Regressive logistic modeling of familial aggregation for asthma in 7,394 population-based nuclear families

Metabolomic profiling reveals extensive adrenal suppression due to inhaled corticosteroid therapy in asthma

The application of large-scale metabolomic profiling provides new opportunities for realizing the potential of omics-based precision medicine for asthma. By leveraging data from over 14,000 individuals in four distinct cohorts, this study identifies and independently replicates 17 steroid metabolites whose levels were significantly reduced in individuals with prevalent asthma. Although steroid levels were reduced among all asthma cases regardless of medication use, the largest reductions were associated with inhaled corticosteroid (ICS) treatment, as confirmed in a 4-year low-dose ICS clinical trial. Effects of ICS treatment on steroid levels were dose dependent; however, significant reductions also occurred with low-dose ICS treatment. Using information from electronic medical records, we found that cortisol levels were substantially reduced throughout the entire 24-hour daily period in patients with asthma who were treated with ICS compared to those who were untreated and to patients without asthma. Moreover, patients with asthma who were treated with ICS showed significant increases in fatigue and anemia as compared to those without ICS treatment. Adrenal suppression in patients with asthma treated with ICS might, therefore, represent a larger public health problem than previously recognized. Regular cortisol monitoring of patients with asthma treated with ICS is needed to provide the optimal balance between minimizing adverse effects of adrenal suppression while capitalizing on the established benefits of ICS treatment.

Pharmaco-Metabolomics of Inhaled Corticosteroid Response in Individuals with Asthma

Metabolomic indicators of asthma treatment responses have yet to be identified. In this study, we aimed to uncover plasma metabolomic profiles associated with asthma exacerbations while on inhaled corticosteroid (ICS) treatment. We determined whether these profiles change with age from adolescence to adulthood. We utilized data from 170 individuals with asthma on ICS from the Mass General Brigham Biobank to identify plasma metabolites associated with asthma exacerbations while on ICS and examined potential effect modification of metabolite-exacerbation associations by age. We used liquid chromatography-high-resolution mass spectrometry-based metabolomic profiling. Sex-stratified analyses were also performed for the significant associations. The age range of the participating individuals was 13-43 years with a mean age of 33.5 years. Of the 783 endogenous metabolites tested, eight demonstrated significant associations with exacerbation after correction for multiple comparisons and adjusting for potential confounders (Bonferroni p value < 6.2 × 10^-4). Potential effect modification by sex was detected for fatty acid metabolites, with males showing a greater reduction in their metabolite levels with ICS exacerbation. Thirty-eight metabolites showed suggestive interactions with age on exacerbation (nominal p-value < 0.05). Our findings demonstrate that plasma metabolomic profiles differ for individuals who experience asthma exacerbations while on ICS. The differentiating metabolites may serve as biomarkers of ICS response and may highlight metabolic pathways underlying ICS response variability.

Genetics of Asthma and Allergic Diseases

Asthma genes have been identified through a range of approaches, from candidate gene association studies and family-based genome-wide linkage analyses to genome-wide association studies (GWAS). The first GWAS of asthma, reported in 2007, identified multiple markers on chromosome 17q21 as associates of the childhood-onset asthma. This remains the best replicated asthma locus to date. However, notwithstanding undeniable successes, genetic studies have produced relatively heterogeneous results with limited replication, and despite considerable promise, genetics of asthma and allergy has, so far, had limited impact on patient care, our understanding of disease mechanisms, and development of novel therapeutic targets. The paucity of precise replication in genetic studies of asthma is partly explained by the existence of numerous gene-environment interactions. Another important issue which is often overlooked is that of time of the assessment of the primary outcome(s) and the relevant environmental exposures. Most large GWASs use the broadest possible definition of asthma to increase the sample size, but the unwanted consequence of this is increased phenotypic heterogeneity, which dilutes effect sizes. One way of addressing this is to precisely define disease subtypes (e.g. by applying novel mathematical approaches to rich phenotypic data) and use these latent subtypes in genetic studies.

