Effect of 17q21 variants and smoking exposure in early-onset asthma

Inclusion of gene-gene and gene-environment interactions unlikely to dramatically improve risk prediction for complex diseases

Genome-wide association studies have identified hundreds of common genetic variants associated with the risk of multifactorial diseases. However, their impact on discrimination and risk prediction is limited. It has been suggested that the identification of gene-gene (G-G) and gene-environment (G-E) interactions would improve disease prediction and facilitate prevention. We conducted a simulation study to explore the potential improvement in discrimination if G-G and G-E interactions exist and are known. We used three diseases (breast cancer, type 2 diabetes, and rheumatoid arthritis) as motivating examples. We show that the inclusion of G-G and G-E interaction effects in risk-prediction models is unlikely to dramatically improve the discrimination ability of these models.

Interaction of a 17q12 variant with both fetal and infant smoke exposure in the development of childhood asthma-like symptoms

BACKGROUND

Gene variants on chromosome 17q12-21 are associated with an increased risk of childhood-onset asthma, a risk known to be modified by environmental tobacco smoke (ETS).

OBJECTIVES

To assess whether the association of rs2305480 on chromosome 17q12 in the GSDML gene with asthma-like symptoms in the first 4 years of life is modified by smoke exposure during fetal and early postnatal life.

METHODS

We used data from two independent prospective cohort studies from fetal life onwards in the Netherlands. We genotyped rs2305480 and assessed maternal smoking during pregnancy and ETS exposure at the age of 2. Asthma-like symptoms, defined as any reported wheezing, shortness of breath or dry nocturnal cough, were reported by parents when the children were 1, 2, 3, and 4 years. Analyses were based on a total group of 4461 Caucasian children.

RESULTS

The G risk-allele of rs2305480 was associated with asthma-like symptoms [overall odds ratio 1.17 (1.11, 1.24), 2.66E-9]. The effect of rs2305480 on asthma-like symptoms was stronger among children who were exposed to smoke during fetal life (P-interaction = 0.04). Smoke exposure in early postnatal life was also associated with an increased effect of the 17q12 single nucleotide polymorphism (SNP) on asthma-like symptoms (P-interaction = 5.06E-4). These associations were consistent in both cohorts.

CONCLUSION

A 17q12 variant, rs2305480, was associated with asthma-like symptoms in preschool children, and this association was modified by smoke exposure already during fetal life, and in infancy. Further investigation regarding SNPs in linkage disequilibrium with rs2305480 in relation to pathophysiological pathways is needed.

Frontiers in occupational and environmental lung disease research

Two central challenges in the field of occupational and environmental epidemiology include accurately measuring biologic responses to exposure and preventing subsequent disease. As exposure-related lung diseases continue to be identified, advances in exposure biology have introduced toxicogenomic approaches that detect biomarkers of exposure at the gene, protein, and metabolite levels. Moreover, genetic epidemiology research has focused more recently on common, low-penetrant (ie, low-relative-risk) genetic variants that may interact with commonly encountered exposures. A number of such gene by environment interactions have been identified for airways and interstitial lung diseases, with the goal of preventing disease among susceptible populations that may not otherwise have been identified. Exhaled breath condensate analysis has provided another noninvasive means of assessing toxicant exposures and systemic effects. As these technologies become more refined, clinicians and public health practitioners will need to appreciate the social implications of the individual- and population-level risks conferred by certain genetic polymorphisms or by biomarker evidence of exposure. At present, the primary approach to occupational and environmental lung disease prevention remains elimination or reduction of known hazardous exposures and requires continued application of local and international resources toward exposure control.

17q12-21 variants are associated with asthma and interact with active smoking in an adult population from the United Kingdom

BACKGROUND

Although an association between 17q12-21 and asthma has been replicated across different populations, some inconsistencies have been found between different studies.

OBJECTIVE

We investigated the association between genetic variation in this region with asthma, lung function, airway inflammation, hyperresponsiveness (AHR), and atopy in a case-control study of United Kingdom adults. The interaction between genotype and smoking was also evaluated.

METHODS

Study subjects (n = 983) were carefully phenotyped using questionnaires, measurement of lung function, AHR (methacholine challenge), exhaled nitric oxide (eNO), and assessment of atopic status. Blood/saliva/buccal swabs were collected, and 47 single nucleotide polymorphisms (SNPs) in 17q12-21 were genotyped using MALDI-TOF (Matrix-assisted LASER desorption/ionisation-time of flight) mass spectrometry. We conducted a comprehensive investigation of 28 common SNPs within 6 genes of interest (IKZF3, ZPBP2, ORMDL3, GSDMA, GSDMB, TOP2A).

RESULTS

Sixteen SNPs were significantly associated with asthma after multiple testing correction (P ≤ .01), of which 5 (rs2290400, rs8079416, rs3894194, rs7212938, and rs3859192) were strongly associated (FDR P ≤ .0002), and one was novel (IKZF3-rs1453559). For 3 of these SNPs, we found significant interaction with smoking and asthma (rs12936231, rs2290400, and rs8079416). Smoking modified the associations between 8 SNPs and lung function (rs9911688, rs9900538, rs1054609, rs8076131, rs3902025, rs3859192, rs11540720, and rs11650680). We observed significant interaction between 5 SNPs and smoking on AHR, and 3 interacted with smoking in relation to asthma with AHR (rs4795404, rs4795408, rs3859192).

CONCLUSION

We found 1 novel association and replicated several previously reported associations between 17q12-21 polymorphisms and asthma. We demonstrated significant interactions between active smoking and polymorphisms in 17q12-21 with asthma, lung function, and AHR in adults. Our data confirm that 17q12-21 is an important asthma susceptibility locus.

Development of biomarkers to optimize pediatric patient management: what makes children different?

Despite the frequent utilization of biomarkers in medical practice, there is a relative paucity of information regarding validated pediatric biomarkers. Frequently, biomarkers found to be efficacious in adults are extrapolated to the pediatric clinical setting without considering that the pathogenesis of many diseases is distinctly different in children, and ontogeny directly influences disease evolution and therapeutic response in children. New and innovative approaches are necessary to provide reliable, validated biomarkers that can be used to improve and advance pediatric medical care.

