Genetic factors in childhood asthma

Quality of life in pediatric asthma patients and their parents: a meta-analysis on 20 years of research

INTRODUCTION

This meta-analytic review was conducted to estimate the magnitude of quality of life (QoL) impairments in children/adolescents with asthma and their parents.

METHOD

A systematic search in four electronic databases revealed 15 quantitative studies published between 1994-2013 that directly compared the QoL of 7- to 18-year-old asthma patients/parents to community/healthy controls. Pooled mean differences (MD) with 95% CI were estimated using the inverse-variance random-effects method.

RESULTS

Pediatric asthma patients (n = 1797) presented lower overall QoL (MD = -7.48, CI: -10.67/-4.29), physical functioning (MD = -9.36, CI: -11.85/-6.86), psychological functioning (MD = -5.00, CI: -7.17/-2.82) and social functioning (MD = -3.76, CI: -5.80/-1.72), compared to controls (n = 13,266). For parents (666 cases and 7328 controls), asthma was associated with lower physical functioning (MD = -10.15, CI: -12.21/-8.08). Between-studies heterogeneity was explained by type of informant and selection of controls.

CONCLUSION

The ascertainment of the magnitude of QoL impairments and the most affected QoL dimensions for pediatric asthma patients/parents may contribute to the outlining of realistic goals for multidisciplinary interventions in healthcare settings and evaluate its cost-effectiveness.

Exploration of the Genetic Epidemiology of Asthma: A Review, with a Focus on Prevalence in Children and Adolescents in the Caribbean

Asthma is a chronic disease caused by the inflammation of the main air passages of the lungs. This paper outlines a review of the published literature on asthma. While a few studies show a trend of rising asthma cases in the Caribbean region, even fewer have explored the genetic epidemiological factors of asthma. This is a literature review that seeks to sum the body of knowledge on the epidemiology of asthma. Specifically, the major objective of the literature review is to provide a unified information base on the current state of factors involved in the genetic epidemiology of asthma. The review is a simple, yet detailed summary of the literature sources and their methodology and findings on the genetic epidemiology of asthma. Further, it seeks to direct this effort to the Caribbean region. The paper then reviews a summarized and synthesized collection of the body of previous research. Of specific interest are peer-reviewed sources that have been published in recent times. The paper provides more recent insight and recapitulates on the previous research, while tracing the intellectual progress on the debate. Where possible, reviewing and discussing the results of the previous literature, this review singles out the gaps and potential future research directions for studying the genetic epidemiology of asthma. Overall, we hope to contribute to a more synthesized knowledge and improved understanding of the previous literature and future potential direction of genetic and epidemiological asthma research.

Risk factors for non-atopic asthma/wheeze in children and adolescents: a systematic review

Background

The study of non-atopic asthma/wheeze in children separately from atopic asthma is relatively recent. Studies have focused on single risk factors and had inconsistent findings.

Objective

To review evidence on factors associated with non-atopic asthma/wheeze in children and adolescents.

Methods

A review of studies of risk factors for non-atopic asthma/wheeze which had a non-asthmatic comparison group, and assessed atopy by skin-prick test or allergen-specific IgE.

Results

Studies of non-atopic asthma/wheeze used a wide diversity of definitions of asthma/wheeze, comparison groups and methods to assess atopy. Among 30 risk factors evaluated in the 43 studies only 3 (family history of asthma/rhinitis/eczema, dampness/mold in the household, and lower respiratory tract infections in childhood) showed consistent associations with non-atopic asthma/wheeze. No or limited period of breastfeeding was less consistently associated with non-atopic asthma/wheeze. The few studies examining the effects of overweight/obesity and psychological/social factors showed consistent associations. We used a novel graphical presentation of different risk factors for non-atopic asthma/wheeze, allowing a more complete perception of the complex pattern of effects.

Conclusions

More research using standardized methodology is needed on the causes of non-atopic asthma.

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.

An understanding of the genetic basis of asthma

Asthma is the most common chronic childhood disease in developed nations and its prevalence has increased in the world over the last 25 years. It is a complex disease with both genetic and environmental risk factors. Asthma is caused by multiple interacting genes, some having a protective effect and others contributing to the disease pathogenesis, with each gene having its own tendency to be influenced by the environment. This article reviews the current state of the genetics of asthma in six categories, viz. epidemiology, management, aetiology, family and twin studies, segregation and linkage studies, and candidate genes and single nucleotide polymorphisms (SNPs).

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.

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.

Repeatability of response to asthma medications

BACKGROUND

Pharmacogenetic studies of drug response in asthma assume that patients respond consistently to a treatment but that treatment response varies across patients; however, no formal studies have demonstrated this.

OBJECTIVE

To determine the repeatability of commonly used outcomes for treatment response to asthma medications: bronchodilator response, FEV(1), and PC(20).

METHODS

The Childhood Asthma Management Program was a multicenter clinical trial of children randomized to receiving budesonide, nedocromil, or placebo. We determined the intraclass correlation coefficient (ICC) for each outcome over repeated visits over a period of 4 years in the Childhood Asthma Management Program by using mixed-effects regression models. We adjusted for the covariates age, race/ethnicity, height, family income, parental education, and symptom score. We incorporated each outcome for each child as repeated outcome measurements and stratified by treatment group.

RESULTS

The ICC for bronchodilator response was 0.31 in the budesonide group, 0.35 in the nedocromil group, and 0.40 in the placebo group, after adjusting for covariates. The ICC for FEV(1) was 0.71 in the budesonide group, 0.60 in the nedocromil group, and 0.69 in the placebo group, after adjusting for covariates. The ICC for PC(20) was 0.67 in the budesonide and placebo groups and 0.73 in the nedocromil group, after adjusting for covariates.

CONCLUSION

The within-treatment group repeatability of FEV(1) and PC(20) is high; thus, these phenotypes are heritable. FEV(1) and PC(20) may be better phenotypes than bronchodilator response for studies of treatment response in asthma.

Timeliness of diagnosis of asthma in children and its predictors

BACKGROUND

There is a paucity of literature using medical records to evaluate the timeliness of asthma diagnosis in children and the predictors associated with timeliness of asthma diagnosis.

METHODS

Subjects were obtained from a convenience sample of 839 children, aged 5-13 years. We conducted comprehensive medical record reviews for these children to determine their asthma status by applying predetermined criteria for asthma. Predictors were evaluated for an association with timeliness of asthma diagnosis.

RESULTS

Of 839 children, 276 children met the criteria for asthma before 18 years of age. Of these subjects, 97 had timely diagnosis of asthma while 179 did not have timely diagnosis of asthma with the median delay of 3.3 years. Children with definite asthma at the time of index date was three times more timely to be diagnosed with asthma [hazard ratios (HR) 3.3, 95% CI: 2.43-4.47, P < 0.001], compared to those with probable asthma. Children with a family history of asthma were more timely to be diagnosed with asthma (HR 1.36, 95% CI: 1.03-1.8, P = 0.031). Children with exercise-induced wheezing or bronchospasm were more timely to be diagnosed with asthma (HR 1.79, 95% CI: 0.95-3.36, P = 0.07), compared to those with spasmodic (or bronchospastic) cough.

