Allelic association of gene markers on chromosomes 5q and 11q with atopy and bronchial hyperresponsiveness

Linkage of asthma to markers on chromosome 12 in a sample of 240 families using quantitative phenotype scores

We present evidence of linkage between markers on chromosome 12 and asthma using the BETA program for nonparametric single- and multipoint linkage analysis. We have used quantitative scores as our phenotypic variables, combining data into indices for asthma and atopy and maximizing heritability. The largest single-locus LODs were achieved for asthma: D12S342 and asthma score (LOD 2.255), D12S324 and asthma affection (LOD 2.214), and D12S366 and wheeze (LOD 3.307). The region of interest identified using multipoint analysis, with a maximum LOD of 2.29, centers around D12S97 at location 173.5 cM with a standard error of 6.5 for the asthma score and close agreement for asthma affection and wheeze. Such evidence merits further investigation of this area in an attempt to define the region with greater precision with a view to identifying candidate genes. We hope that the methods presented will encourage researchers to use phenotypic information in a way that encourages meta-analysis.

Mapping susceptibility genes for asthma and allergy

Using family data, linkage analysis has been performed to determine the location in the genome of susceptibility genes for allergy and asthma. It has now become clear that there are multiple regions of the genome that contain susceptibility genes for allergy and asthma. The results from two genome screen studies will be reviewed and compared with results from candidate gene approaches. Results from several studies show evidence for linkage to chromosomes 5, 6, 11, 12, 13 and 14 for atopy, asthma or a related phenotype such as total serum IgE levels. Many of these regions contain candidate genes involved in regulating processes that may be involved in the development or progression of allergy and asthma. Some susceptibility genes may affect the expression of these disorders while others may affect response to therapy. Susceptibility to developing allergy or asthma appears to be due to the interaction of multiple genes with the environment.

Expression of interleukin 9 in the lungs of transgenic mice causes airway inflammation, mast cell hyperplasia, and bronchial hyperresponsiveness

Interleukin (IL)-9, a pleiotropic cytokine produced by the Th2 subset of T lymphocytes has been proposed as product of a candidate gene responsible for asthma. Its wide range of biological functions on many cell types involved in the allergic immune response suggests a potentially important role in the complex pathogenesis of asthma. To investigate the contributions of IL-9 to airway inflammation and airway hyperresponsiveness in vivo, we created transgenic mice in which expression of the murine IL-9 cDNA was regulated by the rat Clara cell 10 protein promoter. Lung selective expression of IL-9 caused massive airway inflammation with eosinophils and lymphocytes as predominant infiltrating cell types. A striking finding was the presence of increased numbers of mast cells within the airway epithelium of IL-9-expressing mice. Other impressive pathologic changes in the airways were epithelial cell hypertrophy associated with accumulation of mucus-like material within nonciliated cells and increased subepithelial deposition of collagen. Physiologic evaluation of IL-9-expressing mice demonstrated normal baseline airway resistance and markedly increased airway hyperresponsiveness to inhaled methacholine. These findings strongly support an important role for IL-9 in the pathogenesis of asthma.

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.

Linkage and association of an interleukin 4 gene polymorphism with atopic dermatitis in Japanese families

We examined linkage between markers at and near the IL4 gene and atopic dermatitis (AD) in 88 Japanese nuclear families. Affected sib pair analysis suggested linkage between the IL4 gene and AD (SPLINK lod=2.28). Transmission disequilibrium testing showed a significantly preferential transmission to AD offspring of the T allele of the -590C/T polymorphism of the IL4 gene (p=0.001). A case-control comparison suggested a genotypic association of the TT genotype with AD (odds ratio=1.88, p=0.01). Since the T allele was reported to be associated with increased IL4 gene promoter activity compared with the C allele, our data indicate that genetic differences in transcriptional activity of the IL4 gene influence AD predisposition, particularly in Japanese, because of a high frequency of the T allele.