Fetal and infant origins of asthma

Previous studies have suggested that asthma, like other common diseases, has at least part of its origin early in life. Low birth weight has been shown to be associated with increased risks of asthma, chronic obstructive airway disease, and impaired lung function in adults, and increased risks of respiratory symptoms in early childhood. The developmental plasticity hypothesis suggests that the associations between low birth weight and diseases in later life are explained by adaptation mechanisms in fetal life and infancy in response to various adverse exposures. Various pathways leading from adverse fetal and infant exposures to growth adaptations and respiratory health outcomes have been studied, including fetal and early infant growth patterns, maternal smoking and diet, children's diet, respiratory tract infections and acetaminophen use, and genetic susceptibility. Still, the specific adverse exposures in fetal and early postnatal life leading to respiratory disease in adult life are not yet fully understood. Current studies suggest that both environmental and genetic factors in various periods of life, and their epigenetic mechanisms may underlie the complex associations of low birth weight with respiratory disease in later life. New well-designed epidemiological studies are needed to identify the specific underlying mechanisms. This review is focused on specific adverse fetal and infant growth patterns and exposures, genetic susceptibility, possible respiratory adaptations and perspectives for new studies.

Genetic variants on 17q21 are associated with asthma in a Han Chinese population

A genome-wide study has shown an association between SNPs located on 17q21 and asthma. Such associations have been identified in several populations, but little is known about the Han Chinese population. We conducted a case-control study in a Han Chinese population to investigate the relationship between SNPs located on 17q21 and asthma; 241 asthmatic patients and 212 healthy controls were recruited from the outpatient clinics of the Nanfang Hospital, Guangdong Province, southern China. We genotyped six SNPs (rs8067378, rs8069176, rs2305480, rs4795400, rs12603332, and rs11650680) located on 17q21 with the Sequenom MassARRAY iPLEX platform. For two of these six loci (rs2305480 and rs8067378), there was evidence of association with asthma, and there was a weak association of asthma with rs8069176. We confirm that genetic variants on 17q21 are associated with asthma in the Han Chinese population.

The investigation of asthma phenotypes

PURPOSE OF REVIEW

Asthma is a heterogeneous disease constituted by overlapping separate syndromes. This review discusses recent published data relevant to asthma and severe asthma classification, resting either on the 'candidate' approach based on criteria chosen by experts or on the 'exploratory' approach based on unsupervised statistical methods.

RECENT FINDINGS

Following the 'candidate' approach, groups of experts recently reviewed the classification of severe asthma to be applicable in low-income, milddle-income, and high-income countries and provided a systematic algorithm to diagnose severe refractory asthma. The concept of asthma endotypes involving different biological mechanisms has recently being proposed. Results from the 'exploratory' approach support the clinical heterogeneity in severe asthma and the need for new approaches for the classification of asthma severity. The novel childhood and adult asthma phenotypes recently identified using the exploratory approach were supported by first evidence of validity (replication in independent studies, assessment of their discriminative properties, and effect on clinical prognosis).

SUMMARY

Research on asthma phenotypes has increased exponentially in the last year. The main focus has been on severe asthma, likely due to its clinical and socioeconomic burden. Interestingly, many of the phenotypes identified are stable across populations and methodological approaches. Further analyses on the asthma phenotypes are needed to address their stability over time and their relevance from clinical and etiological perspectives.

Relevance and implication of genetic determinants to asthma pathophysiology

PURPOSE OF REVIEW

The number of single nucleotide polymorphisms (SNPs) found to be associated with asthma and related phenotypes outnumbers those with functional impacts. In this review we briefly described some of the approaches used to investigate functionality of SNPs, and summarized recent findings related to the characterization of functional SNPs in asthma.

RECENT FINDINGS

For disease-associated SNPs residing in the promoter or 3' untranslated regions, differential protein binding affinity between the major and minor alleles is often the first logical area of investigation. In this review, we described SNPs associated with asthma or related phenotypes in five genes which in the past 12 months have new data implicating potential mechanisms in asthma development.

SUMMARY

Variability in treatment responses poses a great challenge in asthma management. It is established that the genetic makeup of individuals plays a role in asthma development, yet the mechanisms remain unclear. Investigations on the functional impacts of disease-associated SNPs will help us gain insights into potential disease mechanisms, and ultimately lead to effective therapies for those who suffer from asthma.

Human polymorphisms as clinical predictors in leprosy

Genetic and serum markers in human host can predict leprosy susceptibility per se as well as be useful in classification and/or prediction of clinical variants and immunological responses in leprosy. Adequate and timely assessment of potential risks associated with these 38 host leprosy genes could diminish epidemiological burden and improve life quality of patients with this still prevalent mycobacterial disease.

Association of genetic variants in chromosome 17q21 and adult-onset asthma in a Chinese Han population

BACKGROUND

Genome-wide association studies of asthma have identified a novel region containing ORMDL3 at chromosome 17q21 that is strongly associated with childhood-onset asthma and significantly linked to ORMDL3 transcript abundance. These results have been successfully replicated in childhood-onset asthma cohorts in several ethnic groups. In this study, we aimed to evaluate the association of polymorphisms in ORMDL3, GSDMB, ZPBP2 and IKZF3 and adult-onset asthma in a Chinese Han population.

METHODS

We genotyped 5 single nucleotide polymorphisms (SNPs) at chromosome 17q21 in 1,366 Han Chinese people comprising 710 patients with adult-onset asthma and 656 healthy controls. We compared the 2 groups in terms of allele and haplotype frequencies. Transcript levels were measured in leukocytes from 61 asthma patients by quantitative real-time PCR.

RESULTS

We found the 5 SNPs significantly associated with asthma (P<0.05), of which 2, rs11557467 and rs9303277, were strongly associated (P<0.001). Subjects carrying the G allele of rs11557467 or the C allele of rs9303277 showed increased risk of asthma (odds ratio [OR] 1.27, 95% confidence interval 1.07-1.51, P = 0.006, and OR 1.27, 1.07-1.49, P = 0.005, respectively), even after adjusting for age and sex. The risk of asthma was lower for carriers of the haplotype CTGTT (OR 0.81, 0.67-0.97, P = 0.02). The risk allele for each SNP was associated with increased expression of ORMDL3 and GSDMB in leukocytes (all p<0.05).

CONCLUSIONS

Our replication study suggests that variants in 17q21 are significantly associated with risk of adult-onset asthma and gene expression in a Chinese Han population.

