Differences in familial segregation of FEV1 between asthmatic and nonasthmatic families. Role of a maternal component

Exploring Household-level Risk Factors for Self-reported Prevalence of Allergic Diseases Among Low-income Households in Seoul, Korea

PURPOSE

Indoor risk factors for allergic diseases in low-income households in Korea have been characterized only partially. We evaluated the prevalences of atopic dermatitis, asthma, and allergic rhinitis in Seoul, Korea, to identify key housing and behavioral risk factors of low-income households.

METHODS

Statistical analysis of the prevalence of these diseases and various risk factors was conducted using data from a 2010 Ministry of Environment household survey. Logistic regression models were generated using data from 511 low-income household apartments in districts of Seoul.

RESULTS

In general, housing factors such as renovation history (P<0.1) and crowding status (P<0.01) were associated with allergic rhinitis, whereas behavioral factors such as frequency of indoor ventilation (P<0.05) and cleaning (P<0.1) were inversely correlated with atopic dermatitis. Indoor smoking was a major trigger of asthma and atopic dermatitis in low-income households (P<0.05). The presence of mold and water leakage in houses were the most important risk factors for all three diseases (P<0.05).

CONCLUSIONS

Various risk factors play a role in triggering allergic diseases among low-income households in Seoul, and health or environmental programs mitigating allergic diseases should be tailored to address appropriate housing or behavioral factors in target populations.

Genome-wide association study of lung function decline in adults with and without asthma

BACKGROUND

Genome-wide association studies have identified determinants of chronic obstructive pulmonary disease, asthma, and lung function level; however, none have addressed decline in lung function.

OBJECTIVE

We conducted the first genome-wide association study on the age-related decrease in FEV(1) and its ratio to forced vital capacity (FVC) stratified a priori by asthma status.

METHODS

Discovery cohorts included adults of European ancestry (1,441 asthmatic and 2,677 nonasthmatic participants: the Epidemiological Study on the Genetics and Environment of Asthma, the Swiss Cohort Study on Air Pollution and Lung and Heart Disease in Adults, and the European Community Respiratory Health Survey). The associations of FEV(1) and FEV(1)/FVC ratio decrease with 2.5 million single nucleotide polymorphisms (SNPs) were estimated. Thirty loci were followed up by in silico replication (1,160 asthmatic and 10,858 nonasthmatic participants: Atherosclerosis Risk in Communities, the Framingham Heart Study, the British 1958 Birth Cohort, and the Dutch Asthma Study).

RESULTS

Main signals identified differed between asthmatic and nonasthmatic participants. None of the SNPs reached genome-wide significance. The association between the height-related gene DLEU7 and FEV(1) decrease suggested for nonasthmatic participants in the discovery phase was replicated (discovery, P = 4.8 × 10(-6); replication, P = .03), and additional sensitivity analyses point to a relation to growth. The top ranking signal, TUSC3, which is associated with FEV(1)/FVC ratio decrease in asthmatic participants (P = 5.3 × 10(-8)), did not replicate. SNPs previously associated with cross-sectional lung function were not prominently associated with decline.

CONCLUSIONS

Genetic heterogeneity of lung function might be extensive. Our results suggest that genetic determinants of longitudinal and cross-sectional lung function differ and vary by asthma status.

Food allergy: riding the second wave of the allergy epidemic

Food allergy is a substantial and evolving public health issue, recently emerging over the last 10-15 yr as a 'second wave' of the allergy epidemic. It remains unclear why this new phenomenon has lagged decades behind the 'first wave' of asthma, allergic rhinitis and inhalant sensitization. In regions like Australia, which lead the respiratory epidemic, challenge-proven IgE-mediated food allergy now affects up to 10% of infants. Although their parents were among the first generation to experience the large-scale rise in allergic diseases, disorders of oral tolerance were previously uncommon. Of further concern, this new generation appears less likely to outgrow food allergy than their predecessors with long-term implications for disease burden. Allergic disease has been linked to the modern lifestyle including changing dietary patterns, changing intestinal commensal bacteria and vehicular pollution. It is not yet known whether the rise in food allergy is a harbinger of earlier and more severe effects of these progressive environmental changes or whether additional or unrelated lifestyle factors are implicated. New studies suggest environmental factors can produce epigenetic changes in gene expression and disease risk that may be potentially heritable across generations. The rising rates of maternal allergy, a strong direct determinant of allergic risk, could also be amplifying the effect of environmental changes. Preliminary evidence that non-Caucasian populations may be even more susceptible to the adverse effects of 'westernisation' has substantial global implications with progressive urbanization of the more populous regions in the developing world. Unravelling the environmental drivers is critical to curtail a potential tsunami of allergic disease.

