Lack of linkage between atopy and locus 11q13

Genetics of allergic disease

Currently, more than 20.3 million Americans report having asthma and an even greater number suffer from allergies. The cost for treatment of these dis-eases in the United States is greater than $8 billion with more than 40% of this total representing drug expenditure [59]. An intense effort has been made to understand the genetic components of asthma and allergies and how the identified genetic differences influence disease progression and response to drugs. In the future, it will be possible in the clinical setting to analyze a patient's genetic repertoire. From this information, the physician will gain in-sight into the genes involved in producing that subject's allergic and asthmatic phenotype; understand the natural history of that patient's disease;and predict responses (positive and negative) to pharmacologic agents. The end result will be the ability to tailor a specific treatment regime for each patient and reduce the overall cost of health care related to allergies and asthma.

5. Genetics of hypersensitivity

Genetics provides the basis for the host response to a variety of environmental factors that can play a role in the generation of complex genetic diseases, such as asthma and atopy. An understanding of the genetic bases for these conditions is therefore essential to understand their pathophysiology. Studies of the genetics of asthma and atopy have suffered from several daunting challenges. These include the recognition that these are conditions caused by numerous genes, with each gene assuming variable roles in different individuals. In addition, each gene presumably contributes only a small percentage to a given individual's genetic risk of asthma. This has led to the current situation, in which studies often demonstrate a lack of replication that can be explained by their being insufficiently powered. Furthermore, the pathophysiologies of asthma and atopy are incompletely understood, and the lack of clearly defined phenotypes also contributes to the inadequacies of the current literature. Nonetheless, regions of the human genome have been reproducibly associated with asthma and atopy. These regions have undergone intense study, and many genetic variants within them have been implicated as asthma and allergy genes. In addition, through candidate gene approaches, several genetic polymorphisms have been convincingly linked to increased risks for the development of asthma and atopy. Many of these genes are associated with alterations in responsiveness to therapeutic agents used in the treatment of these conditions. These genetic studies have an exciting potential for individually tailoring the therapeutic regimen to a given subject's genotype. It is to be hoped that they will also define new targets for the next generation of asthma and allergy therapeutic agents.

Genomics and proteomics of allergic disease

The world-wide effort to identify susceptibility genes for allergic diseases is motivated by the conviction that the identification of disease genes may permit the design of new classes of anti-inflammatory compounds. Molecules concerned with the allergic reaction, such as cytokines, chemokines, their receptors, major histocompatibility complex molecules, and transcription factors, could provide the candidate genes of the allergic diseases. On the basis of genetic studies, multiple research groups have attempted to identify a susceptibility gene for allergy using the candidate gene approach and/or genome-wide screening. Both of these approaches suggest genetic heterogeneity of allergic diseases. Many variants of candidate genes are or are not associated with particular diseases in different ethnic groups and the function of variants is now being investigated. Based on the information accumulated thus far and the information on the human genome sequence, future advances in research on genetic factors for allergic diseases will be likely lead to the establishment of more effective prophylaxis and therapy for these diseases.

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.

Atopic dermatitis: pathogenetic mechanisms

Atopic dermatitis (AD) is a chronic inflammatory skin disease with increasing incidence and socio-economical relevance. The diagnosis is made on clinical grounds and different diagnostic criteria sets have been established. The majority of all AD cases is associated with a sensitization to environmental allergens and increased serum IgE (so-called extrinsic AD), but about 10--30% of all cases suffer from the so-called intrinsic AD, which obviously lacks any link to the classical atopic diathesis. The genetic background of AD has been investigated by target gene approach by different groups with mostly contradictory results for each of the genes under study. An imbalance in the spectrum of Th1/Th2 responses, a disturbed prostaglandin metabolism, intrinsic defects in keratinocyte function, delayed eosinophil apoptosis, IgE-mediated facilitated antigen presentation by epidermal dendritic cells, a two phase model of the inflammatory response and staphylococcal superantigen effects are among the currently studied pathogenetical aspects of extrinsic AD, which are reviewed in this paper.