Allergic asthma: influence of genetic and environmental factors

Allergic asthma is a chronic airway inflammatory disease in which exposure to allergens causes intermittent attacks of breathlessness, airway hyper-reactivity, wheezing, and coughing. Allergic asthma has been called a "syndrome" resulting from a complex interplay between genetic and environmental factors. Worldwide, >300 million individuals are affected by this disease, and in the United States alone, it is estimated that >35 million people, mostly children, suffer from asthma. Although animal models, linkage analyses, and genome-wide association studies have identified numerous candidate genes, a solid definition of allergic asthma has not yet emerged; however, such studies have contributed to our understanding of the multiple pathways to this syndrome. In contrast with animal models, in which T-helper 2 (T(H)2) cell response is the dominant feature, in human asthma, an initial exposure to allergen results in T(H)2 cell-dependent stimulation of the immune response that mediates the production of IgE and cytokines. Re-exposure to allergen then activates mast cells, which release mediators such as histamines and leukotrienes that recruit other cells, including T(H)2 cells, which mediate the inflammatory response in the lungs. In this minireview, we discuss the current understanding of how associated genetic and environmental factors increase the complexity of allergic asthma and the challenges allergic asthma poses for the development of novel approaches to effective treatment and prevention.

Genetics of complex airway disease

The past 3 years have seen highly significant genetic effects identified for a wide variety of common complex diseases, including the airway disorders of asthma and chronic obstructive pulmonary disease. It appears that only a portion of the genetically mediated susceptibility to complex diseases has been identified, and there is much left to be discovered. This review briefly describes the results of the genome-wide association studies of asthma and gives an overview of the parallel and increasingly large-scale studies that are taking place with chronic obstructive pulmonary disease. The future impact is discussed of technological advances that allow increasingly large-scale gene expression studies, next-generation sequencing, and genome-wide testing for epigenetic effects. The use of genetic technology to examine the airway microbiota that interact with the mucosa in health and disease is described.

Genome-wide association studies of asthma

Bronchial asthma is a common inflammatory disease caused by a combination of genetic and environmental factors. To discover the genes and cellular pathways underlying asthma, a large number of genetic studies have been conducted. Genome-wide association studies (GWAS), which comprehensively assess genes related to multifactorial diseases and drug reactivity, have enhanced understanding of human diseases. From 2007, GWAS of susceptibility to asthma in Caucasian, Mexican, and African-ancestry populations have been conducted and several susceptible loci were identified. Recently, much larger consortium-based GWAS analyses of collaborative samples with adequate statistical power were performed, and the implicated genes suggested a role for communication of epithelial damage to the adaptive immune system and activation of airway inflammation. Furthermore, GWAS identified candidate loci associated with natural variations in lung function, blood eosinophilia and eosinophilic esophagitis, which is inflammation of the esophagus with abnormal infiltration of eosinophils in an allergic reaction. Comparing GWAS in asthma and these clinical phenotypes might help to clarify the mechanisms underlying asthma. Pharmacogenomics analyses using GWAS regarding genetic factors related to the effectiveness of inhaled corticosteroid (ICS) therapy and inhaled beta(2)- adrenergic agonists are ongoing now. Although a more complete collection of associated genes and pathways is needed, biologic insights revealed by GWAS provide valuable insights into the pathophysiology of asthma and contribute to the development of better treatment and preventive strategies.

Steroid responsiveness and wheezing phenotypes

Oral corticosteroids are the cornerstone of management of acute moderate or severe asthma whilst preventive inhaled corticosteroids are the mainstay of the preventive management of children with asthma. Yet, variation in the magnitude of response to corticosteroids has been observed. There is increasing evidence that preschool-aged children with viral-induced asthma may display a certain degree of corticosteroid resistance, requiring higher doses of corticosteroids to overcome it. The identification of determinants of responsiveness is complicated by design issues, including heterogeneous populations of children with asthma and bronchiolitis or of children with viral-induced and multi-trigger asthma phenotypes in published trials. Potential key determinants of responsiveness may include age, trigger, phenotype, tobacco smoke exposure and genotype. The mechanistic pathway for corticoresistance may originate from a gene-environment interaction, leading to non-eosinophilic airway inflammation. The clinician should carefully confirm the diagnosis of asthma and ascertain the phenotype to select appropriate phenotype-specific therapy.

Asthma phenotypes in adults and clinical implications

It is becoming increasingly recognized that asthma is a heterogeneous disease, whether based on clinical factors, including the patient's age at diagnosis, symptom spectrum and treatment response, triggering factors, or the level and type of inflammation. Attempts to analyze the importance of these characteristics to the clinical presentation of asthma have led to the appreciation of numerous separate and overlapping asthma phenotypes. However, these approaches are 'biased' and based on the clinician/scientist's own experience. Recently, unbiased approaches have also been attempted using both molecular and statistical tools. Early results from these approaches have supported and expanded on the clinician's concepts. However, until specific biologic markers are identified for any of these proposed phenotypes, the definitive nature of any phenotype will remain speculative.

Relationship between the 17q21 locus and adult asthma in a Czech population

Several whole-genome association studies have shown a significant link between childhood asthma and the 17q12 chromosome region. We selected tagging single nucleotide polymorphisms (SNPs) in the ORMDL3 gene (17q12) to investigate gene variability in relation to adult allergic asthma and asthma/atopy traits in a Czech Caucasian population of adults. We conducted a case-control association study comprising 668 unrelated subjects (337 asthmatic and 331 control subjects). Four selected SNPs (rs17608925, rs12603332, rs8076131, and rs3169572) were genotyped using the TaqMan SNP Genotyping Assays. The single locus analysis showed only a borderline association between rs3169572 variant and asthma (p = 0.030, p(corr) > 0.05). However, seven different haplotypes were identified; among them, the TTAA haplotype was marginally associated with asthma (p = 0.045, p(corr) > 0.05) and TCAG haplotype was significantly associated with asthma in males (p = 0.009, p(corr) < 0.05, odds ratio = 1.48, 95% confidence interval = 1.10-2.00). In addition, associations between the ORMDL3 genotypes and the total IgE level (p = 0.05, p(corr) > 0.05) and hypersensitivity to the pollen (p = 0.007, p(corr) < 0.05) were established. However, no relationship between ORMDL3 SNPs and the pulmonary functions was found (p > 0.05). These findings suggest that the genetic variability in the 17q21 region may be one of the risk factors also for adult asthma, especially in male individuals.

