and LTE4 by {gamma}-glutamyltransferase and dipeptidase (23, 24). Typical symptoms of asthma caused by cysLTs (LTC4, LTD4, and LTE4) are mediated by the cysLT1 receptor (17, 25), which is a G-protein–coupled receptor that is expressed in peripheral blood leukocytes and other tissues (26). The major intracellular signaling pathway for the cyLT1 receptor is via calcium release (27).

The present study sought to determine associations between polymorphisms in LT pathway candidate genes with outcomes in individuals receiving montelukast. The underlying rationale for this pharmacogenetic study is that patients with asthma carrying polymorphisms that increase the activity of LT will respond better to montelukast compared with polymorphisms that have no effect or that down-regulate the activity of LT. Data in the present article have not been published previously in abstract or any other form.


   METHODS
TOP
 ABSTRACT
 METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Study Design and Patient Studies
This pharmacogenetic study was ancillary to a randomized, double-masked, parallel-designed trial that compared the efficacy of placebo, theophylline (Theochron Extended Release; Inwood Laboratories, Inc., Inwood, NY) 300 mg daily, and montelukast (Singulair; Merck and Co., Inc., Whitehouse Station, NJ) 10 mg daily, as add-on therapy in patients with poorly controlled mild to moderate persistent asthma. Doses were identically masked within opaque gelatin capsules. Briefly, 488 patients were recruited from 19 centers in the American Lung Association Asthma Clinical Research Centers Network. Before randomization, all patients completed a questionnaire that included queries about demographic characteristics, smoking history, age at onset of asthma, hospitalizations, unscheduled health care visits for asthma, or courses of oral corticosteroids during the preceding 12 mo. In addition, participants completed the Asthma Symptom Utility Index (28), Asthma Control Questionnaire (29), spirometry with bronchodilator, and measurement of peak expiratory flow. DNA was collected from 252 participants who volunteered for the trial and for the pharmacogenetic study. The institutional review boards of each participating center approved the protocols for the trial and for the ancillary pharmacogenetic study.

Outcomes
Associations between genetic variants with two outcomes were analyzed: percentage of change in % predicted FEV1 after 6 mo of montelukast treatment compared with % predicted FEV1 recorded at baseline, and the binary risk of having an asthma exacerbation (no exacerbation or at least one exacerbation) during 6 mo of montelukast treatment. An asthma exacerbation was defined as 1 or more of the following: a more than 30% decrease in peak expiratory flow rate for 2 consecutive days; a course of oral steroids; an unscheduled visit to the clinic, the emergency room, or hospital; or an increase of four puffs of rescue inhaler use in 1 d.

Genotyping
Single nucleotide polymorphisms (SNPs) were genotyped via a Sequenom matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass array spectrometer (Sequenom, San Diego, CA), using a semiautomated primer design program (Spectro Designer; Sequenom) (30–32). In addition, the LTC4S C-444A promoter SNP was genotyped and the number of Sp1 binding motifs (5'GGGCGG3') in the ALOX5 promoter was determined as previously described (16, 33). Hardy-Weinberg equilibrium (HWE) between expected and observed genotype distributions was calculated using {chi}2 goodness-of-fit tests. For SNPs on the CYSLTR1, HWE was determined in females because of the location of this gene on the X chromosome.

Determination of Haplotype
Haplotypes for the ALOX5, LTA4H, and MRP1 SNPs were imputed using an expectation-maximization (EM) algorithm (SNP-EM) (34, 35). HWE between expected and observed genotype distributions was calculated using {chi}2 goodness-of-fit tests. Linkage disequilibrium (LD) was assessed and displayed using Haploview (http://www.broad.mit.edu/mpg/haploview/).

Association Analyses
An analysis of variance (Stata 8.0; StataCorp, College Station, TX) was used to test for differences in mean percentage changes in FEV1 at 6 mo of treatment compared with baseline FEV1 by genotype. Logistic regression models were used to test for increases in risk of exacerbations at any time point during montelukast treatment for particular marker genotypes. A {chi}2 test and two-sample tests of proportions were used to test the differences in frequencies between two groups. Case-control (participants experiencing at least one exacerbation vs. participants with no exacerbations) comparisons were analyzed by an omnibus test (SNP-EM Omnibus likelihood ratio test) (34, 35); p values less than 0.05 were considered significant. For polymorphisms significantly associated with an outcome in participants on montelukast, associations were analyzed in participants assigned to placebo.


