Respiratory symptoms are commonly used to assess the impact of patient-centered interventions.
At the request of National Institutes of Health (NIH) institutes and other federal agencies, an expert group was convened to propose which measurements of asthma symptoms should be used as a standardized measure in future clinical research studies.
Asthma symptom instruments were classified as daily diaries (prospectively recording symptoms between research visits) or retrospective questionnaires (completed at research visits). We conducted a systematic search in PubMed and a search for articles that cited key studies describing development of instruments. We classified outcome instruments as either core (required in future studies), supplemental (used according to study aims and standardized), or emerging (requiring validation and standardization). This work was discussed at an NIH-organized workshop in March 2010 and finalized in September 2011.
Four instruments (3 daily diaries, 1 for adults and 2 for children; and 1 retrospective questionnaire for adults) were identified. Minimal clinically important differences have not been established for these instruments, and validation studies were only conducted in a limited number of patient populations. Validity of existing instruments may not be generalizable across racial-ethnic or other subgroups.
An evaluation of symptoms should be a core asthma outcome measure in clinical research. However, available instruments have limitations that preclude selection of a core instrument. The working group participants propose validation studies in diverse populations, comparisons of diaries versus retrospective questionnaires, and evaluations of symptom assessment alone versus composite scores of asthma control.
Asthma Symptom Utility Index; Asthma Symptom Diary Scales; Pediatric Asthma Caregiver Diary
Common variants at many loci have been robustly associated with asthma but explain little of the overall genetic risk. Here we investigate the role of rare (<1%) and low-frequency (1–5%) variants using the Illumina HumanExome BeadChip array in 4,794 asthma cases, 4,707 non-asthmatic controls and 590 case–parent trios representing European Americans, African Americans/African Caribbeans and Latinos. Our study reveals one low-frequency missense mutation in the GRASP gene that is associated with asthma in the Latino sample (P=4.31 × 10−6; OR=1.25; MAF=1.21%) and two genes harbouring functional variants that are associated with asthma in a gene-based analysis: GSDMB at the 17q12–21 asthma locus in the Latino and combined samples (P=7.81 × 10−8 and 4.09 × 10−8, respectively) and MTHFR in the African ancestry sample (P=1.72 × 10−6). Our results suggest that associations with rare and low-frequency variants are ethnic specific and not likely to explain a significant proportion of the ‘missing heritability’ of asthma.
Common variants account for only a small amount of the heritable risk for developing asthma. Using a meta-analysis approach, Igartua et al. identify one low-frequency missense mutation and two genes with functional variants that are associated with asthma, but only in specific ethnic groups.
Specific patterns of allergic sensitization as well as quantification of the in vitro IgE response in early life may provide relevant clinical insight into future rhinitis and asthma risk.
To define relationships among established sensitization to particular aeroallergens, quantitative analyses of allergen-specific IgE levels, pet exposure and sensitization, and asthma and rhinitis risk.
Children at high-risk for the development of asthma and allergic diseases were enrolled at birth into the Childhood Origins of ASThma (COAST) study. Allergen-specific IgE was assessed at ages 1, 3, 6, and 9 years by fluoroenzyme immunoassay (Unicap® 100, Pharmacia Diagnostics). Current asthma and rhinitis were diagnosed at age 6 and 8 years.
Sensitization to dog was strongly associated with increased asthma risk (p < 0.0001). Sensitization to perennial compared to seasonal allergens was more strongly associated with asthma risk, while sensitization to seasonal allergens was more closely associated with rhinitis risk. Increased levels of specific IgE to perennial allergens were associated with an increased asthma risk (p = 0.05), while any detectable level of IgE to seasonal allergens was associated with increased rhinitis risk (p = 0.0009). While dog and cat sensitization were both independently associated with increased asthma and rhinitis risk, dog exposure at birth was associated with a reduced risk of asthma, regardless of dog sensitization status during the first 6 years of life (p = 0.05).