Meta-analysis of genome-wide association studies of asthma in ethnically diverse North American populations

Asthma is a common disease with a complex risk architecture including both genetic and environmental factors. We performed a meta-analysis of North American genome-wide association studies of asthma in 5,416 individuals with asthma (cases) including individuals of European American, African American or African Caribbean, and Latino ancestry, with replication in an additional 12,649 individuals from the same ethnic groups. We identified five susceptibility loci. Four were at previously reported loci on 17q21, near IL1RL1, TSLP and IL33, but we report for the first time, to our knowledge, that these loci are associated with asthma risk in three ethnic groups. In addition, we identified a new asthma susceptibility locus at PYHIN1, with the association being specific to individuals of African descent (P = 3.9 × 10(-9)). These results suggest that some asthma susceptibility loci are robust to differences in ancestry when sufficiently large samples sizes are investigated, and that ancestry-specific associations also contribute to the complex genetic architecture of asthma.

Effects of a 17q21 chromosome gene variant, tobacco smoke and furred pets on infant wheeze

The first common genetic factor identified for pediatric asthma by genome-wide association is the chromosome 17q21 locus, harbouring the ORMDL3 gene. ORMDL3 is involved in facilitation of endoplasmic reticulum-mediated inflammatory responses, believed to underlie its asthma association. We investigated associations between the rs7216389 polymorphism in the 17q21 locus affecting ORMDL3 expression and the risk for recurrent wheeze and interactions with exposure to tobacco smoke and furred pets during pregnancy and infancy using a birth cohort of 101,042 infants. Rs7216389 was significantly associated with recurrent wheeze risk among 18-month-old infants. There was a 1.35-fold higher risk of recurrent wheeze among homozygous variant allele carriers compared with homozygous wild-type allele carriers. There was significant interaction between rs7216389 and domestic furred pets, with a positive association between pets and wheeze among homozygous wild-type carriers and a negative association among homozygous variant allele carriers. There was no interaction between rs7216389 and tobacco smoke exposure.

Genetics of complex respiratory diseases: implications for pathophysiology and pharmacology studies

There has been a huge influx of data on the genetics and genomics of respiratory diseases in the last few years. Powered by large sample sizes from collaborations worldwide, recent genome-wide association studies have convincingly implicated variants in different regions in the genome for association with complex respiratory traits. These new associations have the potential to offer invaluable insight into the pathophysiology of the normal and diseased respiratory system. The functional mechanisms underlying effects of both identified and novel variants will be the focus of research over the next few years. The identification of these mechanisms will not only increase our understanding of disease but may allow the development of new therapies to alleviate respiratory conditions. The implications of these approaches for studies of asthma and Chronic Obstructive Pulmonary Disease are covered in this review.

The lung: the natural boundary between nature and nurture

Common lung diseases such as asthma, COPD, and pulmonary fibrosis cause significant morbidity and mortality in the U.S. and worldwide. Research investigating the mechanisms of disease etiology has clearly indicated that genetic attributes and environmental exposures each play important roles in the development of these diseases. Emerging evidence underscores the importance of the interplay between genetic predisposition and environmental factors in fully understanding the development of lung disease. Herein we discuss recent advances in knowledge and technology surrounding the role of genetics, the environment, and gene-environment interactions in these common lung diseases.

Polymorphisms in GSDMA and GSDMB are associated with asthma susceptibility, atopy and BHR

The gasdermin A (GSDMA) and gasdermin B (GSDMB) genes are located at 17q21.2. The GSDM family genes have been studied in the gastrointestinal tract but recent reports suggest that GSDMB is associated with childhood asthma in several populations. We investigated the association of the GSDMA and GSDMB variants with asthma in Korean children, and to assess the effect of these variants on intermediate phenotypes of asthma. Asthmatic (n = 778) and normal (n = 522) children were enrolled and genotypes were determined using PCR-RFLP. Asthma susceptibility was associated with GG of the GSDMA (rs7212938) and TT of GSDMB (rs7216389). And a combination of risk alleles of two polymorphisms was associated with asthma susceptibility and a frequency of those was higher in asthmatic children with increased levels of total IgE (aOR 1.77, 95% CI 1.15-2.72) and BHR (aOR 1.54, 95% CI 0.99-2.40) compared to normal. Also, we observed a significant association between haplotype of two polymorphisms and asthma susceptibility. The region including the GSDMA and GSDMB polymorphisms may be associated with asthma susceptibility and intermediate phenotypes of asthma, such as elevated IgE and BHR, in Korean children with asthma. These results strongly support an important role for the GSDMA and GSDMB in the development of childhood asthma.

The genetics of asthma and allergic disease: a 21st century perspective

Asthma and allergy are common conditions with complex etiologies involving both genetic and environmental contributions. Recent genome-wide association studies (GWAS) and meta-analyses of GWAS have begun to shed light on both common and distinct pathways that contribute to asthma and allergic diseases. Associations with variation in genes encoding the epithelial cell-derived cytokines, interleukin-33 (IL-33) and thymic stromal lymphopoietin (TSLP), and the IL1RL1 gene encoding the IL-33 receptor, ST2, highlight the central roles for innate immune response pathways that promote the activation and differentiation of T-helper 2 cells in the pathogenesis of both asthma and allergic diseases. In contrast, variation at the 17q21 asthma locus, encoding the ORMDL3 and GSDML genes, is specifically associated with risk for childhood onset asthma. These and other genetic findings are providing a list of well-validated asthma and allergy susceptibility genes that are expanding our understanding of the common and unique biological pathways that are dysregulated in these related conditions. Ongoing studies will continue to broaden our understanding of asthma and allergy and unravel the mechanisms for the development of these complex traits.

Genome Wide Association Study to predict severe asthma exacerbations in children using random forests classifiers

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

The search for genetic variants and epigenetics related to asthma

For the past two decades, a huge number of genetic studies have been conducted to identify the genetic variants responsible for asthma risk. Several types of genetic and genomic approaches, including linkage analysis, candidate gene single nucleotide polymorphism studies, and whole genome-wide association studies have been applied. In this review article, the results of these approaches are summarized, and their limitations are discussed. Additionally, perspectives for applying upcoming new epigenetic or genomic technologies, such as copy number variation, are introduced to increase our understanding of new omic approaches to asthma genetics.

Asthma-associated polymorphisms in 17q21 influence cord blood ORMDL3 and GSDMA gene expression and IL-17 secretion

BACKGROUND

In a genome-wide association study, genetic variants on chromosome 17q21 were strongly associated with childhood asthma and orosomucoid 1-like 3 (ORMDL3) gene expression. Regulation of the 17q21 locus and its immunologic relevance early in life have not been well characterized.

OBJECTIVE

We investigated the relation between polymorphisms and mRNA expression of 17q21 locus genes and their influence on T-cell subsets in cord blood.