Gene-environment interactions in the development of asthma and atopy

Asthma is a complex multifactorial disorder involving a variety of different mechanisms. Little has changed in asthma treatment over the past five decades. There is evidence for a strong genetic component of asthma, but genetic studies have produced heterogeneous results with little replication, with most of the heritability remaining unexplained. The rapid increase in asthma prevalence over a short time period suggests that environmental exposures play an important role, but there is a considerable heterogeneity in the results describing the effect of different environmental exposures. There are many reasons for the lack of replication in genetic association studies and those of environmental exposures. These include the failure to consider that asthma may arise as a consequence of environmental factors, modulating the risk in genetically susceptible individuals via gene-environment interactions. In addition, many studies rely on oversimplified phenotypes often derived through aggregation of several heterogeneous conditions (e.g., 'physician-diagnosed asthma').

Residential environmental risk factors for childhood asthma prevalence in metropolitan and semirural cities in Korea

To identify the association between residential environmental risk factors and the prevalence of childhood asthma, the authors surveyed the prevalence of asthma, the residential environmental risk factors of 1819 elementary school students, and air pollution in metropolitan (Seongbuk), and semirural (Andong) areas. Although there was no significant difference in the prevalence of self-reported asthma (SA) between the 2 geographic areas (12.8% vs 13.6%), the prevalence of physician-diagnosed asthma (PDA) in Andong (15.0%) was significantly higher than that in Seongbuk (6.8%). After adjusting for confounding factors, logistic regression suggested that there were significant differences in size of the house (adjusted odds ratio [aOR] = 1.82), medical insurance (aOR = 2.59), and number of residents in the household (aOR = 1.54) between the SA and non-SA groups. There was a significant difference in the area of residence (aOR = 2.12) between the PDA and non-PDA groups. In conclusion, residential environmental risk factors and the area of residence affect the prevalence of childhood asthma.

Using genetics to predict the natural history of asthma?

Clinical practice reminds us that there is considerable variability in the course of asthma over time. Treatment of patients with asthma would be considerably improved if one could accurately predict the likely course of disease over the life course. Recently, with the advent of the era of genome-wide association studies, there has been a monumental shift in our understanding of the genetic factors that underlie inherited susceptibility to asthma. Genes have been identified that modulate many aspects of the natural history of asthma, such as susceptibility to atopy, altered lung development, and susceptibility to more severe disease. Heritability studies have even suggested a role for genetic factors in remission of asthma. However, although the discovery of novel genetic factors underlying disease susceptibility has undoubtedly improved our understanding of disease pathogenesis, whether these advances have improved the ability to predict the natural history in individual patients is questionable, and the application of genetic testing to clinical practice remains some way off.

Risk for asthma in offspring of asthmatic mothers versus fathers: a meta-analysis

BACKGROUND

Many human epidemiologic studies demonstrate that maternal asthma confers greater risk of asthma to offspring than does paternal disease. However, a handful have shown the opposite. Given this disparity, a meta-analysis is necessary to determine the veracity and magnitude of the "maternal effect."

METHODOLOGY/PRINCIPAL FINDINGS

We screened the medical literature from 1966 to 2009 and performed a meta-analysis to compare the effect of maternal asthma vs. paternal asthma on offspring asthma susceptibility. Aggregating data from 33 studies, the odds ratio for asthma in children of asthmatic mothers compared with non-asthmatic mothers was significantly increased at 3.04 (95% confidence interval: 2.59-3.56). The corresponding odds ratio for asthma in children of asthmatic fathers was increased at 2.44 (2.14-2.79). When comparing the odds ratios, maternal asthma conferred greater risk of disease than did paternal asthma (3.04 vs. 2.44, p = 0.037). When analyzing the studies in which asthma was diagnosed by a physician the odds ratios were attenuated and no significant differences were observed (2.85 vs. 2.48, N = 18, p = 0.37). Similarly, no significant differences were observed between maternal and paternal odds ratios when analyzing the studies in which the patient population was 5 years or older (3.15 vs. 2.60, p = 0.14). However, in all cases the trend remained the same, that maternal asthma was a greater risk factor for asthma than paternal.

