Importance of genetic factors in adolescent asthma: a population-based twin-family study

Bayesian linear mixed model with multiple random effects for family-based genetic studies

Motivation: Family-based study design is one of the popular designs used in genetic research, and the whole-genome sequencing data obtained from family-based studies offer many unique features for risk prediction studies. They can not only provide a more comprehensive view of many complex diseases, but also utilize information in the design to further improve the prediction accuracy. While promising, existing analytical methods often ignore the information embedded in the study design and overlook the predictive effects of rare variants, leading to a prediction model with sub-optimal performance. Results: We proposed a Bayesian linear mixed model for the prediction analysis of sequencing data obtained from family-based studies. Our method can not only capture predictive effects from both common and rare variants, but also easily accommodate various disease model assumptions. It uses information embedded in the study design to form surrogates, where the predictive effects from unmeasured/unknown genetic and environmental risk factors can be modelled. Through extensive simulation studies and the analysis of sequencing data obtained from the Michigan State University Twin Registry study, we have demonstrated that the proposed method outperforms commonly adopted techniques. Availability: R package is available at https://github.com/yhai943/FBLMM.

[Genetic aspects involved in asthma]

Asthma is an etiologically heterogeneous disease resulting from a complex interaction between genetic. The genetic aspects involved in asthma, which were analyzed from the perspective of the traditional model of multifactorial inheritance, were susceptibility, host factors, and environmental exposures. In the present paper, studies on their family aggregation, concordance in twins, and heritability were analized; as well as the current knowledge about candidate genes, genome wide association studies, and epigenomics contributions and other omic studies that have increased our knowledge about their pathophysiology and environmental interactions.

Multi-Omics Profiling Approach to Asthma: An Evolving Paradigm

Asthma is a complex multifactorial and heterogeneous respiratory disease. Although genetics is a strong risk factor of asthma, external and internal exposures and their interactions with genetic factors also play important roles in the pathophysiology of asthma. Over the past decades, the application of high-throughput omics approaches has emerged and been applied to the field of asthma research for screening biomarkers such as genes, transcript, proteins, and metabolites in an unbiased fashion. Leveraging large-scale studies representative of diverse population-based omics data and integrating with clinical data has led to better profiling of asthma risk. Yet, to date, no omic-driven endotypes have been translated into clinical practice and management of asthma. In this article, we provide an overview of the current status of omics studies of asthma, namely, genomics, transcriptomics, epigenomics, proteomics, exposomics, and metabolomics. The current development of the multi-omics integrations of asthma is also briefly discussed. Biomarker discovery following multi-omics profiling could be challenging but useful for better disease phenotyping and endotyping that can translate into advances in asthma management and clinical care, ultimately leading to successful precision medicine approaches.

Advances in asthma genetics

While asthma has a strong genetic component, our current ability to systematically understand and predict asthma risk remains low, despite over a hundred genetic associations. The reasons for this unfilled gap range from technical limitations of current approaches to fundamental deficiencies in the way we understand asthma. These are discussed in the context of genomic advances.

Integrated genomics analysis highlights important SNPs and genes implicated in moderate-to-severe asthma based on GWAS and eQTL datasets

Background

Severe asthma is a chronic disease contributing to disproportionate disease morbidity and mortality. From the year of 2007, many genome-wide association studies (GWAS) have documented a large number of asthma-associated genetic variants and related genes. Nevertheless, the molecular mechanism of these identified variants involved in asthma or severe asthma risk remains largely unknown.

Methods

In the current study, we systematically integrated 3 independent expression quantitative trait loci (eQTL) data (N = 1977) and a large-scale GWAS summary data of moderate-to-severe asthma (N = 30,810) by using the Sherlock Bayesian analysis to identify whether expression-related variants contribute risk to severe asthma. Furthermore, we performed various bioinformatics analyses, including pathway enrichment analysis, PPI network enrichment analysis, in silico permutation analysis, DEG analysis and co-expression analysis, to prioritize important genes associated with severe asthma.

Results

In the discovery stage, we identified 1129 significant genes associated with moderate-to-severe asthma by using the Sherlock Bayesian analysis. Two hundred twenty-eight genes were prominently replicated by using MAGMA gene-based analysis. These 228 replicated genes were enriched in 17 biological pathways including antigen processing and presentation (Corrected P = 4.30 × 10^− 6), type I diabetes mellitus (Corrected P = 7.09 × 10^− 5), and asthma (Corrected P = 1.72 × 10^− 3). With the use of a series of bioinformatics analyses, we highlighted 11 important genes such as GNGT2, TLR6, and TTC19 as authentic risk genes associated with moderate-to-severe/severe asthma. With respect to GNGT2, there were 3 eSNPs of rs17637472 (P_eQTL = 2.98 × 10^− 8 and P_GWAS = 3.40 × 10^− 8), rs11265180 (P_eQTL = 6.0 × 10^− 6 and P_GWAS = 1.99 × 10^− 3), and rs1867087 (P_eQTL = 1.0 × 10^− 4 and P_GWAS = 1.84 × 10^− 5) identified. In addition, GNGT2 is significantly expressed in severe asthma compared with mild-moderate asthma (P = 0.045), and Gngt2 shows significantly distinct expression patterns between vehicle and various glucocorticoids (Anova P = 1.55 × 10^− 6).

Conclusions

Our current study provides multiple lines of evidence to support that these 11 identified genes as important candidates implicated in the pathogenesis of severe asthma.

Vitamin D receptor polymorphisms are associated with severity of wheezing illnesses and asthma exacerbations in children

Single nucleotide polymorphisms (SNPs) of the vitamin D receptor (VDR) gene have shown linkage and association with asthma development in multiple cohort studies. However, the majority of investigations have focused on asthma phenotypes in cohorts with stable disease. We investigated the relationship between VDR SNPs and the frequency and severity of acute episodes of wheeze/asthma in a cohort of Australian children, as the ability to identify children at risk of more severe exacerbations could lead to personalized and improved genotype-specific treatment pathways. We successfully genotyped five SNPs of the VDR gene (rs2525046, rs9729, rs1544410 (BsmI), rs22239179, and rs2228570 (FokI)) in 657 children presenting to a tertiary children's hospital with acute asthma, bronchiolitis, or a wheezing illness. The relationships between VDR SNPs and exacerbation severity scores, β₂-agonist use, and frequency of respiratory exacerbations were analysed using multiple regression. The rs2525046 (FokI) CT genotype was associated with higher VDR mRNA intensity levels (p = 0.007) compared to the CC genotype. A trend towards significance (p=0.056) was identified between the rs2525046 TT genotype and higher VDR mRNA intensity levels compared to the CC genotype. Children with rs2228570 AA genotype had higher exacerbation severity scores (p=0.001) and poorer β₂-agonist treatment response (doses at 6 h: p = 0.009 and 12 h: p=0.033) compared to those with the GG genotype. Children with rs1544410 (BsmI) TT genotype had lower exacerbation severity scores (p = 0.005) compared to those with the CC genotype. Children with rs2228570 GA genotype presented to and/or were admitted to hospital more times since birth with respiratory (p = 0.011) and wheezing (p = 0.021) illnesses than children with the GG genotype. No associations were identified between rs9729, rs2525046 and r2239179 polymorphisms and acute wheezing/asthma variables. These findings suggest that genetic variants at the VDR locus may play a role in acute wheeze/asthma severity in children.