CONCLUSIONS & CLINICAL RELEVANCE
Analyzing specific patterns of an individual’s allergic sensitization profile reveals additional relevant associations with asthma and rhinitis risk as opposed to the information gained from characterizing an individual as “atopic” by the presence of any demonstrable sensitization alone. Further, protective mechanisms of dog exposure with regards to asthma risk appear to be unrelated to the prevention of sensitization.
asthma; rhinitis; children; IgE; allergic sensitization; pet exposure
Early life respiratory viral infections and atopic characteristics are significant risk factors for the development of childhood asthma. It is hypothesized that repeated respiratory viral infections might induce structural remodeling by interfering with the normal process of lung maturation; however, the specific molecular processes that underlie these pathological changes are not understood. To investigate the molecular basis for these changes, we used an established Sendai virus infection model in weanling rats to compare the post-infection transcriptomes of an atopic asthma susceptible strain, Brown Norway, and a non-atopic asthma resistant strain, Fischer 344. Specific to this weanling infection model and not described in adult infection models, Sendai virus in the susceptible, but not the resistant strain, results in morphological abnormalities in distal airways that persist into adulthood. Gene expression data from infected and control lungs across five time points indicated that specific features of the immune response following viral infection were heightened and prolonged in lungs from Brown Norway rats compared with Fischer 344 rats. These features included an increase in macrophage cell number and related gene expression, which then transitioned to an increase in mast cell number and related gene expression. In contrast, infected Fischer F344 lungs exhibited more efficient restoration of the airway epithelial morphology, with transient appearance of basal cell pods near distal airways. Together, these findings indicate that the pronounced macrophage and mast cell responses and abnormal re-epithelialization precede the structural defects that developed and persisted in Brown Norway, but not Fischer 344 lungs.
Viral illness with wheezing during infancy is associated with the inception of childhood asthma. Small airway dysfunction is a component of childhood asthma, but little is known about how viral illness at an early age may affect the structure and function of small airways. We used a well-characterized rat model of postbronchiolitis chronic airway dysfunction to address how postinfectious small airway lesions affect airway physiological function and if the structure/function correlates persist into maturity. Brown Norway rats were sham- or virus inoculated at 3 to 4 weeks of age and allowed to recover from the acute illness. At 3 to 14 months of age, physiology (respiratory system resistance, Newtonian resistance, tissue damping, and static lung volumes) was assessed in anesthetized, intubated rats. Serial lung sections revealed lesions in the terminal bronchioles that reduced luminal area and interrupted further branching, affecting 26% (range, 13–39%) of the small airways at 3 months of age and 22% (range, 6–40%) at 12 to 14 months of age. At 3 months of age (n = 29 virus; n = 7 sham), small airway lesions correlated with tissue damping (rs = 0.69) but not with Newtonian resistance (rs = 0.23), and Newtonian resistance was not elevated compared with control rats, indicating that distal airways were primarily responsible for the airflow obstruction. Older rats (n = 7 virus; n = 6 sham) had persistent small airway dysfunction and significantly increased Newtonian resistance in the postbronchiolitis group. We conclude that viral airway injury at an early age may induce small airway lesions that are associated quantitatively with small airway physiological dysfunction early on and that these defects persist into maturity.
asthma; lung growth and development; airway injury and repair
Tiotropium has activity as an asthma controller. However, predictors of a positive response to tiotropium have not been described.
To describe individual and differential response of patients with asthma to salmeterol and tiotropium, when added to an ICS, as well as predictors of a positive clinical response.
Data from the double-blind, three-way crossover NHLBI Asthma Clinical Research Network’s TALC trial (ClinicalTrials.gov number, NCT00565266) were analyzed for individual and differential treatment responses to salmeterol and tiotropium, and predictors of a positive response to the endpoints FEV1, morning peak expiratory flow (AM PEF), and asthma control days (ACDs).