Epidemiology of stress and asthma: from constricting communities and fragile families to epigenetics

Several epidemiologic frameworks, exemplified through extant research examples, provide insight into the role of stress in the expression of asthma and other allergic disorders. Biologic, psychological, and social processes interact throughout the life course to influence disease expression. Studies exploiting a child development framework focus on critical periods of exposure, including the in utero environment, to examine the influence of stress on disease onset. Early stress effects that alter the normal course of morphogenesis and maturation that affect both structure and function of key organ systems (eg, immune, respiratory) may persist into adult life underscoring the importance of a life course perspective. Other evidence suggests that maternal stress influences programming of integrated physiologic systems in their offspring (eg, neuroendocrine, autonomic, immune function) starting in pregnancy; consequently stress effects may be transgenerational. A multilevel approach that includes an ecological perspective may help to explain heterogeneities in asthma expression across socioeconomic and geographic boundaries that to date remain largely unexplained. Evolving studies incorporating psychological, behavioral, and physiologic correlates of stress more specifically inform underlying mechanisms operating in these critical periods of development. The role of genetics, gene by environment interactions, and epigenetic mechanisms of gene expression have been sparsely examined in epidemiologic studies on stress and asthma although overlapping evidence provides proof of concept for such studies in the future.

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

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

Examining the association between childhood asthma and parent and grandparent asthma status: implications for practice

Examination of intergenerational asthma beyond maternal asthma has been limited. The association between childhood asthma and intergenerational asthma status among a national cohort of children was examined. The genealogical sample (2552 children) participating in the Child Development Supplement of the Panel Study of Income Dynamics was studied. Multivariate regression was used to determine intergenerational asthma. Children with a parent with asthma were almost twice as likely (odds ratio [OR] = 1.96) to have asthma compared with those without a parent with asthma. Children with a parent and grandparent with asthma were more than 4 times more likely to have asthma compared with those without a parent and grandparent with asthma (OR = 4.27). Children with a grandparent with asthma were more likely to have asthma (OR = 1.52). A family history of asthma was a significant predictor of physician diagnosed asthma in children regardless of race/ethnicity and socioeconomic status. Findings support the collection of family history, including grandparent asthma status.

Recent findings on the pathogenesis of bronchial asthma

In the first part of this series of papers (Székely and Pataki, 102) the pathogenesis of asthma was approached as a pathological antigen-antibody complex induced vago-vagal axon reflex. In the next part (103) the contribution of individual hormonal predisposition, the environmental and the most frequent allergizing factors have been reviewed. In the first section of this last (third) part of the review the genetic factors contributing to the asthma are surveyed. In this field a great progress has been made during the last decade, a lot of genes have been pinpointed which contribute to the heredity of the disease. In the second section of this last paper on the etiology of asthma an attempt is made to summarize the previously reviewed data and some new ones. Actually a new hypothesis is proposed that beyond the multitude of genetic, environmental and hormonal factors the underlying biochemical mechanism is simple: the disequilibrium of two functionally opposing second messenger systems in the airways: the Ca i ++ liberating PLC-PKC cascade and the Ca i ++ level reducing cAMP mediated one with preponderance of the former.