CONCLUSIONS

Many asthmatic children are not diagnosed with asthma in a timely manner, especially in those without the commonly recognized factors associated with asthma. Health care providers need to be reminded that asthma can still occur in those without commonly recognized risk factors. Asthma guidelines need to emphasize this aspect.

Genetics of asthma: potential implications for reducing asthma disparities

Although genetic factors may partly explain the differences in asthma prevalence, morbidity, and mortality among ethnic groups in the United States, few studies of the genetics of asthma have included members of ethnic minority groups. Only one genome-wide linkage analysis of asthma and/or asthma-related phenotypes (conducted by the Collaborative Study on the Genetics of Asthma) has included any members of ethnic minority populations. The interpretation of the findings of genetic association studies of asthma in ethnic minority groups is complicated by reduced statistical power due to small sample sizes; the failure to correct for multiple comparisons; a lack of homogeneity of the populations studied with regard to area of residence, ancestral background, and/or country of origin; a lack of measurement of relevant environmental exposures; and (for case-control studies of genetic association) a lack of detection and control of potential population stratification. Genetic studies may improve our understanding of asthma and lead to new methods to prevent, diagnose, and treat this disease. Limited study of asthma genetics in ethnic minority populations is unacceptable, as it may prevent these groups from benefiting from future developments in asthma management and thus widen existing disparities in asthma care. Future genetic association studies of asthma among ethnic minorities in the United States should include large samples of populations that have been adequately defined with regard to area of residence, self-designated ancestry, and country of origin. These studies should also include an adequate assessment of potentially relevant environmental exposures and (for case-control association studies) population stratification.

A brief targeted review of susceptibility factors, environmental exposures, asthma incidence, and recommendations for future asthma incidence research

Relative to research on effects of environmental exposures on exacerbation of existing asthma, little research on incident asthma and environmental exposures has been conducted. However, this research is needed to better devise strategies for the prevention of asthma. The U.S. Environmental Protection Agency (EPA) and National Institute of Environmental Health Sciences held a conference in October 2004 to collaboratively discuss a future research agenda in this area. The first three articles in this mini-monograph summarize the discussion on potential putative environmental exposure; they include an overview of asthma and conclusions of the workshop participants with respect to public health actions that could currently be applied to the problem and research needs to better understand and control the induction and incidence of asthma, the potential role of indoor/outdoor air pollutants in the induction of asthma), and biologics in the induction of asthma. Susceptibility is a key concept in the U.S. EPA "Asthma Research Strategy" document and is associated with the U.S. EPA framework of protecting vulnerable populations from potentially harmful environmental exposures. Genetics, age, and lifestyle (obesity, diet) are major susceptibility factors in the induction of asthma and can interact with environmental exposures either synergistically or antagonistically. Therefore, in this fourth and last article we consider a number of "susceptibility factors" that potentially influence the asthmatic response to environmental exposures and propose a framework for developing research hypotheses regarding the effects of environmental exposures on asthma incidence and induction.

Coincidence of atopy and its profile (monosensitization/polysensitization) between sibling pairs

BACKGROUND

Results of epidemiologic studies have shown that childhood atopy is probably a hereditary disorder. In the atopic population, some individuals are sensitized to only 1 class of allergens (monosensitized), whereas others are sensitized to more than 1 class of allergens (polysensitized).

OBJECTIVE

To investigate whether atopy and its profile (monosensitization/polysensitization) tend to coincide in sibling pairs.

METHODS

We evaluated sensitization to 5 classes of aeroallergens (house dust mites, animal danders, pollens, molds, and cockroach) using skin prick testing in 564 children with symptoms suggestive of allergic diseases (index children) and their paired siblings.

RESULTS

The frequency of sibling atopy was highest (56.8%) for polysensitized index children (n=222), intermediate (45.4%) for monosensitized index children (n=196), and lowest (30.8%) for nonsensitized index children (n=146). The proportion of polysensitization among atopic siblings was significantly higher for polysensitized (47.6%) than for monosensitized (32.6%) index children. Polysensitized index children were found to more frequently have polysensitized siblings (27.0%) than were monosensitized index children (14.8%), with an odds ratio of 2.13 (95% confidence interval, 1.30-3.49), whereas the likelihood of having a monosensitized sibling was similar for monosensitized and polysensitized index children.

CONCLUSION

These data suggest a coincidence of atopy and its profile in terms of monosensitization and polysensitization in sibling pairs, although the relative importance of genetic and environmental influences requires further study.

Asthma in Hispanics

Hispanic individuals trace their ancestry to countries that were previously under Spanish rule, including Mexico, large parts of Central and South America, and some Caribbean islands. Most--but not all--Hispanics have variable proportions of European, Amerindian, and African ancestry. Hispanics are diverse with regard to many factors, including racial ancestry, country of origin, area of residence, socioeconomic status, education, and access to health care. Recent findings suggest that there is marked variation in the prevalence, morbidity, and mortality of asthma in Hispanics in the United States and in Hispanic America. The reasons for differences in asthma and asthma morbidity among and within Hispanic subgroups are poorly understood but are likely due to the interaction between yet-unidentified genetic variants and other factors, including environmental tobacco smoke exposure, obesity, allergen exposure, and availability of health care. Barriers to optimal management of asthma in Hispanics in the United States and in Hispanic America include inadequate access to health care, suboptimal use of antiinflammatory medications, and lack of reference values for spirometric measures of lung function in many subgroups (e.g., Puerto Ricans). Future studies of asthma in Hispanics should include large samples of subgroups that are well characterized with regard to self-reported ethnicity, country of origin, place of birth, area of residence, and indicators of socioeconomic status. Because Hispanics are disproportionately represented among the poor in the United States, implementation of adequate access to health care and social reforms (e.g., improving housing conditions) would likely have a major impact on reducing asthma morbidity in this population.

Risk factors of bronchial hyperresponsiveness in children with wheezing-associated respiratory infection

The objectives of this study were to identify possible risk factors of bronchial hyperesponsiveness (BHR) in children up to 5 years of age with wheezing-associated respiratory infection (WARI), and to study the prevalence of BHR. Children up to 5 years of age with WARI were enrolled in the study. The parents or caregivers of children were asked about their demographic data and clinical histories. Physical examination and clinical score assessment were performed. Pulmonary function tests, i.e., tidal breathing flow volume (TBFV), were performed to measure tidal breathing parameters before and after salbutamol nebulization. If volume at peak tidal expiratory flow/expiratory tidal volume and time to peak expiratory flow/total expiratory time increased > or = 20%, or tidal expiratory flow at 25% of tidal volume/peak tidal expiratory flow increased > or = 20% after nebulization therapy, BHR was diagnosed. The number in the positive BHR group was used to calculate the prevalence of BHR, and clinical features were compared with those of the negative BHR group. Categorical data were analyzed for statistical significance (P < 0.05) by chi-square test or Fisher's exact test, or Student's t-test, as appropriate. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for those with statistical significance. One hundred and six wheezing children underwent pulmonary function tests before and after salbutamol nebulization. With the aforementioned criteria, 41 cases (38.7%) were diagnosed with BHR. History of reactive airway disease, (OR, 6.31; 95% CI, 1.68-25), maternal history of asthma (OR, 3.45; 95% CI, 1.34-9), breastfeeding less than 3 months (OR, 3.18; 95% CI, 1.26-8.12), and passive smoking (OR, 3; 95% CI, 1.15-7.62) were significant risk factors of BHR. The eosinophil count was significantly higher in the BHR (+) group particularly, in children 1-5 years of age (P < or = 0.01). Patchy infiltrates were more commonly found in patients with negative BHR but not statistically significant. In conclusion, a history of reactive airway disease, maternal history, breastfeeding less than 3 months, and passive smoking were significant risk factors for BHR.

