Asthma is a chronic inflammatory respiratory disease that affects over 300 million people worldwide. Glucocorticoids are a mainstay therapy for asthma because they exert anti-inflammatory effects in multiple lung tissues, including the airway smooth muscle (ASM). However, the mechanism by which glucocorticoids suppress inflammation in ASM remains poorly understood. Using RNA-Seq, a high-throughput sequencing method, we characterized transcriptomic changes in four primary human ASM cell lines that were treated with dexamethasone—a potent synthetic glucocorticoid (1 µM for 18 hours). Based on a Benjamini-Hochberg corrected p-value <0.05, we identified 316 differentially expressed genes, including both well known (DUSP1, KLF15, PER1, TSC22D3) and less investigated (C7, CCDC69, CRISPLD2) glucocorticoid-responsive genes. CRISPLD2, which encodes a secreted protein previously implicated in lung development and endotoxin regulation, was found to have SNPs that were moderately associated with inhaled corticosteroid resistance and bronchodilator response among asthma patients in two previously conducted genome-wide association studies. Quantitative RT-PCR and Western blotting showed that dexamethasone treatment significantly increased CRISPLD2 mRNA and protein expression in ASM cells. CRISPLD2 expression was also induced by the inflammatory cytokine IL1β, and small interfering RNA-mediated knockdown of CRISPLD2 further increased IL1β-induced expression of IL6 and IL8. Our findings offer a comprehensive view of the effect of a glucocorticoid on the ASM transcriptome and identify CRISPLD2 as an asthma pharmacogenetics candidate gene that regulates anti-inflammatory effects of glucocorticoids in the ASM.
Rationale: To date, most studies aimed at discovering genetic factors influencing treatment response in asthma have focused on biologic candidate genes. Genome-wide association studies (GWAS) can rapidly identify novel pharmacogenetic loci.
Objectives: To investigate if GWAS can identify novel pharmacogenetic loci in asthma.
Methods: Using phenotypic and GWAS genotype data available through the NHLBI-funded Single-nucleotide polymorphism Health association-Asthma Resource Project, we analyzed differences in FEV1 in response to inhaled corticosteroids in 418 white subjects with asthma. Of the 444,088 single nucleotide polymorphisms (SNPs) analyzed, the lowest 50 SNPs by P value were genotyped in an independent clinical trial population of 407 subjects with asthma.
Measurements and Main Results: The lowest P value for the GWAS analysis was 2.09 × 10−6. Of the 47 SNPs successfully genotyped in the replication population, three were associated under the same genetic model in the same direction, including two of the top four SNPs ranked by P value. Combined P values for these SNPs were 1.06 × 10−5 for rs3127412 and 6.13 × 10−6 for rs6456042. Although these two were not located within a gene, they were tightly correlated with three variants mapping to potentially functional regions within the T gene. After genotyping, each T gene variant was also associated with lung function response to inhaled corticosteroids in each of the trials associated with rs3127412 and rs6456042 in the initial GWAS analysis. On average, there was a twofold to threefold difference in FEV1 response for those subjects homozygous for the wild-type versus mutant alleles for each T gene SNP.
Conclusions: Genome-wide association has identified the T gene as a novel pharmacogenetic locus for inhaled corticosteroid response in asthma.
polymorphism; genome; pharmacogenomics; glucocorticoid
The response to treatment for asthma is characterized by wide interindividual variability, with a significant number of patients who have no response. We hypothesized that a genomewide association study would reveal novel pharmacogenetic determinants of the response to inhaled glucocorticoids.
We analyzed a small number of statistically powerful variants selected on the basis of a family-based screening algorithm from among 534,290 single-nucleotide polymorphisms (SNPs) to determine changes in lung function in response to inhaled glucocorticoids. A significant, replicated association was found, and we characterized its functional effects.