While approximately equal numbers of patients showed a differential response to salmeterol and tiotropium in terms of AM PEF (90 and 78, respectively), and ACDs (49 and 53, respectively), more showed a differential response to tiotropium for FEV1 (104) than salmeterol (62). An acute response to a short-acting bronchodilator, especially albuterol, predicted a positive clinical response to tiotropium for FEV1 (OR 4.08 [CI 2.00–8.31], P < 0.001) and AM PEF (OR 2.12 [CI 1.12–4.01], P = 0.021), as did a decreased FEV1/FVC ratio (FEV1 response increased 0.39% of baseline for every 1% decrease in the FEV1/FVC ratio). Higher cholinergic tone was also a predictor, while ethnicity, gender, atopy, IgE Level, sputum eosinophils, FENO, asthma duration, and BMI were not.
While these results need confirmation, predictors of a positive clinical response to tiotropium include a positive response to albuterol and airway obstruction, factors which could help identify appropriate patients for this therapy.
asthma; tiotropium; salmeterol; responder analysis; predictor of response
The National Heart, Lung and Blood Institute (NHLBI) Asthma Clinical Research Network (ACRN) recently completed its work after 20 years of collaboration as a multicentre clinical trial network. When formed, its stated mission was to perform multiple controlled clinical trials for treating patients with asthma by dispassionately examining new and existing therapies, and to rapidly communicate its findings to the medical community. The ACRN conducted 15 major clinical trials. In addition, clinical data, manual of operations, protocols and template informed consents from all ACRN trials are available via NHLBI BioLINCC (https://biolincc.nhlbi.nih.gov/studies/). This network contributed major insights into the use of inhaled corticosteroids, short-acting and long-acting ß-adrenergic agonists, leukotriene receptor antagonists, and novel agents (tiotropium, colchicine and macrolide antibiotics). They also pioneered studies of the variability in drug response, predictors of treatment response and pharmacogenetics. This review highlights the major research observations from the ACRN that have impacted the current management of asthma.
Asthma is a complex genetic disease caused by a combination of genetic and environmental risk factors. We sought to test classes of genetic variants largely missed by genome-wide association studies (GWAS), including copy number variants (CNVs) and low-frequency variants, by performing whole-genome sequencing (WGS) on 16 individuals from asthma-enriched and asthma-depleted families. The samples were obtained from an extended 13-generation Hutterite pedigree with reduced genetic heterogeneity due to a small founding gene pool and reduced environmental heterogeneity as a result of a communal lifestyle. We sequenced each individual to an average depth of 13-fold, generated a comprehensive catalog of genetic variants, and tested the most severe mutations for association with asthma. We identified and validated 1960 CNVs, 19 nonsense or splice-site single nucleotide variants (SNVs), and 18 insertions or deletions that were out of frame. As follow-up, we performed targeted sequencing of 16 genes in 837 cases and 540 controls of Puerto Rican ancestry and found that controls carry a significantly higher burden of mutations in IL27RA (2.0% of controls; 0.23% of cases; nominal p = 0.004; Bonferroni p = 0.21). We also genotyped 593 CNVs in 1199 Hutterite individuals. We identified a nominally significant association (p = 0.03; Odds ratio (OR) = 3.13) between a 6 kbp deletion in an intron of NEDD4L and increased risk of asthma. We genotyped this deletion in an additional 4787 non-Hutterite individuals (nominal p = 0.056; OR = 1.69). NEDD4L is expressed in bronchial epithelial cells, and conditional knockout of this gene in the lung in mice leads to severe inflammation and mucus accumulation. Our study represents one of the early instances of applying WGS to complex disease with a large environmental component and demonstrates how WGS can identify risk variants, including CNVs and low-frequency variants, largely untested in GWAS.
Recent meta-analyses of genome-wide association studies in general populations of European descent have identified 28 loci for lung function.
We sought to identify novel lung function loci specifically for asthma and to confirm lung function loci identified in general populations.
Genome-wide association studies of lung function (percent predicted FEV1 [ppFEV1], percent predicted forced vital capacity, and FEV1/forced vital capacity ratio) were performed in 4 white populations of European descent (n = 1544), followed by meta-analyses.