TOLL-like receptor 10 genetic variation is associated with asthma in two independent samples

TOLL-like receptor 10 (TLR10) is the most recently identified human homolog of the Drosophila TOLL protein. In humans, the TOLL-like receptors recognize pathogen-associated molecular patterns (PAMPs) as part of innate immune host defenses. Localized to chromosome 4p14, the specific ligands and functions of TLR10 are currently unknown, although it is expressed in lung and in B-lymphocytes. TLR10 is a potential asthma candidate gene because early life innate immune responses to ubiquitous inhaled allergens and PAMPs may influence asthma susceptibility. Resequencing in 47 subjects revealed a total of 78 single nucleotide polymorphisms (SNPS) (1 SNP per 106 bp) of which only 11 had been previously published. A significant association (p < or = 0.02) between two SNPs (c.+1031G>A, c.+2322A>G) and physician-diagnosed asthma was observed in a case control study (517 cases, 519 control subjects) of European American subjects nested within the Nurses' Health Study cohort. The association for these same two SNPs (p < or = 0.015) replicated in an independent family based cohort, where a measure of airway hyperresponsiveness (PC20) was also associated (p = 0.026 for c.+1031G>A). Consistent association in two independent samples and association with an intermediate phenotype provides strong support for TLR10 genetic variation contributing to asthma risk.

Asthmatic disease among urban preschoolers: an observational study

Asthma is of increasing concern especially in industrialized countries. This cross-sectional study was to assess the influence of spatial and temporal variations in the urban air pollution profile on asthmatic disease. The prevalences presented are based on physician-diagnosed asthmatic and allergic disease data, collected between 1993 and 1995. Seven hundred and thirty-six preschool children (age 2 to 7, mean 5.7 years) of 37 daycare centres in the City of Leipzig participated in the study. Variations were observed in the lifetime prevalences of asthma and allergy with differences in a residential area's ambient pollution profile. Depending on the level of traffic (high or low), children residing in areas with a dominant coal-heating emission profile had more frequently a diagnosis of asthma, 17.5% and 8.8% (95% confidence intervals [CI]: 10.8...23.5 and 5.8...11.6, respectively), as compared to those, living in centrally heated areas 13.4% and 5.8% (CI: 6.6...19.3 and 1.2...9.6, respectively). Allergic disorders occurred more often in areas with a predominantly traffic-associated pollution profile, 14.3% and 9.6% vs. 5.8% and 3.7% (CI: 7.4...20.3 and 6.4...12.5; 1.2...9.6 and 0.2...6.5, respectively). Interestingly, asthmatic disease was not necessarily associated with a clinical history of allergies. Of the children with physician-diagnosed asthma, 83.7% were not reported to have a concurrent diagnosis of allergies nor to show clinical symptoms. This suggests that environmental exposures (i.e., complex pollution mixtures associated with residential coal-heating and/or traffic) may have differentially influenced the phenotypic expression of asthma. A qualitative discussion is presented on the occurrence of "asthma without reported allergies" in Leipzig.

Allergic conditions in 5-8-year-old Maltese schoolchildren: prevalence, severity, and associated risk factors [ISAAC]

Allergic conditions, especially asthma, seem to be increasingly common worldwide. The International Study of Asthma and Allergies in Childhood (ISAAC) was the first study carried out worldwide using standardized questionnaires in order to create a reliable global map of childhood allergy. The Maltese Islands were one of the centres that participated in this study and in this article the data obtained from 3,506 5-8-year-old children from 24 state schools (78.5% response rate), and also data obtained from some added 'local' questions addressed to the same children, were analyzed in order to evaluate the problem of allergic conditions in Maltese schoolchildren. Of the participants, 19.1% were wheezers 'ever,' while 8.8% were current wheezers. Of the latter, 15.9% experienced nocturnal wheezing at least once a week and 13.3% had a wheezing episode of sufficient severity to limit speech. Nasal problems were present in 23.4% of these children, and in 20.7% of all respondents these symptoms persisted up to the year of answering the questionnaire. Hay fever had been diagnosed in 14.7% of all the children. Seven per cent of respondents had a recurrent, itchy rash (suggestive of eczema) for at least 6 months of their lives and 5.5.% had it currently. The prevalence of wheezing and eczema were slightly lower than the global mean, unlike rhinitis which in Malta was commoner than the world average. Multiple variables, such as gender, breast-feeding, passive smoking, family history of atopy, pets, soft furnishings, and living next to busy roads, were factors that affected the prevalence and severity of the allergic conditions studied. In conclusion, allergic conditions are very common in Maltese schoolchildren and cause great hardship to these same youngsters. The results of this study should serve as a stimulus to try to decrease this suffering through better management of these conditions, measures to control identified detrimental factors (such as passive smoking), and further research on asthma, allergic rhinitis and eczema.

Familial resemblance of asthma severity in the EGEA* study

Familial resemblance of asthma is well known but epidemiological research focused on familial resemblance of asthma severity is scanty. We studied whether asthma and asthma severity in first-degree relatives of cases with asthma were related to asthma severity of the index case. The analysis was based upon the examination of 944 subjects (348 cases, 239 relatives with asthma, and 357 subjects without asthma) and upon the information on 3467 first- degree relatives of probands. The risks of asthma in relatives of adult and pediatric cases were significantly higher than in relatives of subjects without asthma (OR 3.4 [95% CI 2.5-4.7] and 4.5 [2.6- 8.1], respectively). Proportions of asthma in relatives were not related to the asthma severity of cases for the three severity criteria studied (clinical score, FEV(1) % predicted, and inhaled corticosteroid use). Using both regression models and intraclass correlation coefficients, there was a significant familial resemblance for the clinical severity score (ICC = 0.23 and 0.23) and for FEV(1) (ICC = 0.19 and 0.25) among families of pediatric and adult probands, respectively. In conclusion, asthma occurrence in relatives may be independent of the severity of the cases with asthma, but results suggest familial resemblance in the severity of asthma when it occurs.