The association of nucleotide-binding oligomerization domain 2 gene polymorphisms with the risk of asthma in the Chinese Han population

BACKGROUND

Genetic background is one of the important risk factors for development of asthma. The nucleotide-binding oligomerization domain 2 (NOD2) has been involved in the pathogenesis of asthma. The purpose of this study was to explore the relationship between NOD2 gene polymorphisms and asthma susceptibility in the Chinese Han population.

METHODS

Children with asthma (n = 309) and Healthy children (n = 163) were recruited from Yancheng Third People's Hospital, Yancheng, China, between January 2016 and December 2017. The NOD2 gene polymorphisms were measured by the Snapshot SNP genotyping assays. Genotyping was performed for 4 tag SNPs of NOD2. Serum IFN-β levels were measured by ELISA.

RESULTS

The serum IFN-β levels were significantly lower in Asthmatic children than those in the controls (p < 0.001). Low levels of IFN-β may be related to the susceptibility to severe asthma. The rs3135499 C allele was associated with a significantly increased risk of asthma as compared with the rs3135499 A allele.

CONCLUSION

The rs3135499 polymorphism of NOD2 gene and IFN-β may play a role in the pathogenesis of asthma.

Severe Asthma: Have We Made Progress?

Tremendous efforts have been invested in research to (1) discover risk factors, biomarkers, and clinical characteristics; (2) understand the pathophysiology and treatment response variability in severe asthma; and (3) design new therapies. However, to combat severe asthma, many questions concerning the pathogenesis of severe asthma, including its natural history, genetic and environmental risk factors, and disease mechanisms, must be answered. In this article we highlight some of the major discoveries concerning the pathogenesis of severe asthma and its therapeutic development. We conclude that discoveries on numerous fronts of severe asthma, from disease heterogeneity, features of airway remodeling, cytokine mediators and signaling pathways underlying disease pathogenesis, disease mechanisms, potential biomarkers, to new therapeutic targets, demonstrate that progress has been made in understanding and developing more effective treatments for this difficult-to-treat disease.

Prevention of food allergy

The past few decades have witnessed an increase in the prevalence of IgE-mediated food allergy (FA). For prevention strategies to be effective, we need to understand the causative factors underpinning this rise. Genetic factors are clearly important in the development of FA, but given the dramatic increase in prevalence over a short period of human evolution, it is unlikely that FA arises through germline genetic changes alone. A plausible hypothesis is that 1 or more environmental exposures, or lack thereof, induce epigenetic changes that result in interruption of the default immunologic state of tolerance. Strategies for the prevention of FA might include primary prevention, which seeks to prevent the onset of IgE sensitization; secondary prevention, which seeks to interrupt the development of FA in IgE-sensitized children; and tertiary prevention, which seeks to reduce the expression of end-organ allergic disease in children with established FA. This review emphasizes the prevention of IgE-mediated FA through dietary manipulation, among other strategies; in particular, we focus on recent interventional studies in this field.

Indoor air risk factors for schoolchildren's health in Portuguese homes: Results from a case-control survey

Allergic diseases have been on the rise in many countries over the past few decades and indoor exposure may be a possible cause. An overall investigation of children's health status and residential indoor air pollutants known or suspected to affect respiratory health was conducted in the homes of primary schoolchildren during winter in Porto, Portugal. In a case-control study (30 case children with asthma and 38 controls) and over a 1-wk monitoring period, air sample collection was conducted in children's bedrooms for the analysis of 12 volatile organic compounds (VOC), aldehydes, particulate matter (PM)2.5, PM10, bacteria, and fungi. Home exposures to indoor pollutants are similar for children with and without asthma, except for d-limonene. For both groups, most VOC were present at low concentrations (median < 5 µg/m(3)) and below the respective World Health Organization (WHO) guidelines. Concentrations of PM2.5, PM10, and bacteria were frequently higher than WHO/reference values (80, 25, and 60% of all studied dwellings, respectively). Concentrations of carbon dioxide (CO2) exceeding 1000 ppm were encountered in 60% of the homes. Although this study does not provide evidence of causative factors for asthmatic status, the postulation that poor indoor air quality in homes heightens the risk of allergic symptoms development among children is conceivable.

Heritability and confirmation of genetic association studies for childhood asthma in twins

BACKGROUND

Although the genetics of asthma has been extensively studied using both quantitative and molecular genetic analysis methods, both approaches lack studies specific to the childhood phenotype and including other allergic diseases. This study aimed to give specific estimates for the heritability of childhood asthma and other allergic diseases, to attempt to replicate findings from genomewide association studies (GWAS) for childhood asthma and to test the same variants against other allergic diseases.

METHODS

In a cohort of 25 306 Swedish twins aged 9 or 12 years, data on asthma were available from parental interviews and population-based registers. The interviews also inquired about wheeze, hay fever, eczema, and food allergy. Through structural equation modeling, the heritability of all phenotypes was calculated. A subset of 10 075 twins was genotyped for 16 single nucleotide polymorphisms (SNPs) selected from previous GWAS; these were first tested for association with asthma and significant findings also against the other allergic diseases.

RESULTS

The heritability of any childhood asthma was 0.82 (95% CI 0.79-0.85). For the other allergic diseases, the range was approximately 0.60-0.80. Associations for six SNPs with asthma were replicated, including rs2305480 in the GSDMB gene (OR 0.80, 95% CI 0.74-0.86, P = 1.5*10(-8) ; other significant associations all below P = 3.5*10(-4) ). Of these, only rs3771180 in IL1RL1 was associated with any other allergic disease (for hay fever, OR 0.64, 95% CI 0.53-0.77, P = 2.5*10(-6) ).