Genetic control of immune response to recombinant antigens carried by an attenuated Salmonella typhimurium vaccine strain: Nramp1 influences T-helper subset responses and protection against leishmanial challenge

Attenuated strains of Salmonella typhimurium have been widely used as vehicles for delivery and expression of vaccine antigens in murine models of infectious disease. In mice, early bacterial replication following infection with S. typhimurium is controlled by the gene (Nramp1, formerly Ity/Lsh/Bcg) encoding the natural-resistance-associated macrophage protein (Nramp1). Nramp1 regulates macrophage activation and has multiple pleiotropic effects, including regulation of tumor necrosis factor alpha, interleukin 1beta (IL-1beta), and major histocompatibility complex class II molecules, all of which influence antigen processing and presentation. Nramp1 also has a direct effect on antigen processing, possibly by regulating the activity of proteases in the late endosomal compartment. Hence, there are multiple ways (regulation of bacterial load or recombinant antigen dose, class II molecule expression, costimulatory or adjuvant activity, and antigen processing) that Nramp1 might influence responses to recombinant salmonella vaccines. To test the hypothesis that Nramp1 influences responses to vaccination, congenic mouse strains have been used to analyze immune responses to recombinant antigens (tetanus toxoid antigen and leishmanial gp63) carried by live attenuated S. typhimurium aroA aroD mutants. Results show that congenic mice carrying the wild-type (S. typhimurium resistance) Nramp1 allele mount a predominantly T-helper-1 (IL-2 and gamma interferon) response to vaccination and show enhanced resolution of lesions following challenge infection with Leishmania major. In contrast, mice carrying mutant (S. typhimurium susceptibility) Nramp1 mount a T-helper-2 (immunoglobulin E and IL-4) response and show exacerbated lesion growth upon challenge.

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.

Association study of asthma and atopy traits and chromosome 5q cytokine cluster markers

BACKGROUND

Linkage studies have provided evidence for the presence of gene(s) in the 5q cytokine cluster region which control total serum immunoglobulin E (IgE) concentration, and bronchial hyperreactivity (BHR). However, the identification of the gene(s) involved has been confounded by the lack of power of the published linkage studies and the presence of multiple candidate genes mapped to the region.

OBJECTIVE

To define the important loci on 5q31-33 which are implicated in the control of total serum IgE and BHR through a case/control study of association.

METHODS

We performed an association study between 11 polymorphic markers (spanning the region 5q31.1-33.1) and total serum IgE and BHR traits. A case/control sample of 181 individuals was drawn from a larger set of 2415 adults, sampled at random from a district in Nottingham, UK. Half of the subjects in this case/control sample were hyperreactive to methacholine and asthmatic (cases), while the other half were non-reactive and non-asthmatic (controls). Association analysis was performed using the non-parametric chi-squared and Mann-Whitney U-tests.

RESULTS

We observed no evidence of strong allelic association between any of the above markers and the studied traits. Markers D5S404, interferon regulatory factor 1 (IRF-1) and D5S210 showed evidence of borderline association with BHR (P = 0.04, 0.03 and 0.04 respectively), and D5S404 showed borderline significance with IgE levels (P = 0.029).

CONCLUSIONS

This study presents evidence against the presence of a strong association between markers mapped to 5q31-33 and either BHR or total serum IgE. The significance of the weaker associations observed with markers D4S404, IRF-1 and D5S210 is not clear. Whether this represents a type I error secondary to multiple hypothesis testing or a true association is uncertain.

The spectrum of irritant-induced asthma: sudden and not-so-sudden onset and the role of allergy

A retrospective investigation of 86 asthmatic subjects defined clinical features of irritant-induced asthma and assessed the contributory role of an allergic predisposition. Three categories of asthma were evaluated: (1) occupational asthma due to a sensitizer (11 subjects, 13%); (2) irritant-induced asthma (54 persons, 63%); and (3) not occupational/environmental exposure-related asthma (21 subjects, 24%). Two distinct clinical presentations of irritant-induced asthma emerged: the first was sudden onset (29 subjects) and the second was not so sudden in onset (25 subjects). Sudden-onset, irritant-induced asthma was analogous to the reactive airways dysfunction syndrome. Clinical manifestations began immediately or within a few hours (always within 24 h) following an accidental, brief, and massive exposure. In contrast, for the not-so-sudden-onset asthma subjects, the causative irritant exposure was not brief, usually not massive, continued for > 24 h, and the initiation of asthma took longer to evolve. Eighty-eight percent of individuals with not-so-sudden irritant-induced asthma displayed an atopy/allergy status (p < 0.01). Some of the atopy/allergy subjects with presumed new-onset asthma were found to have suffered preexisting asthma that had been clinically quiescent for at least 1 year before the triggering exposure (16 persons). We conclude that preexisting allergic/atopy and/or preexisting asthma were significant contributors to the pathogenesis of not-so-sudden, irritant-induced asthma and emphasizes a critical interaction between environmental and host factors in the pathogenesis of asthma.