METHODS

In 200 children of our cord blood study, 17q21 polymorphisms were genotyped by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Gene expression was assessed for ORMDL3; gasdermin A (GSDMA, alias GSDM1); gasdermin B (GSDMB, alias GSDML); Ikaros family zinc finger 3 (ZNFN1A3), zona pellucida binding protein 2 (ZPBP2); and proteasome (prosome, macropain) 26S subunit, non-ATPase, 3 (PSMD3), in cord blood mononuclear cells (CBMCs) and for ORMDL3 in peripheral blood (real-time RT-PCR). Mononuclear cells were assessed before and after microbial (lipid A/peptidoglycan), phytohemagglutinin, or allergen (Der p 1) stimulation. Regulatory T-associated markers (forkhead box protein 3, glucocorticoid-induced TNF receptor, lymphocyte activation gene 3 mRNA expression) and T(h)2/T(h)1/T(h)17 cytokines were examined.

RESULTS

In CBMCs, single genetic risk variants within 17q21 were associated with increased ORMDL3 (Der p 1 stimulation; P ≤ .01) and GSDMA expression (phytohemagglutinin/Der p 1 stimulation; P ≤ .05). Children homozygous for all 4 risk alleles for 17q21 tagging single nucleotide polymorphisms showed increased expression for ORMDL3 (Der p 1; P = .002) and GSDMA (phytohemagglutinin; P = .0009/Der p 1; P = .004). CBMC ORMDL3 expression was lower compared with PBMCs (P ≤ .0003) and increased in both CBMC and PBMC after stimulation (phytohemagglutinin/lipid A/peptidoglycan/Der p 1; P ≤ .006 and phytohemagglutinin/peptidoglycan; P < .05, respectively). No correlation between 17q21 polymorphisms and regulatory T/T(h)2/T(h)1 lineages was detectable. However, 17q21 risk allele carriers showed significantly increased IL-17 secretion (unstimulated, phytohemagglutinin-stimulated).

CONCLUSION

Our results suggest an association of 17q21 polymorphisms with ORMDL3, GSDMA expression, and IL-17 secretion early in life. These observations may imply a functional role of the 17q21 locus affecting T-cell development during immune maturation.

Genetic studies of the etiology of asthma

Asthma is a heterogeneous disease for which a strong genetic basis is firmly established. Although the generally accepted definition includes three domains of symptoms (variable airway obstruction, airway hyper-responsiveness, and airway inflammation), there is general agreement that, rather than being a single disease entity, asthma consists of related, overlapping syndromes. A considerable proportion of asthma is IgE-mediated, but the observation that not all individuals with asthma are atopic adds to the heterogeneity. Although a genetic basis for asthma is undeniable, elucidation of polymorphisms that are "causal" is greatly hampered by variability in the clinical phenotype, which is likely due to the multiple molecular mechanisms underlying the complex pathological processes involved in disease development and progression. One objective of this review is to consider progress that has been made to date in gene discovery in the field of asthma, with a focus on the evolution of molecular genetic methods that have led to the discoveries thus far, and with a particular focus on the major advances owed to the published genome-wide association studies (GWAS) on asthma to date. A second objective is to consider a Darwinian approach toward understanding the genetic underpinnings of asthma, including evidence supporting a modified Hygiene Hypothesis, which suggests that there are co-associations between asthma risk polymorphisms and polymorphisms associated with another IgE-mediated disease, schistosomiasis. The overall conclusion is that the huge research efforts and expense committed to asthma genetics have changed the perception about disease etiology in general and the functional relevance of the asthma genes identified thus far in particular.

MeDALL (Mechanisms of the Development of ALLergy): an integrated approach from phenotypes to systems medicine

The origin of the epidemic of IgE-associated (allergic) diseases is unclear. MeDALL (Mechanisms of the Development of ALLergy), an FP7 European Union project (No. 264357), aims to generate novel knowledge on the mechanisms of initiation of allergy and to propose early diagnosis, prevention, and targets for therapy. A novel phenotype definition and an integrative translational approach are needed to understand how a network of molecular and environmental factors can lead to complex allergic diseases. A novel, stepwise, large-scale, and integrative approach will be led by a network of complementary experts in allergy, epidemiology, allergen biochemistry, immunology, molecular biology, epigenetics, functional genomics, bioinformatics, computational and systems biology. The following steps are proposed: (i) Identification of 'classical' and 'novel' phenotypes in existing birth cohorts; (ii) Building discovery of the relevant mechanisms in IgE-associated allergic diseases in existing longitudinal birth cohorts and Karelian children; (iii) Validation and redefinition of classical and novel phenotypes of IgE-associated allergic diseases; and (iv) Translational integration of systems biology outcomes into health care, including societal aspects. MeDALL will lead to: (i) A better understanding of allergic phenotypes, thus expanding current knowledge of the genomic and environmental determinants of allergic diseases in an integrative way; (ii) Novel diagnostic tools for the early diagnosis of allergy, targets for the development of novel treatment modalities, and prevention of allergic diseases; (iii) Improving the health of European citizens as well as increasing the competitiveness and boosting the innovative capacity of Europe, while addressing global health issues and ethical issues.

Unraveling the complex genetic underpinnings of asthma and allergic disorders

PURPOSE OF REVIEW

Asthma and other allergic diseases are complex genetic disorders that result from interactions between multiple genes and environmental factors. In this review, we summarize findings from candidate gene analyses, discuss the recent success of genome-wide association (GWA) studies, and outline challenges facing the field.

RECENT FINDINGS

In the past year, five GWA studies have been reported for asthma, one for atopic dermatitis, and four for intermediate phenotypes using quantitative trait loci. These results have in general been more robust to replication than prior candidate gene studies, and have allowed the identification of novel loci for both asthma (i.e. 1q31, 9q21.31) and atopic dermatitis (11q13).

SUMMARY

The integration of results from recent GWA studies with careful analyses of candidate gene associations studies has confirmed the importance of immune detection and TH2-cell mediated immune responses in the pathogenesis of allergic disease, and has raised new interest in the role of epithelial barrier function and tissue-level responses. GWA studies appear to provide a robust way to identify novel gene loci contributing to disease susceptibility. Dissecting gene-gene and gene-environment interactions, and exploring the contribution of epigenetic phenomena to allergic disease susceptibility remain important challenges to understanding the complex nature of asthma and other allergic diseases.