Allergy-associated polymorphisms of the Fc epsilon RI beta subunit do not impact its two amplification functions

Two variants of the beta-chain of the high affinity IgE receptor Fc epsilon RI, I181L-V183L and E237G, have been found associated with allergy. We have previously shown that the beta-chain plays at least two distinct amplifier functions. It amplifies Fc epsilon RI surface expression and signaling, resulting in an estimated 12- to 30-fold amplification of downstream events. To test the hypothesis that the I181L-V183L and E237G beta variants may be functionally relevant and could directly contribute to an allergic phenotype, we have evaluated the functional impact of the beta variants on the two amplifier functions of beta. We found that these variants have no direct effect on the beta amplifier functions. However, the possibility remains that these variants are in linkage disequilibrium with other more relevant polymorphisms or are affecting unknown beta-chain functions.

Contributing factors to the pathobiology. The genetics of asthma

Markers in 19 chromosomal regions have shown some evidence of linkage to asthma, atopy, or related phenotypes in multiple independent genome-wide searches. Linkages to five of these regions (5q, 6p, 11q, 12q, and 13q) have also been reported in non-genome-wide screens. In addition, at least two independent studies have reported linkages to markers on 16p. Numerous candidate genes in these regions have shown varying levels of association to asthma or atopic phenotypes, potentially implicating them as disease susceptibility loci. These include the IL4, CD14, and B2ADR genes on 5q, the HLA-DRB1 and TNF genes on 6p, the FCERB1 and CC16 genes on 11q, and the IL4RA gene on 16p. It still remains to be determined whether polymorphisms in these genes account for the reported linkages in these regions. Studies are underway in laboratories around the world to identify the disease-causing variations in these genes that account for the linkages just discussed. Identifying specific genetic polymorphisms that influence asthma and atopic phenotypes will shed light on the molecular pathways involved in these complex disorders and provide a better understanding of the pathophysiology of asthma and atopy.

Chromosome 11q13 and atopic asthma

Asthma is a complex syndrome in which bronchial inflammation and smooth muscle hyperactivity lead to labile airflow obstruction. The commonest form of asthma is that due to atopy, which is an immune disorder where production of IgE to inhaled antigens leads to bronchial mucosal inflammation. The ultimate origins of asthma are interactive environmental and genetic factors. The genetics is acknowledged to be heterogeneous, and one chromosomal region of interest and controversy has been 11q13. To clarify the nature of the chromosome 11q13 effect in atopy and asthma, we conducted a genetic association study in subjects with marked atopic asthma and matched controls, which incorporated the study of 13 genetic variants over a distance of 10-12 cM and which took account of detailed immune and clinical phenotyping. Association with high IgE levels was limited to the interval flanked by D11S1335 and CD20 in a 0.8-Mb interval and was greatest for variants of Fc epsilonRIbeta and HTm4; these variants also associated with asthma (recurrent wheeze with labile airflow obstruction and need for regular inhaler treatment). At the more telomeric marker, D11S480, variants associated with asthma, but not with high IgE levels. The data might support the possibility of multiple loci relevant to atopic asthma on chromosome 11q13.

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.

Mutational analysis of the high affinity immunoglobulin E receptor beta subunit gene in asthma

BACKGROUND

The gene for the beta subunit of the high affinity receptor for immunoglobulin E (FcepsilonRI-beta) on chromosome 11q13 is linked with clinical asthma and certain mutations have been identified. A study was undertaken to identify DNA variation in the FcepsilonRI-beta gene in a population sample in which linkage between 11q13 and asthma was explained by bronchial hyperreactivity (BHR) but not atopy.

METHODS

DNA samples from 71 subjects with asthma, atopy, or BHR were analysed. The complete coding region, some of the introns, and some of the 5' untranscribed region of the FcepsilonRI-beta gene were sequenced.

RESULTS

In the subjects studied there were no deviations from the published sequence in any of the seven coding exons of the FcepsilonRI-beta gene. In particular, the three previously reported mutations (Ile181, Leu183, Glu237) were not detected. Two new polymorphisms were discovered, one at position 243 in the 5' untranscribed region and one at position 4390 in intron III. Neither of these variants showed significant association with asthma, atopy, or BHR.

CONCLUSIONS

These results suggest that, in the population studied, linkage of asthma and BHR to 11q13 is not explained by mutations in the FcepsilonRI-beta gene. Other mutations in the non-coding region of this gene or in adjacent genes must explain the linkage findings in this study.