Familial risk of asthma among adolescents and their relatives in Taiwan

Although family studies have established that asthma has a hereditary basis, little evidence has been presented about the family risk of simple asthma (AS or nonatopic asthma) and asthma with other atopic diseases (AWAD or atopic asthma) after adjusting for potential risk factors. In this study, data were collected on demographic variables and a wide range of known risk factors for asthma. Study participants were asthmatic adolescents and controls, and their relatives. The role of a familial history of asthma and atopic diseases in predicting asthma risk among asthmatic adolescents and their relatives was evaluated in a population-based family study conducted in southern Taiwan. Asthma risk factor data were collected through telephone interviews with students' parents for 207 asthmatic adolescents 11-16 years of age, their 1600 relatives, and 207 nonasthmatic adolescents in the control group and their 1638 relatives. The results show (after adjusting potential confounders) that a family history of asthma is highly associated with asthma in adolescents. Having two or more family members with asthma was associated with a 3.4-fold (95% confidence interval [CI] = 1.0-12.0) increased risk of asthma among adolescents. Logistic regression was used to assess the effects of having an asthmatic relative and the effect of atopic diseases among relatives of cases. Having a family history of asthma and other atopic conditions, such as rhinitis and atopic dermatitis (adjusted odds ratio [AOR] = 3.64, 95% CI = 2.29-5.74 and AOR = 1.94, 95% CI = 1.53-2.46, respectively), was found to be a significant predictor of asthma in children. Along with a history of allergic rhinitis or atopic dermatitis, familial risks of asthma occurring in adolescents with and without other atopic diseases will be analyzed separately. A critical finding was the significant difference in a risk of asthma and atopic diseases among the relatives of asthma cases with atopic diseases and controls. However, for relatives of asthma cases without atopic diseases compared to control probands, AORs were highly significant for family history of asthma, but not for the family history of atopic diseases. These findings suggest that both forms of asthma may be hereditary, but there are differences in their modes of inheritance. Atopic status itself did not predispose a child to AS. A concomitant inheritance of a predisposition to asthma and atopic condition for AWAD cases was suggested.

Molecular genetics of allergic diseases

Allergic diseases affect approximately one third of the general population. This class of disease, characterized by elevated serum IgE levels and hypersensitivity to normally innocuous antigen, can manifest in practically any mucosal tissue or as a systemic response. A few examples of serious allergic diseases include asthma, dermatitis, bee sting allergy, food allergy, conjunctivitis, and severe systemic anaphylaxis. Taken together, allergic diseases constitute one of the major problems of modern day medicine. A considerable portion of the healthcare budget is expended in the treatment of allergic disease, and morbidity rates of inner city asthmatics are rising steadily. Due to the enormity of the problem, there has been a worldwide effort to identify factors that contribute to the etiology of allergic diseases. Epidemiologic studies of multigeneration families and large numbers of twins clearly indicate a strong genetic component to atopic diseases. At least two independently segregating diseasesusceptibility genes are thought to come together with environmental factors to result in allergic inflammation in a particular tissue. On the basis of the strong genetic studies, multiple groups have attempted to identify disease-susceptibility genes via either a candidate gene approach or by genome-wide scans. Both of these approaches have implicated multiple regions in the human and mouse genomes, which are currently being evaluated as harboring putative atopy genes.

[Epidemiology of respiratory allergy in children]

Epidemiology of paediatric respiratory allergic disorders allows the approach to causal and preventive risk factors by studying groups or sub groups of children in different locations and under different conditions. This is, however, complicated by the lack of consensus on disease definitions, which renders comparisons between studies difficult. Atopy is usually defined by the presence of positive skin tests (wheal size of at least a mean diameter > or = 3 mm), by the presence of specific IgE, or by the presence of increased total IgE (> or = 100 UI/mL). Infantile asthma is not well defined, complicated by the high prevalence of bronchiolitis; one thus questions between wheezing or wheezy bronchitis. Prevalence is high: among early wheezers, two populations will be defined by the medium term evolution: transient wheezers and persistent wheezers. Risk factors for these two conditions are different. Childhood asthma may be defined by the diagnosis of asthma (specific but fairly non-sensitive), by asthmatic symptoms (wheezing, waking by an attack of shortness of breath) (sensitive but not very specific), or by the combination of symptoms and airway hyperresponsiveness. The ISAAC study has standardised a questionnaire to assess the prevalence of asthma. The preliminary results show that there are wide variations across the world. The prevalence is low in Africa and Asia, intermediate in Europe, and high in Anglo-Saxon countries. The prevalence of asthma has gradually increased over the past 20 years in developed countries. Asthma and atopy are closely associated in children. Risk factors are genetic, associated with sex and environmental factors. Among these, allergic sensitisation is associated with the degree of exposure to allergens. Westernization of way of life is associated with increased prevalence of atopy, allergic rhinitis and asthma. Atopy seems inversely correlated to certain infections. Passive smoking is clearly associated with early wheezing. This and atmospheric pollution aggravate childhood asthma. However, the inducing role of pollution on asthma is still controversial.

Family patterns of asthma, atopy and airway hyperresponsiveness: an epidemiological study

BACKGROUND

The patterns of inheritance of asthma have largely been explored using data of symptom history collected by questionnaires which are subject to bias and which may therefore distort the measured relationship.

OBJECTIVE

The purpose of this study was to examine family patterns of allergic disease using objective measurements of atopy and of airway hyperresponsiveness (AHR).

METHODS

A large random sample of children aged 8-11 years was studied and 3 months later, their parents were also invited for study. Of the sample of 1655 children, both parents of 661 children were studied. In all subjects, respiratory illness history was measured by questionnaire, atopy by skin tests and AHR by responsiveness to histamine.

RESULTS

The odds ratio for a child to have AHR if either parent had the same condition was approximately 2. 0, which was the same as the odds ratio for wheeze or diagnosed asthma in the presence of the same condition in either parent. The odds ratio for atopy was smaller (approximately 1.4, NS) but the risk of a nonatopic child having AHR if the parent had AHR was 3.0 (P = 0.01). The correlation between weal size in the child and parent was poor and the severity of AHR in the child was only modestly correlated with the severity of AHR in the parent (R = 0.51, P = 0.04).

CONCLUSION

The use of objective measurements did not strengthen the association between atopic or asthmatic conditions in the parent and child, but did suggest that atopy and AHR are inherited independently.

Risk factors for development of bronchial asthma in children in Delhi

BACKGROUND

Information on the magnitude of the problem of childhood asthma in India and the factors influencing its occurrence is inadequate.

OBJECTIVE

To measure the prevalence of asthma in schoolchildren in Delhi and study the factors determining its occurrence.

METHODS

A questionnaire-based study carried out in nine randomly selected schools in Delhi. The age range was 5 to 17 years. The questionnaires were distributed to all the children (n = 21,367) for answering by either parent. The key questions relate to complaints of recurrent wheezing in the past, during the immediate last 1-year, and also wheezing exclusively induced by exercise or colds. In all, 19,456 questionnaires were received back (response rate 91%). Out of these, 18,955 were complete and analyzed.