   RESULTS
TOP
 ABSTRACT
 METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Patients
Baseline characteristics of participants are shown in Table 1. A total of 252 individuals participated in the pharmacogenetic study: 88 were randomized to receive montelukast, 77 received theophylline, and 86 received placebo (baseline data were not collected on one participant assigned to theophylline treatment). Baseline characteristics were reasonably evenly distributed between the three groups. Approximately 77 to 79% were on inhaled corticosteroids at randomization. Mean values of post-bronchodilator pulmonary function measures and scores of Asthma Symptom Utility Index and of Asthma Control Questionnaire indicated that this cohort had mild to moderately severe persistent asthma that was not well controlled at baseline. The percentage of participants who smoked and who were exposed to second-hand smoke was reasonably evenly distributed among the three treatment groups (data not shown). Asthma exacerbation rates in participants after 6 mo of placebo, montelukast, and theophylline treatment were 6.1, 3.7, and 5.2 events/person-year, respectively. Whites and African Americans comprised 69 and 24%, respectively, of the participants randomized to receive montelukast for 6 mo (Table 1). Because of the relatively low number of African Americans and the potential for population stratification (36), analyses were restricted to 61 whites in the montelukast arm.


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  		TABLE 1. BASELINE CHARACTERISTICS AMONG PHARMACOGENETIC STUDY PARTICIPANTS

 
Allele Frequencies, HWE, and LD
A total 42 SNPs and the ALOX5 promoter sp1 tandem repeat polymorphism were genotyped. Three nonsynonymous SNPs failed optimization, nine were monomorphic, and two were dropped because they did not pass quality control for discordant samples. The overall percentage of successful genotyping calls was 96%. Table 2 lists p values for HWEs, minor allele frequencies, and racial differences of the remaining 28 SNPs. Two SNPs in whites (rs2247570 on LTA4H and rs152033 in MRP1) and three in African Americans (rs129081, rs35587N_N, and re3902401 in MRP1) were not in HWE. There were significant racial disparities in allele frequencies for 16 SNPs.


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  		TABLE 2. HARDY-WEINBERG EQUILIBRIA AND MINOR ALLELE FREQUENCIES OF 28 SINGLE NUCLEOTIDE POLYMORPHISMS IN LEUKOTRIENE PATHWAY CANDIDATE GENES IN WHITES AND AFRICAN AMERICANS

 
The allelic and genotypic frequencies of Sp1 binding motifs (5'GGGCGG3') in the ALOX5 promoter polymorphisms for whites and African Americans are shown in Table 3. The percentage of successful genotyping calls was 97%. In whites and African Americans, 80 and 47%, respectively, carried five tandem repeats (p < 0.001), followed by four repeats, which represented 17% in both races. One-third of African-American alleles carried three repeats compared with less than 1% in whites. The most common genotype in whites was 5/5 followed by 4/6. In African Americans, the most common genotype was 3/5, followed by 5/5, 4/5, and 3/4 (Table 3). When collapsed into three genotypes based on the wild-type (n = 5) and the mutant form X (n != 5), significant racial differences were observed. The distribution of genotypes in whites in our study was similar to those published previously (12, 37–39).


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  		TABLE 3. ALLELIC AND GENOTYPIC FREQUENCIES OF Sp1 BINDING MOTIFS IN THE ALOX5 PROMOTER FOR 165 WHITES AND 65 AFRICAN AMERICANS

 
Figure E1R (see online supplement) shows LD between ALOX5 SNPs. Strong pairwise LD was observed between ALOX5 SNPs 1 (rs892690) and 5 (rs892691), SNPs 2 (rs745986) and 3 (rs2029253), and between SNPs 3 and 4 (rs2115819), as determined by D' values greater than 0.9 (x100). Modest LD was found between SNPs 1 and 3, SNPs 1 and 4, and between SNPs 3 and 5 (rs892691). For the LTA4H gene, SNPs rs2241136 and rs26606845 were in modest pairwise LD with a D' value of 0.69 (data not shown).

Figure E2R shows LD between MRP1 SNPs. Strong pairwise LD was observed between SNPs rs246271 and rs35587 (SNPs 5 and 6), SNPs 1, 2, and 3, and SNPs 2 and 3.