CONCLUSION

Asthma and allergic diseases of childhood are highly heritable, and these high-risk genetic variants associated specifically with childhood asthma, except for one SNP shared with hay fever.

A genome-wide association study of asthma symptoms in Latin American children

Background

Asthma is a chronic disease of the airways and, despite the advances in the knowledge of associated genetic regions in recent years, their mechanisms have yet to be explored. Several genome-wide association studies have been carried out in recent years, but none of these have involved Latin American populations with a high level of miscegenation, as is seen in the Brazilian population.

Methods

1246 children were recruited from a longitudinal cohort study in Salvador, Brazil. Asthma symptoms were identified in accordance with an International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire. Following quality control, 1 877 526 autosomal SNPs were tested for association with childhood asthma symptoms by logistic regression using an additive genetic model. We complemented the analysis with an estimate of the phenotypic variance explained by common genetic variants. Replications were investigated in independent Mexican and US Latino samples.

Results

Two chromosomal regions reached genome-wide significance level for childhood asthma symptoms: the 14q11 region flanking the DAD1 and OXA1L genes (rs1999071, MAF 0.32, OR 1.78, 95 % CI 1.45–2.18, p-value 2.83 × 10⁻⁸) and 15q22 region flanking the FOXB1 gene (rs10519031, MAF 0.04, OR 3.0, 95 % CI 2.02–4.49, p-value 6.68 × 10⁻⁸ and rs8029377, MAF 0.03, OR 2.49, 95 % CI 1.76–3.53, p-value 2.45 × 10⁻⁷). eQTL analysis suggests that rs1999071 regulates the expression of OXA1L gene. However, the original findings were not replicated in the Mexican or US Latino samples.

Conclusions

We conclude that the 14q11 and 15q22 regions may be associated with asthma symptoms in childhood.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-015-0296-7) contains supplementary material, which is available to authorized users.

ADRB2 polymorphisms in allergic asthma in Han Chinese children

BACKGROUND

Single-nucleotide polymorphisms (SNPs) in the human β2 adrenergic receptor (ADRB2) gene have been linked to pathogenesis of and treatment responses in asthma. In China, where asthma is common, little information exists regarding ADRB2 variants and their effects on asthma. The current study sought to investigate the relationship between variations in ADRB2 and childhood asthma.

METHODS

Blood samples were collected from 298 pediatric asthma cases treated in our hospital from July 2013 to September 2014; 304 samples were collected from healthy children for a control group. Six loci (at base positions -47, 79, -2387, 46, 523, and 491) of ADRB2 were genotyped using the TaqMan probe assay; SHEsis was used to determine haplotypes. Allele frequencies and genotype distributions were compared between groups using chi square and t tests.

RESULTS

No significant differences in genotype or allele frequencies were found between the groups for the polymorphic loci -2387 bp (T>C), 46 bp (G>A), and 523 bp (C>A) (p > 0.05). However, genotype frequencies for the ADRB2 SNPs at -47 bp (C>T) and 79 bp (G>C) differed significantly between asthma and control groups (p < 0.05). Further, linkage disequilibrium was found between these 2 SNPs (D' = 0.990, r(2) = 0.962), as well as between SNPs at 46 and 523 bp (D' = 0.985, r(2) = 0.607). Finally, of the 4 haplotypes analyzed in these samples (haplotypes III, IV, IX, and XI), the frequency of haplotype III was significantly lower in the asthma group than the control group (p < 0.05; odds ratio [OR] = 0.72; 95% confidence interval [CI], 0.48 to 0.97).

CONCLUSION

Variations of ADRB2 at base positions -47 (C>T) and 79 (G>C), as well as haplotype III, may contribute to susceptibility to childhood asthma.

Polymorphisms of RAD50, IL33 and IL1RL1 are associated with atopic asthma in Chinese population

Genetic architecture of asthma remains obscure. This study aimed to investigate whether the genetic polymorphisms of CDHR3 (rs6967330), GSDMB (rs2305480), IL33 rs928413, RAD50 (rs6871536) and IL1RL1 (rs1558641) are associated with the development of atopic asthma in Chinese population. Genotype and allele frequencies were compared between 516 patients and 552 controls by Chi-square test. Patients were found to have significantly higher allele G of rs928413 and allele C of rs6871536 (9.5% vs 6.2%, P = 0.004 for rs928413; 26.1% vs 19.9%, P < 0.001 for rs6871536). Besides, patients were found to have significantly lower frequency of allele A of rs1558641 (17.2% vs 21.7%, P = 0.007). This is the first study validating that IL33, IL1R1, and RAD50 genes are associated with the risk of asthma in Chinese population.

The contribution of twin studies to the understanding of the aetiology of asthma and atopic diseases

The prevalence of asthma and other atopic diseases has increased markedly during the past decades and the reasons for this are not fully understood. Asthma is still increasing in many parts of the world, notably in developing countries, and this emphasizes the importance of continuing research aimed at studying the aetiological factors of the disease and the causes of its increase in prevalence. Twin studies enable investigations into the genetic and environmental causes of individual variation in multifactorial diseases such as asthma. Thorough insight into these causes is important as this will ultimately guide the development of preventive strategies and targeted therapies. This review explores the contribution of twin studies to the understanding of the aetiology of asthma and atopic diseases.

Modest genetic influence on bronchodilator response: a study in healthy twins

Aim

To determine the reasons for large standard deviation of bronchodilator response (BDR) and establish whether there is a potential heritable component in healthy subjects.

Methods

67 monozygotic and 42 dizygotic adult twin pairs were assessed for bronchodilator response (%change in FEV₁ after inhaling 400 µg salbutamol). Univariate quantitative genetic modeling was performed.

Results

Multiple regression modeling showed a significant association between BDR and sex and baseline FEV1 (P < 0.05), while no association was found with smoking habits, body mass index, or age. Within pair correlation in monozygotic twins was modest (0.332), but higher than in dizygotic twins (0.258). Age-, sex-, and baseline FEV1-adjusted genetic effect accounted for 14.9% (95% confidence interval, CI 0%-53.1%) of the variance of BDR, shared environmental effect for 18.4% (95% CI 0%-46.8%), and unshared environmental effect for 66.8% (95% CI 46.8%-88.7%).