CONCLUSIONS/SIGNIFICANCE

The results show that maternal asthma increases offspring disease risk to a greater extent than paternal disease.

Major gene effect and additive familial pattern of inheritance of asthma exist among families of probands with sickle cell anemia and asthma

In the United States, sickle cell anemia (SCA) affects approximately 1 in 400 African-American newborns. Acute episodes of pain and acute chest syndrome (ACS) are the two leading causes of hospitalization. A relationship between the diagnosis of asthma and the incidence of pain and ACS has been established. We tested the hypothesis that a familial pattern of inheritance of asthma exists among first degree relatives of probands with SCA and asthma. Segregation analysis was performed in 104 families ascertained through affected probands. Of these, 19.7% (41/208) of the parents and 31.8% (28/88) of siblings of affected probands reported having been told by a doctor he or she had asthma at any age. Modes of inheritance were tested, using the Pedigree Analysis Package parameterized for the discrete trait of asthma affection status. A major effect was present and significant. Further tests were performed to determine whether transmission probabilities of the major effect followed Mendelian expectations. The additive mode of inheritance was the most parsimonious, while the residual heritability was found negligible. Our results support the hypothesis that a familial pattern of inheritance of asthma exists among first degree relatives of probands with SCA and asthma, suggesting that asthma is a co-morbid condition with SCA rather than a lung disease phenotype mimicking asthma.

Interpatient variability in rates of asthma progression: can genetics provide an answer?

Asthma is a heterogeneous disorder with a variable natural history. In children 3 patterns of the natural history of asthma have been described: early onset but transient, persistent, and later onset, with only the former leading to persistent asthma later in childhood. In adults a range of different asthma phenotypes differing in their environmental, inflammatory, and prognostic characteristics have also been described. These extend beyond allergic (extrinsic) and nonallergic (intrinsic) asthma to include persistent airflow obstruction and accelerated decrease in lung function over time. Asthma progression can be defined as the change in an individual's phenotype along a continuum ranging from nonasthmatic to asthmatic and subsequent development of severe chronic disease. It is clear that for prevention of asthma progression in patients, there is a need for both better understanding of the pathophysiology of asthma and identification of predictors of progression. Interpatient genetic variability has been shown to affect multiple facets of asthma progression, including increased susceptibility to atopy and subsequent asthma, progression to severe disease, and modification of the response to treatment. Thus genetic testing might provide a means for predicting the likely progression of an individual along the continuum, allowing targeting of preventative treatment. However, the prospect of the use of genetic information in clinical practice raises important social and ethical issues that will need to be addressed before genetic testing can be used to inform the preventative treatment of patients to prevent the development of progression of asthma in individuals.

Self-reported home environmental risk factors for childhood asthma: a cross-sectional study of children in Buffalo, New York

We present prevalence estimates of indoor and outdoor environmental risk factors for asthma from a cross-sectional study of children 1 to 17 years of age living in Buffalo, New York. A child's primary caretaker completed a questionnaire about the household's demographics, lifestyle habits, housing, indoor and outdoor environment, and the child's activity patterns, family history of asthma, asthma symptoms and treatment, and medical care access. Significant environmental risk factors were presence of smokers in the household, humidifier or vaporizer use, chemical odors indoors, frequent truck traffic, and chemical odors outdoors. Most of these risk factors can be mitigated or controlled.

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.

The potential for reducing asthma disparities through improved family and social function and modified health behaviors

The National Workshop To Reduce Asthma Disparities assembled a multidisciplinary group comprised of scientists, clinicians, and community representatives to examine factors related to asthma disparities. Attention was given to the importance of discerning family, social, and behavioral factors that facilitate or impede the use of health-care services suitable to the medical status of an individual. This review highlights select biopsychosocial factors that contribute to these disparities, the manner in which they may contribute or protect persons affected by asthma, and recommended directions for future research.

A genealogical assessment of heritable predisposition to asthma mortality

RATIONALE

Asthma is a multifactorial disease; genetic factors have been suggested but have not been well defined.

