Distinct receptors likely exist for leukotriene(LT)E4, a potent mediator of airway inflammation. Purinergic receptor P2Y12 is needed for LTE4-induced airways inflammation, and P2Y12 antagonism attenuates house dust mite-induced pulmonary eosinophilia in mice. Although experimental data support a role for P2Y12 in airway inflammation, its role in human asthma has never been studied.
To test for association between variants in the P2Y12 gene (P2RY12) and lung function in human subjects with asthma, and to examine for gene-by-environment interaction with house dust mite exposure.
19 single nucleotide polymorphisms (SNPs) in P2RY12 were genotyped in 422 children with asthma and their parents (n=1266). Using family-based methods, we tested for associations between these SNPs and five lung function measures. We performed haplotype association analyses and tested for gene-by-environment interactions using house dust mite exposure. We used the false discovery rate to account for multiple comparisons.
Five SNPs in P2RY12 were associated with multiple lung function measures (P values 0.006–0.025). Haplotypes in P2RY12 were also associated with lung function (P values 0.0055–0.046). House dust mite exposure modulated associations between P2RY12 and lung function, with minor allele homozygotes exposed to house dust mite demonstrating worse lung function than those unexposed (significant interaction P values 0.0028–0.040).
Conclusions and clinical relevance
P2RY12 variants were associated with lung function in a large family-based asthma cohort. House dust mite exposure caused significant gene-by-environment effects. Our findings add the first human evidence to experimental data supporting a role for P2Y12 in lung function. P2Y12 could represent a novel target for asthma treatment.
Purinergic receptor; leukotriene; asthma; house dust mite; lung function
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
The Commonwealth of Massachusetts increased the copayment for prescription drugs by $1.50 for Medicaid (MassHealth) beneficiaries in 2003. We sought to determine the likely health outcomes and cost shifts attributable to this copayment increase using the example of inhaled corticosteroids (ICS) use among adult asthmatic Medicaid beneficiaries.
We compared the predicted costs and health outcomes projected over a 1-year time horizon with and without the increase in copayment from the perspective of MassHealth, providers, pharmacies, and MassHealth beneficiaries by employing decision analysis simulation model.
In a target population of 17,500 adult asthmatics, increased copayments from 50¢ to $2.00 would result in an additional 646 acute events per year, caused by increased drug nonadherence. Annual combined net savings for the state and federal governments would be $2.10 million. Projected MassHealth savings are attributable to both decreased drug utilization and lower pharmacy reimbursement rates; these more than offset the additional costs of more frequent acute exacerbations. Pharmacies would lose $1.98 million in net revenues, MassHealth beneficiaries would pay an additional $0.28 million, and providers would receive additional $0.16 million.
Over its first year of implementation, increase in the prescription drug copayment is expected to produce more frequent acute exacerbations among asthmatic MassHealth beneficiaries who use ICS and to shift the financial burden from government to other stakeholders.
asthma; copayment; medicaid; prescription drug
Omalizumab (trade name Xolair) is approved by the US Food and Drug Administration for treatment of moderate-to-severe allergic asthma. Given the high acquisition cost of omalizumab, its role and cost-effectiveness in disease management require definition.
We sought to identify the clinical and economic circumstances under which omalizumab might or might not be a cost-effective option by using a mathematic model.
We merged published data on clinical and economic outcomes (including acute event incidence, frequency/severity of hospitalizations, and health-related quality of life) to project 10-year costs, quality-adjusted life years (QALYs), and cost-effectiveness of treatment with omalizumab in addition to inhaled corticosteroids. Sensitivity analyses were conducted by using input data ranges from a variety of sources (published clinical trials and observational databases).
For patients with baseline acute event rates, omalizumab conferred an additional 1.7 quality-adjusted months at an incremental cost of $131,000 over a 10-year planning horizon, implying a cost-effectiveness ratio of $821,000 per QALY gained. For patients with 5 times the baseline acute event rate, the cost-effectiveness ratio was $491,000 per QALY gained. The projected cost-effectiveness ratio could fall within a range of other programs that are widely considered to be cost-effective if the cost of omalizumab decreases to less than $200.