Conclusion

Our twin study showed that individual differences in BDR can be mostly explained by unshared environmental effects. In addition, it is the first study to show low, insignificant hereditary influences, independently from sex, age, and baseline FEV1.

Exploring the origins of asthma: Lessons from twin studies

This thesis explores the contribution of twin studies, particularly those studies originating from the Danish Twin Registry, to the understanding of the aetiology of asthma. First, it is explored how twin studies have established the contribution of genetic and environmental factors to the variation in the susceptibility to asthma, and to the variation in several aspects of the clinical expression of the disease such as its age at onset, its symptomatology, its intermediate phenotypes, and its relationship with other atopic diseases. Next, it is explored how twin studies have corroborated theories explaining asthma's recent increase in prevalence, and last, how these fit with the explanations of the epidemiological trends in other common chronic diseases of modernity.

Introduction to genetics and genomics in asthma: genetics of asthma

While asthma is a heterogeneous disease, a strong genetic basis has been firmly established. Rather than being a single disease entity, asthma consists of related, overlapping syndromes [Barnes (Proc Am Thor Soc 8:143-148, 2011)] including three general domains: variable airway obstruction, airway hyper-responsiveness, and airway inflammation with a considerable proportion, but not all, of asthma being IgE-mediated further adding to its heterogeneity. This chapter reviews the approaches to the elucidation of genetics of asthma from the early evidence of familial clustering to the current state of knowledge with genome-wide approaches. The conclusion is that research efforts have led to a tremendous repository of genetic determinants of asthma, most of which fall into the above phenotypic domains of the syndrome. We now look to future integrative approaches of genetics, genomics (Chap. 10), and epigenetics (Chap. 11) to better understand the causal mechanism through which, these genetic loci act in manifesting asthma.

Association between interleukin-4 receptor α chain (IL4RA) I50V and Q551R polymorphisms and asthma risk: an update meta-analysis

BACKGROUND

The associations between the interleukin-4 receptor α chain (IL4RA) I50V and Q551R polymorphisms and asthma risk remained controversial.

METHODS

We searched the Pubmed, Embase, Chinese National Knowledge Infrastructure (CNKI) and Wanfang databases for studies published before February 2013. The strengths of the associations were calculated using odds ratios (ORs) with 95% confidence intervals (CIs).

RESULTS

A total of 50 studies were included in this meta-analysis. There was a significant association between the IL4RA I50V polymorphism and asthma risk in a dominant genetic model (OR = 1.13, 95% CI 1.04-1.23, P = 0.005). The IL4RA Q551R polymorphism was associated with a significantly elevated asthma risk in a recessive genetic model (OR = 1.46, 95% CI 1.22-1.75, P<0.0001). Subgroup analyses found that the IL4RA I50V polymorphism was significantly associated with asthma risk in Asians (OR = 1.72, 95% CI 1.31-2.25, P<0.0001), pediatric asthma risk (OR = 1.50, 95% CI 1.13-1.99, P = 0.005), and atopic asthma risk (OR = 1.88, 95% CI 1.27-2.79, P = 0.002).

CONCLUSIONS

The results of this meta-analysis suggested that the IL4RA I50V and Q551R polymorphisms may be risk factors for developing asthma.

Gene-environment interaction between interleukin-4 promoter and molds in childhood asthma

PURPOSE

To assess the role of gene-environment interaction between interleukin (IL)-4 promoter and mold exposure on the development of asthma.

METHODS

We conducted a cohort-based, incident, case-control study. The case group consisted of 188 children with new asthma and the control group (n = 376) was matched for age and gender. The outcome of interest was the development of asthma over the 6-year study period. The studied determinants were three polymorphisms of IL-4 promoter (TT, CT, and CC) and three indicators of exposure including histories of water damage, presence of visible molds, and perceived mold odor in the home.

RESULTS

Apparent joint effects between IL-4 promoter and mold exposure were observed on both additive and multiplicative scales. Specially, the risk of asthma was significantly associated with children carrying the CT genotype and visible mold exposure comparing with those carrying the TT genotype without any exposure indicator (adjusted odds ratio [OR], 2.14; 95% confidence interval [CI], 1.05-4.34; modified Rothman synergy index for directly use of odds and OR [s] = 1.41; P for interaction = .03). A similar tendency was found (s = 1.30; P for interaction = .04) for children who were exposed to mold odor and carried CT genotype (adjusted OR, 1.99; 95% CI, 1.03-4.41).

CONCLUSIONS

The results of this study suggest that gene-environment interactions between the IL-4 promoter and an indoor mold problem may play an important role in childhood asthma.

Perinatal Risk Factors for Hay Fever — A Study Among 2550 Finnish Twin Families

Previous studies have suggested that perinatal factors influence the risk for asthma but population studies on perinatal factors and risk for hay fever are few. We studied the effect of perinatal factors on the risk for hay fever among adolescent twins by a questionnaire study involving five consecutive nation-wide birth cohorts of 16-year-old twins and their parents. The risk for parent-reported, doctor-diagnosed hay fever in the adolescents associated with several perinatal characteristics was assessed with logistic regression analysis among individuals and by a discordant pair analysis. In the univariate analysis of the birth factors, the risk for hay fever increased with increasing birth weight (p for trend = 0.048, OR for those ≥ 3000g 1.35, 95% CI 0.91–2.02 compared to those < 2000g) and gestational age (p for trend = 0.04, OR for those born after 40 weeks of gestation 2.24, 95% CI 1.03–4.86, compared to those born before 33 weeks of gestation) and was lower in those subjects hospitalised in the neonatal period (OR 0.74, 95% CI 0.58–0.93). Because of significant interactions between parental hay fever status and birth factors (ponderal index, p = 0.03 and maternal age p = 0.04), stratified analysis were performed. The positive association between birth weight and hay fever was most obvious among adolescents with no parental history of hay fever (p for trend = 0.03). Similar, though not significant, trends were found with other birth factors among these families, whereas no such trend was found among adolescents with parental hay fever, suggesting that gestational maturity increases the risk for hay fever in the absence of genetic predisposition. However, of the perinatal factors only neonatal hospitalisation (OR 0.75, 95% CI 0.59–0.96) remained a significant risk factor for the development of hay fever, when adjusted for non-perinatal factors.