OBJECTIVES

This study examined evidence for a heritable component to asthma mortality using a unique data resource consisting of Utah death certificates linked to a genealogy of Utah.

METHODS

Cases were defined as individuals whose death certificate listed asthma as a cause of death in a registry of all Utah deaths since 1904 (n = 1,553). The genealogical index of familiality analysis was used to compare the average relatedness of asthma deaths to the expected relatedness in the Utah population. Relative risks for asthma death in relatives of individuals who died of asthma are provided for close and distant relatives.

MEASUREMENTS AND MAIN RESULTS

The genealogical index of familiality identified a significantly higher average relatedness in cases (P < 0.001), even when close relationships were ignored. In addition, a significantly increased risk of dying of asthma was observed in first-degree relatives of cases (relative risk = 1.69, P < 0.001) and in second-degree relatives of cases (relative risk = 1.34, P = 0.003).

CONCLUSIONS

These results support a heritable contribution to asthma mortality.

What are we learning from genetic cohort studies?

Although genetic component of asthma has been well recognised, genetics alone cannot explain the rise in asthma prevalence. This increase is likely a consequence of environmental factors increasing the risk in genetically susceptible individuals. As wheezing illness usually begins within months of birth, prospective birth cohorts with detailed measures of environmental exposures and objective measures of disease are essential to study gene-environment interactions in the development of different wheeze phenotypes. Such studies will enable identification of children at increased risk of disease because of a genetic predisposition when exposed to a particular environmental factor. Tailor-made evidence-based strategies for prevention of asthma and atopic sensitization applicable to individuals at risk (rather than the whole population) will then be developed to reduce the risk of asthma and allergy development.

Familial aggregation of airway responsiveness: a community-based study

PURPOSE

We investigated the familial aggregation of airway hyper-responsiveness (AHR) to methacoline among randomly chosen families in a rural community in Anqing, China.

METHODS

Airway responsiveness (AR) to methacoline and related risk factors were assessed in each subject. We first modeled the within family correlation in AR and demonstrated the familial aggregation of this trait. Furthermore, we examined the effect size (e.g., odds ratio, OR) of this correlation in a "subsequent offspring model."

RESULTS

The correlation coefficient is significantly positive for parent-offspring and offspring-offspring pairs, but not significant in father-mother pairs, suggesting a genetic component. The strength of the relationships is in the order of father-offspring < mother-offspring < offspring-offspring. The OR of a positive AHR test for subsequent offspring who had mothers and an eldest sibling with positive AHR is 4.12 (95% CI, 1.72-9.87), compared with subsequent offspring whose mother and eldest sibling were negative in the test.

CONCLUSION

Our study supports a familial clustering of AHR in a Chinese population, which points to a role for genetic factors.

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.

ADAM33: a newly identified protease involved in airway remodelling

Asthma is a complex disorder in which major genetic and environmental factors interact to both initiate the disease and modify its progression. While asthma is recognised as a disorder of the conducting airways characterised by Th2-directed inflammation, it is being increasingly apparent that alteration of the structural cells of the airways (airway remodelling) is also fundamental to disease chronicity and severity. The gene ADAM33, encoding a novel member of a identified as an asthma susceptibility gene as the result of a positional cloning effort in a cohort of families recruited form the UK and USA. Subsequent genetic studies have now provided evidence that ADAM33 may be involved in determining lung function throughout life, associated with early life lung function as well as increased decline therapeutic intervention in asthma and future work will focus on the mechanisms by which it alters lung function and bronchial hyperresponsiveness.

Asthma genetics: pitfalls and triumphs

Asthma is a complex genetic disorder. Significant progress has been made in identifying genes that convey risk of development and expression of the asthma phenotype. This review critically examines the approaches that have been used, the successes achieved and the difficulties that have been encountered. The multi-factorial nature of the disease and the complex interplay of the various risk factors with one another have highlighted the importance of adequate power and study design in pinpointing genes of real interest.