Impact of environmental tobacco smoke on children admitted with status asthmaticus in the pediatric intensive care unit

INTRODUCTION

Environmental tobacco smoke (ETS) and allergens are risk factors in children with critical status asthmaticus. Genetic studies support that ETS-associated asthma is a special inflammatory entity, causing significant number of hospital admissions and relapses. Accordingly, the course and outcome of patients with ETS-induced status asthmaticus might also be different.

HYPOTHESIS

We hypothesized that the progression, course, and outcome of patients with ETS-induced status asthmaticus would be worse than those of patients without ETS exposure.

METHODS

Medical records of children who were admitted to the Pediatric Intensive Care Unit (PICU) with the diagnosis of asthma at the Children's Hospital of Winnipeg, Manitoba, over 10 years were audited after Institutional Review Board (IRB) approval. Two hundred thirty records were reviewed. We extracted data including demographics and analyzed the patient's deterioration defined as clinical asthma score (CAS) drift between the ED and PICU. We computed the treatment response, expressed as length of stay (LOS) in the PICU and in hospital. The risk factors were stratified as none, ETS exposure, allergies, and ETS with allergies.

RESULTS

There were 55 (25%) patients with no risk factors, 66 (30%) with ETS exposure only, 46 (21%) with allergies only, and 53 (24%) with both. There was a 25% decrease in CAS deterioration when patients were exposed to ETS (P < 0.05). For patients with or without allergies but with exposure to ETS, both the PICU and overall hospital LOS were ∼15% longer (P < 0.05) than for those not exposed to ETS. Stratifying for gender and race in multivariate analysis did not alter the results.

CONCLUSIONS

Patients with ETS-associated critical status asthmaticus deteriorate and recover slower than non-ETS-exposed patients.

Asthma in childhood reduces smoking initiation in subsequent teens among males

BACKGROUND

The association between smoking habits and asthma is complex because subjects with asthma could avoid smoking, whereas smoking could increase asthma severity or incidence.

PURPOSE

The relation between asthma in childhood (0-10 years) and smoking initiation in the second decade (11-20 years) was investigated using the database of the Italian Study on Asthma in Young Adults, performed in 1998-2000 on people aged 20-45 years.

METHODS

The cumulative incidence of smoking initiation was compared among (1) subjects not reporting asthma attacks in the first 20 years of life (n = 17,384), (2) subjects reporting asthma onset in the first decade and no disease remission by the age of 20 years (n = 305), (3) subjects reporting asthma onset in the first decade and remission in the first and second decades (n = 573).

RESULTS

Among men, the cumulative incidence of smoking onset was higher among nonasthmatics (49%) than among asthmatics (35.6%), and intermediate among asthmatics with disease remission (44.2%) (p = .001). These differences were larger in males born between 1953 and 1965, and tended to decrease in males born between 1966 and 1979: cumulative incidence of smoking onset decreased from 54.3% to 43.8% in nonasthmatics, whereas it remained stable in asthmatics (from 36.8% to 35%). Women, instead, had similar cumulative incidence of smoking initiation, irrespective of asthma onset or remission (p = .849).

CONCLUSION

Asthma in childhood reduces smoking initiation during the subsequent teenage in men, but not in women. This protective effect tends to fade when asthma remission occurs. In the last decades, smoking initiation has decreased among nonasthmatic males, but not among asthmatic males.

Mitochondrial Dysfunction and Oxidative Stress in Asthma: Implications for Mitochondria-Targeted Antioxidant Therapeutics

Asthma is a complex, inflammatory disorder characterized by airflow obstruction of variable degrees, bronchial hyper-responsiveness, and airway inflammation. Asthma is caused by environmental factors and a combination of genetic and environmental stimuli. Genetic studies have revealed that multiple loci are involved in the etiology of asthma. Recent cellular, molecular, and animal-model studies have revealed several cellular events that are involved in the progression of asthma, including: increased Th2 cytokines leading to the recruitment of inflammatory cells to the airway, and an increase in the production of reactive oxygen species and mitochondrial dysfunction in the activated inflammatory cells, leading to tissue injury in the bronchial epithelium. Further, aging and animal model studies have revealed that mitochondrial dysfunction and oxidative stress are involved and play a large role in asthma. Recent studies using experimental allergic asthmatic mouse models and peripheral cells and tissues from asthmatic humans have revealed antioxidants as promising treatments for people with asthma. This article summarizes the latest research findings on the involvement of inflammatory changes, and mitochondrial dysfunction/oxidative stress in the development and progression of asthma. This article also addresses the relationship between aging and age-related immunity in triggering asthma, the antioxidant therapeutic strategies in treating people with asthma.

Asthma and chronic obstructive pulmonary disease: common genes, common environments?

Asthma and chronic obstructive pulmonary disease (COPD) show similarities and substantial differences. The Dutch hypothesis stipulated that asthma and COPD have common genetic and environmental risk factors (allergens, infections, smoking), which ultimately lead to clinical disease depending on the timing and type of environmental exposures (Postma and Boezen, Chest 2004;126:96S-104S). Thus, a particular group of shared genetic factors may lead to asthma when combined with specific environmental factors that are met at a certain stage in life, whereas combination with other environmental factors, or similar environmental factors at a different stage in life, will lead toward COPD. Multiple genes have been found for asthma and COPD. In addition to genes unique to these diseases, some shared genetic risk factors exist. Moreover, there are both common host risk factors and environmental risk factors for asthma and COPD. Here we put forward, based on the data available, that genes that affect lung development in utero and lung growth in early childhood in interaction with environmental detrimental stimuli, such as smoking and air pollution, are contributing to asthma in childhood and the ultimate development of COPD. Additional genes and environmental factors then drive specific immunological mechanisms underlying asthma, and others may contribute to the ultimate development of specific subtypes of COPD (i.e., airway disease with mucous hypersecretion, small airway disease, and emphysema). The genetic predisposition to the derailment of certain pathways may further help to define subgroups of asthma and COPD. In the end this may lead to stratification of patients by their genetic make-up and open new therapeutic prospects.

Diagnosis of allergy and asthma in childhood

Childhood asthma is a widespread health problem because of its epidemic prevalence, as asthma affects more than 300 million people worldwide. Results from cross-sectional and cohort studies show that asthma starts in childhood in a large proportion of cases. A proper diagnosis is easier to make in adults and school-age children, as permanent changes in lung development, the strong impact of environmental factors on the airways, the immunologic maturity process, and the use of some diagnostic tools make asthma more difficult to diagnose in preschool children. This period of a child's life is an interesting challenge for pediatricians and specialists. The aim of the present review is to analyze the current knowledge regarding making an early and accurate asthma diagnosis and therefore deciding on the correct treatment to gain control over asthma symptoms and minimize health risks.