Seven of 28 previously identified lung function loci (HHIP, FAM13A, THSD4, GSTCD, NOTCH4-AGER, RARB, and ZNF323) identified in general populations were confirmed at single nucleotide polymorphism (SNP) levels (P < .05). Four of 32 loci (IL12A, IL12RB1, STAT4, and IRF2) associated with ppFEV1 (P < 10−4) belong to the TH1 or IL-12 cytokine family pathway. By using a linear additive model, these 4 TH1 pathway SNPs cumulatively explained 2.9% to 7.8% of the variance in ppFEV1 values in 4 populations (P = 3 × 10−11). Genetic scores of these 4 SNPs were associated with ppFEV1 values (P = 2 × 10−7) and the American Thoracic Society severe asthma classification (P = .005) in the Severe Asthma Research Program population. TH2 pathway genes (IL13, TSLP, IL33, and IL1RL1) conferring asthma susceptibility were not associated with lung function.
Genes involved in airway structure/remodeling are associated with lung function in both general populations and asthmatic subjects. TH1 pathway genes involved in anti-virus/bacterial infection and inflammation modify lung function in asthmatic subjects. Genes associated with lung function that might affect asthma severity are distinct from those genes associated with asthma susceptibility.
Lung function; FEV1; asthma; TH1; IL12A; IL12RB1; STAT4; IRF2
Maternal asthma and child’s sex are among the most significant and reproducible risk factors for the development of asthma. Although the mechanisms for these effects are unknown, they likely involve non-classical genetic mechanisms. One such mechanism could involve the transfer and persistence of maternal cells to her offspring, a common occurrence known as maternal microchimerism (MMc). MMc has been associated with many autoimmune diseases, but has not been investigated for a role in asthma or allergic disease.
We hypothesized that some of the observed risks for asthma may be due to different rates of transmission or persistence of maternal cells to children of mothers with asthma compared to children of mothers without asthma, or to sons compared to daughters. We further hypothesized that rates of MMc differ between children with and without asthma.
We tested these hypotheses in 317 subjects from three independent cohorts using a real-time quantitative PCR assay to detect a non-inherited HLA allele in the child.
MMc was detected in 20.5% of subjects (range 16.8% – 27.1% in the three cohorts). We observed lower rates of asthma among MMc positive subjects compared to MMc negative subjects (odds ratio [OR] 0.38, 95% CI 0.19, 0.79; P=0.029). Neither maternal asthma nor sex of the child was a significant predictor of MMc in the child (P = 0.81 and 0.15, respectively).
Our results suggest for the first time that MMc may protect against the development of asthma.
Microchimerism; maternal; asthma
Oral corticosteroids (OCSs) are recommended for severe wheezing episodes in children. However, limited evidence supports this intervention in preschool children with outpatient wheezing illnesses.
We sought to investigate whether OCSs reduce symptom scores during acute lower respiratory tract illnesses (LRTIs) in preschool children with recurrent wheeze
We performed post hoc and replication analyses in 2 outpatient cohorts of children aged 1 to 5 years with episodic wheezing participating in clinical trials. We compared symptom scores during LRTIs that were or were not treated with OCSs, adjusting for differences in disease and episode severity covariates.We stratified episodes by severity by using a propensity model. The primary outcome was the area under the curve (AUC) of total symptom scores among the more severe episodes.
Two hundred fifteen participants from the Acute Intervention Management Strategies trial experienced 798 acute LRTIs, 112 of which were defined as severe based on propensity scores. The AUCs of total symptom scores did not differ between the episodes that were (n = 70) and were not (n = 42) treated with OCSs (P = .46) nor was there an OCS treatment effect on individual symptom scores. Similar analyses of the Maintenance Versus Intermittent Inhaled Corticosteroids in Wheezing Toddlers trial, involving 278 participants with 133 severe LRTIs, confirmed the above findings (P =.46 for AUC of total symptoms score comparison).
In 2 separate cohorts of preschool children with episodic wheezing, OCS treatment during clinically significant LRTIs did not reduce symptom severity during acute LRTIs, despite asthma controller medication use during most episodes. These findings need to be confirmed in a prospective randomized controlled trial.