ADAM 33 and its association with airway remodeling and hyperresponsiveness in asthma

Asthma is known to be a Th2 inflammatory syndrome that leads to intermittent airway obstruction. However, the mechanisms involved in development of the clinical features remain enigmatic, although genetic elements clearly are involved. Recently, based on a large genome wide screen involving families in the United Kingdom and the United States with at least two siblings with asthma, a locus was identified that encoded for a family of proteases. This group of proteins is now known as the ADAM superfamily. In this review, we discuss the ADAM superfamily and, in particular, ADAM 33, a member of a family of genes which encode a subgroup of zinc dependent metalloproteinase (metzincin). The potential for therapeutic intervention with ADAM 33 is extremely attractive and further work will not only focus on the specific domains of ADAM 33, but also the mechanisms by which they lead to bronchial hyperreactivity.

Single-nucleotide polymorphisms of the KCNS3 gene are significantly associated with airway hyperresponsiveness

Airway hyperresponsiveness (AHR) is one of the major clinical symptoms and intermediate phenotypes of asthma. A recent genome-wide search for asthma quantitative trait loci has revealed a significant linkage signal between a p-terminal region of chromosome 2 and AHR. Thus, the gene encoding the potassium voltage-gated channel delayed-rectifier protein S3 (KCNS3) in this region is considered a positional candidate for asthma. We have evaluated a total of 12 single-nucleotide polymorphisms (SNPs) of the KCNS3 gene in a validation panel of 48 lymphoblastoid cell line DNA samples of Chinese origin. Three SNPs were found to be polymorphic and were tested. Two independent sets (an initial screening set and a replication set) of cases and controls from the original linkage study sample were collected. In the initial screening set, two SNPs (rs1031771 and rs1031772) showed suggestive association and were further confirmed by the replication set. In combined single-SNP analysis, the rs1031771 G allele (odds ratio=1.42, P=0.006) and rs1031772 T allele (odds ratio=1.40, P=0.018) were associated with a significantly higher risk of AHR. Haplotype analysis also detected significant association (P=0.006). Our findings suggest that SNPs located at the 3' downstream region of KCNS3 have a significant role in the etiology of AHR.

Respiratory health consequences of environmental tobacco smoke

Over the last several decades there has been a growing interest in examining the health consequences of environmental tobacco smoke (ETS). As a result of a wide body of research, ETS is now considered an unacceptable and entirely preventable public health hazard, and public policy increasingly discourages the presence of tobacco smoke in the public domain. This article provides an overview of the composition of ETS and the major diseases and disorders strongly linked to ETS, emphasizing the effects of ETS on pulmonary function, asthma, and lung cancer.

ADAM33: a novel therapeutic target for asthma

The incidence of asthma worldwide is increasing, and the disease has a large unmet clinical need. Despite the availability of anti-inflammatory and bronchodilator medication, there is persisting morbidity and mortality. New approaches are needed to understand the role that structural changes in the airways (remodelling) play in this process. Studies of the genetic basis of asthma have identified the ADAM33 (a disintegrase and metalloproteinase 33) gene, a novel member of the ADAM family of zinc-dependent metalloproteases, as a risk factor for the development of asthma and bronchial hyperresponsiveness (BHR). The identification of ADAM33 as a major risk factor involved in the pathogenesis of BHR and airway wall remodelling provides insight into the pathogenesis of asthma and represents a novel therapeutic target.

Evidence for gene-environment interactions in a linkage study of asthma and smoking exposure

BACKGROUND

Asthma, a common and chronic disease of the airways, has a multifactorial cause involving both genetic and environmental factors. As a result, mapping genes that influence asthma susceptibility has been challenging.

OBJECTIVE

This study tests the hypothesis that inclusion of exposure to environmental tobacco smoke (ETS), a potential risk factor for asthma, would improve the ability to map genes for asthma.

METHODS

By using 144 white families from the Collaborative Study for the Genetics of Asthma, environmental information about exposure to ETS during infancy was incorporated into a genome-wide multipoint linkage analysis. Statistical significance of observed gene-environment interactions was assessed by means of simulation.