RESULTS

The prevalence of current asthma was 11.9% while past asthma was reported by 3.4% of children. Exclusive exercise-induced asthma was reported by 2.1% while that associated with colds by 2.4% of children. Boys had a significantly higher prevalence of current asthma as compared with girls (12.8% and 10.7%, respectively). Multiple logistic regression analysis showed that male sex, a positive family history of atopic disorders, and the presence of smokers in the family were significant factors influencing the development of asthma while economic class, air pollution (total suspended particulates), and type of domestic kitchen fuel were not.

CONCLUSIONS

The prevalence of current asthma in children in Delhi is 11.9%. Significant risk factors for its development are male sex, a positive family history of atopic disorders, and the presence of smokers in the family.

Genetics of allergy and asthma

LEARNING OBJECTIVES

This article summarizes the latest information regarding the role of genetic influences in the development of allergic disorders and asthma and reviews our current information on some of the most likely genes responsible for these conditions. After reading this article, the reader will have a better understanding of the current molecular biologic techniques that are being used to understand complex genetic disorders such as allergies and asthma. The reader should understand the value of how this genetic insight will lead to the recognition of the presence of specific subtypes of these disorders that require unique therapeutic interventions. This information can also be used to identify genetically at risk children and thereby offer earlier intervention. Finally, understanding the genetic causes of allergies and asthma will lead to the development of the next--hopefully curative--generation of asthma and allergy therapeutics.

DATA SOURCES

A detailed literature search was conducted. Studies considered relevant, well performed, and appropriately controlled were used. Only human studies are included and only the English language literature was reviewed. Some of the information presented is based on the author's own research experience.

STUDY SELECTION

Material was only taken from peer-reviewed journals and appropriate reviews.

RESULTS AND CONCLUSIONS

Asthma and allergic diseases are examples of disorders having an unmistakable genetic predisposition, but in the absence of a classic Mendelian inheritance pattern. These "complex" genetic disorders are caused by the interactions of multiple interacting genes some having protective value and some contributing to disease development and with each gene having its own variable tendency to be expressed. In addition, these disorders require the presence of appropriate environmental triggers for their expression. One approach to identifying the genetic basis for these conditions is to perform a genome-wide search in which the location of the disease-causing gene on a human chromosome is identified and nearby genes that may be responsible are subsequently identified. An alternative approach to identifying heritable components to asthma and allergy is to evaluate disordered structure or regulation within genes known to be involved in these disorders. Using these approaches, studies have suggested that genes within the cytokine gene cluster on chromosome 5 (including interleukins-3, -4, -5, -9, and -13), chromosome 11 (the beta chain of the high affinity IgE receptor), chromosome 16 (the IL-4 receptor), and chromosome 12 (stem cell factor, interferon-gamma, insulin growth factor, and Stat 6 [IL-4 Stat]) may contribute to asthma and allergy development. In addition, data support involvement of genes involved in antigen-presentation (MHC class II genes) and T cell responses (the T cell receptor alpha chain). Finally, disease-contributing alleles may be present on genes for the beta-adrenergic receptor, 5-lipoxygenase, and leukotriene C4 synthase.

Absence of genetic linkage of chromosome 5q31 with asthma and atopy in the general population

BACKGROUND

Clinical asthma is associated with increased serum total immunoglobulin E (IgE), atopy (skin prick test positivity to common aeroallergens), and bronchial hyperreactivity (BHR) to non-specific stimuli (positive methacholine challenge test). A region on chromosome 5q31-33 has been linked with increased total serum IgE and BHR. A study of the genetic linkage of this region with clinical asthma and atopy was therefore undertaken.

METHODS

A polymorphic microsatellite marker in chromosome 5q31 (D5S399) was studied in 119 sibling pairs recruited from the general population who shared asthma, atopy, and/or BHR. Based on our population distribution of 13 different alleles, it was expected that by chance alone sibling pairs would share on average 1.24 alleles and that a significant excess would indicate genetic linkage.

RESULTS

No evidence of linkage was found in 45 siblings concordant for asthma (shared alleles = 1.09, p = 0.95), in 103 sibling pairs with atopy (shared alleles = 1.18, p = 0.82), in 51 sibling pairs with BHR (shared alleles = 1.22, p = 0.62), or in 68 sibling pairs who shared atopy in the absence of BHR (shared alleles = 1.22, p = 0.61). A slight non-significant excess of shared alleles (1.44, p = 0.11) was observed in siblings who shared BHR without atopy.

CONCLUSIONS

No evidence of genetic linkage of chromosome 5q31 with either clinical asthma or atopy was therefore detected in the population studied. Linkage between chromosome 5q and BHR needs further investigation.

The prevalence of allergic diseases in primary school children in Edirne, Turkey

BACKGROUND

Allergic diseases present a major health burden for children as shown by the rising morbidity and increased mortality from asthma. Information on the prevalences of allergic disorders and contributing factors as well will help to establish feasible measures to change this trend, and more efficient assignment of the limited health resources.

OBJECTIVE

To assess the prevalences of asthma and other allergic diseases and the contribution of various risk factors in primary school children in Edirne, Turkey.

METHODS

Children aged 7 to 12 in primary schools in the municipality and 24 villages of Edirne were surveyed via a questionnaire completed by the parents. The cumulative (lifetime) and current (last 12 months) prevalences of allergic diseases and the presence of passive smoking, atopic family history, animal contact and breast-feeding in infancy were determined.

RESULTS

A total of 5412 children (70.1% from the metropolitan and 29.9% from the rural area) were enrolled. The cumulative and current prevalences of all allergic diseases were 24.6% and 9.9% respectively. The cumulative (lifetime) prevalences of bronchial asthma, wheezing, allergic rhinitis and atopic dermatitis were 16.4%, 18.9%, 12.3% and 2.2%, and the current (last 12 months) prevalences were 5.6%, 5.8%, 4.5% and 0.9% respectively. Three-fourths of the children were exposed to tobacco smoke at home. Atopic heredity appeared the most prominent risk factor for any allergic disorder. Neither age, breast-feeding nor place of habitation affected the occurrence of allergic disorders. Animal contact was a significant risk factor for asthma and wheezing (adjusted odd ratios (OR) and 95% confidence intervals (CI) for current prevalences are 1.38 (CI = 1.04-1.83) and 1.35 (CI = 1.02-1.78) respectively), exposure to indoor tobacco smoke for wheezing (OR = 1.52, CI = 1.10-2.09), and male gender for asthma (OR = 1.50, CI = 1.16-1.93). Current prevalences for all allergic diseases were significantly lower than those previously reported in Ankara, Turkey.

CONCLUSIONS

Allergic diseases are a major health burden for primary school children in Edirne, Turkey. Although atopic heredity appears to be the foremost important risk factor, reduction of exposure to indoor tobacco smoke and animal contact, especially for those with atopic family history, are important preventive measures. The impact of environmental exposures on distinguishing prevalences of allergic diseases in Ankara and Edirne should be further investigated.