Oral corticosteroids; episodic wheezing; preschool children
The association of early onset wheezing with common viral and bacterial infections has raised significant interest in the role of infections in childhood asthma inception. This article serves to review these relationships among infections, host factors, and asthma inception in childhood.
inception; asthma; infection; wheezing; virus; childhood; genetics
Full-length or nearly full-length RNA genome sequences for 98 rhinovirus (RV) A isolates (from the Enterovirus genus of the Picornaviridae family), representing 43 different genotypes, were resolved as part of ongoing studies to define RV genetic diversity and its potential link to respiratory disease.
Nearly full-length RNA genome sequences for 39 rhinovirus B isolates (RV-B), representing 13 different genotypes, were resolved as part of ongoing studies at the University of Wisconsin that attempt to link rhinovirus (RV) diversity and respiratory disease in infants.
Human rhinovirus (RV) isolates from the RV-C species are recently discovered infectious agents that are closely linked to asthma and wheezing etiologies in infants. Clinical study samples collected at the University of Wisconsin–Madison describe 41 nearly complete genome sequences representing 21 RV-C genotypes.
Prediction of subsequent school-age asthma during the preschool years has proven challenging.
To confirm in a post hoc analysis the predictive ability of the modified Asthma Predictive Index (mAPI) in a high-risk cohort and a theoretical unselected population. We also tested a potential mAPI modification with a 2-wheezing episode requirement (m2API) in the same populations.
Subjects (n = 289) with a family history of allergy and/or asthma were used to predict asthma at age 6, 8, and 11 years with the use of characteristics collected during the first 3 years of life. The mAPI and the m2API were tested for predictive value.
For the mAPI and m2API, school-age asthma prediction improved from 1 to 3 years of age. The mAPI had high predictive value after a positive test (positive likelihood ratio ranging from 4.9 to 55) for asthma development at years 6, 8, and 11. Lowering the number of wheezing episodes to 2 (m2API) lowered the predictive value after a positive test (positive likelihood ratio ranging from 1.91 to 13.1) without meaningfully improving the predictive value of a negative test. Posttest probabilities for a positive mAPI reached 72% and 90% in unselected and high-risk populations, respectively.
In a high-risk cohort, a positive mAPI greatly increased future asthma probability (eg, 30% pretest probability to 90% posttest probability) and is a preferred predictive test to the m2API. With its more favorable positive posttest probability, the mAPI can aid clinical decision making in assessing future asthma risk for preschool-age children.
Asthma; Wheezing; Children; Asthma predictive index; Modified asthma predictive index
Magnetic resonance imaging (MRI) with 3He does not require ionizing radiation and has been shown to detect regional abnormalities in lung ventilation and structure in adult asthma, but the method has not been extended to childhood asthma. Measurements of regional lung ventilation and microstructure in childhood asthma could advance our understanding of disease mechanisms.
To determine whether 3He MRI in children can identify abnormalities related to diagnosis of asthma or prior history of respiratory illness.
Forty-four children aged 9-10 years were recruited from a birth cohort at increased risk of developing asthma and allergic diseases. For each subject a time-resolved three-dimensional (3D) image series and a 3D diffusion-weighted image were acquired in separate breathing maneuvers. The number and size of ventilation defects were scored, and regional maps and statistics of average 3He diffusion length were calculated.
Children with mild to moderate asthma had lower average diffusion length,
Xrms¯ (p=0.004), increased regional standard deviation of diffusion length (p=0.03), and higher defect scores (p=0.03) than those without asthma. Children with histories of wheezing illness with rhinovirus infection prior to the third birthday had lower
Xrms¯ (p=0.01) and higher defect score (p=0.05).
MRI with 3He detected more and larger regions of ventilation defect and a greater degree of restricted gas diffusion in children with asthma compared to those without asthma. These measures are consistent with regional obstruction and smaller and more regionally variable dimensions of the peripheral airways and alveolar spaces.
asthma; pediatric; hyperpolarized MRI; apparent diffusion coefficient
Rationale: The function of the P2X7 nucleotide receptor protects against exacerbation in people with mild-intermittent asthma during viral illnesses, but the impact of disease severity and maintenance therapy has not been studied.