Genetic influences of chromosomes 5q31-q33 and 11q13 on specific IgE responsiveness to common inhaled allergens among African American families. Collaborative Study on the Genetics of Asthma (CSGA)

BACKGROUND

We have recently conducted a genome-wide screening for genes influencing Dermatophagoides pteronyssinus-specific IgE responsiveness as a part of the Collaborative Study on the Genetics of Asthma (CSGA), which showed evidence for linkage in some regions, including chromosomes 5131-q33 and 11q13 in African American families.

OBJECTIVES

To clarify relative contributions of these regions to atopy in the same African American population, we have conducted further genetic linkage studies of specific IgE responses toward common inhaled allergens.

METHODS

We studied 328 individuals in 58 African American families participating in the CSGA. Specific IgE responses toward Dermatophagoides farinae, cat, dog, American cockroach, rye grass, and Bermuda grass, as measured by skin tests, were used for multipoint linkage analysis with polymorphic markers on chromosomes 5q31-q33 and 11q13.

RESULTS

Specific IgE response toward American cockroach showed evidence for linkage to chromosomes 5q31-q33 (P = .0050) and 11q13 (P = .017). Specific IgE response toward dog showed evidence for linkage with chromosome 5q31-q33 (P = .0043). Evidence for linkage with chromosome 11q13 was obtained for specific IgE responses toward Dermatophagoides farinae (P = .012), cat (P = .035), and Bermuda grass (P = .017). The presence of a positive ST response for at least 1 of 30 common allergens showed evidence for linkage to chromosomes 5q31-q33 (P = .017) and 11q13 (P = .00058).

CONCLUSIONS

These data support that genes on both chromosomes 5q31-q33 and 11q13 confer susceptibility to upregulated IgE-mediated immune responses in this African American population. The putative genes on chromosomes 5q31-q33 and 11q13, however, showed contrasting effects on atopy, which may result from strong gene-environmental interactions.

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.

Evidence for linkage between asthma/atopy in childhood and chromosome 5q31-q33 in a Japanese population

Susceptibility to the development of asthma and other atopic diseases is known to be associated with genetic components, and several candidate genes have been reported to be linked to atopy in Caucasian populations. We conducted a study of linkage between asthma and markers on chromosomes 5q31-q33 and 11q13 in 68 Japanese families (306 members) by affected sib-pair analysis. Families for the linkage study were ascertained through asthmatic children visiting the allergy clinic. The results provide supportive evidence for linkage between asthma and gene markers in or near the interleukin-4 (IL-4) gene, the IL-9 gene, and D5S393 on chromosome 5q31-q33 (p = 0.0013, p = 0.018, and p = 0.0077, respectively). Linkage between atopic phenotype and these genetic markers was also suggested (p = 0.006, p = 0.01, and p < 0.0001 for atopy, respectively). However, we failed to find evidence for linkage of asthma or atopy to the IgE high-affinity receptor gene on 11q13 (p > 0.1). These findings indicate that beyond ethnicity, there are specific loci that contribute to susceptibility to atopy on chromosome 5q31-q33. In addition, our findings suggest that loci on chromosome 5q31-q33 are linked to the development of asthma in childhood.

Linkage analysis of bronchial hyperreactivity and atopy with chromosome 11q13

There are two key clinical features of asthma: allergy and bronchial hyperreactivity (BHR). Some pedigree studies of atopy have indicated linkage with the high affinity IgE receptor (Fc epsilon RI-beta) gene on chromosome 11q13, but others failed to confirm this linkage. We examined the genetic linkage of three polymorphic microsatellite markers to atopy and BHR in 120 affected sibling pairs recruited from the general community. We found no linkage to atopy at any of the three 11q13 loci studied. Our findings also do not favour linkage between BHR and loci approximately 8-9 cM either side of the Fc epsilon RI-beta gene.