Genetic susceptibility to asthma in a changing environment

There is a major interest in investigating the genetic components of allergy and asthma. Four different areas are involved in the study of complex genetic diseases: family studies, assessment of phenotype, segregation analysis and gene mapping. Initial assessment of phenotype must be practical, reproducible and relatively independent of compounding variables. Phenotypes important in allergy and asthma include atopic parameters such as total serum IgE, bronchial hyper-responsiveness and the presence/ absence of clinical asthma. Numerous family and twin studies have suggested the presence of a heritable component for allergy, bronchial hyper-responsiveness and asthma. The number of genes involved in these complex genetic disorders and their mode of inheritance have not been fully determined. Our group has been involved in a collaborative US-Dutch study in which 92 families with over 500 individuals have been phenotyped and DNA has been obtained for genotyping. Initial results of the classification of family members show that approximately 26% of the offspring of families ascertained through a parent with asthma have an asthmatic phenotype. A large number of these offspring with clinical evidence of asthma do not have a prior physician diagnosis of asthma, suggesting that there is a spectrum which ranges from preclinical to symptomatic asthma. The familial aggregation of asthma and other obstructive airway diseases in these families is consistent with a significant genetic component. Initial linkage studies have been performed on two characteristics of the allergic and asthmatic phenotype. Total serum IgE was analysed because this measure correlates with the clinical expression of allergy, bronchial hyper-responsiveness and asthma. Segregation analysis of total serum IgE provided evidence for a recessive mode of inheritance. Sib pair analyses and maximum likelihood scores suggest that a gene regulating IgE production maps to chromosome 5q. Bronchial hyper-responsiveness and total serum IgE are related to asthma in population-based studies. Sib pair analyses for bronchial responsiveness showed significant linkage to markers on chromosome 5q.

Factors associated with asthma in school children

To investigate the factors associated with asthma in school children, a case-control study of 203 asthmatic and 203 non-asthmatic children (103 males and 100 females in each group) aged 6 to 18 years, was organized during the period September 1992 to May 1993 in Al Ain city, United Arab Emirates. Cases comprised known asthmatic children who were regularly receiving medication for asthma and were confirmed as asthmatics by a physician. Cases and controls were matched by age and sex. A questionnaire was used to obtain information about respiratory illnesses (pneumonia, bronchitis, bronchiolitis, sinusitis and croup); atopy (allergic rhinitis and atopic dermatitis) and familial allergic diseases (parental asthma and atopy). Information about socioeconomic status and limitations to children as a result of asthma were also obtained. Logistic regression analysis showed that bronchitis, atopy (allergic rhinitis and atopic dermatitis), croup, parental asthma and parental atopic dermatitis were significant risk factors for childhood asthma after adjusting for other confounding covariates. The model also showed that parental asthma (p < 0.0001) is much more influential than parental atopic dermatitis (p = 0.01) as a risk factor for asthma. Although pneumonia and sinusitis were significant risk factors when analyzed univariately, they were not significant after adjusting for other covariates. Bronchiolitis, smoking and socioeconomic status were beyond the reach of statistical significance as risk factors to asthma in our sample.

Linkage of high-affinity IgE receptor gene with bronchial hyperreactivity, even in absence of atopy

Asthma is a manifestation of bronchial hyperreactivity (BHR) and forms part of the spectrum of atopic disease. Some pedigree studies of atopy have suggested linkage with the high-affinity IgE receptor (Fc epsilon RI beta) gene on chromosome 11q13, but others find no linkage. The molecular genetics of asthma and BHR have not been studied in the general population. We examined the genetic linkage of the Fc epsilon RI beta gene with clinical asthma and the underlying phenotypes of BHR (to methacholine) and atopy (defined by skinprick testing) in 123 affected sibling-pairs recruited from the general population. We found evidence of significant linkage of a highly polymorphic microsatellite marker in the fifth intron of the Fc epsilon RI beta gene to a diagnosis of asthma (18.0% excess of shared alleles, p = 0.002) and to BHR (21.7% excess of shared alleles, p = 0.001). Significant linkage was also observed in siblings sharing BHR when those with atopy were excluded (32.8% excess of shared alleles, p = 0.004). Atopy in the absence of BHR did not show significant linkage to the Fc epsilon RI beta gene (7.2% excess of shared alleles, p = 0.124). These findings suggest that mutations in the Fc epsilon RI beta gene or a closely linked gene influence the BHR underlying asthma, even in the absence of atopy.

Pet ownership in the UAE: its effect on allergy and respiratory symptoms

The aim of this paper was to study the effect of pets and other domestic animals on bronchial asthma among United Arab Emirates (UAE) schoolchildren aged 6-14 years. A cross-sectional study of 850 schoolchildren living in both urban and rural areas (average age 9.36 +/- 2.11 years, 46.8% boys and 53.2% girls) was conducted using self-administered questionnaires between October 1992 and May 1993. Prevalence rate for asthma, rhinitis, wheeze, cough, and eczema in children from families with and without animals were investigated. A total of 40.7% of families studied were found to keep animals in their homes. Children from families with animals were found to have a significantly higher prevalence rate of respiratory symptoms than those without. The prevalence rate for asthma in children with animals was found to be twice that of children without (RR: 2.03; 95% CI: 1.40-2.95). The risk of having chronic cough (RR: 1.93; 95% CI: 1.21-3.10), breathlessness/chest tightness (RR: 2.53; 95% CI: 1.59-4.02), chronic wheeze (RR: 2.10; 95% CI: 1.20-3.67), allergic rhinitis (RR: 1.53; 95% CI: 1.17-2.00) was significantly higher in children with animals than in children without. Similarly, the risk of having eczema (RR: 2.55; 95%, CI: 1.74-3.75) was significantly higher among children with animals than among those without. Overall, there was a highly statistically significant difference in the prevalence of asthma, wheeze, nocturnal cough, eczema, and rhinitis between children in families with animals and those without (p < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Association of allergic symptoms in children with those in their parents

This study investigated the association of asthma, allergic rhinitis, and eczema in United Arab Emirates (UAE) schoolchildren with allergic conditions in their parents. A cross-sectional, population-based study among schoolchildren aged 6-14 years was conducted in Al-Ain City, UAE. The field survey was conducted from October 1992 to May 1993. A questionnaire was distributed to 850 UAE government school students from representative, randomly selected schools with a majority of UAE nationals. The student and both or either of the parents were present during the interview. A detailed clinical history of asthma and wheezing in the target children and a history of asthma and allergic rhinitis in their parents and siblings were obtained. It was found that 13.1% of asthmatic children had mothers with asthma (relative risk (RR) = 2.67; 95% confidence intervals (CI) = 1.65-4.35), and 15.2% had fathers who were asthmatic (RR = 2.85; 95% CI = 1.81-4.49). This contrasted with 4.4% of nonasthmatic children who had fathers with asthma, and 4.1% who had mothers with asthma. A similar pattern was seen with symptoms of allergic rhinitis when it was found that 34.3% of children who had asthma had mothers with allergic rhinitis (RR: 2.74; 95% CI: 1.90-3.94). The corresponding figure for fathers was 12.7% (RR: 0.92; 95% CI: 0.5-1.7). The frequency of either parent of the asthmatic children having allergic rhinitis was 28.6%; for both parents, it was 14.5%. It was also found that asthmatic children had 12.5% of their fathers, 32.8% of their mothers, 26.4% of either of their parents, and 33.3% of both their parents suffering from allergic rhinitis.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between atopy and frequent bronchial response to exercise in school children