RESULTS

Three regions with nominal evidence for linkage when stratified on the basis of ETS exposure were identified (P <.01) and showed a significant increase from the baseline lod score (1p at 97 cM, D1S1669-D1S1665; 5q at 135 cM, D5S1505-D5S816; and 9q at 106 cM, D9S910; all P <.05). In addition, 2 other regions, although not meeting nominal significance after stratification on the basis of ETS exposure, showed a significant increase from baseline lod score when ETS was taken into account (1q at 240 cM, D1S549; 17p at 3 cM, D17S1308; all P <.01).

CONCLUSION

These results illustrate how evidence for linkage of asthma can depend on exposure to an environmental factor, such as ETS. Future linkage analyses should include information on suspected environmental factors for asthma to help target new candidate susceptibility genes for asthma.

Regressive logistic and proportional hazards disease models for within-family analyses of measured genotypes, with application to a CYP17 polymorphism and breast cancer

Various statistical methods have been proposed to evaluate associations between measured genetic variants and disease, including some using family designs. For breast cancer and rare variants, we applied a modified segregation analysis method that uses the population cancer incidence and population-based case families in which a mutation is known to be segregating. Here we extend the method to a common polymorphism, and use a regressive logistic approach to model familial aggregation by conditioning each individual on their mother's breast cancer history. We considered three models: 1) class A regressive logistic model; 2) age-of-onset regressive logistic model; and 3) proportional hazards familial model. Maximum likelihood estimates were calculated using the software MENDEL. We applied these methods to data from the Australian Breast Cancer Family Study on the CYP17 5'UTR T-->C MspA1 polymorphism measured for 1,447 case probands, 787 controls, and 213 relatives of case probands found to have the CC genotype. Breast cancer data for first- and second-degree relatives of case probands were used. The three methods gave consistent estimates. The best-fitting model involved a recessive inheritance, with homozygotes being at an increased risk of 47% (95% CI, 28-68%). The cumulative risk of the disease up to age 70 years was estimated to be 10% or 22% for a CYP17 homozygote whose mother was unaffected or affected, respectively. This analytical approach is well-suited to the data that arise from population-based case-control-family studies, in which cases, controls and relatives are studied, and genotype is measured for some but not all subjects.

Genetics and genomics of asthma and allergic diseases

Asthma and eczema (atopic dermatitis) are characterized by a number of unexplained phenomena: the familial aggregation of disease, the initiation of disease by apparently trivial exposure to allergens, the preferential transmission of disease from affected mothers and the large increase in prevalence of disease in Westernized societies in the last century. A number of genes and chromosomal regions have been identified that consistently show linkage to asthma and its related phenotypes. Known loci modify the strength of the atopic response, nonspecific inflammation, the ability to respond to particular allergens and nonspecific airway reactivity. Eczema has been shown to be due to a different set of genetic loci that are shared with other skin diseases such as psoriasis and leprosy. Genetic and genomic studies both provide evidence that epithelial surfaces are active in the induction of allergic disease.

Segregation analysis of asthma and respiratory allergy in population-based samples of families

Class A regressive multiple logistic segregation models with a sibling covariate were used to investigate the underlying determinants of asthma and respiratory allergy (defined from specific IgE levels to inhaled allergens) in the randomly recruited Caucasian families from the Genetic Analysis Workshop 12 asthma data sets--Perth, Busselton, and Southampton. For asthma, both a purely multifactorial model and a major gene (dominant or recessive) model with multifactorial effects fitted the data. For respiratory allergy, a dominant, dominant with multifactorial effects and a purely multifactorial model all fitted the data. However, homogeneity of the three studies was rejected for both traits indicating that the three populations are significantly different and should be analyzed separately. This finding has implications for the meta-analysis of asthma linkage studies.

Multipoint linkage analysis under heterogeneity: incorporation of parametric and nonparametric approaches

Using a recently developed multipoint parametric method, which tests for linkage in the presence of heterogeneity, we performed a genome-wide search for linkage using the German asthma data. Both dominant and recessive models were assumed in this parametric approach. Identity-by-descent (IBD) sharing for affected sibs was also calculated to help identify an appropriate genetic model and localize the trait locus. The strongest evidence for linkage was on chromosome 6 (p-value = 0.00006) under the dominant model with heterogeneity. Using both linkage and IBD sharing information for D6S422 (36.55 cM) on chromosome 6, we conducted exploratory analyses to locate additional trait loci that might explain the linkage heterogeneity. We found evidence of heterogeneity between D6S422 and D11S4111 based on a test of association (p-value = 0.0015).