We identified a significant pharmacogenetic association at SNP rs37972, replicated in four independent populations totaling 935 persons (P = 0.0007), which maps to the glucocorticoid-induced transcript 1 gene (GLCCI1) and is in complete linkage disequilibrium (i.e., perfectly correlated) with rs37973. Both rs37972 and rs37973 are associated with decrements in GLCCI1 expression. In isolated cell systems, the rs37973 variant is associated with significantly decreased luciferase reporter activity. Pooled data from treatment trials indicate reduced lung function in response to inhaled glucocorticoids in subjects with the variant allele (P = 0.0007 for pooled data). Overall, the mean (± SE) increase in forced expiratory volume in 1 second in the treated subjects who were homozygous for the mutant rs37973 allele was only about one third of that seen in similarly treated subjects who were homozygous for the wild-type allele (3.2 ± 1.6% vs. 9.4 ± 1.1%), and their risk of a poor response was significantly higher (odds ratio, 2.36; 95% confidence interval, 1.27 to 4.41), with genotype accounting for about 6.6% of overall inhaled glucocorticoid response variability.
A functional GLCCI1 variant is associated with substantial decrements in the response to inhaled glucocorticoids in patients with asthma. (Funded by the National Institutes of Health and others; ClinicalTrials.gov number, NCT00000575.)
It has recently been shown that vitamin D deficiency can increase asthma development and severity and that variations in vitamin D receptor genes are associated with asthma susceptibility.
We sought to find genetic factors that might interact with vitamin D levels to affect the risk of asthma exacerbation. Methods: We conducted a genome-wide study of gene–vitamin D interaction on asthma exacerbations using population-based and family-based approaches on 403 subjects and trios from the Childhood Asthma Management Program. Twenty-three polymorphisms with significant interactions were studied in a replication analysis in 584 children from a Costa Rican cohort. Results: We identified 3 common variants in the class I MHC–restricted T cell–associated molecule gene (CRTAM) that were associated with an increased rate of asthma exacerbations based on the presence of a low circulating vitamin D level. These results were replicated in a second independent population (unadjusted combined interaction, P =.00028–.00097; combined odds ratio, 3.28–5.38). One variant, rs2272094, is a nonsynonymous coding polymorphism of CRTAM. Functional studies on cell lines confirmed the interaction of vitamin D and rs2272094 on CRTAM expression. CRTAM is highly expressed in activated human CD8+ and natural killer T cells, both of which have been implicated in asthmatic patients.
The findings highlight an important gene-environment interaction that elucidates the role of vitamin D and CD8+ and natural killer T cells in asthma exacerbation in a genome-wide gene-environment interaction study that has been replicated in an independent population. The results suggest the potential importance of maintaining adequate vitamin D levels in subsets of high-risk asthmatic patients.
Gene-environment interaction; genome-wide association study; vitamin D; asthma exacerbation
Bronchodilator response (BDR) is an important asthma phenotype that measures reversibility of airway obstruction by comparing lung function (i.e. FEV1) before and after the administration of a short-acting β2-agonist, the most common rescue medications used for the treatment of asthma. BDR also serves as a test of β2-agonist efficacy. BDR is a complex trait that is partly under genetic control. A genome-wide association study (GWAS) of BDR, quantified as percent change in baseline FEV1 after administration of a β2-agonist, was performed with 1,644 non-Hispanic white asthmatic subjects from six drug clinical trials: CAMP, LOCCS, LODO, a medication trial conducted by Sepracor, CARE, and ACRN. Data for 469,884 single-nucleotide polymorphisms (SNPs) were used to measure the association of SNPs with BDR using a linear regression model, while adjusting for age, sex, and height. Replication of primary P-values was attempted in 501 white subjects from SARP and 550 white subjects from DAG. Experimental evidence supporting the top gene was obtained via siRNA knockdown and Western blotting analyses. The lowest overall combined P-value was 9.7E-07 for SNP rs295137, near the SPATS2L gene. Among subjects in the primary analysis, those with rs295137 TT genotype had a median BDR of 16.0 (IQR = [6.2, 32.4]), while those with CC or TC genotypes had a median BDR of 10.9 (IQR = [5.0, 22.2]). SPATS2L mRNA knockdown resulted in increased β2-adrenergic receptor levels. Our results suggest that SPATS2L may be an important regulator of β2-adrenergic receptor down-regulation and that there is promise in gaining a better understanding of the biological mechanisms of differential response to β2-agonists through GWAS.
Bronchodilator response (BDR) is an important asthma phenotype that measures reversibility of airway obstruction by comparing lung function before and after the administration of short-acting β2-agonists, common medications used for asthma treatment. We performed a genome-wide association study of BDR with 1,644 white asthmatic subjects from six drug clinical trials and attempted to replicate these findings in 1,051 white subjects from two independent cohorts. The most significant associated variant was near the SPATS2L gene. We knocked down SPATS2L mRNA in human airway smooth muscle cells and found that β2-adrenergic receptor levels increased, suggesting that SPATS2L may be a regulator of BDR. Our results highlight the promise of pursuing GWAS results that do not necessarily reach genome-wide significance and are an example of how results from pharmacogenetic GWAS can be studied functionally.