Omalizumab is not cost-effective for most patients with severe asthma. The projected cost-effectiveness ratios could fall within a favorable range if the cost of omalizumab decreases significantly.
Based on the high cost of omalizumab, it is especially important that clinicians explore alternative medications for asthma before initiating omalizumab.
Omalizumab; cost-effectiveness; asthma; anti-IgE
Patients with severe or difficult-to-treat asthma account for substantial asthma morbidity, mortality, and healthcare burden despite comprising only a small proportion of the total asthma population. TENOR, a multicenter, observational, prospective cohort study was initiated in 2001. It enrolled 4,756 adults, adolescents and children with severe or difficult-to-treat asthma who were followed semi-annually and annually for three years, enabling insight to be gained into this understudied population. A broad range of demographic, clinical, and patient self-reported assessments were completed during the follow-up period. Here, we present key findings from the TENOR registry in relation to asthma control and exacerbations, including the identification of specific subgroups found to be at particularly high-risk. Identification of the factors and subgroups associated with poor asthma control and increased risk of exacerbations can help physicians design individual asthma management, and improve asthma-related health outcomes for these patients.
Severe asthma; Difficult-to-treat asthma; Asthma control; 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
Despite the availability of several classes of asthma medications and their overall effectiveness, a significant portion of patients fail to respond to these therapeutic agents. Evidence suggests that genetic factors may partly mediate the heterogeneity in asthma treatment response. This review discusses important findings in asthma pharmacogenetics and pharmacogenomics studies conducted to date, examines limitations of these studies and finally, proposes future research directions in this field. The focus will be on the three major classes of asthma medications: β-adrenergic receptor agonists, inhaled corticosteroids and leukotriene modifiers. Although many studies are limited by small sample sizes and replication of the findings is needed, several candidate genes have been identified. High-throughput technologies is also allowing for large-scale genetic investigations. Thus, the future is promising for a personalized treatment of asthma, which will improve therapeutic outcomes, minimize side effects and lead to a more cost-effective care.
asthma; pharmacogenetics; pharmacogenomics
For genomewide association studies with family-based designs, we propose a Bayesian approach. We show that standard TDT/FBAT statistics can naturally be implemented in a Bayesian framework. We construct a Bayes factor conditional on the offspring phenotype and parental genotype data and then use the data we conditioned on to inform the prior odds for each marker. In the construction of the prior odds, the evidence for association for each single marker is obtained at the population-level by estimating the genetic effect size in the conditional mean model. Since such genetic effect size estimates are statistically independent of the effect size estimation within the families, the actual data set can inform the construction of the prior odds without any statistical penalty. In contrast to Bayesian approaches that have recently been proposed for genomewide association studies, our approach does not require assumptions about the genetic effect size; this makes the proposed method entirely data-driven. The power of the approach was assessed through simulation. We then applied the approach to a genomewide association scan to search for associations between single nucleotide polymorphisms and body mass index in the Childhood Asthma Management Program data.
family-based association tests; Bayes factors; complex traits
asthma; microbiome; vitamin D
Genetic variability in the regulation of the nitric oxide (NO) pathway may influence hemodynamic changes in pediatric sepsis. We sought to determine whether functional polymorphisms in DDAH2, which metabolizes the NO synthase inhibitor asymmetric dimethylarginine (ADMA), are associated with susceptibility to sepsis, plasma ADMA, distinct hemodynamic states, and vasopressor requirements in pediatric septic shock.