[Asthma and pregnancy. Review of the current literature and management according to the GINA 2006-2007 guidelines]

INTRODUCTION

Many pregnant women are asthmatics and maternal asthma is a source of questions and complications concerning both the progress of the pregnancy itself and the impact on the foetus. In this situation good asthma control is essential as the disease can deteriorate with acute exacerbations, possibly precipitated by reduction or even withdrawal of treatment on account of fear of teratogenicity.

BACKGROUND

Even though asthma treatments are not totally harmless during pregnancy, their use has been validated by several studies and guidelines. To help clinicians, we undertake here a review of the complications induced by maternal asthma and its medications, and then suggest management guidelines according to the most recent publications.

CONCLUSIONS

The risks and benefits of asthma treatments should be explained in a real partnership between the patient and her general practitioner and specialists (obstetrician, chest physician or allergist). In order to reduce complications to both mother and child, perfect control of asthma is required and inhaled steroids remain the treatment of choice for partially or uncontrolled asthma in the pregnant woman.

Maternal influence in the transmission of asthma susceptibility

Asthma is one of the most common chronic diseases in children, with increasing morbidity and mortality. A genetic predisposition and exposure to allergens have been implicated as major risk factors for the development of asthma. However, increasing evidence indicates that the mother plays a crucial role in mediating the development of fetal-infant immune responses to inhaled allergens. The exact nature and mechanism of this maternal influence and how it might be associated with the development of allergic sensitization and asthma are not clear. Under normal conditions, the maternal environment during pregnancy promotes an initial Th2 skewed immune response in the offspring which transitions to a nonallergic Th1 type response after birth. However, the allergic mother's influence may delay the normal transition to a nonallergic immune response to inhaled allergens in her children, thus increasing the risk for the development of allergic sensitization and/or asthma. Understanding the underlying mechanisms by which the maternal immune environment can influence the development of the fetal-infant immune response to inhaled allergens may lead to identifying new targets for the prevention of allergic sensitization and asthma.

Inheritance of total serum IgE in the isolated Tangier Island population from Virginia: complexities associated with genealogical depth of pedigrees in segregation analyses

OBJECTIVES

This study was aimed at performing a segregation analysis of total serum immunoglobulin E (tIgE) in an isolated population using maximal genealogical information permitted by current software and computer capacities, while assessing the reliability of the best-fitting model of inheritance for tIgE through simulations.

METHODS

All current Tangier Island, VA, residents (n = 664) belonged to one large extended pedigree (n = 3,501) spanning 13 generations, with an average inbreeding coefficient of 0.009. Phenotype data were obtained on 453 (68.2%) of the residents using a population-based recruitment scheme. Due to computational limitations resulting from the extremely complex pedigree structure, analysis on only two pedigree reconstructions was feasible: a reduced pedigree retaining all phenotyped individuals and their parents as 57 distinct families, and 922 nuclear families.

RESULTS

Familial correlations and heritability calculations reveal a significant genetic component to tIgE in these data (heritability = 26%). The most parsimonious model to explain tIgE distribution indicated by the reduced pedigree structure was a two-distribution Mendelian model. However, larger and non-genetic models could not be rejected. Simulations over 200 replicates performed to evaluate the reliability of this model, indicated that using restricted genealogical information had minimal impact on results of segregation analyses performed here.

Familial correlations and inter-relationships of four asthma-associated quantitative phenotypes in 320 French EGEA families ascertained through asthmatic probands

Asthma is a complex disease, associated with biological and physiological phenotypes including immunoglobulin E (IgE) levels, sum of positive skin prick tests to allergens (SPTQ), eosinophil counts (EOS) and percent predicted forced expiratory volume in 1 s (%FEV1). We investigated the patterns of familial correlations and the inter-relationships of these four quantitative phenotypes, using the general class D regressive model, in 320 French EGEA nuclear families ascertained through 204 offspring (set A) and 116 parents (set B). Familial correlations of IgE and SPTQ were consistent with a model including no spouse correlation and equal parent-offspring and sib-sib correlations (rhoPO = rhoSS = 0.25 for IgE and 0.15 for SPTQ), this model being compatible with an additive polygenic model in the whole sample and the two family subsets A and B. Different patterns of familial correlations of EOS and %FEV1 were observed in these two sets. In set A, the best fitting model included no spouse correlation and equality of parent-offspring and sib-sib correlations (rhoPO = rhoSS = 0.14 for EOS and 0.23 for %FEV1). In set B, EOS had only a significant rhoSS of 0.28, while %FEV1 had significant rhoMO of 0.28 and rhoSS of 0.16. Analysis of shared familial determinants between these phenotypes indicated an overlap of at most 30% in rhoFO for IgE and SPTQ and in both rhoFO and rhoMO for IgE and EOS, while determinants of %FEV1 and atopy-related phenotypes appear distinct. These results may have implications for further linkage and association studies with genetic markers.