Thymic stromal lymphopoietin (TSLP) triggers dendritic cell–mediated T helper (Th) 2 inflammatory responses. A single-nucleotide polymorphism (SNP), rs3806933, in the promoter region of the TSLP gene creates a binding site for the transcription factor activating protein (AP)–1. The variant enhances AP-1 binding to the regulatory element, and increases the promoter–reporter activity of TSLP in response to polyinosinic-polycytidylic acid (poly[I:C]) stimulation in normal human bronchial epithelium (NHBE). We investigated whether polymorphisms including the SNP rs3806933 could affect the susceptibility to and clinical phenotypes of bronchial asthma. We selected three representative (i.e., Tag) SNPs and conducted association studies of the TSLP gene, using two independent populations (639 patients with childhood atopic asthma and 838 control subjects, and 641 patients with adult asthma and 376 control subjects, respectively). We further examined the effects of corticosteroids and a long-acting β2-agonist (salmeterol) on the expression levels of the TSLP gene in response to poly(I:C) in NHBE. We found that the promoter polymorphisms rs3806933 and rs2289276 were significantly associated with disease susceptibility in both childhood atopic and adult asthma. The functional SNP rs3806933 was associated with asthma (meta-analysis, P = 0.000056; odds ratio, 1.29; 95% confidence interval, 1.14–1.47). A genotype of rs2289278 was correlated with pulmonary function. Moreover, the induction of TSLP mRNA and protein expression induced by poly(I:C) in NHBE was synergistically impaired by a corticosteroid and salmeterol. TSLP variants are significantly associated with bronchial asthma and pulmonary function. Thus, TSLP may serve as a therapeutic target molecule for combination therapy.
asthma; TSLP; bronchial epithelial cells; combination therapy; genetic polymorphisms
A 900-KB inversion exists within a large region of conserved linkage disequilibrium (LD) on chromosome 17. CRHR1 is located within the inversion region and associated with inhaled corticosteroid response in asthma. We hypothesized that CRHR1 variants are in LD with the inversion, supporting a potential role for natural selection in the genetic response to corticosteroids. We genotyped 6 single nucleotide polymorphisms (SNPs) spanning chr17:40,410,565–42,372,240, including 4 SNPs defining inversion status. Similar allele frequencies and strong LD were noted between the inversion and a CRHR1 SNP previously associated with lung function response to inhaled corticosteroids. Each inversion-defining SNP was strongly associated with inhaled corticosteroid response in adult asthma (p-values 0.002–0.005). The CRHR1 response to inhaled corticosteroids may thus be explained by natural selection resulting from inversion status or by long-range LD with another gene. Additional pharmacogenetic investigations into to regions of chromosomal diversity, including copy number variation and inversions, are warranted.
CRHR1; tau haplotype; MAPT; inversion; asthma; corticosteroid; pharmacogenetics
Corticotropin - releasing hormone receptor 2 (CRHR2) participates in smooth muscle relaxation response and may influence acute airway bronchodilator response to short – acting β2 agonist treatment of asthma. We aim to assess associations between genetic variants of CRHR2 and acute bronchodilator response in asthma.
We investigated 28 single nucleotide polymorphisms in CRHR2 for associations with acute bronchodilator response to albuterol in 607 Caucasian asthmatic subjects recruited as part of the Childhood Asthma Management Program (CAMP). Replication was conducted in two Caucasian adult asthma cohorts – a cohort of 427 subjects enrolled in a completed clinical trial conducted by Sepracor Inc. (MA, USA) and a cohort of 152 subjects enrolled in the Clinical Trial of Low-Dose Theopylline and Montelukast (LODO) conducted by the American Lung Association Asthma Clinical Research Centers.
Five variants were significantly associated with acute bronchodilator response in at least one cohort (p-value ≤ 0.05). Variant rs7793837 was associated in CAMP and LODO (p-value = 0.05 and 0.03, respectively) and haplotype blocks residing at the 5’ end of CRHR2 were associated with response in all three cohorts.
