Exclusion from proximal 11q of a common gene with megaphenic effect on atopy

The role of the FcepsilonRI beta-chain in allergic diseases

The high affinity receptor for IgE, FcepsilonRI, is a multimeric surface receptor that is expressed exclusively as a tetramer on rodent cells, but exists as a tetramer or trimer on human cells. The tetrameric form is expressed on effector cells of allergic responses such as mast cells and basophils and is composed of an IgE-binding alpha-subunit, a beta-subunit and a gamma-subunit dimer. Complexes lacking the beta-subunit are found on human antigen-presenting cells. On mast cells and basophils, FcepsilonRI is essential for IgE-mediated acute allergic reactions. Crosslinking of FcepsilonRI by IgE and multivalent antigen induces a signaling cascade that culminates in the release of preformed mediators and the synthesis of lipid mediators and cytokines. The beta-subunit functions as an amplifier of FcepsilonRI expression and signaling. As a consequence, strongly enhanced mast cell effector functions and in vivo allergic reactions can be observed in the presence of FcepsilonRIbeta. In contrast, a truncated beta-isoform (betaT) that is produced by alternative splicing acts as an inhibitor of FcepsilonRI surface expression. Thus, by producing two proteins with antagonistic functions, the FcepsilonRIbeta gene could serve as a potent regulator of allergic responses. In addition, the genomic region encompassing the beta-chain has been linked to atopy and a number of polymorphisms within the FcepsilonRIbeta gene are associated with various atopic diseases. It remains to be elucidated how these polymorphisms might affect the allergic phenotype. These functions of the beta-chain together with the described genetic linkages to atopy make it a candidate for a role in the pathophysiology of allergic diseases.

Evidence for asthma susceptibility genes on chromosome 11 in an African-American population

Initial genome-wide scan data provided suggestive evidence for linkage of the asthma phenotype in African-American (AA), but not Caucasian, families to chromosome 11q markers (peak at D11S1985; LOD=2). To refine this region, mapping analysis of 91 AA families (51 multiplex families and 40 asthmatic case-parent trios) was performed with an additional 17 markers flanking the initial peak linkage marker. Multipoint analyses of the 51 multiplex families yielded significant evidence of linkage with a peak non-parametric linkage score of 4.38 at marker D11S1337 (map position 68.6 cM). Furthermore, family-based association and transmission disequilibrium tests conducted on all 91 families showed significant evidence of linkage in the presence of disequilibrium for several individual markers in this region. A putative susceptibility locus was estimated to be at map position 70.8 cM with a confidence interval spanning the linkage peak. Evidence from both linkage and association analyses suggest that this region of chromosome 11 contains one or more susceptibility genes for asthma in these AA families.

Linkage analysis of markers on chromosome 11q13 with asthma and atopy in a United Kingdom population

Previous studies have suggested that atopy is linked to the beta chain of the high affinity IgE receptor (Fcepsilon R1-beta) on chromosome 11q13. Fcepsilon R1-beta polymorphisms, I181L, V183L, and E237G, are reported to be associated with asthma and atopy. The aim of this study was to investigate linkage to Fcepsilon R1-beta in a UK population and to assess the frequency of the polymorphisms and their association with asthma and atopy. A sample of 131 families was recruited at random with a sample of 109 families ascertained via an asthmatic proband. Each subject completed a written and video-assisted questionnaire and underwent bronchial challenge and skin prick testing. Serum total and specific IgE levels were measured. Quantitative scores were derived for asthma and atopy using principal component analysis. Four microsatellite markers were genotyped, including Fcepsilon R1-beta. The frequency of the I181L and V183L polymorphisms were determined by sequencing, and the E237G polymorphism was determined using the amplification refractory mutation system. We found no evidence for linkage to Fcepsilon R1-beta and only weak evidence for linkage to the less informative marker E237G. We found no examples of the I181L/V183L polymorphism in our population sample. Our study has failed to strengthen the evidence for a candidate gene on chromosome 11q13.

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.

The high-affinity IgE receptor (Fc epsilon RI): from physiology to pathology

The high affinity receptor for immunoglobulin E (designated Fc epsilon RI) is the member of the antigen (Ag) receptor superfamily responsible for linking pathogen-or allergen-specific IgEs with cellular immunologic effector functions. This review provides background information on Fc epsilon RI function combined with more detailed summaries of recent progress in understanding specific aspects of Fc epsilon RI biology and biochemistry. Topics covered include the coordination and function of the large multiprotein signaling complexes that are assembled when Fc epsilon RI and other Ag receptors are engaged, new information on human receptor structures and tissue distribution, and the role of the FcR beta chain in signaling and its potential contribution to atopic phenotypes.