The natural history of a bronchial response to exercise (BRE) was studied in a cohort of primary-school children, who were followed over a 2-year period. In 1,094 children, three free-running tests were performed in 1-year intervals. Children who responded in one of the tests were designated as "infrequent" responders (20.5%), whereas those responding at two or all three occasions were designated as "frequent" responders (7.4%). A frequent positive BRE was closely associated with atopy (defined as skin test positivity to 1 of 7 common aeroallergens) and respiratory symptom status. Compared to atopics without respiratory symptoms, an increased risk for a frequent positive BRE was seen for atopic children who were symptomatic during the whole study period [odds ratio (OR) 25.4; confidence interval (CI) 6.9-94.0], who had gained symptoms (OR, 11.0; CI, 2.8-43.2) or who had symptoms at the beginning of the study but had lost them during follow-up (OR, 4.6; CI, 1.0-20.6). A sensitization to dust mites (OR, 8.0; CI, 4.3-15.0) but not to animal dander (OR, 2.3; CI, 1.0-5.2) or pollen (OR, 0.7; CI, 0.3-1.6) was significantly related to a frequent positive BRE. Our findings support the notion that while "children grow out of asthma," they might maintain their bronchial hyperresponsiveness. Regarding specific sensitization, mite allergy seems to play the predominant role.

Asthma, allergy and atopy in southern Chinese school students

In order to determine the prevalence of asthma, allergy and atopy in southern China and the relative importance of atopy and parental history in predicting asthma and allergic diseases, we carried out a cross-sectional study on 737 secondary school students aged 12-20 (492 boys, 245 girls; mean age = 16.4 years, SD = 1.8 years) in the city of San Bu, Guangdong, China. Standard questionnaires on respiratory and allergic symptoms were distributed for completion by parents with an overall response of 98.6%. Skinprick tests to common aeroallergens were performed on 647 subjects (87.8%) to determine atopic status. The prevalence (and 95% CI) of a history of hay fever, eczema, wheeze or asthma ever and wheeze in past 12 months were 1.6% (0.7-2.5), 10.4% (8.2-12.6), 1.9% (0.9-1.9) and 1.1% (0.3-1.9) respectively. Forty-nine per cent (45.2-52.9) of students had one or more positive skin tests to common aeroallergens. Amongst atopic subjects, 87.3% reacted to house dust mite (Dermatophagoides pteronyssinus) and 73.3% to cockroach. There was a close association between the degree of atopy and the prevalence of a history of wheeze (P < 0.05) but not with hay fever or eczema. After adjusting for age and sex, parental histories of hay fever, eczema and wheeze were strongly associated with the respective symptoms in the subjects (OR = 17.4 (3.2-93.9) for hay fever, 27.4 (12.7-59.0) for eczema, 79.4 (21.9-288.4) for wheeze). It is concluded that respiratory and allergic symptoms were uncommon in Chinese school students despite a high prevalence of atopy, and that parental history is more important in predicting asthma and allergy than atopy.

Airway response to a bronchodilator in healthy parents of infants with bronchiolitis

In order to assess the role of genetic factors and environmental influences in bronchial responsiveness, we studied the airway response to an inhaled bronchodilator in 66 nonasthmatic parents (age, 30.9 +/- 5.9 years) of infants with bronchiolitis (group 1). It was a placebo-controlled double-blind study. A control group (group 2) of healthy parents of infants who did not have bronchiolitis also were investigated with the test of bronchodilator response. All subjects showed normal expiratory airflow and lung volumes (forced vital capacity [FVC], forced expiratory volume in 1 s [FEV1], and mean forced expiratory flow during the middle half of FVC [FEF25-75%] > 80 percent of predicted) at baseline forced expiratory maneuver. In 16 (24.2 percent) subjects of group 1, there was significant increase in at least one parameter after salbutamol administration, but not after placebo inhalation, with respect to baseline levels. Furthermore, no significant changes in FVC, FEV1, or FEF25-75% values were found in group 2. In conclusion, this study confirms that parents of infants with bronchiolitis have an enhanced airway responsiveness, greater than control parents. Further studies are needed to assess whether one may infer the outcome of infants with bronchiolitis from this characteristic in their parents.

Risk factors for childhood asthma and recurrent wheezy bronchitis

Using cross-sectional data of an epidemiological study, risk factors for asthma and recurrent wheezy bronchitis were investigated in 1812 primary school children. Children with asthma (n = 63) had a similar pattern but a higher frequency of chronic respiratory symptoms than those with recurrent wheezy bronchitis (n = 136). Logistic regression analyses showed similar risk factors for both disorders, however, more pronounced for asthma. Prematurity was a significant risk factor for asthma and for recurrent wheezy bronchitis. Children with asthma more often had a family history of paternal or maternal asthma and their mothers tended to be younger. Effects of paternal asthma and prematurity were also found when the atopic status of the child (defined as skin test positivity to any of seven aero allergens) was taken into account. Next to genetic effects, adverse circumstances in early life seem to be important for the development of asthma. In school children recurrent wheezy bronchitis and asthma seem to be similar disorders which differ in quantitative but not qualitative aspects.

Intraepithelial mast cells in allergic and nonallergic asthma. Assessment using bronchial brushings

Mast cell mediators are known to contribute to the pathogenesis of asthma. There is some disagreement concerning the numbers of mast cells in asthmatic mucosa. In this study a standardized bronchial brush technique was developed and used to assess intraepithelial mast cells and other inflammatory cells in allergic and nonallergic asthmatic and nonasthmatic subjects. A total of 10 nonasthmatic (5 allergic) and 13 asthmatic (8 allergic) subjects with stable controlled asthma treated with beta-agonist only were assessed by history, spirometry, allergy prick tests, and methacholine airway responsiveness. During fiberoptic bronchoscopy, bronchoalveolar lavage (BAL) was performed from the middle lobe and standardized bronchial brushings were taken from the lingula and left lower lobe bronchi. Quantitative cell counts were performed blind to the clinical characteristics of the subjects. The average total cell recovery from the brushings was 1.04 (SEM 0.09) x 10(6) ml, with a cell viability of 64% (5.3%). Reproducible total cell and mast cell counts were obtained from brushings taken from two lobar bronchi (ICC 0.86). Mast cells were significantly elevated in asthmatic compared with nonasthmatic subjects (1.5 +/- 0.34 versus 0.15 +/- 0.06%). Allergic asthmatic subjects had the greatest numbers of mast cells (1.86 +/- 0.48%); however, the numbers present in brushings from nonallergic asthmatic subjects were also increased (1.03 +/- 0.45%). The mast cells had the staining characteristics of mucosal mast cells, with formalin-blockable metachromatic staining and positive staining for tryptase. Both asthmatic groups also had elevated BAL eosinophils, and neutrophils were elevated in nonallergic asthmatic subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