We report for the first time, at the gene level, replicated associations between CRHR2 and acute bronchodilator response. While no single variant was significantly associated in all three cohorts, the findings that variants at the 5’ end of CRHR2 are associated in each of three cohorts strongly suggest that the causative variants reside in this region and its genetic effect, although present, is likely to be weak.
Asthma; genetics; corticotrophin releasing hormone receptor 2; CRHR2; bronchodilator response; polymorphism; β2 adrenergic receptor agonist
Rationale: Current understanding of the molecular regulation of lung development is limited and derives mostly from animal studies.
Objectives: To define global patterns of gene expression during human lung development.
Methods: Genome-wide expression profiling was used to measure the developing lung transcriptome in RNA samples derived from 38 normal human lung tissues at 53 to 154 days post conception. Principal component analysis was used to characterize global expression variation and to identify genes and bioontologic attributes contributing to these variations. Individual gene expression patterns were verified by quantitative reverse transcriptase–polymerase chain reaction analysis.
Measurements and Main Results: Gene expression analysis identified attributes not previously associated with lung development, such as chemokine-immunologic processes. Lung characteristics attributes (e.g., surfactant function) were observed at an earlier-than-anticipated age. We defined a 3,223 gene developing lung characteristic subtranscriptome capable of describing a majority of the process. In gene expression space, the samples formed a time-contiguous trajectory with transition points correlating with histological stages and suggesting the existence of novel molecular substages. Induction of surfactant gene expression characterized a pseudoglandular “molecular phase” transition. Individual gene expression patterns were independently validated. We predicted the age of independent human lung transcriptome profiles with a median absolute error of 5 days, supporting the validity of the data and modeling approach.
Conclusions: This study extends our knowledge of key gene expression patterns and bioontologic attributes underlying early human lung developmental processes. The data also suggest the existence of molecular phases of lung development.
microarrays; surfactant; principal component analysis
Among asthmatics, bronchodilator response (BDR) to inhaled ß2- adrenergic agonists is variable, and the significance of a consistent response over time is unknown.
We assessed baseline clinical variables and determined the clinical outcomes associated with a consistently positive BDR over 4 years in children with mild-moderate persistent asthma.
In the 1,041 participants in the Childhood Asthma Management Program (CAMP), subjects with a change in FEV1 of 12% or greater (and 200mLs) after inhaled ß2 agonist at each of their yearly follow-up visits (consistent BDR) were compared with those who did not have a consistent BDR.
We identified 52 children with consistent BDR over the 4-year trial. Multivariable logistic regression modeling demonstrated that baseline pre-bronchodilator FEV1 (OR=0.71, p<0.0001), log 10 IgE level (OR=1.97, p=0.002), and lack of treatment with inhaled corticosteroids (OR=0.31, p=0.009) were associated with a consistent BDR. Individuals who had a consistent BDR had more hospital visits (p=0.007), required more prednisone bursts (p=0.0007), had increased nocturnal awakenings due to asthma (p<0.0001), and missed more days of school (p=0.03) than non-responders during the 4-year follow-up.
We have identified predictors of consistent BDR and determined that this phenotype is associated with poor clinical outcomes.
asthma; consistent bronchodilator response; outcomes
Purpose of review
Patient response to the asthma drug classes, bronchodilators, inhaled corticosteroids and leukotriene modifiers, are characterized by a large degree of heterogeneity, which is attributable in part to genetic variation. Herein, we review and update the pharmacogenetics and pharmaogenomics of common asthma drugs.
Early studies suggest that bronchodilator reversibility and asthma worsening in patients on continuous short-acting and long-acting β-agonists are related to the Gly16Arg genotype for the ADRB2. More recent studies including genome-wide association studies implicate variants in other genes contribute to bronchodilator response heterogeneity and fail to replicate asthma worsening associated with continuous β-agonist use. Genetic determinants of the safety of long-acting β-agonist require further study. Variants in CRHR1, TBX21, and FCER2 contribute to variability in response for lung function, airways responsiveness, and exacerbations in patients taking inhaled corticosteroids. Variants in ALOX5, LTA4H, LTC4S, ABCC1, CYSLTR2, and SLCO2B1 contribute to variability in response to leukotriene modifiers.