Asthma, wheezy bronchitis, and atopy across two generations

Although the prevalence of asthma has risen significantly during the last 30 yr, it is not clear whether this has occurred primarily in persons with a strong genetic predisposition to asthma and atopy or in other sections of the population. We have investigated outcomes in children of nuclear families selected through probands previously characterized by studies in 1964 and 1989 as having histories of persistent childhood onset atopic asthma, transient childhood wheezy bronchitis, and no respiratory symptoms or atopy. Children of wheezy bronchitic probands had a significantly better symptomatic outcome in adolescence, irrespective of the atopic status of the parent proband, than do children of either asthmatic or asymptomatic probands, suggesting that this may be a syndrome that shows familial aggregation and is distinct from asthma. Total serum IgE levels were significantly lower in children of nonatopic asymptomatic probands, including those with wheezing symptoms. In contrast children of nonatopic asymptomatic probands had an unexpectedly high prevalence of wheezing (33%), positive skin prick tests (56%), and positive specific serum IgE to common allergens (48%) that was similar to that found in children of atopic asthmatic probands. Our findings support the concept that wheezy bronchitis is a separate syndrome from atopic asthma. High total serum IgE levels within our population appear to be an important marker of genetic predisposition to atopy. Our data also suggest that much of the increase in asthma prevalence is associated with specific IgE sensitization and is occurring in persons previously considered to be at low risk of developing asthma or atopy.

Linkage of chromosome 5q and 11q gene markers to asthma-associated quantitative traits in Australian children

Asthma is a genetically complex disease, and the investigation of putative linkages to candidate loci in independent populations is an important part of the gene discovery process. This study investigated the linkage of microsatellite markers in the 5q and 11q regions to asthma-associated quantitative traits in 121 Australian Caucasian nuclear families. The families were recruited on the basis of a child proband: a cohort of 95 randomly recruited families of unselected probands (n = 442 subjects) and a cohort of 26 families of probands selected on the basis of severe symptomatic asthma (n = 134 subjects). The quantitative traits assessed included serum levels of total IgE and specific IgE to house dust mite and mixed grass, blood eosinophil counts, and the dose-response slope (DRS) of FEV1 to histamine provocation. Multipoint linkage analysis using Haseman-Elston sib-pair methods provided evidence of significant linkage between the chromosome 5q markers and loge total serum IgE levels, specific serum IgE levels, and loge blood eosinophil counts. The chromosome 11q markers showed evidence of significant linkage to specific serum IgE levels. Neither region demonstrated significant linkage to the loge DRS to histamine. Phenotypes were residualized for age and sex. These data are consistent with the existence of loci regulating asthma-associated quantitative traits in both the 5q31-33 and 11q13 chromosomal regions.

Parental history and the risk for childhood asthma. Does mother confer more risk than father?

Although heredity plays a major role in asthma and in other allergic diseases, mechanisms underlying the inheritance of these disorders are poorly understood, as is the relative contribution of maternal and paternal conditions to risk of disease. We investigated doctor-diagnosed maternal and paternal asthma, eczema, and hay fever as cross-sectional predictors of childhood asthma and allergic disease in 306 children with a median age of 3.5 yr from families in which at least one parent had a history of either asthma or other allergic conditions. For both childhood asthma and eczema, the strongest parental predictors were the same conditions in the parents. For asthma in particular, maternal asthma was most strongly associated with asthma in the child over all ages in both univariate (OR = 3.2, 95% CI = 1.5 to 6.7) and multivariable (OR = 4.1, 95% CI = 1.7 to 10.1) models. Paternal asthma was weakly associated with childhood asthma in the univariate model (OR = 1.4, 95% CI = 0.6 to 3.2), but this association increased in magnitude in the multivariable model (OR = 2.7, 95% CI = 1.0 to 7.2). Among the children < 5 yr of age, the risk for childhood asthma associated with maternal asthma (OR = 5.0, 95% CI = 1.7 to 14.9) was greater than the risk associated with paternal asthma (OR = 1.6, 95% CI = 0. 5 to 5.9), whereas both maternal asthma and paternal asthma were associated with similar risks among children >= 5 yr of age (OR = 4. 6, 95% CI = 1.1 to 19.0 and OR = 4.1, 95% CI = 1.0 to 16.0, respectively). The odds of having a child with asthma were three times greater in families with one asthmatic parent and six times greater in families with two asthmatic parents than in families where only one parent had inhalant allergy without asthma; furthermore, inhalant allergy in one parent also conferred additional risk in the presence of asthma in the other parent. Further investigation is needed into the relative importance of genetic factors and in utero and postnatal exposures in determining the differential effects of maternal and paternal asthma on the development of childhood asthma.