Parental allergic status influences the risk of developing allergic sensitization and an asthmatic-like phenotype in canine offspring

Increasing evidence suggests that parental allergic status, especially that of the mother, may play a unique and important role in influencing the development of fetal infant immune responses to inhaled allergens, independently of genetic predisposition. We have developed an experimental model in dogs where the offspring from allergic parents, when exposed to inhaled allergen, develop allergic sensitization and an asthmatic phenotype, whereas the offspring from non-allergic parents do not. Offspring from ragweed-sensitized (two litters, n = 10) or non-sensitized (two litters, n = 11) Beagle dogs were exposed repeatedly, by inhalation, to ragweed or filtered air (negative control) beginning within 1 week after birth. Serum levels of total immunoglobulin (Ig)E, and ragweed-specific IgE and IgG, were measured at specific time-points up to 40 weeks after birth. Cell differentials in the bronchoalveolar lavage were determined on days 1 and 4 following ragweed instillation into the offspring's lungs at 26 weeks of age. Changes in pulmonary resistance following challenge with histamine and ragweed (five breaths) were measured at 40 weeks after birth. Offspring from sensitized parents exposed to ragweed developed elevated serum total IgE and ragweed-specific IgE and IgG, and showed an increased pulmonary resistance to histamine and ragweed, and increased numbers of eosinophils in bronchoalveolar lavage. In contrast, offspring from non-sensitized parents did not exhibit this immune response. These results suggest that parental allergic sensitivity is important in the development of allergic sensitization and an asthmatic phenotype in the offspring.

Allergen-induced airway disease is mouse strain dependent

We investigated the development of airway hyperreactivity (AHR) and inflammation in the lungs of nine genetically diverse inbred strains of mice [129/SvIm, A/J, BALB/cJ, BTBR+(T)/tf/tf, CAST/Ei, C3H/HeJ, C57BL/6J, DBA/2J, and FVB/NJ] after sensitization and challenge with ovalbumin (OVA). At 24, 48, and 72 h post-OVA exposure, the severity of AHR and eosinophilic inflammation of the mouse strains ranged from relatively unresponsive to responsive. The severity of the airway eosinophilia of some strains did not clearly correlate with the development of AHR. The temporal presence of T helper type 2 cytokines in lung lavage fluid also varied markedly among the strains. The levels of IL-4 and IL-13 were generally increased in the strains with the highest airway eosinophilia at 24 and 72 h postexposure, respectively; the levels of IL-5 were significantly increased in most of the strains with airway inflammation over the 72-h time period. The differences of physiological and biological responses among the inbred mouse strains after OVA sensitization and challenge support the hypothesis that genetic factors contribute, in part, to the development of allergen-induced airway disease.

Tucson Children's Respiratory Study: 1980 to present

The Tucson Children's Respiratory Study (TCRS), begun in 1980, has followed 1246 subjects from birth together with their family members to delineate the complex interrelationships between a large number of potential risk factors, acute lower respiratory tract illnesses, and chronic lung disorders later in childhood and early adult life, especially asthma. Nine hundred seventy-four (78%) of the original subjects are still being followed. Among its numerous findings, the TCRS has (1) described various wheezing disorders (transient, nonatopic, atopic) and their characteristics; (2) developed an Asthma Predictive Index; (3) delineated the respiratory and atopic outcomes for children who had respiratory syncytial virus-related wheezing illnesses in infancy; and (4) evaluated a large number of risk factors for acute respiratory tract illnesses during the first 3 years of life. Future TCRS studies will focus on (1) factors in infancy and early childhood that relate to persistent asthma and atopy; (2) role of genetic factors in persistent asthma; and (3) determinants of lung function decline in early adult life.