Greater severity of new onset asthma in allergic subjects who smoke: a 10-year longitudinal study

BACKGROUND

Little is known about the association between cigarette smoking and asthma severity. We assessed smoking as a determinant of disease severity and control in a cohort of clinic-referred allergic subjects who developed new onset asthma.

METHODS

Allergic rhinitis subjects with no asthma (n = 371) were followed-up for 10 years and routinely examined for asthma diagnosis. In those who developed asthma (n = 152), clinical severity and levels of asthma control were determined. Among these subjects, 74 (48.7%) were current smokers, 17 (11.2%) former smokers, and 61 (40.1%) never smokers.

RESULTS

When comparing current or past smokers to never smokers they had a higher risk of severe asthma in the univariate analysis, which became non-significant in the multivariate analysis. On the other hand, the categories of pack-years were significantly related to severe asthma in a dose response relationship in both the univariate and multivariate analysis: compared to 0 pack years, those who smoked 1-10 pack-years had an OR(95% CI) of 1.47(0.46-4.68), those who smoked 11-20 pack-years had an OR of 2.85(1.09-7.46) and those who smoked more than 20 pack-years had an OR of 5.59(1.44-21.67) to develop more severe asthma. Smokers with asthma were also more likely to have uncontrolled disease. A significant dose-response relationship was observed for pack-years and uncontrolled asthma. Compared to 0 pack years, those who smoked 1-10 pack-years had an OR of 5.51(1.73-17.54) and those who smoked more than 10 pack-years had an OR of 13.38(4.57-39.19) to have uncontrolled asthma.

CONCLUSIONS

The current findings support the hypothesis that cigarette smoking is an important predictor of asthma severity and poor asthma control.

Gene-environment interactions in human disease: nuisance or opportunity?

Many environmental risk factors for common, complex human diseases have been revealed by epidemiologic studies, but how genotypes at specific loci modulate individual responses to environmental risk factors is largely unknown. Gene-environment interactions will be missed in genome-wide association studies and could account for some of the 'missing heritability' for these diseases. In this review, we focus on asthma as a model disease for studying gene-environment interactions because of relatively large numbers of candidate gene-environment interactions with asthma risk in the literature. Identifying these interactions using genome-wide approaches poses formidable methodological problems, and elucidating molecular mechanisms for these interactions has been challenging. We suggest that studying gene-environment interactions in animal models, although more tractable, might not be sufficient to shed light on the genetic architecture of human diseases. Lastly, we propose avenues for future studies to find gene-environment interactions.

Nature, nurture and socioeconomic policy-what can we learn from molecular genetics?

Many countries use public resources to compensate individuals with genetic disorders, identified by behaviors/symptoms such as chronic diseases and disabilities. This paper draws attention to molecular genetic research which may provide a new dimension to our understanding of how socioeconomic outcomes are generated. We provide an overview of the recently emerging evidence of gene-environment interaction effects. This literature points out specific areas where policies may compensate groups of individuals carrying genetic risks, without the need to identify anyone's genetic endowments. Moreover, epigenetics studies, which concern heritable changes in gene functions that occur independently of the DNA sequence, have shown that environments may affect heritable traits across generations. It means that policies which neutralize adverse environments may also increase intergenerational mobility, given that genetic and/or environmental risk factors are more common in socially disadvantaged groups.

Interaction between early maternal smoking and variants in TNF and GSTP1 in childhood wheezing

BACKGROUND

Children exposed to tobacco smoke early in life have a higher risk of wheeze. Individual susceptibility may depend on genetic factors.

OBJECTIVE

We studied whether variations in single nucleotide polymorphisms (SNPs) in the TNF, glutathione S transferase P1 (GSTP1) and beta2-adrenoreceptor (ADRB2) genes modify the effect of early maternal smoking on the development of childhood asthma, wheeze and allergic sensitization.

METHODS

In the Swedish prospective birth cohort BAMSE (Children, Allergy, Milieu, Stockholm, Epidemiological Survey) (n=4089), data collection included questionnaires to measure tobacco smoke exposure and clinical outcomes up to age 4 and medical examinations with blood sampling for specific IgE measurements and genotyping. We defined early maternal smoking as daily smoking by the mother during pregnancy and/or postnatally. We investigated five TNF, six GSTP1 and three ADRB2 SNPs in 982 selected wheezers and non-wheezers.

RESULTS

An interaction with early maternal smoking was found for three TNF SNPs (-857C/T, Intron 1, Intron 3) with respect to early wheeze (up to 2 years of age). For example, the odds ratio (OR) for developing early wheeze related to early maternal smoking was 2.4 [95% confidence interval (CI) 1.6-3.7] in children with a wild-type CC homozygote genotype of the TNF-857 SNP, while no tobacco-related risk was seen in children carrying the rare T allele. A clear dose response was observed in children with the CC genotype, with an OR of 1.3 (95% CI 1.1-1.5) per each additional pack per week smoked by the mother during pregnancy. A suggestive interaction with early maternal smoking was also seen for three GSTP1 SNPs (Intron 5, Intron 6 and Ile105Val) with respect to transient wheeze, but not for ADRB2 and wheeze phenotypes. No effect modifications were observed for allergic sensitization.

CONCLUSION

Our results suggest that the risk of early childhood wheeze associated with early maternal smoking may be modified by TNF and GSTP1 polymorphisms.

The epidemiology of cough

Cough is a common symptom that affects a large proportion of the general population, but has been somewhat neglected in the epidemiological literature in the recent years. Various types of coughs are described based on life-long epidemiological surveys. Using published and unpublished data from three epidemiological studies (the European Community Respiratory Health survey, the French Epidemiological study on the Genetics and environment of asthma (EGEA) and the French E3N study), some specific aspects are discussed in detail. Phenotypic heterogeneity according to chronicity, or its productive nature, or its daytime or nocturnal characteristics are discussed. The association of cough with asthma and gender is described, together with its evolution over a 12-year period. The potential for genetic studies of cough is discussed.