Genotype Association Analysis
Significant associations were found between two LT pathway SNPs and the change in % predicted FEV1 observed after 6 mo of montelukast treatment compared with baseline (Figure 1). Compared with CC homozygotes (n = 41), heterozygotes (n = 8) for the MRP1 rs119774 SNP had higher percentage changes in % predicted FEV1: 24% (95% confidence interval [CI], –0.105 to 0.577) versus 2.2% (95% CI, –0.005 to 0.049) increase (p = 0.004). Compared with AA homozygotes (n = 11) and heterozygotes (n = 38), GG homozygotes (n = 6) for the ALOX5 rs2115819 SNP had a significantly higher FEV1 response to montelukast at 6 mo of treatment: 30% (95% CI = –0.017 to 1.21) versus 4.4% (95% CI, –0.025 to 0.66) and 2.0% (95% CI, 0.013–0.075) in the AA and AG genotype groups, respectively (p = 0.017). No significant associations were observed between changes in FEV1 and MRP1 rs119774 (p = 0.56) and ALOX5 rs2115819 (p = 0.33) in participants assigned to placebo.


Figure 1
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  		Figure 1. Influence of genotype on percentage change in % predicted FEV1 over baseline in 61 white participants taking montelukast. Percentage change in % predicted FEV1 over baseline after 6 mo of montelukast treatment was compared by genotypes of MRP1 marker rs119774 and of ALOX5 marker rs2115819.

 
Table 4 summarizes the influence of LT pathway polymorphisms on the risk of having at least one asthma exacerbation in participants receiving montelukast. Individuals carrying a variant number (either 2, 3, 4, 6, or 7) of repeats of the ALOX5 promoter on one allele had a 73% reduction in the risk of having one or more asthma exacerbations compared with homozygotes for the five repeat alleles (p = 0.045). For participants on placebo for 6 mo, there were no differences in exacerbation risk by genotype (p = 0.134).


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  		TABLE 4. GENOTYPE AND FREQUENCIES OF ALOX5, LTA4H, AND LTC4S POLYMORPHISMS AND ODDS RATIOS OF ASSOCIATIONS BETWEEN GENOTYPE AND LIKELIHOOD OF HAVING AN ASTHMA EXACERBATION IN WHITES TAKING MONTELUKAST FOR 6 MO

 
For the LTA4H rs2660845 SNP, the risk of having at least one exacerbation was 4- to 4.5-fold higher in heterozygotes and GG homozygotes compared with AA homozygotes. The odds ratio for asthma exacerbations for GG homozygotes did not achieve statistical significance, which was probably related to the small number of individuals carrying this genotype. When collapsed into carriers of the G allele (AG + GG), the odds ratio for having an exacerbation was greater than 4.0 (p < 0.001). For participants receiving placebo, no differences in exacerbation rate were noted by genotype (p = 0.85 for AG genotype; p = 0.776 for GG homozygotes).

For the LTC4S A-444C SNP (rs730012), heterozygotes receiving montelukast had a 76% reduced risk of having an asthma exacerbation compared with AA homozygotes (p = 0.023). The risk of having an exacerbation was reduced even more in CC homozygotes; however, this difference was not statistically significant. This may be related to the relatively low frequency of CC homozygotes (11%). When collapsed into carriers of the C allele (AC + CC), the risk was reduced by 80% compared with AA homozygotes (p < 0.001). Heterozygotes assigned to placebo had a 74% reduced risk of having an asthma exacerbation compared with AA homozygotes (p = 0.034). The risk of having an exacerbation in CC homozygotes was no different compared with AA homozygotes (p = 0.57). When collapsed into carriers of the C allele, the risk was reduced by 69% compared with AA (p = 0.05).

Haplotype Association Analysis
Significant associations were found between ALOX5 2-, 3- and 4-SNP haplotypes and exacerbation rates using the omnibus logistical regression test (SNP-EM; data not shown). A {chi}2 analysis was used to compare differences in cases (frequency of participants having at least one asthma exacerbation while receiving montelukast) and control subjects (frequency of participants with no exacerbations) among haplotypes (Table 5). Haplotypes with the A alleles for SNPs 2 and 3 are strongly associated with the risk of having an asthma exacerbation and addition of the C allele from SNP 1 to two or three SNP haplotypes (CAA, CAAA) tended to increase the strength of the association.


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  		TABLE 5. ASSOCIATION ANALYSES FOR ALOX5 HAPLOTYPES AND FREQUENCIES OF WHITE PARTICIPANTS HAVING AT LEAST ONE ASTHMA EXACERBATION DURING MONTELUKAST TREATMENT

 

   DISCUSSION
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Montelukast is recommended as an alternative to low-dose inhaled corticosteroids for patients with mild persistent asthma and as alternative add-on therapy to inhaled corticosteroid treatment in patients with moderate persistent (step 3) and severe persistent (step 4) asthma (2). Although the drug is safe and effective in controlling asthma symptoms, responsiveness is highly variable among patients, which is believed to be due to genetic variation. Several studies have reported that the repeat polymorphism in the ALOX5 promoter (12) and the LTC4S A-444C SNP (13–16) contributes to the variability in response montelukast and other LT modifiers. However, the allele frequency of the ALOX5 repeat polymorphism in whites is too low to contribute much to the variability in response to LT modifiers, and the influence of the LTC4S A-444C SNP on response to LT receptor antagonists has been questioned (40, 41).