Objectives: To evaluate the association between P2X7, asthma exacerbations, and incomplete symptom control in a more diverse population.
Methods: A matched P2RX7 genetic case-control was performed with samples from Asthma Clinical Research Network trial participants enrolled before July 2006, and P2X7 pore activity was determined in whole blood samples as an ancillary study to two trials completed subsequently.
Measurements and Main Results: A total of 187 exacerbations were studied in 742 subjects, and the change in asthma symptom burden was studied in an additional 110 subjects during a trial of inhaled corticosteroids (ICS) dose optimization. African American carriers of the minor G allele of the rs2230911 loss-of-function single nucleotide polymorphism were more likely to have a history of prednisone use in the previous 12 months, with adjustment for ICS and long-acting β2-agonists use (odds ratio, 2.7; 95% confidence interval, 1.2–6.2; P = 0.018). Despite medium-dose ICS, attenuated pore function predicted earlier exacerbations in incompletely controlled patients with moderate asthma (hazard ratio, 3.2; confidence interval, 1.1–9.3; P = 0.033). After establishing control with low-dose ICS in patients with mild asthma, those with attenuated pore function had more asthma symptoms, rescue albuterol use, and FEV1 reversal (P < 0.001, 0.03, and 0.03, respectively) during the ICS adjustment phase.
Conclusions: P2X7 pore function protects against exacerbations of asthma and loss of control, independent of baseline severity and the maintenance therapy.
asthma; P2X7; exacerbation; Asthma Clinical Research Network; corticosteroids
Genome-wide association studies of asthma have implicated many genetic risk factors, with
well-replicated associations at approximately 10 loci that account for only a small proportion of
the genetic risk.
We aimed to identify additional asthma risk loci by performing an extensive replication
study of the results from the EVE Consortium meta-analysis.
We selected 3186 SNPs for replication based on the p-values from the EVE Consortium
meta-analysis. These SNPs were genotyped in ethnically diverse replication samples from nine
different studies, totaling to 7202 cases, 6426 controls, and 507 case-parent trios. Association
analyses were conducted within each participating study and the resulting test statistics were
combined in a meta-analysis.
Two novel associations were replicated in European Americans: rs1061477 in the
KLK3 gene on chromosome 19 (combined OR = 1.18; 95% CI 1.10 – 1.25)
and rs9570077 (combined OR =1.20 95% CI 1.12–1.29) on chromosome 13q21. We could not
replicate any additional associations in the African American or Latino individuals.
This extended replication study identified two additional asthma risk loci in populations
of European descent. The absence of additional loci for African Americans and Latino individuals
highlights the difficulty in replicating associations in admixed populations.
Asthma; genetic risk factors; meta-analysis; KLK3
Background. The risk of developing childhood asthma
has been linked to the severity and etiology of viral respiratory illnesses in early
childhood. Since inner-city infants have unique environmental exposures, we hypothesized
that patterns of respiratory viral infections would also be distinct.
Methods. We compared the viral etiology of respiratory
illnesses in 2 groups: a cohort of 515 infants from 4 inner-city areas and a cohort of 285
infants from mainly suburban Madison, Wisconsin. Nasal secretions were sampled during
periods of respiratory illness and at 1 year of age and were analyzed for viral pathogens
by multiplex polymerase chain reaction.
Results. Overall, inner-city infants had lower rates
of viral detection. Considering specific viruses, sick urban infants had lower rates of
detectable rhinovirus or respiratory syncytial virus infection and higher rates of
adenovirus infection. Every urban site had a higher proportion of adenovirus-positive
samples associated with illnesses (10%–21%), compared with Madison
Conclusions. These findings provide evidence that
inner-city babies have different patterns of viral respiratory illnesses than babies who
grow up in a more suburban location. These findings raise important questions about the
etiology of virus-negative illnesses in urban infants and the possibility of long-term
consequences of early life infections with adenovirus in this population.
Rationale: Human rhinoviruses (HRVs) consist of approximately 160 types that cause a wide range of clinical outcomes, including asymptomatic infections, common colds, and severe lower respiratory illnesses.