Ordered subset analysis for case-control studies

Genetic heterogeneity, which may manifest on a population level as different frequencies of a specific disease susceptibility allele in different subsets of patients, is a common problem for candidate gene and genome-wide association studies of complex human diseases. The ordered subset analysis (OSA) was originally developed as a method to reduce genetic heterogeneity in the context of family-based linkage studies. Here, we have extended a previously proposed method (OSACC) for applying the OSA methodology to case-control datasets. We have evaluated the type I error and power of different OSACC permutation tests with an extensive simulation study. Case-control datasets were generated under two different models by which continuous clinical or environmental covariates may influence the relationship between susceptibility genotypes and disease risk. Our results demonstrate that OSACC is more powerful under some disease models than the commonly used trend test and a previously proposed joint test of main genetic and gene-environment interaction effects. An additional unique benefit of OSACC is its ability to identify a more informative subset of cases that may be subjected to more detailed molecular analysis, such as DNA sequencing of selected genomic regions to detect functional variants in linkage disequilibrium with the associated polymorphism. The OSACC-identified covariate threshold may also improve the power of an additional dataset to replicate previously reported associations that may only be detectable in a fraction of the original and replication datasets. In summary, we have demonstrated that OSACC is a useful method for improving SNP association signals in genetically heterogeneous datasets.

Genomewide association studies in allergy and the influence of ethnicity

PURPOSE OF REVIEW

Asthma and allergic diseases are common and disproportionately affect racial and ethnic minorities. Large-scale research efforts and the expense committed to multiple genomewide association studies (GWAS) have led to the identification of numerous susceptibility loci for the allergic diseases, but few successes have been reported in populations that are not of European ancestry.

RECENT FINDINGS

Of the more than two dozen GWAS for asthma and allergic disease performed to date, very few have included racial/ethnic minorities. Lessons learned from the studies conducted so far suggest that the GWAS approach must include considerations unique to the ancestral populations represented in the sample, population stratification due to admixture, and recognition that the current coverage of common variants both in the public database and on commercially available single-nucleotide polymorphism chips is inadequate to detect true genetic associations among ethnic/racial groups.

SUMMARY

Advancements in the GWAS technology for identifying genes relevant to asthma and allergic disease among under-represented ethnic and racial minorities who suffer most will facilitate the identification and confirmation of validated genetic risk factors that are both unique to minority groups as well as confirm risk factors that are generic to the population at large.

A large-scale, consortium-based genomewide association study of asthma

BACKGROUND

Susceptibility to asthma is influenced by genes and environment; implicated genes may indicate pathways for therapeutic intervention. Genetic risk factors may be useful in identifying subtypes of asthma and determining whether intermediate phenotypes, such as elevation of the total serum IgE level, are causally linked to disease.

METHODS

We carried out a genomewide association study by genotyping 10,365 persons with physician-diagnosed asthma and 16,110 unaffected persons, all of whom were matched for ancestry. We used random-effects pooled analysis to test for association in the overall study population and in subgroups of subjects with childhood-onset asthma (defined as asthma developing before 16 years of age), later-onset asthma, severe asthma, and occupational asthma.

RESULTS

We observed associations of genomewide significance between asthma and the following single-nucleotide polymorphisms: rs3771166 on chromosome 2, implicating IL1RL1/IL18R1 (P=3×10(−9)); rs9273349 on chromosome 6, implicating HLA-DQ (P=7×10(−14)); rs1342326 on chromosome 9, flanking IL33 (P=9×10(−10)); rs744910 on chromosome 15 in SMAD3 (P=4×10(−9)); and rs2284033 on chromosome 22 in IL2RB (P=1.1×10(−8)). Association with the ORMDL3/GSDMB locus on chromosome 17q21 was specific to childhood-onset disease (rs2305480, P=6×10(−23)). Only HLA-DR showed a significant genomewide association with the total serum IgE concentration, and loci strongly associated with IgE levels were not associated with asthma.

CONCLUSIONS

Asthma is genetically heterogeneous. A few common alleles are associated with disease risk at all ages. Implicated genes suggest a role for communication of epithelial damage to the adaptive immune system and activation of airway inflammation. Variants at the ORMDL3/GSDMB locus are associated only with childhood-onset disease. Elevation of total serum IgE levels has a minor role in the development of asthma. (Funded by the European Commission and others.)

Gene-environment interactions in asthma and allergy: the end of the beginning?

PURPOSE OF REVIEW

The pathogenesis of asthma and allergy typically involves not only distinct genetic and environmental factors, but also interactions between the two. Innate-immunity genes [particularly CD14, toll-like receptor (TLR)4 and TLR2, the critical mediators of responses to bacteria in the extracellular space] play a prominent role in gene-environment interactions relevant to asthma-related phenotypes because the interaction between microbial load and the innate-immune system is a critical determinant of both immune function and allergy/asthma susceptibility. This review presents recent findings illustrating the role of gene-environment interactions in asthma/allergy susceptibility.

RECENT FINDINGS

Population studies have extended our understanding of the role of CD14 and innate-immune genes in the interplay between genetic variants and the environment, highlighting the complexity of these interactions and their significant influence on susceptibility to asthma and allergy.

SUMMARY

Gene-environment interactions have become a leitmotiv in asthma and allergy genetics, especially over the last 3 years. The next challenge awaiting asthma and allergy geneticists will be to define the extent to which the search for gene-environment interactions can be successfully integrated with hypothesis-generating, genome-wide approaches aimed at the identification of genetic variants involved in the pathogenesis of complex-lung diseases.

Long-term studies of the natural history of asthma in childhood

Segmentation of children with asthma and other wheezy disorders remains the main research challenge today, as it was when described 2 centuries ago. Early childhood wheezy disorders follow different temporal trajectories, probably representing different underlying mechanisms (endophenotypes). Prospective identification of endophenotypes allowing accurate prediction of the clinical course is currently not possible. The variability of the clinical course remains an enigma and difficult to predict. Three of 4 school-aged children with asthma have outgrown disease by midadulthood. The risk of persistence increases with severity, sensitization, smoking, and female sex. Genetic risk variants might help disentangle the heterogeneity of asthma and other wheezy disorders. At early school age, children with asthma have reduced lung function. It is an important and unresolved question whether the airflow limitation associated with asthma already existed at birth or developed along with symptoms. Likewise, the association between the infant's bronchial responsiveness and development of asthma and other wheezy disorders is unclear. Neither primary prevention through manipulation of environmental factors nor secondary prevention through the use of inhaled corticosteroids can effectively halt the long-term disease progression in childhood. In conclusion, the natural history of asthma and the associated airway changes is still poorly understood, and we have not managed to translate findings from long-term studies into a deeper understanding of the underlying endophenotypes or improved disease management. We propose the need for a translational research approach based on long-term clinical studies of birth cohorts with comprehensive and objective assessments of intermediate phenotypes and environmental exposures combined with interdisciplinary basic research and a systems biology approach.