The associations between childhood asthma and atopy, and parental asthma, hay fever and smoking

The aim of this analysis was to examine the degree to which a life time prevalence of asthma in a 7-year-old child is statistically associated with atopic conditions of the child, and with parental asthma, hay fever and smoking. In 1968, 8585 children who were born in 1961 and who were attending school in Tasmania were surveyed. This comprised 99% of the eligible population. The prevalence of a history of asthma in the 7-year-olds was 16.2% (males 19.0%, females 13.2%). Multiple logistic regression analysis showed that a history of asthma in a 7-year-old was associated with the child being male (odds ratio [OR] 1.56; 99% confidence interval 1.30-1.86), having a history of hay fever (3.86; 3.12-4.78), eczema (2.04; 1.63-2.55), hives (1.34; 1.09-1.65) or allergy to foods or medicines (1.70; 1.26-2.30), the child's mother or father having a history of asthma (2.63; 2.08-3.31 or 2.52; 1.99-3.19, respectively), and the mother being a smoker (1.26; 1.05-1.51). Parental hay fever and paternal smoking were not independently associated with childhood asthma. The strength of association between childhood asthma and parental asthma was independent of the sex of either the parent or the child, and of atopic conditions in the child. In the 133 children for whom both parents were asthmatic, 65 (49%) had a history of asthma.(ABSTRACT TRUNCATED AT 250 WORDS)

Risk factors for developing wheezing and asthma in childhood

Wheezing lower respiratory tract illness in infancy and asthma share the clinical findings of wheezing and respiratory distress. Although the link between wheezing lower respiratory tract illness in infancy and the subsequent development of asthma is a limited one, both conditions do share some common risk factors, including exposure to environmental tobacco smoke, difficult living conditions (low socioeconomic class, crowding, allergen exposure), and increased risk in males. The impact of baseline lung function on wheezing lower respiratory tract illness risk is substantial and may be independent of airway reactivity. In contrast, the development of chronic airway inflammation mediated by allergic sensitization plays a central role in the development of persistent asthma. Although the endogenous risks for these two outcomes may be fixed, it is clear that caregivers may help to reduce or eliminate the exogenous risks listed earlier by parental education and improvement of the living conditions of young children.

Heredity of asthma in Saudi population

In a cross-sectional study, the prevalence of asthma, hay fever and eczema was studied in 1150 schoolchildren attending school in Jeddah Western region of Saudi Arabia. The family histories of asthma, hay fever and eczema were examined in first degree relatives. The age range of children studied was 7-12 years, with a mean of 9.3 years (47% boys and 53% girls). A self-administered questionnaire was completed by the parents of the child to collect information concerning bronchial asthma, hay fever, and eczema in the target child and family history of respiratory allergy. A detailed family history and personal histories of asthma were available for 1035 Saudi children aged 7-12 years old. The rate of asthma and hay fever were significantly higher among siblings and offspring (cases) compared to their parents (p < 0.001). The results showed a high positive correlation between the relatives of affected children with respect to asthma and hay fever. These findings support the hypothesis that asthma and hay fever may be inherited in the Saudi population, but the mode of inheritance has yet to be determined.

Is intrinsic asthma a hereditary disease?

Although studies of families, inbred populations and twins have established that asthma has a hereditary basis, little evidence has shown that intrinsic asthma has an increased familial occurrence. To document this issue, we compared the prevalence of asthma in families of intrinsic asthmatics, extrinsic asthmatics and non-asthmatics. The intrinsic asthma group included those with negative skin tests to common aero-allergens (n = 117). The extrinsic asthma group included those with one or more positive skin tests (n = 164). The non-asthmatic group (n = 224) was recruited at a check-up center. The siblings of each subject completed a standardized questionnaire on history of asthma. The results showed that asthma was more prevalent (P less than 0.001) in siblings of intrinsic asthmatics (8.9%) than in siblings of the non-asthmatic group (2.4%). The prevalence of asthma in siblings of intrinsic and extrinsic asthmatics was similar. In conclusion, both intrinsic and extrinsic asthma have an increased family occurrence.

The influence of a family history of asthma and parental smoking on airway responsiveness in early infancy

BACKGROUND

Airway responsiveness to inhaled nonspecific bronchoconstrictive agents has been demonstrated in normal, healthy infants. However, it is unknown whether airway responsiveness is present from birth or if it develops as a result of subsequent insults to the respiratory tract. To investigate this question, we assessed airway responsiveness in 63 normal infants at a mean age of 4 1/2 weeks.

METHODS

Respiratory function was measured with use of the partial forced expiratory flow-volume technique to determine the maximal flow at functional residual capacity (VmaxFRC). The infants inhaled nebulized histamine at sequentially doubled concentrations (0.125 to 8.0 g per liter), until a concentration was reached at which the VmaxFRC fell by 40 percent from the base-line value (PC40) or until a concentration of 8.0 g per liter was reached. We also assessed maternal serum levels of IgE, cord-serum levels of IgE, the infants' skin reactivity to several allergens, and the parents' responsiveness to histamine and obtained family histories of asthma and smoking.

RESULTS

Airway responsiveness was increased in infants with a family history of asthma (n = 19; median PC40, 0.78 g per liter; 95 percent confidence interval, 0.44 to 1.15; P less than 0.01), parental smoking (n = 13; median PC40, 0.52 g per liter; 95 percent confidence interval, 0.43 to 5.40; P less than 0.05), or both (n = 20; median PC40, 0.69 g per liter; 95 percent confidence interval, 0.37 to 2.10; P less than 0.05), as compared with the infants with no family history of asthma or smoking. The infants with no family history of asthma or smoking had a median PC40 of 2.75 g per liter (95 percent confidence interval, 1.48 to 4.00). No significant relations were detected between the immunologic variables and the PC40 in the infants.

CONCLUSIONS

This study indicates that airway responsiveness can be present early in life and suggests that a family history of asthma or parental smoking contributes to elevated levels of airway responsiveness at an early age.

Assessment and prediction of asthma and its severity in the pediatric community

Seventy four asthmatic children aged 7 to 11 years were examined along with controls matched by age and sex. Clinical and laboratory investigations preceded a 28-day follow-up where data about morning and evening peak expiratory flow rate (PEF), symptoms and treatment were recorded. The coefficient of variation of PEF was found to be an objective measurement of asthma severity that has statistically significant correlation with both symptoms (rs = .36) and treatment (rs = .60). Moreover, it separates mild and severe asthmatics, as confirmed by statistically significant differences (p = .008 or less) in symptoms, treatment, skin allergy and airways response to exercise. Skin allergy and airways responsiveness to exercise were found to be predictors of both disease and severity. By means of logistic regression analysis it was possible to establish the probabilities for both asthma and severe asthma when children presenting and not presenting these characteristics are compared. One single positive skin test represent a probability of 88% for the development of asthma and a probability of 70% for severe disease. A PEF reduction of 10% after an exercise test implies a probability of 73% for disease and a probability of 64% for severe disease. Increases in these variables imply geometrically increased risks and their presence together have a multiplicative effect in the final risk.