The present study explored associations between polymorphisms in candidate genes encoding key proteins in the LT pathway with response in patients randomized to montelukast treatment as participants in a large clinical trial. We identified five polymorphisms that were associated with changes in FEV1 or with the risk of exacerbations while receiving montelukast. When analyzed in participants assigned to placebo, no associations were found between outcomes and genotype, with the possible exception of heterozygotes for the LTC4S –444 SNP (see below). Our results support the idea that genetic variation contributes in a significant way to the interpatient variability in response to montelukast and other LT receptor antagonists. In addition, our data point to the possibility of individualizing LT receptor antagonist treatment using genotyping information.

The ALOX5 gene located on 10q11.21 encodes a key enzyme in the synthesis of cysLTs (18). Early studies identified addition and deletion variants in the core promoter of the ALOX5 gene that were associated with diminished promoter-reporter activity in tissue culture (33). In a later study, Drazen and colleagues (12) hypothesized that there would be decreased ALOX5 product production and diminished response to drugs treating this pathway because of diminished gene transcription associated with addition and deletion variants. Indeed, ABT-761, an ALOX5 inhibitor, increased FEV1 over baseline in wild-type homozygotes (5/5) and heterozygotes (5/X) compared with variant allele homozygotes (X/X) (12). The results of the present study are not consistent with expectations based on this study. We found that montelukast was associated with a 73% reduced risk of an exacerbation in carriers of the mutant allele (X/X and 5/X) compared with wild-type homozygotes, suggesting that mutant variants up-regulated ALOX5 activity. Consistent with our data, Dwyer and coworkers (39) reported that compared with wild-type and heterozygotes (5/5 + 5/X), homozygous mutants (X/X) had increased carotid intima-media thickness, an atherogenic effect that was exacerbated by increased intake of dietary arachidonic acid, and had higher C-reactive protein levels. In addition, patients with aspirin-intolerant asthma, who are known to be responsive to LT antagonists, carrying the mutant allele (X) showed increased hyperresponsiveness compared with patients with the wild-type genotype (42). Taken together, these data suggest that the repeat polymorphism in the ALOX5 promoter is an important pharmacogenetic locus, and underscore the need for additional pharmacogenetic studies that target the ALOX5 gene.

LTC4 synthase catalyzes the formation of LTC4 from LTA4 (18). In the present study, the LTC4S A-444C promoter SNP (rs730012; 5q35) was associated with a reduced risk of an asthma exacerbation: the C allele reduced risk by 80% compared with AA homozygotes receiving montelukast (Table 4). In the placebo group, the exacerbation rate was significantly reduced in heterozygotes compared with A homozygotes, which questions our findings with montelukast. However, the exacerbation risk in C homozygotes was not different compared with A homozygotes (p = 0.569). Moreover, when placebo participants were collapsed into carriers of the C allele, they were not at greater risk of an exacerbation compared with A homozygotes (p = 0.05). In contrast, carriers of the C allele on montelukast had an 80% reduced risk of an exacerbation compared with A homozygotes (p < 0.001). This suggests that the significant association observed in heterozygotes on placebo is spurious, probably because of small numbers. Therefore, we conclude that the LTC4S –A444C SNP contributes to the variability in response to montelukast. These data are in agreement with previous studies reporting that carriers of the C allele responded better to LT receptor antagonists compared with AA homozygotes (14–16). The mechanisms underlying the favorable response to montelukast in carriers of the C allele compared with AA homozygotes may be related to up-regulation of LTC4 synthase expression, which would result in higher concentrations of cysLTs and increased inflammation (43). Thus, our study replicates previous studies and supports the idea that LTC4S is an important gene, which contributes to variability in response to LT receptor antagonists.

The present study identified three novel associations between LT pathway SNPs and responsiveness to montelukast. The genotype of rs2115819 located in intron 2 of ALOX5 was associated with differences in the FEV1 response to montelukast (Figure 1), and is in tight LD with rs2029253 (Figure E1R). Moreover, it is one of four SNPs that comprise a haplotype that is associated with the highest proportion of participants having an asthma exacerbation (Table 5). It is also possible that one or more of these intronic SNPs could by themselves be functional. Further studies are required to replicate these data in a larger clinical trial, and to identify the functional SNPs that may be in LD with rs2115819.

