Genetic regulation of Dermatophagoides pteronyssinus-specific IgE responsiveness: a genome-wide multipoint linkage analysis in families recruited through 2 asthmatic sibs. Collaborative Study on the Genetics of Asthma (CSGA)

Genome-wide association study identifies BTNL2 associated with atopic asthma in children

Asthma is a heterogeneous disease characterized by chronic airway inflammation with a genetic predisposition. Butyrophilin-like 2 (BTNL2) is a member of the immunoglobulin superfamily that plays an important role in regulating T cell activation and immune homeostasis. Here, we aimed to investigate the association of the genetic variants of BTNL2 with childhood asthma and asthma-related traits by utilizing extreme asthma phenotypes and employing a genome-wide association study. Our study included 243 children with well-defined moderate to severe atopic asthma and 134 healthy children with no history of allergic diseases and allergic sensitization. DNA from these subjects was genotyped using AxiomTM Genome-Wide Array Plates. Although no single nucleotide polymorphisms (SNPs) reached a genome-wide threshold of significance, 3 SNPs, rs3817971, rs41355746, and rs41441651, at BTNL2 were significantly associated with moderate to severe atopic asthma after performing Bonferroni correction. These SNPs were also associated with the risk of allergic sensitization toward house dust mites and the presence and degree of bronchial hyperresponsiveness. Thus, we identified that BTNL2 was associated with atopic moderate to severe persistent asthma in Korean children, and this may play an important role in disease development and susceptibility.

International consensus (ICON) on: clinical consequences of mite hypersensitivity, a global problem

Since mite allergens are the most relevant inducers of allergic diseases worldwide, resulting in significant morbidity and increased burden on health services, the International Collaboration in Asthma, Allergy and Immunology (iCAALL), formed by the American Academy of Allergy, Asthma and Immunology (AAAAI), the American College of Allergy, Asthma and Immunology (ACAAI), the European Academy of Allergy and Clinical Immunology (EAACI), and the World Allergy Organization (WAO), has proposed to issue an International Consensus (ICON) on the clinical consequences of mite hypersensitivity. The objectives of this document are to highlight aspects of mite biology that are clinically relevant, to update the current knowledge on mite allergens, routes of sensitization, the genetics of IgE responses to mites, the epidemiologic aspects of mite hypersensitivity, the clinical pictures induced by mites, the diagnosis, specific immunotherapeutic approaches, and prevention.

HLA and asthma phenotypes/endotypes: a review

Asthma is a complex chronic inflammatory disease of the airways caused by the interaction of genetic susceptibility with environmental influences. Genome-wide association studies (GWAS) represent the most powerful approach for asthma, that have identified several genes (e.g., IL18R1, IL33, SMAD3, ORMDL3, HLA-DQ and IL2RB loci). HLA super-locus is a genomic region in the chromosomal position 6p21. Since no gene can be considered as an asthma gene, able to reflect the complex etiology and the heterogeneity of the disease the terms 'phenotype' and more recently 'endotype' have been used. This review, according to literature availability, focuses on the relationship between human leukocyte antigens (HLA) region specifically the HLA class II genes and different asthma phenotypes/endotypes, such as allergic asthma/Th2 associated, occupational and aspirin-sensitive asthma. The most common HLA haplotypes in the different asthma phenotypes are HLA-DRB1in allergic asthma, HLA-DQB1in occupational asthma and HLA-DPB1 in aspirin-sensitive asthma. However, it is difficult to study the role of class II genes in vivo because of the heterogeneity of human population, the complexity of MHC, and the strong linkage disequilibrium among different class II genes. Despite the variation and the inconsistency of the HLA haplotypes and alleles in different types of asthma, the association between HLA class II genes and asthma has been demonstrated in the majority of studies.

Current concepts of IgE regulation and impact of genetic determinants

Immunoglobulin E (IgE) mediated immune responses seem to be directed against parasites and neoplasms, but are best known for their involvement in allergies. The IgE network is tightly controlled at different levels as outlined in this review. Genetic determinants were suspected to influence IgE regulation and IgE levels considerably for many years. Linkage and candidate gene studies suggested a number of loci and genes to correlate with total serum IgE levels, and recently genome-wide association studies (GWAS) provided the power to identify genetic determinants for total serum IgE levels: 1q23 (FCER1A), 5q31 (RAD50, IL13, IL4), 12q13 (STAT6), 6p21.3 (HLA-DRB1) and 16p12 (IL4R, IL21R). In this review, we analyse the potential role of these GWAS hits in the IgE network and suggest mechanisms of how genes and genetic variants in these loci may influence IgE regulation.

Allele-specific transcription of the asthma-associated PHD finger protein 11 gene (PHF11) modulated by octamer-binding transcription factor 1 (Oct-1)

BACKGROUND

Asthma is a common, chronic inflammatory airway disease of major public health importance with multiple genetic determinants. Previously, we found by positional cloning that PHD finger protein 11 (PHF11) on chromosome 13q14 modifies serum immunoglobulin E (IgE) concentrations and asthma susceptibility. No coding variants in PHF11 were identified.

OBJECTIVE

Here we investigate the 3 single nucleotide polymorphisms (SNPs) in this gene most significantly associated with total serum IgE levels--rs3765526, rs9526569, and rs1046295--for a role in transcription factor binding.

METHODS

We used electrophoretic mobility shift assays to examine the effect of the 3 SNPs on transcription factor binding in 3 cell lines relevant to asthma pathogenesis. Relative preferential expression of alleles was investigated by using the allelotyping method.