Molds, parental atopy and pediatric incident asthma

To assess the independent and joint effects of parental atopy and exposure to molds on the development of asthma in childhood, the authors conducted a cohort-based, incident case-control study in 2008. The case group consisted of 188 children with new asthma, and the control group (n=376) was matched one to two for age and sex. The outcome of interest was the development of asthma during the study period. The studied determinants were parental atopy and three indicators of exposure including histories of water damage, presence of visible molds, and perceived mold odor in the home at baseline in 2002. In conditional logistic regression adjusting for confounding, parental atopy [adjusted odds ratio (aOR) 3.29, 95% CI 2.19-4.94] and the presence of mold odor (aOR 2.09, 95% CI 1.30-3.37) and visible mold (aOR 1.76, 95% CI 1.18-2.62) were independent determinants of incident asthma, and apparent interaction in additive scale was observed. Our finding suggests that the interaction between parental atopy and molds may play a role in the development of asthma in children.

PRACTICAL IMPLICATIONS

Our study strengthens the evidence for the roles of indoor dampness problem and parental atopy as determinants of asthma in children. Furthermore, the interaction between parental atopy and exposure to molds suggests a role for the development of childhood asthma, i.e., the children whose parents had atopic disease and molds exposure are more susceptible to develop asthma.

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.

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.

Risk of asthma in young adults who were born preterm: a Swedish national cohort study

OBJECTIVE

Preterm birth is associated with asthma-like symptoms in childhood and possibly in adolescence, but the longer-term risk of asthma is unknown and increasingly relevant as larger numbers of these individuals enter adulthood. Our objective was to evaluate whether those who were born preterm are more likely to be prescribed asthma medications in young adulthood than those who were born term.

PATIENTS AND METHODS

We conducted a national cohort study of all singleton infants born in Sweden from 1973 through 1979 (n = 622 616), followed to ages 25.5 to 35.0 years to determine whether asthma medications were prescribed in 2005-2007. Asthma medication data were obtained from all outpatient and inpatient pharmacies throughout Sweden. To improve the positive predictive value for asthma, the outcome was defined as prescription of (1) both a β-2 agonist inhalant and a glucocorticoid inhalant or (2) a combination inhalant containing a β-2 agonist and other drugs for obstructive airway diseases.

RESULTS

Young adults who were born extremely preterm (23-27 weeks' gestation) were 2.4 times more likely (adjusted 95% CI: 1.41-4.06) to be prescribed asthma medications than those who were born term. No association was found between later preterm birth (28-32 or 33-36 weeks' gestation) and asthma medications in young adulthood.

CONCLUSIONS

This is the first study with sufficient statistical power to evaluate the risk of asthma beyond adolescence in individuals who were born extremely preterm. The results suggest that extreme preterm birth (23-27 weeks' gestation), but not later preterm birth, is associated with an increased risk of asthma at least into young adulthood.

A complex role for complement in allergic asthma

Allergic asthma is a chronic inflammatory disease of the upper airway. It is well appreciated that maladaptive Th2 immunity promotes the allergic phenotype, the underlying mechanisms of which remain elusive. The disease is associated with activation of complement, an ancient danger-sensing component of the innate immune system. Different models of experimental allergic asthma suggest that the small complement fragments of C3 and C5, the anaphylatoxins C3a and C5a, not only promote proallergic effector functions during the allergic effector phase but regulate the development of Th2 immunity during allergen sensitization. The available data support a concept in which C5a is dominant during allergen sensitization and protects against the development of maladaptive Th2 immunity. By contrast, C3a and C5a appear to act synergistically and drive allergic inflammation during the effector phase. In this article, we will review the recent findings in the field to judge the benefit of complement targeting in allergic asthma.

Factors influencing the incidence and prevalence of food allergy

Food allergy is an increasing problem in Europe and elsewhere and severe reactions to food are also becoming more common. As food allergy is usually associated with other forms of allergic sensitisation it is likely that many risk factors are common to all forms of allergy. However the potential severity of the disease and the specific public heath measures required for food allergy make it important to identify the specific risk factors for this condition. Food allergy is unusual in that it often manifests itself very early in life and commonly remits with the development of tolerance. Hypotheses that explain the distribution of food allergy include specific genetic polymorphisms, the nature of the allergens involved and the unique exposure to large quantities of allergen through the gut. Progress has been made in developing more specific and testable hypotheses but the evidence for any of these is still only preliminary. Further collaborative research is required to develop an appropriate public health response to this growing problem.

Drosophila in asthma research

Genetic research has revealed a number of asthma-susceptibility genes. In addition, with the development of genome-wide association studies, which has gained unprecedented momentum, the roles of many more candidate genes in asthma will be uncovered. In parallel with such genetic insight, a detailed understanding of the function of susceptibility genes in asthma is required, a task best suited for genetically tractable model organisms. The inherent limitations of models like the mouse necessitate finding complementary systems for study. Although the fruit fly Drosophila has not been used previously in asthma-related research, it might prove to be extremely helpful in relating genetic processes to biological function. We discuss the usefulness of the Drosophila model by analyzing potential homologs of known asthma-susceptibility genes in the fly. Except for those associated with adaptive immunity, we and others found unequivocal orthologs for all of them. Most asthma-related genes are indeed expressed in the airway epithelium. In addition, some are regulated upon airway infection of the Drosophila airway epithelium, pointing to an important role in airway immunity and development of asthma-like phenotypes in the fruit fly. Finally, high throughput functional analyses are needed to complete genome-wide comparison studies in complex diseases such as asthma. Because such studies are most readily performed in the fruit fly, it may be a particularly useful asthma model system.

Gene-environment interactions and airway disease in children

Asthma is the most common chronic disease of childhood in the United States, affecting nearly 6.5 million children. The prevalence and severity of childhood asthma have continued to increase over the past 2 decades, despite major advances in the recognition and treatment of this condition. Representing a heterogeneous collection of airway diseases, asthma has multiple pathologic processes resulting from the interactions of genetic susceptibility and environmental exposures. Preventing and treating airway disease in children will require new research approaches to understanding these complex interactions.

A new focus on assessing and treating asthma control in the African-American community: a call to action

Asthma continues to be a highly prevalent disease characterized by significant morbidity, unnecessary mortality, and substantial cost to the health care system. After decades of increasing prevalence, the number of current asthmatics in recent years has plateaued at approximately 22 million people in the United States. An additional 10 million Americans have a past history of asthma that is not active. The burden of asthma is higher among African Americans than in any other racial or ethnic group in America. The African-American community continues to experience a disproportional increase in asthma prevalence, morbidity, and mortality. The educational initiatives stemming from the newly revised National Heart Lung and Blood Institute (NHLBI) guidelines provide the opportunity to address the increased burden of asthma in the African American community. These new guidelines, released in August 2007, focus on asthma control as the primary goal of therapy, routine monitoring of asthma control, and use of asthma control assessments to direct treatment. The present review discusses the following: I. The impact of health disparities on outcomes of African Americans with asthma, II. The barriers that prevent asthmatic patients from achieving optimal control, III. The unique factors that challenge practitioners and patients in achieving optimal asthma control in the African American Community, IV. The impact of good asthma control and the need for patients and clinicians to assess asthma control in with a standardized assessment tool, and V. Strategic initiatives and the role of the End The Attacks NOW program in improving outcomes for African American patients with asthma.