In a prospective study, blood and buccal swabs were obtained from 82 patients ≤18 years (29 with severe sepsis/septic shock plus 27 febrile and 26 healthy controls). Plasma ADMA was measured using tandem mass spectrometry. DDAH2 gene was partially sequenced to determine the −871 6g/7g insertion/deletion and −449G/C single nucleotide polymorphisms. Shock type (“warm” versus “cold”) was characterized by clinical assessment. The −871 7g allele was more common in septic (17%) then febrile (4%) and healthy (8%) patients, though this was not significant after controlling for sex and race (p = 0.96). ADMA did not differ between −871 6g/7g genotypes. While genotype frequencies also did not vary between groups for the −449G/C SNP (p = 0.75), septic patients with at least one −449G allele had lower ADMA (median, IQR 0.36, 0.30–0.41 µmol/L) than patients with the −449CC genotype (0.55, 0.49–0.64 µmol/L, p = 0.008) and exhibited a higher incidence of “cold” shock (45% versus 0%, p = 0.01). However, after controlling for race, the association with shock type became non-significant (p = 0.32). Neither polymorphism was associated with inotrope score or vasoactive infusion duration.
The −449G polymorphism in the DDAH2 gene was associated with both low plasma ADMA and an increased likelihood of presenting with “cold” shock in pediatric sepsis, but not with vasopressor requirement. Race, however, was an important confounder. These results support and justify the need for larger studies in racially homogenous populations to further examine whether genotypic differences in NO metabolism contribute to phenotypic variability in sepsis pathophysiology.
The mechanisms and consequences of the observed association between obesity and childhood asthma are unclear.
To determine the effect of obesity on treatment responses to inhaled corticosteroids in asthmatic children.
We performed a post hoc analysis to evaluate the interaction between body mass index (BMI) and treatment with inhaled budesonide on lung function in the Childhood Asthma Management Program (CAMP) trial. Participants were then stratified into overweight/obese and non-overweight, and their response to inhaled budesonide was analyzed longitudinally over the 4 years of the trial.
There was a significant interaction between BMI and budesonide for pre-BD FEV1/FVC (P=0.0007) and bronchodilator response (BDR) (P=0.049), and a non-significant trend for an interaction between BMI and budesonide on pre-BD FEV1 (P=0.15). Non-overweight children showed significant improvement with inhaled budesonide in lung function (FEV1, FEV1/FVC, and BDR) during the early (years 1–2) and late stages (years 3–4) of the trial. Overweight/obese children had improved FEV1 and BDR during the early but not the late stage of the trial, and showed no improvement in FEV1/FVC. When comparing time points where both groups showed significant response, the degree of improvement among non-overweight children was significantly greater than in overweight/obese children at most visits. Non-overweight children had a 44% reduction in the risk of ER visits or hospitalizations throughout the trial (P=0.001); there was no reduction in risk among overweight/obese (P=0.97).
Compared to children of normal weight, overweight/obese children in CAMP showed a decreased response to inhaled budesonide on measures of lung function and ER visits/hospitalizations for asthma.
Asthma; obesity; pediatric asthma; childhood obesity; budesonide
Few prospective data link early childhood adiposity with asthma-related symptoms.
We sought to examine the associations of weight-for-length (WFL) at age 6 months with incidence of wheezing by age 3 years.
We studied 932 children in a prospective cohort of children. The main outcome was recurrent wheezing, which was defined as parents’ report of wheezing between 2 and 3 years of age plus wheezing in either year 1 or 2 of life. Secondary outcomes included any wheezing from 6 months to 3 years and current asthma. We used multiple logistic regression to examine associations of 6-month WFL z scores with these outcomes.
At 6 months, the infants’ mean WFL z score was 0.68 (SD, 0.94; range −2.96 to 3.24). By age 3 years, 14% of children had recurrent wheezing. After adjustment for a variety of potential confounders, we found that each 1-unit increment in 6-month WFL z score was associated with greater odds of recurrent wheezing (odds ratio [OR], 1.46; 95% CI, 1.11–1.91) and any wheezing (OR, 1.23; 95% CI, 1.03–1.48). We observed a weaker association between 6-month WFL z score and current asthma (OR, 1.22; 95% CI, 0.94–1.59).