Segregation analyses of asthma and respiratory allergy: the Humboldt family study

We performed segregation analyses of asthma and respiratory allergy based on data from 309 nuclear families comprising 1,053 individuals living in the town of Humboldt, Saskatchewan, in 1993, using the REGD program of the S.A.G.E. program package. For adults, information on asthma and history of respiratory allergy was provided by the subjects themselves, and for children by their parents. When asthma was considered as the trait in segregation analysis, models of no major effect, with or without familial effects, were rejected, but they were not rejected after adjusting for history of respiratory allergy. The major gene hypothesis was not rejected before adjusting for history of respiratory allergy. When respiratory allergy was analyzed as the trait, both major gene and multifactorial models fitted the data well, regardless of whether there was adjustment for asthma or not. Other covariates adjusted for in the segregation analyses were age, sex, number of household smokers, current smoking, number of household members, generation, and house type. The data suggest that a major gene related to respiratory allergy may explain the familial aggregation of asthma.

Risk factors for childhood asthma in Costa Rica

BACKGROUND

Little is known about factors determining the pathogenesis and severity of asthma in Latin American countries. Costa Rica, one of the most prosperous Latin American nations, has a very high asthma prevalence.

OBJECTIVE

To examine the relation between potential risk factors and childhood asthma in Costa Rica.

METHODS

Cross-sectional study of 214 schoolchildren aged 10 to 13 years participating in phase II of the International Study of Asthma and Allergies in Childhood.

RESULTS

After adjustment for age, gender, area of residence, maternal smoking during pregnancy, and airway responsiveness to hypertonic saline solution, sensitization to house dust mites was associated with asthma (odds ratio [OR], 2.2; 95% confidence interval [CI], 1.1 to 4.4; p = 0.02). In the multivariate analysis, parental education no higher than high school (OR, 3.0; 95% CI, 1.4 to 6.4; p < 0.01) and parental history of asthma (OR, 2.6; 95% CI, 1.3 to 5.2; p < 0.01) were also independent predictors of childhood asthma.

CONCLUSIONS

Sensitization to house dust mites, low parental education, and parental history of asthma are associated with asthma in Costa Rica.

Genomic approaches to understanding asthma

Asthma is the most common chronic childhood disease in developed nations, and it is a complex disease that has high social and economic costs. Asthma and its associated intermediate phenotypes are under a substantial degree of genetic control. The genetic aetiology of asthma offers a means of better understanding its pathogenesis and, thus, improving preventive strategies, diagnostic tools, and therapies. Considerable effort and expense have been expended in attempts to detect genetic loci contributing to asthma susceptibility, and extensive candidate gene studies and a number of whole-genome screens have been undertaken. This article reviews the current state of knowledge of the genetics of asthma, with a focus on genomic approaches to understanding allergic diseases.

Familial association between allergic disorders and depression in adult Finnish twins

Clinical studies have shown a relationship between allergic disorders and depression, panic disorder, attention deficit/hyperactivity disorder, and social anxiety for a significant subset of patients with these disorders. The nature of the relationship, whether due to shared environmental or biologic vulnerabilities or as a result of the stress of chronic illness, has been less clear. By examining the covariance of atopic disorders and depressive symptoms in a community sample of monozygotic (MZ) and dizygotic (DZ) twins, the contribution of genetic and/or shared environmental etiological factors can be established. A Finnish sample of 1337 MZ and 2506 DZ twin pairs, ages 33-60 years, was sent questionnaires inquiring about history of asthma, eczema, and atopic rhinitis, as well as the Beck Depression Inventory (BDI). The nature of the covariation between twins of these symptoms was investigated by fitting competing genetic and environmental models. Within-person correlation between atopic symptoms and BDI was 0.103 (P < 0.001) for the total sample. Using the Mx statistical modeling program to fit the data to competing quantitative genetic models, the best fitting model estimated that 64% of the association between atopy and BDI was due to shared familial vulnerability, primarily additive genetic influences. Although the measures for allergic disorders and depression are crude, this study supports the hypothesis that there is a small shared genetic risk for atopic and depressive symptoms, and if replicated, may open research for common mechanisms between allergic and depressive disorders. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:146-153, 2000.