Familial Aggregation and Segregation Analysis of Snoring and Symptoms of Obstructive Sleep Apnea

To investigate possible modes of inheritance that would explain familial aggregation in obstructive sleep apnea (OSA), familial correlation and segregation analyses were performed on data derived from 584 pedigrees with 2019 cases enrolled in the Tucson Epidemiologic Study of Obstructive Airways Disease (TESOAD) who were at least 10 years of age and who had information pertaining to snoring and daytime sleepiness. Data were obtained from the 9th (May 1984 to October 1985) and 12th (February 1990 to October 1992) surveys of the TESOAD, which is a random, stratified sample of the non-Hispanic Caucasian population of Tucson, Arizona. A snoring phenotype was considered present if it occurred on at least some nights. A "sleep apnea" phenotype was constructed if participants snored and experienced daytime sleepiness. Familial correlations for snoring showed significant mother-child and sibling correlations but not father-child correlations. For sleep apnea, significant parent-daughter but not parent-son or sibling correlations were observed. Segregation analyses for snoring with regressive familial effects and sibling, age, and obesity covariates showed no evidence for mendelian transmission. However, additional familial effects were present that suggested phenotype aggregation from polygenic or environmental factors, or both. For the sleep apnea phenotype, similar segregation analyses indicated that mendelian dominant or codominant models were possible. However, the analyses also suggested that a nongenetic model fit the data as well. In addition, consistent with the familial correlations, specific maternal- and sibling-related effects remained even after inclusion of age, gender, and obesity covariates. These data support the concept that inheritable or shared environmental factors contribute to the development of OSA and that maternal components may be more important than paternal ones.

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 correlation in the decline of forced expiratory volume in one second

Studies have shown evidence of significant parent-offspring and sibling correlation in FEV1, but familial aggregation of decline of FEV1 over time has not been reported. Our study population comprised 392 families enrolled in the Tucson Epidemiological Study of Airway Obstructive Diseases. Subjects were older than 18 yr of age and performed at least 3 pulmonary function tests over 5 to 20 yr. The slope of FEV1 was calculated for each subject using simple linear regression. Multiple regression models were used to compute standardized residual slope values adjusted for possible confounders. Familial correlation analysis on residual slope values demonstrated no evidence of spousal or parent-offspring correlation. However, sibling pairs were highly correlated (r = 0.256, p < 0.001, n = 166), especially smoking-concordant pairs (r = 0.483, p < 0.01 for ever-smokers, and r = 0.280, p < 0.05 for never-smokers). The residual slopes of smoking-discordant siblings were not significantly correlated (r = 0.031, p < 0.77). Genetic susceptibility to an accelerated rate of decline associated with smoking may be evidenced in the increased correlation among smoking sibling pairs, and in the lack of correlation among smoking-discordant sibling pairs. High sibling correlation in the absence of parent-offspring correlation is compatible with a recessive model of inheritance.

Familial correlation and segregation analysis of forced expiratory volume in one second (FEV1), with and without smoking adjustments, in a Tucson population

BACKGROUND

Previous researchers have found significant familial aggregation but no evidence of Mendelian inheritance of forced expiratory volume in one second (FEV1) in general population studies. However, the influence of cigarette smoking on familial aggregation of FEV1 has been difficult to assess in these studies.

OBJECTIVES

The main objective of our study was to attempt to discern the effects of smoking on familial correlation and segregation models of FEV1.

SUBJECTS AND METHODS

In a randomly selected sample of white, non-Mexican American families in Tucson, Arizona, we performed two separate familial correlation and segregation analyses of FEV1, one adjusted for cigarette smoking and one unadjusted for smoking. In both, initial survey measures of FEV1 for 1329 females and 1291 males in 746 families were standardized for gender, age, height and height-squared using piecewise linear regression models. In the smoking-adjusted model, total number of pack-years smoked, current and ex-smoking status, and the interaction between total pack-years and current smoking status were also included.