Identification of novel variants that contribute to response heterogeneity supports future studies of single nucleotide polymorphism discovery and include gene expression and genome-wide association studies. Statistical models that predict the genomics of response to asthma drugs will complement single nucleotide polymorphism discovery in moving toward personalized medicine.
asthma; genes; personalized medicine; polymorphisms; response heterogeneity
Rationale: Inhaled β-agonists are one of the most widely used classes of drugs for the treatment of asthma. However, a substantial proportion of patients with asthma do not have a favorable response to these drugs, and identifying genetic determinants of drug response may aid in tailoring treatment for individual patients.
Objectives: To screen variants in candidate genes in the steroid and β-adrenergic pathways for association with response to inhaled β-agonists.
Methods: We genotyped 844 single nucleotide polymorphisms (SNPs) in 111 candidate genes in 209 children and their parents participating in the Childhood Asthma Management Program. We screened the association of these SNPs with acute response to inhaled β-agonists (bronchodilator response [BDR]) using a novel algorithm implemented in a family-based association test that ranked SNPs in order of statistical power. Genes that had SNPs with median power in the highest quartile were then taken for replication analyses in three other asthma cohorts.
Measurements and Main Results: We identified 17 genes from the screening algorithm and genotyped 99 SNPs from these genes in a second population of patients with asthma. We then genotyped 63 SNPs from four genes with significant associations with BDR, for replication in a third and fourth population of patients with asthma. Evidence for association from the four asthma cohorts was combined, and SNPs from ARG1 were significantly associated with BDR. SNP rs2781659 survived Bonferroni correction for multiple testing (combined P value = 0.00048, adjusted P value = 0.047).
Conclusions: These findings identify ARG1 as a novel gene for acute BDR in both children and adults with asthma.
pharmacogenetics; asthma; bronchodilator agents
Rationale: Airway responsiveness is a prognostic marker for asthma symptoms in later life.
Objectives: To evaluate characteristics responsible for persistence of airway responsiveness in children with asthma.
Methods: A total of 1,041 children, initially aged 5–12 years, with mild to moderate persistent asthma enrolled in the Childhood Asthma Management Program (CAMP) were studied prospectively for 8.6 ± 1.8 years with methacholine challenges yearly.
Measurements and Main Results: Least squares geometric mean models were fit to determine effects of sex and age on airway responsiveness (provocative concentration producing 20% decrease in FEV1 [PC20]). Multiple linear regression analysis was performed to determine factors at baseline and over time, which were associated with PC20 at end of follow-up. A total of 7,748 methacholine challenges were analyzed. PC20 increased with age, with boys having greater increase after age 11 years than girls (P < 0.001). The divergence coincided with the mean age for Tanner stage 2. Postpubertal girls had greater airway responsiveness, even after adjustment for FEV1 and other potential confounders. Although multivariable regression analyses noted a variety of factors that influenced airway responsivness in both sexes, a history of hay fever (β= −0.30, P = 0.005), respiratory allergy (β= −0.32, P = 0.006), or recent inhaled corticosteroid usage (β= −0.18, P = 0.02) were associated with decrements in final log PC20 only in girls.
Conclusions: Airway responsiveness (PC20) is more severe in the postpubertal female with asthma than in males. Although there are factors associated with airway responsiveness in both males and females, sex-specific factors may contribute to new insights into asthma pathogenesis.
methacholine; PC20; FEV1; bronchoconstriction
Maternal and perinatal environmental exposures, as well as inherited factors, may influence neonatal immune responses.
To determine relations of maternal and perinatal exposures to antigen-specific cord blood lymphoproliferative responses.
In 427 newborns from a Boston pregnancy/birth cohort, lymphoproliferative responses in cord blood mononuclear cells to stimulation with cockroach (Bla g 2), house dust mite (Der f 1), ovalbumin, and mitogen phytohemagglutinin were measured as stimulation index (SI). We used the Wilcoxon rank sum and χ2 tests to evaluate predictors of ovalbumin SI as a continuous ranked or dichotomous outcome. We used t test and Spearman correlation for univariate testing and linear regression to evaluate predictors of natural log-transformed Bla g 2, Der f 1, and phytohemagglutinin SI. Logistic multivariate regression was applied to evaluate predictors of Bla g 2, Der f 1, and phytohemagglutinin SI dichotomized at 2 or at the median for phytohemagglutinin.