Exclusion of chromosome 11q and the FcepsilonRI-beta gene as aetiological factors in allergy and asthma in a population of Dutch asthmatic families

BACKGROUND

The beta subunit of the high-affinity receptor for IgE (FcepsilonRI-beta) is localized to chromosome 11q13 and has been reported by Cookson et al. to be in close genetic linkage with a gene for atopy. A maternally inherited association was found between the presence of a variant of FcepsilonRI-beta, Ile181Leu, and high total serum IgE levels (IgE > 100 IU). In a previous study of 20 Dutch families, we found no evidence for linkage of atopy or bronchial hyperresponsiveness (BHR) to chromosome 11q.

OBJECTIVE

Recently segregation analysis in 92 families has given us evidence for two independent major loci accounting for 78% of the observed variance in total serum IgE levels, and linkage analysis using both sib-pair and LOD score methods has identified one major locus for regulation of IgE levels and BHR near the cytokine gene complex on chromosome 5q. The objective of this study is to pursue the identification of the second major locus.

METHODS

We have studied markers in the area of the high affinity IgE receptor (FcepsilonRI-beta) on chromosome 11q (D11S1314, FcepsilonRI-beta and D11S987) in 83 families for whom DNA was available. Furthermore, our families have been examined for variance in the FcepsilonRI-beta gene, specifically for Leu181 and Leu181/Leu183 mutations.

RESULTS

By sib-pair analysis, there is no evidence for linkage of total serum IgE levels or number of positive skin tests to these markers in our population. Similar negative results were obtained for affected sib-pair analysis of BHR, with the exception of D11S1314, which was significant at P=0.046. The FcepsilonRI-beta gene in 36 female probands, 44 male probands and 46 female spouses was sequenced for these mutations. For each of these 126 individuals sequencing of FcepsilonRI-beta demonstrated a wild-type sequence pattern, with no mutations found in anyone, male or female.

CONCLUSION

We are unable to confirm the presence of significant mutations in FcepsilonRI-beta gene in our population, and we cannot confirm that the FcepsilonRI-beta gene is crucial to the pathogenesis of allergic inflammation in asthma.

The candidate region approach to the genetics of asthma and allergy

To date, the strongest linkage claims for genes underlying asthma and atopy have been for chromosomes 5 and 11. Chromosome 5q contains the cytokine cluster and the beta2 adrenoceptor, and the beta chain of the high-affinity IgE receptor (FCepsilonRI-beta) is encoded on chromosome 11q13. We have attempted to replicate these findings in two distinct sample populations from the United Kingdom. Allelic associations were identified in both regions, but there was no significant evidence for linkage. Although we could not substantiate the existence of the nucleotide changes reported within exon 6 of the FCepsilonRI-beta gene, an amino acid substitution in exon 7 was strongly linked to asthma and atopy. We have also identified positive linkage and allelic associations to several markers on chromosome 12q in both our UK populations. Independent evidence from another study also supports linkage to 12q, so although our data could not confirm linkage to chromosomes 5 or 11, we have identified an additional region of the genome that could be important for the genetic predisposition to asthma and atopy.

Prenatal origins of asthma and allergy

The prevalence of asthma and related allergic disorders has increased considerably over the last 25 years. Genetic stock has not changed, so environmental factors must have influenced the phenotype. Infants who develop allergy already have an altered immune response at birth. We have investigated the development of immune responses during gestation and the effect of maternal allergen exposure during pregnancy and infant exposure in the first month of life on the development of allergy and disease. There was higher specific peripheral blood mononuclear cell proliferation to house dust mite (P = 0.01) and birch pollen (P = 0.004) in the third trimester compared with the second trimester, with the first positive responses seen at 22 weeks gestation. Maternal exposure to birch pollen after 22 weeks resulted in higher (P = 0.005) infant peripheral blood mononuclear cell responses to birch pollen at birth. Infants born at term, with at least one atopic, asthmatic parent, who developed allergic symptoms and positive skin prick test by one year of age had raised proliferative responses to house dust mites at birth compared to those with no symptoms (P = 0.01). In genetically predisposed individuals, antenatal factors, including maternal and thereby fetal exposure to allergens and maternoplacental-fetal immunological interactions, are active in determining whether an allergic predisposition is manifested as disease.