Infants with higher WFL z scores at 6 months of age had a greater risk of recurrent wheezing by age 3 years. It is unclear whether the relationship of infant adiposity and early-life wheeze extends to allergic asthma or wheeze that can persist into later childhood. Our findings suggest that early interventions to prevent excess infant adiposity might help reduce children’s risk of asthma-related symptoms.
Asthma; wheeze; adiposity; children; prospective study
Asthma is the leading serious pediatric chronic illness in the United States, affecting 7.1 million children. The prevalence of asthma in children under 4 years of age has increased dramatically in the last 2 decades. Existing evidence suggests that this increase in prevalence derives from early environmental exposures acting on a pre-existing asthma-susceptible genotype. We studied the origins of asthma susceptibility in developing lung in rat strains that model the distinct phenotypes of airway hyperresponsiveness (Fisher rats) and atopy (brown Norway [BN] rats). Postnatal BN rat lungs showed increased epithelial proliferation and tracheal goblet cell hyperplasia. Fisher pups showed increased lung resistance at age 2 weeks, with elevated neutrophils throughout the postnatal period. Diverse transcriptomic signatures characterized the distinct respiratory phenotypes of developing lung in both rat models. Linear regression across age and strain identified developmental variation in expression of 1,376 genes, and confirmed both strain and temporal regulation of lung gene expression. Biological processes that were heavily represented included growth and development (including the T Box 1 transcription factor [Tbx5], the epidermal growth factor receptor [Egfr], the transforming growth factor beta-1-induced transcript 1 [Tgfbr1i1]), extracellular matrix and cell adhesion (including collagen and integrin genes), and immune function (including lymphocyte antigen 6 (Ly6) subunits, IL-17b, Toll-interacting protein, and Ficolin B). Genes validated by quantitative RT-PCR and protein analysis included collagen III alpha 1 Col3a1, Ly6b, glucocorticoid receptor and Importin-13 (specific to the BN rat lung), and Serpina1 and Ficolin B (specific to the Fisher lung). Innate differences in patterns of gene expression in developing lung that contribute to individual variation in respiratory phenotype are likely to contribute to the pathogenesis of asthma.
asthma susceptibility; lung development; developmental gene expression
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
Sequence variants in genes functioning in folate-mediated one-carbon metabolism are hypothesized to lead to changes in levels of homocysteine and DNA methylation, which, in turn, are associated with risk of cardiovascular disease.
330 SNPs in 52 genes were studied in relation to plasma homocysteine and global genomic DNA methylation. SNPs were selected based on functional effects and gene coverage, and assays were completed on the Illumina Goldengate platform. Age-, smoking-, and nutrient-adjusted genotype--phenotype associations were estimated in regression models.
Using a nominal P ≤ 0.005 threshold for statistical significance, 20 SNPs were associated with plasma homocysteine, 8 with Alu methylation, and 1 with LINE-1 methylation. Using a more stringent false discovery rate threshold, SNPs in FTCD, SLC19A1, and SLC19A3 genes remained associated with plasma homocysteine. Gene by vitamin B-6 interactions were identified for both Alu and LINE-1 methylation, and epistatic interactions with the MTHFR rs1801133 SNP were identified for the plasma homocysteine phenotype. Pleiotropy involving the MTHFD1L and SARDH genes for both plasma homocysteine and Alu methylation phenotypes was identified.
No single gene was associated with all three phenotypes, and the set of the most statistically significant SNPs predictive of homocysteine or Alu or LINE-1 methylation was unique to each phenotype. Genetic variation in folate-mediated one-carbon metabolism, other than the well-known effects of the MTHFR c.665C>T (known as c.677 C>T, rs1801133, p.Ala222Val), is predictive of cardiovascular disease biomarkers.
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
Few studies have examined the effects of in utero smoke exposure (IUS) on lung function in children with asthma, and there are no published data on the impact of IUS on treatment outcomes in asthmatic children.
To explore whether IUS exposure is associated with increased airway responsiveness among children with asthma, and whether IUS modifies the response to treatment with inhaled corticosteroids (ICS).