The LTA4H gene, located on chromosome 12q22, encodes the enzyme that catalyzes the formation of LTB4 (44), a potent chemoattractant agent (45, 46), from LTA4. In the present study, compared with AA homozygotes, carriers of the G allele of rs2660845 had a four- to fivefold increased probability of having an asthma exacerbation while receiving montelukast. The mechanism underlying the association between the genotype of this SNP and the risk of an asthma exacerbation is unknown. One possibility could be related to the G allele down-regulating the activity of LTA4H, which would result in shunting LTA4 away from the LTA4H pathway and increasing the formation of cysLTs.

LTC4 is transported to the extracellular space by MRP1, a member of the ABC family of transmembrane transport proteins (22, 47). MRP1 is highly expressed in human bronchial epithelial cells (48). The MRP1 gene is located on 16p13.12 and is highly polymorphic (49, 50). A mutation in the last transmembrane segment influences LTC4 transport (51) and it is possible that MRP1 genetic variants could have significant effects on LTC4 transport, cysLT expression, and response to montelukast. The genotype of rs119774, which is located in intron 1, was associated with increases in % predicted FEV1 in participants receiving montelukast for 6 mo (Figure 1): heterozygotes (CT) had a 24% increase in % predicted FEV1 compared with a 2% increase in CC homozygotes. No association between genotype and changes in % predicted FEV1 was observed in participants on placebo. In addition, rs119774 is in fairly tight LD with rs215066, which is also in intron 1and showed a positive trend for an association between montelukast-evoked changes in % predicted FEV1 and rs215066 (p = 0.066). To our knowledge, this is the first report of a genotype–phenotype association for the MRP1 gene in patients with asthma receiving montelukast and warrants further study.

The present study has several limitations. Gene variants that contribute to variable drug response in complex phenotypes, like asthma, may have modest effects, thus requiring large sample sizes to detect associations (52). Our sample size was small, and it is possible that the associations we observed between LT pathway SNPs and responsiveness to montelukast could represent false-positive results. Because of our small sample size and the potential for population stratification (36), we restricted our analysis to whites. We did not correct for multiple hypothesis testing, which could also contribute to false-positive associations (52). We chose not to adjust for multiple comparisons because, given the small numbers of participants, we reasoned that it is important not to dismiss differences that could be real. For these reasons, the results of our study should be regarded as exploratory and underscore the need for replication in larger, more diverse populations.

In summary, we found significant associations between several common polymorphisms in LT pathway candidate genes with either the risk of having an asthma exacerbation or an increase in % predicted FEV1 over baseline in whites with asthma who received montelukast for 6 mo. For two polymorphisms, the ALOX5 tandem repeat promoter polymorphism and the LTC4S A-444C SNP, our results replicate previous studies; for three SNPs in ALOX5, LTA4H, and MRP1 genes, our results show novel associations. Further studies are required to replicate our associations.


   FOOTNOTES
 
Supported by the American Lung Association, the Nemours Research Foundation, and National Institutes of Health grants R01 HL071394 (J.J.L.) and U01 HL65899 (S.T.W.).

This article has an online supplement, which is accessible from this issue's table of contents at www.atsjournals.org

Originally Published in Press as DOI: 10.1164/rccm.200509-1412OC on November 17, 2005

Conflict of Interest Statement: J.J.L. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. S.Z. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. A.G. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. L.S. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. K.G.T. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. H.A. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. J.W. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. J.S. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. J.H. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. R.W. received consulting fees from GlaxoSmithKline, Pfizer, Sanofi-Aventis, Emphasys, and Spiration in the past 3 yr for research oversight and review committees. He has served on advisory boards for Boehringer-Ingelheim, Pfizer, GlaxoSmithKline, Hill-Rom, Otsuka, Ortho, and Amgen. S.T.W. has also received research grants from Boehringer-Ingelheim, Otsuka, and Pfizer. Conflicts of interest regarding human research are managed by Johns Hopkins University. S.T.W. received a grant for $900,065, Asthma Policy Modeling Study, from AstraZeneca for 1997–2003. He has been a coinvestigator on a grant from Boehringer-Ingelheim to investigate a COPD natural history model, which began in 2003. He has received no funds for his involvement in this project. He had been an advisor to the TENOR Study for Genentech and has received $5,000 for 2003–2004. He received a grant from Glaxo-Wellcome for $500,000 for genomic equipment for 2000–2003. He was a consultant for Roche Pharmaceuticals in 2000 and received no financial remuneration for this consultancy. K.B. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

Received in original form September 9, 2005; accepted in final form November 17, 2005


   REFERENCES
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
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