Objectives: To identify factors that influence the severity of HRV illnesses.
Methods: HRV species and types were determined in 1,445 nasal lavages that were prospectively collected from 209 infants participating in a birth cohort who had at least one HRV infection. Questionnaires were used during each illness to identify moderate to severe illnesses (MSI).
Measurements and Main Results: Altogether, 670 HRV infections were identified, and 519 of them were solitary infections (only one HRV type). These 519 viruses belonged to 93 different types of three species: 49 A, 9 B, and 35 C types. HRV-A (odds ratio, 8.2) and HRV-C (odds ratio, 7.6) were more likely to cause MSI compared with HRV-B. In addition, HRV infections were 5- to 10-fold more likely to cause MSI in the winter months (P < 0.0001) compared with summer, in contrast to peak seasonal prevalence in spring and fall. When significant differences in host susceptibility to MSI (P = 0.004) were considered, strain-specific rates of HRV MSI ranged from less than 1% to more than 20%.
Conclusions: Factors related to HRV species and type, season, and host susceptibility determine the risk of more severe HRV illness in infancy. These findings suggest that anti-HRV strategies should focus on HRV-A and -C species and identify the need for additional studies to determine mechanisms for seasonal increases of HRV severity, independent of viral prevalence, in cold weather months.
rhinovirus; severe illness; species; type; seasonality
Asthma is a heterogenous disorder that is characterized by variable airflow obstruction, airway inflammation and hyperresponsiveness, and reversibility either spontaneously or as a result of treatment. Multiple etiologies no doubt exist for both its inception and symptom exacerbation once the disease is established. Factors underlying inception can range from viral respiratory tract infections in infancy(1,2) to occupational exposures in adults.(3) Factors underlying asthma exacerbations include allergen exposure in sensitized individuals, viral infections, exercise, irritants, ingestion of nonsteroidal anti-inflammatory agents, among others. Exacerbating factors may include one or all of these exposures, and vary both among and within patients. Asthma treatment is determined to a large extent following an initial assessment of severity and subsequent establishment of control, both of which can be variable over time and assessed in two domains: impairment (current) and risk (long term consequences).(4) Unfortunately, despite the availability of effective therapies, suboptimal asthma control exists in many patients on a world-wide basis.(5) The future development of novel therapies and treatment paradigms should address these disparities.
Asthma; Respiratory syncytial virus; Rhinovirus; Allergen; Prevention; Exacerbation; Inception; Treatment
Both genetic variation at the 17q21 locus and virus-induced respiratory wheezing illnesses are associated with the development of asthma. Our aim was to determine the effects of these two factors on the risk of asthma in the Childhood Origins of Asthma (COAST) and the Copenhagen Prospective Study on Asthma in Childhood (COPSAC) birth cohorts.
We tested genotypes at the 17q21 locus for associations with asthma and with human rhinovirus (HRV) and respiratory syncytial virus (RSV) wheezing illnesses and tested for interactions between 17q21 genotypes and HRV and RSV wheezing illnesses with respect to the risk of asthma. Finally, we examined genotype-specific expression of 17q21 genes in unstimulated and HRV-stimulated peripheral-blood mononuclear cells (PBMCs).
The 17q21 variants were associated with HRV wheezing illnesses in early life, but not with RSV wheezing illnesses. The associations of 17q21 variants with asthma were restricted to children who had had HRV wheezing illnesses, resulting in a significant interaction effect with respect to the risk of asthma. Moreover, the expression levels of ORMDL3 and of GSDMB were significantly increased in HRV-stimulated PBMCs, as compared with unstimulated PBMCs. The expression of these genes was associated with 17q21 variants in both conditions, although the increase with exposure to HRV was not genotype-specific.
Variants at the 17q21 locus were associated with asthma in children who had had HRV wheezing illnesses and with expression of two genes at this locus. The expression levels of both genes increased in response to HRV stimulation, although the relative increase was not associated with the 17q21 genotypes. (Funded by the National Institutes of Health.)