To assess the impact of parent-reported IUS exposure on airway responsiveness in childhood asthma we performed a repeated-measures analysis of methacholine PC20 data from the Childhood Asthma Management Program (CAMP), a four-year, multicenter, randomized double masked placebo controlled trial of 1041 children ages 5–12 comparing the long term efficacy of ICS with mast cell stabilizing agents or placebo.
Although improvement was seen in both groups, asthmatic children with IUS exposure had on average 26% less of an improvement in airway responsiveness over time compared to unexposed children (p=.01). Moreover, while children who were not exposed to IUS who received budesonide experienced substantial improvement in PC20 compared to untreated children (1.25 fold-increase, 95% CI 1.03, 1.50, p=.02) the beneficial effects of budesonide were attenuated among children with a history of IUS exposure (1.04 fold-increase, 95% CI 0.65, 1.68, p=.88).
IUS reduces age-related improvements in airway responsiveness among asthmatic children. Moreover, IUS appears to blunt the beneficial effects of ICS use on airways responsiveness. These results emphasize the importance of preventing this exposure through smoking cessation counseling efforts with pregnant women.
asthma; in utero smoke exposure; airway responsiveness; inhaled corticosteroids
Asthma exacerbations, most often due to respiratory tract infections, are the leading causes of asthma morbidity and comprise a significant proportion of asthma-related costs. Vitamin D status may play a role in preventing asthma exacerbations.
To assess the relationship between serum vitamin D levels and subsequent severe asthma exacerbations.
We measured 25-hydroxyvitamin D (25(OH)D) levels in serum collected from 1,024 mild to moderate persistent asthmatic children at the time of enrollment in a multi-center clinical trial of children randomized to receiving budesonide, nedocromil, or placebo (as-needed beta-agonists), the Childhood Asthma Management Program. Using multivariable modeling we examined the relationship between baseline vitamin D level and the odds of any hospitalization or emergency department (ED) visit over the 4 years of the trial.
35% of all subjects were vitamin D insufficient, as defined by a level ≤ 30 ng/ml 25(OH)D. Mean vitamin D levels were lowest in African-American subjects, and highest in whites. After adjusting for age, sex, BMI, income, and treatment group, insufficient vitamin D status was associated with a higher odds of any hospitalization or ED visit (odds ratio [OR] 1.5 [95% confidence interval [CI]: 1.1 – 1.9] P =0.01).
Vitamin D insufficiency is common in this population of North American children with mild to moderate persistent asthma, and is associated with higher odds of severe exacerbation over a four year period.
Asthma; Vitamin D; inhaled corticosteroids; asthma exacerbations
Personalized health-care promises tailored health-care solutions to individual patients based on their genetic background and/or environmental exposure history. To date, disease prediction has been based on a few environmental factors and/or single nucleotide polymorphisms (SNPs), while complex diseases are usually affected by many genetic and environmental factors with each factor contributing a small portion to the outcome. We hypothesized that the use of random forests classifiers to select SNPs would result in an improved predictive model of asthma exacerbations. We tested this hypothesis in a population of childhood asthmatics.
In this study, using emergency room visits or hospitalizations as the definition of a severe asthma exacerbation, we first identified a list of top Genome Wide Association Study (GWAS) SNPs ranked by Random Forests (RF) importance score for the CAMP (Childhood Asthma Management Program) population of 127 exacerbation cases and 290 non-exacerbation controls. We predict severe asthma exacerbations using the top 10 to 320 SNPs together with age, sex, pre-bronchodilator FEV1 percentage predicted, and treatment group.
Testing in an independent set of the CAMP population shows that severe asthma exacerbations can be predicted with an Area Under the Curve (AUC) = 0.66 with 160-320 SNPs in comparison to an AUC score of 0.57 with 10 SNPs. Using the clinical traits alone yielded AUC score of 0.54, suggesting the phenotype is affected by genetic as well as environmental factors.