Association study of the chromosomal region containing the FCER2 gene suggests it has a regulatory role in atopic disorders

On the basis of studies with animal models, the gene for the low-affinity receptor for immunoglobulin E (IgE) (FCER2, CD23) has been implicated as a candidate for IgE-mediated allergic diseases and bronchial hyperreactivity, or related traits. Given evidence for genetic complexity in atopic disorders, we sought to study two European subpopulations, Finnish and Catalonian. We studied three phenotypic markers: (1) total serum IgE level; (2) asthma; and (3) specific IgE level for a mixture of the most common aeroallergens in Finland. Altogether, eight polymorphic markers spanning a region of 10 cM around the FCER2 gene on chromosome 19p13 were analyzed in 124 families. The physical order of the markers and the location of the FCER2 gene were confirmed by using radiation hybrids. The allele and haplotype association study showed a suggestive haplotype association (significance of p </= 0.03 based on a permutation test) for a high serum IgE response. In a subset of chromosomes segregating with asthma in families with two or more affected members, a single haplotype was found to be highly enriched (p = 8.3 x 10(-6)). However, sequence polymorphisms, which would verify structural differences in the FCER2 gene, were not detected in the coding region of the receptor. Our results suggest that chromosome 19p13 might harbor a genetic determinant of IgE-related traits. Studies in other population samples are needed to verify this finding.

Familial aggregation of pulmonary function in a rural Chinese community

We investigated familial aggregation of pulmonary function among asthma index families and randomly selected nuclear families in a rural community in China. Measurements of pulmonary function and related risk factors were obtained from each family member. A generalized estimation equation model was used to explore the independent relation of pulmonary function among family members, with adjustment for sex, age, height, weight, education, smoking, and asthma status. There was a significant parent-child and sib-sib correlation of pulmonary function. The parent-child correlation of pulmonary function was similar for the first and second children. The correlation was greatest between sib-sibs, followed by mother-child, and less pronounced between father-child among asthma families. The rate of reduced pulmonary function in a subsequent sibling was lowest (4.0%) when both of the parents and the first sibling were in the high-pulmonary-function tertile (high-high group) and was highest (18.4%) when both the parents and the first sibling were in the low-pulmonary-function tertile (low-low group). The rates were intermediate if only the parents (7.0%, low-high group) or only the first sibling (11.5%, high-low group) was in the reduced-pulmonary-function tertile. Our data indicate a strong familial aggregation of pulmonary function in both asthma and random families in this population.

The alliance of genes and environment in asthma and allergy

The diseases of asthma, eczema and hay fever are typified by reactions to common allergens, which are mediated by immunoglobulin E. These allergic diseases are increasing in prevalence, and are now a major source of disability throughout the developed world. They are the result of complex interactions between largely unknown genetic and environmental mechanisms. The identification of the environmental factors offers the real possibility of prevention of disease, and unravelling the genetics of allergic illnesses is likely to change their classification and treatment. Early life seems particularly important, when the initiation of allergic disease may result from genetic and environmental modification of the immune interaction between mother and child.

Gene by environment interactions in the development of asthma

Present knowledge suggests that asthma is a heterogeneous condition. Different genetic backgrounds may or may not express themselves as asthma-like symptoms, depending on both the nature and the timing of exposures in the individual. Although particular attention has been paid to environmental factors that may increase the risk of asthma, it is equally important to understand 'protective' exposures that may have decreased during the last decades and may thus explain the reported increases in asthma prevalence. Among these 'protective' factors are certain infections and the role they may have in the inception of allergics and asthma, particularly when they occur at critical times in the development of the immune system.