Genetic factors in lung disease: atopy and bronchial asthma

Atopy defined as high IgE responsiveness has now been subject to genetic studies at the molecular level owing to the development of a great number of DNA markers over the human genome. Either by linkage analysis or by association study strong candidate genes of atopy have been proposed to be located on chromosome 11q13 and 5q31 where high-affinity IgE Fc receptor beta subunit and allergy-associated cytokines, respectively, have been mapped. Meanwhile, we found a novel association between one of alleles of D11S97, an anonymous DNA marker on 11q13, and high total serum IgE in a large number of Japanese general population and atopic family members. However, failure to replicate linkage or association studies by different investigators suggest polygenic nature of atopy. In addition to the genes regulating IgE synthesis, the requirement of local (pulmonary) genetic factors in the development of bronchial asthma have been speculated. Linkage analysis suggested possible existence of gene(s) regulating susceptibility and/or clinical characteristics of bronchial asthma also on chromosome 5q. One of the candidate is beta 2-adrenergic receptor gene polymorphism. Mutated gene transfection studies suggested functional significance of some polymorphisms and clinical evaluations have revealed their contribution to airway responsiveness and severity of asthma.

Genetic susceptibility to asthma in a changing environment

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

Cord blood immunoglobulin E in like-sexed monozygotic and dizygotic twins

Genetic and environmental factors have been implicated in the etiology of atopy and of serum IgE levels. In order to eliminate post-natal environmental influences we measured IgE in cord blood (CB-IgE) from a cohort of unselected, like-sexed twins. IgE determination was performed with a sensitive radioimmunoassay with a detection limit of 0.01 kU/l. Samples with contamination by maternal blood were identified by IgA determination and excluded. CB-IgE was evaluated in 29 monozygotic (MZ) and 28 dizygotic (DZ) twin pairs. The means and variances for IgE values were comparable for MZ and DZ twins when sex was controlled for. Placental anatomy (MZ twins with mono- and dichorial placenta and DZ twins with one or two placentae) had no significant influence on the IgE levels. In an analysis of variance with sub-sampling the among-pair, within-pair and analytical variance components were calculated. The analytical variance was well below the biological variances. Biometrical analysis showed that the best model by Akaike Information Criteria was a model including only additive genetic and non-shared environmental factors. With this model the heritability estimate was 0.8. These data suggest that the majority of the variation in CB-IgE is accounted for by genetic factors, but a substantial effect of a common environment cannot be excluded with the present sample size.

Atopy and the ectopic immune response

A hypothesis if formulated for the mode of action of the 'atopy gene': the gene(s) causing an increased tendency to mount an IgE immune response to trivial environmental antigens. It is postulated that some antigens are not efficiently transported to the lymphoid organs, the location of the 'eutopic' immune system; migratory lymphoid cells may occasionally react and start an inefficient immune response in sites not so destined. This is called an ectopic immune response. This response lacks the regulatory influences prevailing in the lymphoid organs, which results in approximately equal quantities of the various immunoglobulin isotypes, including IgE. The atopy gene(s) work by increasing the risk of such an ectopic immune response.

Candidate gene loci in asthmatic and allergic inflammation

New techniques for scanning the human genome promise great advances in tracking the origins of disorders caused by multiple genes. However, it is clear from the studies presented in this overview that we are far from understanding the genetic basis of asthma and atopy and their interaction with the environment. It is also clear that agreement must be reached on definition of the phenotype and methods of ascertainment in order to carry out large multicentre collaborative studies. Positive findings need to be validated in different populations selected for the presence of the disease and then confirmed in a random population where the prevalence of asthma and atopy will also be expected to be significant.

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

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

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

We have typed three markers on proximal 11q in 131 random families with three or more children studied for atopy. A summary map that includes the FCER1B candidate was constructed. Using a 2-locus disease model, we performed combined segregation and linkage analysis of three models, none of which suggested linkage. Nine marker loci on other chromosomes were also negative. In the regions swept by these 12 markers we cannot rule out a rare gene, perhaps of large effect, nor a common gene of small effect. However, a common gene of large effect is excluded. These results and alternative strategies are discussed in the perspective of inconsistent evidence for a major atopy gene.