Deciphering gene-environment interactions through mouse models of allergic asthma

Identifying the genetic origins of human complex traits is a time-consuming and labor-intensive process that has as yet only yielded a relatively small number of confirmed susceptibility genes and an even smaller number of confirmed susceptibility alleles. One potential explanation for these difficulties might be the presence of unrecognized environmental factors that moderate the contribution of genetic loci to disease and vary between populations. These factors need not necessarily be limited to environmental parameters of intuitive importance (eg, cigarette smoke or allergen exposure) but also can include more cryptic sources of variation associated with the specific study environment (eg, study apparatus or ambient temperature). Analysis of these interactions in human subjects, although a gold standard, is time-consuming and constrained by ethical and technical issues. Investigations in mouse models, on the other hand, represent a simple and flexible system in which to explore gene-environment interaction effects. In this review we discuss the utility of mouse models in the detection of gene-environment interaction effects and consider the limitations on their application.

A note on twin-singleton differences in asthma

Twins constitute a valuable resource for genetic studies of asthma. However, critics argue that twins are 'special' in terms of prenatal environment and upbringing and therefore nonrepresentative. In respect to asthma a small range of studies report differential morbidity in twins compared with singletons. We review some of the possible explanations for these findings and conclude that results from twin studies of asthma can be extrapolated to the general population.

Heritability of self-reported asthma and allergy: a study in adult Dutch twins, siblings and parents

The present study assessed the prevalence of asthma and allergy, and estimated the importance of genetic and environmental influences on asthma and allergy liability and their association. Longitudinal data on self-reported, doctor-diagnosed asthma and allergy were collected in over 14,000 individuals registered with the Netherlands Twin Register. Structural equation modeling was used for univariate and bivariate genetic analyses on data from twins, their siblings, and parents. Results showed no sex, age, and minimal birth cohort effects for asthma prevalence (11.8%). For allergy, prevalence was higher in women (19.8%) than in men (13.9%). Allergy prevalence at ages 22, 23, and 24 years increased from the 1970 to the 1980 birth cohort. The prevalence of allergy, but not of asthma, was higher in nontwin siblings than in twins. No assortative mating was observed. High (broad-sense) heritabilities were found for asthma (75%) and allergy (66%), with evidence for nonadditive genetic effects in asthma. The association between asthma and allergy (correlation=.65) was largely due to common genes (70%). No sex differences in genetic architecture were found. In conclusion, the prevalence of allergy but not of asthma increased in recent years. Individual differences in the liability to asthma, allergy and their co-occurrence are for a large part accounted for by differences in genetic background. Nonadditive gene action is important, which may have consequences for gene hunting strategies.

An exploration of gene-environment interaction and asthma in a large sample of 5-year-old Dutch twins

A consistent finding from twin studies is that the environment shared by family members does not contribute to the variation in susceptibility to asthma. At the same time, it is known that environmental risk factors that are shared by family members are associated with the liability for asthma. We hypothesize that the absence of a main effect of shared environmental factors in twin studies can be explained by gene-environment interaction, that is, that the effect of an environmental factor shared by family members depends on the genotype of the individual. We explore this hypothesis by modeling the resemblance in asthma liability in twin pairs as a function of various environmental risk factors and test for gene-environment interaction. Asthma data were obtained by parental report for nearly 12,000 5-year-old twin pairs. A series of environmental risk factors was examined: birth cohort, gestational age, time spent in incubator, breastfeeding, maternal educational level, maternal smoking during pregnancy, current smoking of parents, having older siblings, and amount of child care outside home. Results revealed that being a boy, born in the 1990s, premature birth, longer incubator time, and child care outside home increased the risk for asthma. With the exception of premature birth, however, none of these factors modified the genetic effects on asthma. In very premature children shared environmental influences were important. In children born after a gestation of 32 weeks or more only genetic factors were important to explain familial resemblance for asthma.

Heritability and shared genetic effects of asthma and hay fever: an Italian study of young twins

A number of studies have provided evidence of a significant familial aggregation for both asthma and hay fever, and have reported a substantial comorbidity between the two conditions. However, far fewer, especially in Italy, have aimed at clarifying the origins of such comorbidity. The main aims of the present study were (a) to estimate heritability of asthma and hay fever, (b) to measure the association between asthma and hay fever at the individual level, and (c) to assess the extent to which genetic and environmental factors, shared by the two conditions, mediate this association. The twin method was used. The study sample was derived from the Italian Twin Registry, and included 392 twin pairs aged 8 to 17 years. Data collection was performed through parent self-administered questionnaire. Bivariate structural equation twin modeling was applied to asthma and hay fever. Genetic factors accounted for 92% and 78% of the variance in liability to asthma and hay fever, respectively, with the remaining contributions due to unique environmental influences. The within-individual association between asthma and hay fever was substantial. The genetic correlation between the two conditions was .58, whereas no evidence of overlapping unique environmental effects was found. In conclusion, this study showed a high heritability of asthma and hay fever in the Italian child and adolescent population. It also indicated that asthma and hay fever share, to a large extent, a common genetic background, and environmental factors are not relevant to explain the comorbidity.

Prevalence of asthma and risk factors for asthma-like symptoms in Aboriginal and non-Aboriginal children in the northern territories of Canada

BACKGROUND

Few studies have investigated the prevalence and risk factors of asthma in Canadian Aboriginal children.

OBJECTIVE

To determine the prevalence of asthma and asthma-like symptoms, as well as the risk factors for asthma-like symptoms, in Aboriginal and non-Aboriginal children living in the northern territories of Canada.

METHODS

Data on 2404 children, aged between 0 and 11 years, who participated in the North component of the National Longitudinal Survey of Children and Youth were used in the present study. A child was considered to have an asthma-like symptom if there was a report of ever having had asthma, asthma attacks or wheeze in the past 12 months.