Maternal smoking during pregnancy, inadequate or excessive maternal weight gain during pregnancy, neonate black race/ethnicity (compared with white), and Apgar score less than 8 were each independently associated with increased cord blood mononuclear cell proliferative responses to stimulation with Bla g 2 and/or Der f 1. Maternal history of asthma was associated only with increased lymphoproliferative response to ovalbumin stimulation.
Distinct fetal and perinatal exposures and black race/ethnicity may be associated with increased cord blood lymphoproliferative responses. The implications of these findings for future development of allergy or asthma are, as yet, unknown.
Background. N-3 and n-6 polyunsaturated fatty acids (PUFAs) have been hypothesized to have opposing influences on neonatal immune responses that might influence the risk of allergy or asthma. However, both n-3 eicosapentaenoic acid (EPA) and n-6 arachidonic acid (AA) are required for normal fetal development.
Objective. We evaluated whether cord blood fatty acid levels were related to neonatal immune responses and whether n-3 and n-6 PUFA responses differed.
Methods. We examined the relation of cord blood plasma n-3 and n-6 PUFAs (n = 192) to antigen- and mitogen-stimulated cord blood lymphocyte proliferation (n = 191) and cytokine (IL-13 and IFN-γ; n = 167) secretion in a US birth cohort.
Results. Higher levels of n-6 linoleic acid were correlated with higher IL-13 levels in response to Bla g 2 (cockroach, P = .009) and Der f 1 (dust mite, P = .02). Higher n-3 EPA and n-6 AA levels were each correlated with reduced lymphocyte proliferation and IFN-γ levels in response to Bla g 2 and Der f 1 stimulation. Controlling for potential confounders, EPA and AA had similar independent effects on reduced allergen-stimulated IFN-γ levels. If neonates had either EPA or AA levels in the highest quartile, their Der f 1 IFN-γ levels were 90% lower (P = .0001) than those with both EPA and AA levels in the lowest 3 quartiles. Reduced AA/EPA ratio was associated with reduced allergen-stimulated IFN-γ level.
Conclusion. Increased levels of fetal n-3 EPA and n-6 AA might have similar effects on attenuation of cord blood lymphocyte proliferation and IFN-γ secretion.
Clinical implications. The implications of these findings for
Asthma; child; cord blood; cytokine; fatty acids; lymphocyte proliferation; AA: Arachidonic acid; BMI: Body mass index; CBMC: Cord blood mononuclear cell; CI: Confidence interval; DHA: Docosohexaenoic acid; EPA: Eicosapentaenoic acid; FA: Fatty acid; LA: Linoleic acid; NICU: Neonatal intensive care unit; OVA: Ovalbumin; PG: Prostaglandin; PUFA: Polyunsaturated fatty acid; SI: Stimulation index
Little is known about the relation between cytokine profile at birth and acute lower respiratory illnesses in the first year of life. The purpose of this work was to examine the relation between cytokine secretions by cord blood mononuclear cells and acute lower respiratory illness in a birth cohort of 297 children.
Cord blood mononuclear cells were isolated, and secretion of interferon-γ, interleukin-13, interleukin-10, and tumor necrosis factor-α at baseline and in response to allergens (Blatella germanica 2 and Dermatophagoides farinae 1) and mitogen (phytohemagglutinin) were quantified using enzyme-linked immunosorbent assay. Acute lower respiratory illness was defined as a parental report of a diagnosis of bronchiolitis, pneumonia, bronchitis, and/or croup by a health care professional in the first year of life. Differences in the levels of cord blood cytokines between children with and without acute lower respiratory illness were examined using 2-sample Wilcoxon tests. Logistic regression models were used to examine the relation between various categories of cord blood cytokines and acute lower respiratory illness.
Median levels of interferon-γ secreted by cord blood mononuclear cells in response to Blatella germanica 2 and Dermatophagoides farinae 1 were higher among children without acute lower respiratory illness as compared with children with acute lower respiratory illness. After adjustment for other covariates, the odds of acute lower respiratory illness was reduced among children in the top category (at or more than the median of detectable values) of interferon-γ level, significantly so in response to Blatella germanica 2.
In a cohort of children from the general population, we found that upregulated interferon-γ secretion at birth is associated with reduced risk of acute lower respiratory illness in the first year of life.
lower respiratory illnesses; cytokines; neonates; IFN-γ
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, χ2 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.
antiinflammatory; montelukast; pharmacodynamic; pharmacogenetic