Association between high serum total IgE levels and D11S97 on chromosome 11q13 in Japanese subjects

The genetic linkage of atopy to chromosome 11q13 through maternally derived alleles has been previously reported. Linkage analysis in Japanese families did not confirm the existence of a major gene for atopy at this locus under the model of autosomal dominant inheritance. However, we observed a significant association between serum total IgE levels and genetic markers at this locus both in 14 Japanese atopic families and in 120 unrelated Japanese subjects. We detected eight alleles at the D11S97 locus and eight alleles in the CA/GT repeat region in the fifth intron of the Fc epsilon RI beta gene. A significantly increased frequency of the D11S97/PstI 0.96 kb allele was observed in the chromosomes of the subjects with high serum total IgE levels both in the family study (p < 0.001) and in the population study (p < 0.05). However, multipoint linkage analysis again did not show any evidence for the existence of a major gene regulating atopy on chromosome 11q13 with location scores to -35 under the model of maternal inheritance. Evidence against linkage was confirmed by the non-parametric linkage analysis, using the affected pedigree member method. Also, there was no substitution of isoleucine for leucine in the fourth transmembrane domain of Fc epsilon RI beta (Leu181), which was reported to be responsible for a subset of atopy in the British population. Therefore, the association of serum total IgE levels with chromosome 11q13 indicates that a gene or genes at this locus may contribute to the expression of high IgE levels in the Japanese population as well as in the British population, but the heterogeneity of the genetic regulation of serum total IgE levels is evident between the two populations.

Familial atopy in Australian pedigrees: adventitious linkage to chromosome 8 is not confirmed nor is there evidence of linkage to the high affinity IgE receptor

Atopy frequently displays autosomal dominant inheritance and recent studies have favoured genetic linkage between atopy and the human chromosome 11q13. We have studied 12 extended families with aggregation of atopy consistent with autosomal dominant inheritance. The families have been studied for linkage of asthma and atopy to loci on chromosome 8p following the observation that one family suggested preliminary evidence of linkage to an anonymous hypervariable locus cloned from a DNA fingerprint and mapped to 8pter-p22. Subsequent analysis shows this putative linkage to be adventitious as the remaining 11 families do not support linkage between atopy and 8p. We have analysed the same families for evidence of linkage of atopy to loci on 11q13. In these families there is no evidence of association between atopy and the 11q loci stronger than that expected by chance alone; furthermore there is no suggestion that a subpopulation of these families display linkage between atopy and the loci. In addition neither the 8p loci nor the 11q loci exhibit evidence of linkage to atopy by affected sib-pair analysis. This also conflicts with previously published data for 11q.

Linkage between severe atopy and chromosome 11q13 in Japanese families

Atopy, characterised by allergic asthma and rhinitis, is due to increased IgE responses to common aeroallergens. An Oxford group has described maternal inheritance of atopy, where there is significant linkage between IgE responsiveness and a VNTR marker D11S97 and a CA microsatellite within a candidate gene, the high affinity IgE receptor beta subunit (Fc epsilon RI beta), on chromosome 11q. Attempts at independent replication have produced conflicting results. We therefore recruited 270 atopic asthmatic probands in a Japanese community population for genetic linkage analysis. Four families, each with more than 15 meioses and a clear phenotype for atopy, were selected for genetic analysis. Atopy was defined as presence of all of raised total IgE, positive RAST and skin tests to three or more aeroallergens; non-atopy, as absence of all these criteria. Linkage analysis showed a maximum two-point lod score of 9.35 for D11S97 and Fc epsilon RI beta under the assumption of unequal rates of maternal and paternal recombination. Two families showed close genetic linkage with Fc epsilon RI beta with a pattern of maternal inheritance. These results from a Japanese population provide further evidence for genetic linkage between severe atopy and chromosome 11q13 and the likelihood of genomic imprinting at the locus.

Association between atopy and variants of the beta subunit of the high-affinity immunoglobulin E receptor

The beta-subunit of the high-affinity IgE receptor (Fc epsilon RI-beta) on chromosome 11 is maternally linked to atopy, the state of enhanced IgE responsiveness underlying allergic asthma and rhinitis. We have identified a common variant of Fc epsilon RI-beta, lle181Leu within the 4th transmembrane domain. Leu181 shows significant association with positive IgE responses in a random patient sample. Amongst 60 unrelated nuclear families with allergic asthmatic probands, Leu181 is identified in 10 (17%), is maternally inherited in each, and shows a strong association with atopy. Our data indicate that Fc epsilon RI-beta, subject to maternal modification, may be the atopy-causing locus on chromosome 11q.

Asthma, allergy and atopy in southern Chinese school students

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