Interleukin 9: a candidate gene for asthma

Asthma is a complex heritable inflammatory disorder of the airways associated with clinical signs of atopy and bronchial hyperresponsiveness. Recent studies localized a major gene for asthma to chromosome 5q31-q33 in humans. Thus, this segment of the genome represents a candidate region for genes that determine susceptibility to bronchial hyperresponsiveness and atopy in animal models. Homologs of candidate genes on human chromosome 5q31-q33 are found in four regions in the mouse genome, two on chromosome 18, and one each on chromosomes 11 and 13. We assessed bronchial responsiveness as a quantitative trait in mice and found it linked to chromosome 13. Interleukin 9 (IL-9) is located in the linked region and was analyzed as a gene candidate. The expression of IL-9 was markedly reduced in bronchial hyporesponsive mice, and the level of expression was determined by sequences within the qualitative trait locus (QTL). These data suggest a role for IL-9 in the complex pathogenesis of bronchial hyperresponsiveness as a risk factor for asthma.

Why are we not all allergic: basic mechanisms for tolerance development

Harmless antigens encountered on the mucosal surface are normally tolerated in the sense that they do not induce inflammatory immune responses. Oral tolerance is the type of mucosal immune regulation that prevents inflammatory reactions to food proteins. However, parasites and invasive microorganisms at the mucosal surfaces must be recognised and dealt with in a proper manner. The immune system does so by cross-regulating the response where it either produces IgA to exclude invasion, IgE to fight parasites, or IgG to destroy the invasive organisms. Allergy is an anti-parasitic reaction to a misinterpreted but harmless antigen. This lack of tolerance induction is influenced by genetic factors controlling the amount of interleukin (IL)-4 produced initially in the immune response. IL-4 directs B-cells to produce IgE, induces naive T-cells to become IL-4 producing T-helper cells (Th2 cells) and prevent other T-cells from entering into the IFN-γ-producing Th1 pathway. Long lasting Th2 clones lose their IL-12 responsiveness and can no longer be induced to produce IFN-γ thus they are locked in an allergy inducing Th2 phenotype. Environmental factors play on the genetic background and influence the outcome of the immune response. Mucosal tolerance depends on an intact mucosal surface, is influenced by the age of the subject, and can be manipulated through antigen dose and place of entry. Immune-manipulating therapy may be more successful in primary than in secondary prevention of allergy.

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.

Genetic control of serum IgE levels and asthma: linkage and linkage disequilibrium studies in an isolated population

Immunoglobulin E (IgE) concentration in serum is elevated in atopic diseases such as asthma. A large genomic region on chromosome 5 has previously been implicated in the control of IgE levels and bronchial hyperreactivity and may, therefore, harbor genes predisposing to asthma. In an effort to confirm this linkage and to delimit the critical region, we took advantage of an isolated founder subpopulation in Finland to study genetic linkage and haplotype associations. Sixteen polymorphic markers, including the Interleukin-4 and -9 genes (IL4, IL9), were physically ordered and genotyped in 157 nuclear families. Genetic linkage studies involving sib- and cousin-pair analyses found no evidence of genetic linkage between markers in 5q and either serum IgE levels or asthma. Haplotype association studies were also performed. Although initial inspection suggested the possibility of linkage disequilibrium in the region of IL9, we developed a rigorous permutation test for assessing association and determined that the association was no greater than would be expected by chance. Sequence analysis of the IL9 gene in three patients sharing a possibly conserved haplotype revealed a T113M coding polymorphism, but this variant showed no association with either serum IgE levels or asthma. We conclude that allelic variation at chromosome 5q31 is not likely to contribute to inheritance of serum IgE levels or the development of asthma in this Finnish subpopulation.

Evidence for multiple genetic susceptibility loci for asthma

Genetic susceptibility to asthma is due to multiple genes that interact with each other and the environment. There are many known environmental influences, such as viral and other respiratory infections and exposure to allergens, air pollutants, and active or passive cigarette smoke (1). Genome-wide screens for asthma and atopy have been completed and show statistical evidence for linkage in different racial groups and population samples (4, 5). Some of these linkages have already been replicated in different studies, and most of them are in chromosomal regions containing relevant candidate genes that may regulate inflammatory processes including cytokine synthesis, T-cell responses, or other immune functions. These associations support the relevance of this genetic approach in understanding susceptibility to and expression of asthmatic and allergic phenotypes. Once specific sequence variants are identified, it will become important to test for gene-environment interaction in order to understand the significance and relative effect of each gene on the overall phenotype.

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.