Our study shows that a random forests algorithm can effectively extract and use the information contained in a small number of samples. Random forests, and other machine learning tools, can be used with GWAS studies to integrate large numbers of predictors simultaneously.
Little is known about the role of most asthma susceptibility genes during human lung development. Genetic determinants for normal lung development are not only important early in life, but also for later lung function.
To investigate the role of expression patterns of well-defined asthma susceptibility genes during human and murine lung development. We hypothesized that genes influencing normal airways development would be over-represented by genes associated with asthma.
Asthma genes were first identified via comprehensive search of the current literature. Next, we analyzed their expression patterns in the developing human lung during the pseudoglandular (gestational age, 7-16 weeks) and canalicular (17-26 weeks) stages of development, and in the complete developing lung time series of 3 mouse strains: A/J, SW, C57BL6.
In total, 96 genes with association to asthma in at least two human populations were identified in the literature. Overall, there was no significant over-representation of the asthma genes among genes differentially expressed during lung development, although trends were seen in the human (Odds ratio, OR 1.22, confidence interval, CI 0.90-1.62) and C57BL6 mouse (OR 1.41, CI 0.92-2.11) data. However, differential expression of some asthma genes was consistent in both developing human and murine lung, e.g. NOD1, EDN1, CCL5, RORA and HLA-G. Among the asthma genes identified in genome wide association studies, ROBO1, RORA, HLA-DQB1, IL2RB and PDE10A were differentially expressed during human lung development.
Our data provide insight about the role of asthma susceptibility genes during lung development and suggest common mechanisms underlying lung morphogenesis and pathogenesis of respiratory diseases.
Asthma; Development; Expression; Genetics; Lung
We propose an omnibus family-based association test (MFBAT) that can be applied to multiple markers and multiple phenotypes and that has only one degree of freedom. The proposed test statistic extends current FBAT methodology to incorporate multiple markers as well as multiple phenotypes. Using simulation studies, power estimates for the proposed methodology are compared with the standard methodologies. On the basis of these simulations, we find that MFBAT substantially outperforms other methods, including haplotypic approaches and doing multiple tests with single single-nucleotide polymorphisms (SNPs) and single phenotypes. The practical relevance of the approach is illustrated by an application to asthma in which SNP/phenotype combinations are identified and reach overall significance that would not have been identified using other approaches. This methodology is directly applicable to cases in which there are multiple SNPs, such as candidate gene studies, cases in which there are multiple phenotypes, such as expression data, and cases in which there are multiple phenotypes and genotypes, such as genome-wide association studies that incorporate expression profiles as phenotypes. This program is available in the PBAT analysis package.
family-based association testing (FBAT); genome-wide association studies; FBAT-PC; multiple marker; multiple phenotypes; multiple testing
Alveolarization depends on circulating glucocorticoid (GC), retinoid (RA) and Vitamin D (VitD). Bronchopulmonary dysplasia (BPD), a leading cause of neonatal morbidity, is associated with arrested alveolarization. In hyperoxia-exposed rats displaying features of BPD, reduced levels of Lgl1 normalize during recovery. We show that GC (100nM) stimulates (7–115 fold) and VitD (100µM) suppresses (2 fold) Lgl1 expression. RA (all trans/9-cis, 10µM) effects are biphasic. From postnatal (PN) days 7–10, RA was stimulatory (2 fold) at 24h, after which effects were inhibitory (3–15 fold). Lgl1 promoter-luciferase reporter assays confirmed that these agents operated at the transcriptional level. Interestingly, the individual inhibitory effects of VitD and RA on GC induction of Lgl1 were abrogated when both agents were present, suggesting that steric hindrance may influence promoter accessibility. Analysis of the proximity (<50 base pairs) of binding sites for overlapping VitD and RA receptors to that of the GC receptor identified 81% of promoters in 66 genes (including Lgl1) important in human lung development compared to 48% in a random set of 1000 genes. Complex integration of the effects of GC, RA, and VitD on gene expression in the postnatal lung is likely to contribute to the timely advance of alveolarization without attendant inflammation.