RESULTS

After excluding 59 children with missing information about race, 1399 children (59.7%) were of Aboriginal ancestry. The prevalence of asthma was significantly lower (P<0.05) in Aboriginal children (5.7%) than non-Aboriginal children (10.0%), while the prevalence of wheeze was similar between Aboriginal (15.0%) and non-Aboriginal (14.5%) children. In Aboriginal children, infants and toddlers had a significantly greater prevalence of asthma-like symptoms (30.0%) than preschool-aged children (21.5%) and school-aged children (11.5%). Childhood allergy and a mother's daily smoking habit were significant risk factors for asthma-like symptoms in both Aboriginal and non-Aboriginal children. In addition, infants and toddlers were at increased risk of asthma-like symptoms in Aboriginal children. In analyses restricted to specific outcomes, a mother's daily smoking habit was a significant risk factor for current wheeze in Aboriginal children and for ever having had asthma in non-Aboriginal children.

CONCLUSIONS

Asthma prevalence appears to be lower in Aboriginal children than in non-Aboriginal children. The association between daily maternal smoking and asthma-like symptoms, which has been mainly reported for children living in urban areas, was observed in Aboriginal and non-Aboriginal children living in northern and remote communities in Canada.

Gene mapping in asthma-related traits

In asthma, as in many other common multifactorial diseases, the identification of the susceptibility genes has been challenging because consistent results at the genome-wide significance level have been scarce. So far, genome-wide scans have been reported in 17 study populations. By means of genome-wide linkage and hierarchical association analysis, six positional candidate genes (ADAM33, PHF11, DPP10, GPR154, HLA-G, and CYFIP2) for asthma-related traits have been cloned. The interactions of the proteins encoded by these genes and the biological relevance of these signaling pathways in the development of asthma are still poorly understood. Also, the disease mechanisms resulting from the genetic variance in the genes identified remain largely unknown. Although this information is gradually accumulating, we can examine the statistical robustness of each genetic finding in combination with the limited data available on the functional properties of the corresponding proteins to estimate the strengths and weaknesses in the chains of evidence.

Home indoor pollutant exposures among inner-city children with and without asthma

BACKGROUND

Evidence for environmental causes of asthma is limited, especially among African Americans. To look for systematic differences in early life domestic exposures between inner-city preschool children with and without asthma, we performed a study of home indoor air pollutants and allergens.

METHODS

Children 2-6 years of age were enrolled in a cohort study in East Baltimore, Maryland. From the child's bedroom, air was monitored for 3 days for particulate matter <or= 2.5 and <or= 10 microm in aerodynamic diameter (PM(2.5), PM(10)), nitrogen dioxide, and ozone. Median baseline values were compared for children with (n = 150) and without (n = 150) asthma. Housing characteristics related to indoor air pollution were assessed by caregiver report and home inspection. In addition, indoor allergen levels were measured in settled dust.

RESULTS

Children were 58% male, 91% African American, and 88% with public health insurance. Housing characteristics related to pollutant exposure and bedroom air pollutant concentrations did not differ significantly between asthmatic and control subjects [median: PM(2.5), 28.7 vs. 28.5 microg/m(3); PM(10), 43.6 vs. 41.4 microg/m(3); NO(2), 21.6 vs. 20.9 ppb; O(3), 1.4 vs. 1.8 ppb; all p > 0.05]. Settled dust allergen levels (cat, dust mite, cockroach, dog, and mouse) were also similar in bedrooms of asthmatic and control children.

CONCLUSIONS

Exposures to common home indoor pollutants and allergens are similar for inner-city preschool children with and without asthma. Although these exposures may exacerbate existing asthma, this study does not support a causative role of these factors for risk of developing childhood asthma.

Age and gender specific lung function predictive equations provide similar predictions for both a twin population and a general population from age 6 through adolescence

BACKGROUND

There have been numerous studies of asthma in twins, but no study has evaluated whether lung function predictive models yield similar results between twin and general populations. We sought to evaluate this in late childhood and adolescent subjects.

METHODS

We generated cross-sectional, sex- and age-specific regression models of FEV(1), and FVC, in a community-based cohort of 3140 healthy, non-smoking Chinese twins using generalized estimating equations to adjust for correlations within twin pairs. We applied the model to a healthy non-smoking general population cohort of 2187 subjects from the same region, and compared %predicted FEV(1) and FVC values between the two populations.

RESULTS

Stratified by age and sex, the associations of height with FEV(1) or FVC varied by age group. During the adolescent growth spurt (age 13 for girls and ages 14-16 for boys), the associations of height with FEV(1) or FVC were nonlinear and greater than that seen at other ages. During adolescence, FEV(1) and FVC for a given height increased with age. The percent predicted values of FEV(1) and FVC in the twin population were similar to that of the general population.

CONCLUSIONS

Twin and general populations have similar patterns of lung function change over middle childhood and adolescence. Similar equations may be used to estimate percent predicted values. Finally, a single prediction equation cannot completely describe patterns of lung function from childhood through adolescence due to puberty related changes.

Identifying novel genes contributing to asthma pathogenesis

PURPOSE OF REVIEW

To illustrate recent examples of novel asthma genes such as those encoding G-protein-coupled receptor for asthma susceptibility, filaggrin and tenascin-C, and to describe the process that is needed to translate these findings to the clinic.

RECENT FINDINGS

Many hundreds of studies have been published investigating the association of genetic polymorphisms in candidate genes with asthma. These genes were selected on the basis of the gene's product known involvement in the disease process. Moreover, it is the identification of novel genes through hypothesis-independent approaches such as genome-wide linkage studies that is likely to radically alter our understanding of asthma pathophysiology. The identification of a gene is, however, only the first step in a long process that may eventually lead from gene to treatment. This process includes replication, functional studies and, finally, intervention studies.

SUMMARY

While significant progress has been made in the identification of asthma susceptibility genes, it is clear that issues such as replication and functional characterization mean that considerably more research is required. This may enable us to realize benefits to patient treatment that studies of the genetic basis of asthma have the potential to deliver.

Association between the IL-4 promoter polymorphisms and asthma or severity of hyperresponsiveness in Taiwanese

BACKGROUND AND OBJECTIVES

Recent family-based studies have revealed a linkage between human chromosome 5q31 and asthma, elevated serum IgE levels and airway hyperresponsiveness (AHR). Among the candidate genes in this region is the gene encoding IL-4. This gene could be a candidate gene for asthma. The aim of this prospective case-control study was to assess the frequency of polymorphisms in the IL-4 gene promoter among asthmatic patients from Taiwan.