RESULTS

FEV1 was significantly correlated among sibling pairs and parent-offspring pairs (both p < 0.001), regardless of smoking adjustment, but sibling correlation was significantly higher than parent-offspring correlation (p < 0.05), suggesting additional effects beyond common parentage. Spousal correlations were not significant even when both spouses smoked. We found no evidence of major gene segregation of FEV1, with or without smoking adjustment, and all of the segregation models were significantly different from the unrestricted model.

CONCLUSIONS

The best-fitting model was an environmental model with three distinct distributions of FEV1 and significant residual familial effects. A significant familial component suggests the presence of polygenic factors and/or effects due to a shared environment (multifactorial). That familial correlations of smoking-adjusted and smoking-unadjusted residuals were not appreciably different suggests that current smoking status and number of pack-years smoked do not account for the observed familial aggregation of FEV1.

Segregation analyses and a genome-wide linkage search confirm genetic heterogeneity and suggest oligogenic inheritance in some Milroy congenital primary lymphedema families

We previously described six families with Milroy congenital lymphedema, only one of which showed possible linkage to a candidate locus on chromosome 5 [Witte et al., 1998]. We have now performed a complex segregation analysis of these families, and performed linkage analyses with the other 387 markers used in our genome-wide search. Our results confirm that Milroy lymphedema is generally inherited as a dominant condition. However, this mode of inheritance, as elucidated from the segregation analyses, did not account for all observed familial correlations. The segregation analysis also suggested that shared environmental or additional genetic factors are important in explaining the observed familial aggregation. The finding of linkage to multiple locations in the largest family studied by multipoint parametric mapping (one of which was confirmed by sib-pair non-parametric mapping), suggests that Milroy congenital lymphedema may be oligogenic in this family.

Childhood infections and asthma: at the crossroads of the hygiene and Barker hypotheses

The hygiene hypothesis states that childhood asthma develops as a result of decreased exposure to infectious agents during infancy and early childhood. This results in the persistence of the neonatal T helper lymphocyte 2 immunophenotype, thereby predisposing the child to atopic disease. While multiple studies support the hygiene hypothesis in asthma ontogeny, the evidence remains inconclusive; multiple other environmental exposures in early childhood also alter predisposition to asthma. Moreover, the current paradigm for asthma development extends far beyond simple childhood environmental exposures to include fetal development, genetic predisposition, and interactions of the developmental state and genetics with the environment.

Familial aggregation and segregation analysis of eosinophil levels

The number of circulating eosinophils is associated with the risk of asthma in population samples. Therefore, eosinophil levels may be an intermediate phenotype for asthma amenable to genetic analysis. We examined familial aggregation of the number of eosinophils x 10(6) L(-1) and the percentage of eosinophils based on a 300 count differential in 644 Hispanic and non-Hispanic white families, with 2, 097 subjects, enrolled in the Tucson Children's Respiratory Study. Both measures were adjusted for age, season and year at the time blood was drawn, sex, and ethnicity. Segregation analysis was conducted in the 458 non-Hispanic white families, as there were no significant familial correlations in the Hispanic families, and there was significant heterogeneity by ethnic group. Familial correlations (rho) in the non-Hispanic white families were as follows: mother-father, 0.05; mother-child, 0.18 (p < 0.001); father-child, 0.07; sibling-sibling, 0.31 (p < 0.001). Without covariates analyses indicated a polygenic/multifactorial mode of inheritance. After adjusting for current and past asthma an oligogenic mode of inheritance was suggested, plus additional residual familial components that were mainly maternally mediated. This study supports the notion of multiple, relatively common genes interacting to determine genetic susceptibility to asthma. Holberg CJ, Halonen M, Wright AL, Martinez FD. Familial aggregation and segregation analysis of eosinophil levels.

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.