Immunogenetics of leishmanial and mycobacterial infections: the Belem Family Study

In the 1970s and 1980s, analysis of recombinant inbred, congenic and recombinant haplotype mouse strains permitted us to effectively 'scan' the murine genome for genes controlling resistance and susceptibility to leishmanial infections. Five major regions of the genome were implicated in the control of infections caused by different Leishmania species which, because they show conserved synteny with regions of the human genome, immediately provides candidate gene regions for human disease susceptibility genes. A common intramacrophage niche for leishmanial and mycobacterial pathogens, and a similar spectrum of immune response and disease phenotypes, also led to the prediction that the same genes/candidate gene regions might be responsible for genetic susceptibility to mycobacterial infections such as leprosy and tuberculosis. Indeed, one of the murine genes (Nramp1) was identified for its role in controlling a range of intramacrophage pathogens including leishmania, salmonella and mycobacterium infections. In recent studies, multicase family data on visceral leishmaniasis and the mycobacterial diseases, tuberculosis and leprosy, have been collected from north-eastern Brazil and analysed to determine the role of these candidate genes/regions in determining disease susceptibility. Complex segregation analysis provides evidence for one or two major genes controlling susceptibility to tuberculosis in this population. Family-based linkage analyses (combined segregation and linkage analysis; sib-pair analysis), which have the power to detect linkage between marker loci in candidate gene regions and the putative disease susceptibility genes over 10-20 centimorgans, and transmission disequilibrium testing, which detects allelic associations over 1 centimorgan (ca. 1 megabase), have been used to examine the role of four regions in determining disease susceptibility and/or immune response phenotype. Our results demonstrate: (i) the major histocompatibility complex (MHC: H-2 in mouse, HLA in man: mouse chromosome 17/human 6p; candidates class II and class III including TNF alpha/beta genes) shows both linkage to, and allelic association with, leprosy per se, but is only weakly associated with visceral leishmaniasis and shows neither linkage to nor allelic association with tuberculosis; (ii) no evidence for linkage between NRAMP1, the positionally cloned candidate for the murine macrophage resistance gene Ity/Lsh/Bcg (mouse chromosome 1/human 2q35), and susceptibility to tuberculosis or visceral leishmaniasis could be demonstrated in this Brazilian population; (iii) the region of human chromosome 17q (candidates NOS2A, SCYA2-5) homologous with distal mouse chromosome 11, originally identified as carrying the Scl1 gene controlling healing versus nonhealing responses to Leishmania major, is linked to tuberculosis susceptibility; and (iv) the 'T helper 2' cytokine gene cluster (proximal murine chromosome 11/human 5q; candidates IL4, IL5, IL9, IRF1, CD14) controlling later phases of murine L. major infection, is not linked to human disease susceptibility for any of the three infections, but shows linkage to and highly significant allelic association with ability to mount an immune response to mycobacterial antigens. These studies demonstrate that the 'mouse-to-man' strategy, refined by our knowledge of the human immune response to infection, can lead to the identification of important candidate gene regions in man.

Atopy phenotype in subjects with variants of the beta subunit of the high affinity IgE receptor

BACKGROUND

Fc epsilon RI plays a central role in atopy, thus genetic variants of Fc epsilon RI-beta may alter receptor function to enhance atopic responses and may manifest as a more severe atopic phenotype and more symptomatic atopic disease. The immunological and clinical features of atopy in children with and without the Leu 181 variant of Fc epsilon RI-beta were compared.

METHODS

Sixty British nuclear families, including 10 families with the Fc epsilon RI-beta variant Leu 181, recruited via a young proband with atopic asthma were analysed for atopic parameters including total IgE, specific IgE, and clinical atopic disorder.

RESULTS

Compared with other children (combined atopic and non-atopic subjects), maternally inherited Leu 181 was associated with increased levels of total IgE (odds ratio (OR) 4.82, 95% confidence interval (CI) 1.02 to 27.66, p < 0.01) and a positive IgE response to grass pollen allergen (OR 7.45, 95% CI 1.56 to 35.52, p < 0.005) but not wheeze (OR 1.97, 95% CI 0.56 to 7.69), asthma (OR 2.25, 95% CI 0.65 to 7.85), or required medications (OR 0.95, 95% CI 0.29 to 3.14). There were trends for each atopic parameter to be more marked in atopic children with maternally inherited Leu 181 than in atopic children without Leu 181. Children with maternal Leu 181 had significantly raised eosinophils but there was no difference in basophil levels compared with other atopic children.

CONCLUSIONS

The Leu 181 variant of Fc epsilon RI-beta, or another identified variant in linkage disequilibrium, may promote the development of atopy.

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.