METHODS

The study consisted of 167 patients with asthma and 111 healthy subjects. PCR amplification followed by Bsm F1 restriction digestion were used to assign genotypes at the IL-4 promoter C-589T locus. Pulmonary function tests, methacholine challenge tests, total IgE, specific IgE antibodies against common inhalant allergens and total eosinophil counts were assessed in asthmatic patients.

RESULTS

The T allele frequency for the C-589T IL-4 gene promoter in asthma patients was higher than for normal subjects (P < 0.0001). The frequency discrepancy was found to be even higher for asthmatic patients with severe AHR (P < 0.05). There were no significant differences for the T allele frequency among asthmatic patients with the various other phenotypes such as high versus normal total eosinophil, high versus normal total IgE and high versus normal levels of specific IgE against mite, cockroach or cat dander, or dog dander.

CONCLUSIONS

Polymorphism in the promoter of the IL-4 gene is associated with asthma and is a disease modifier in terms of the severity of AHR.

No association of polymorphisms in the 5' region of the CD14 gene and food allergy in a Japanese population

BACKGROUND

The gene encoding CD14 is a positional candidate gene for allergic diseases as it is localized on chromosome 5q31, a region that is linked to atopy-related phenotypes. Although it has been shown that a polymorphism in the 5' region of the CD14 gene is associated with food allergy in white subjects, it is not clear whether this association is also present in the Japanese population.

METHODS

Eighty-eight children with food allergy were recruited along with 101 children controls without food allergy. DNA samples from these subjects were genotyped by PCR-based restriction fragment length polymorphism (RFLP) assay to investigate the relationship between two polymorphisms in the 5' region of the CD14 gene (C-159T and C-550T) and food allergy.

RESULTS

There was no association among the CD14 alleles, dominant model or recessive model of either polymorphism with food allergy.

CONCLUSIONS

The CD14-159 and -550 polymorphisms might not play a major role in the pathogenesis of food allergy in Japanese children.

NO2 and children's respiratory symptoms in the PATY study

OBJECTIVES

NO2)is a major urban air pollutant. Previously reported associations between ambient NO2)and children's respiratory health have been inconsistent, and independent effects of correlated pollutants hard to assess. The authors examined effects of NO2 on a spectrum of 11 respiratory symptoms, controlling for PM10 and SO2, using a large pooled dataset.

METHODS

Cross sectional studies were conducted in Russia, Austria, Italy, Switzerland, and the Netherlands, during 1993-99, contributing in total 23 955 children. Study-specific odds ratios for associations with ambient NO2 are estimated using logistic regressions with area-level random effects. Heterogeneity between study-specific results, and mean estimates (allowing for heterogeneity) are calculated.

RESULTS

Long term average NO2 concentrations were unrelated to prevalences of bronchitis or asthma. Associations were found for sensitivity to inhaled allergens and allergy to pets, with mean odds ratios around 1.14 per 10 microg/m3 NO2. SO2 had little confounding effect, but an initial association between NO2 and morning cough was reduced after controlling for PM10. Associations with reported allergy were not reduced by adjustment for the other pollutants. Odds ratios for allergic symptoms tended to be higher for the 9-12 year old children compared with the 6-8 year old children.

CONCLUSIONS

Evidence for associations between NO2 and respiratory symptoms was robust only for inhalation allergies. NO2 most likely is acting as an indicator of traffic related air pollutants, though its direct effect cannot be ruled out. This remains important, as policies to reduce traffic related air pollution will not result in rapid reductions.

Acute infections, infection pressure, and atopy

BACKGROUND

During the recent years, a new theory postulating that lack of early childhood infections would increase the prevalence rate of allergies has rapidly gained momentum. This hygiene hypothesis has been widely disseminated to the general public and it has been suggested that vaccinations would accordingly indirectly increase rates of atopy. We thus investigated associations between acute infections, infection pressure (i.e. number of daily child contacts) and atopy in one of the largest population-based medical surveys ever published in the medical literature.

METHODS

Almost all Finns born between 1976 and 1984 and a sample of older teenagers aged up to 19 years (n=5 47 190) were vaccinated and questioned to establish clinical history of mumps and rubella and manifestations of atopy (rhinoconjunctivitis, eczema, and asthma) in 1982-1986. A subsample (n=37 733) including all those subjects who were vaccinated during the first 2 months of the measles, mumps, and rubella (MMR) programme were also queried information about upper respiratory infections (URIs) and infection pressure. Crude and adjusted prevalence ratios of atopy among those with infectious disease history compared with those without it were calculated.

RESULTS

The risk of URI and a history of mumps and rubella increased with the number of daily contacts. This association was apparent especially among the youngest subjects with regard to URIs whereas the proportion with histories of mumps and rubella increased with increasing infection pressure more clearly among the 6-year-olds. Atopy was not associated with daily child contacts among pre-schoolers. Children with histories of repeated URIs and MMR diseases had substantially more atopy than those with lower URI or MMR disease rates.

CONCLUSIONS

Atopic subjects seem to be especially prone to clinically apparent acute respiratory tract infections, and might be in particular need of protection by immunizations. This study does not support the idea that the prevalence of atopy in affluent countries would be affected from disappearing respiratory tract infections.

High prevalence of aeroallergen sensitization among infants of atopic parents

OBJECTIVE

To present methodology to identify atopic parents and determine the prevalence of sensitization to 15 aeroallergens in their infant offspring.

STUDY DESIGN

A birth cohort of infants was identified from birth records; an infant was enrolled if 1 of the parents reported allergy respiratory symptoms and had a positive skin prick test (SPT) to a common aeroallergen. At age 1 year, these infants were tested to the same aeroallergens.

RESULTS

Of the 680 enrolled infants, 28.4% were SPT+ to 1 or more aeroallergens and/or food, and 18.0% were positive to 1 or more aeroallergens. By category of allergens, 9.7% were sensitized to pollens, 7.5% to molds, 4.3% to house dust mite and/or cockroach, and 3.4% to dog and/or cat. Of the infants who were positive to an aeroallergen, 65.7% remained positive at age 2 years.

CONCLUSIONS

Infants born to atopic parents with percutaneous sensitization to aeroallergens are at increased risk for aeroallergen sensitization during infancy, which persists to age 2 years. These findings suggest that current clinical practices, which generally avoid skin testing before age 2 years, be reassessed in this population of high-risk children.