RESULTS

Electrophoretic mobility shift assays show that rs1046295 modulates allele-specific binding by the octamer-binding transcription factor 1 (Oct-1). Analysis of the relative expression levels of the 2 alleles of this SNP in heterozygous individuals showed a modest, but highly significant (P = 6.5 × 10(-16)), preferential expression of the A allele consistent with a functional role for rs1046295.

CONCLUSION

These results suggest a mechanism by which rs1046295 may act as a regulatory variant modulating transcription at this locus and altering asthma susceptibility.

Human leukocyte antigen type and progression from onset of symptoms to development of asthma

This study investigated the influence of human leukocyte antigen (HLA) genes on the progression of asthma, from the initial onset of symptoms to when criteria for asthma are met. Study subjects were a subsample (n = 340) of 838 healthy children, aged 5-12 years, who participated in a previous study, and who had HLA data and asthma status. The duration in time from the initial onset of asthma symptoms documented in each subject's medical records to the index date when the subject first met criteria for asthma was determined. The time duration was compared between carriers and noncarriers of HLA genes of interest of the 340 original subjects with HLA data available, 114 children (33.5%) met criteria for asthma before 18 years of age. The median ages at onset of asthma symptoms and at the index date of asthma were 4.4 years and 7.2 years, respectively. The median time intervals between onset of symptoms and index date for HLA DRB1*11 carriers and noncarriers were 552 versus 61 days, respectively (p = 0.004). The same time intervals for HLA DQB1*0301 carriers and noncarriers were 420 versus 59 days, respectively (p = 0.012). However, HLA DQB1*0302 or DRB1*03 carriers had shorter median intervals, when compared with noncarriers (119 versus 266 days, respectively, p = 0.20; and 86 versus 258 days, respectively, p = 0.38) but they did not reach statistical significance. HLA type appears to influence the progression of asthma from initial symptoms to disease. Thus, genetic factors may affect the natural history of asthma.

Genetic and environmental contributions to allergen sensitization in a Chinese twin study

BACKGROUND

Allergic disease is on the rise worldwide. Effective prevention of allergic disease requires comprehensive understanding of the factors that contribute to its intermediate phenotypes, such as sensitization to common allergens.

OBJECTIVE

To estimate the degree of genetic and environmental contributions to sensitization to food and aeroallergens.

METHODS

Sensitization was defined as a positive skin prick test to an allergen. We calculated the zygosity-specific concordance rates and odds ratios (ORs) for sensitization to food and aeroallergens in 826 Chinese twin pairs [472 monozygotic (MZ) and 354 dizygotic (DZ)] aged 12-28 years. We also applied structural equation modelling procedures to estimate genetic and environmental influences on sensitization.

RESULTS

The concordance rates and risk of sensitization in one twin given the presence vs. the absence of sensitization in the other twin were higher in MZ twins than those in DZ twins. However, a large number of MZ twins were discordant in sensitization to common allergens. These observations suggest both genetic and environmental factors influence sensitization. Consistently, the estimated heritability and individual environmental components of the liability to sensitization ranged from 0.51 to 0.68 and 0.32 to 0.49, respectively, based on the best-fitted structural equation model. We also observed high phenotypic correlations between sensitization to two aeroallergens (cockroach and dust mite: 0.83) and two food allergens (peanut and shellfish: 0.58), but only moderate correlations for the pairs between sensitization to a food and an aeroallergen (0.31-0.46). The shared genetic and environmental factors between paired sensitizations contribute to the observed correlations.

CONCLUSION

We demonstrated that sensitization to common food and aeroallergens were influenced by both genetic and environmental factors. Moreover, we found that paired allergen sensitizations might share some common sets of genes and environmental factors. This study underscores the need to further delineate unique and/or pleiotropic genetic and environmental factors for allergen sensitization.

Genetic impact of a butyrophilin-like 2 (BTNL2) gene variation on specific IgE responsiveness to Dermatophagoides farinae (Der f) in Japanese

BACKGROUND

Dermatophagoides farinae (Der f) is one of the most frequently implicated allergens in several allergic diseases. Several genome-wide screens have identified a linkage between chromosome 6p21 and mite-specific IgE responsiveness. Butyrophilin-like 2 (BTNL2) is a member of the immunoglobulin superfamily and, on the basis of its homology to B7-1, has been implicated as a costimulatory molecule involved in T-cell activation. BTNL2 resides in the HLA region on chromosome 6p21, and significant associations between BTNL2 gene polymorphisms and several inflammatory diseases have been reported.

OBJECTIVE

The aim of this study was to examine whether BTNL2 gene polymorphisms are associated with specific IgE responses to Der f.

METHODS

Three single nucleotide polymorphisms (SNPs), including 2 coding SNPs and 1 intron SNP, were studied. One of the coding SNPs was the rs2076530 A > G, which has a functional consequence. A total of 863 unrelated Japanese subjects (447 positive and 416 negative for IgE to Der f) were recruited for a case-control study.

RESULTS

Controlling for gender, age, smoking, and the presence of asthma, multiple logistic regression analyses showed that homozygosity of the rs2076530 A allele, which has been reported to be a risk allele for sarcoidosis, was associated with a risk of sensitization towards Der f (Odds ratio; 1.55, p = 0.0060).

CONCLUSIONS

Although an association which may be due to the linkage disequilibrium with other genes in 6p21 needs to be ruled out, the present findings suggest that the BTNL2 gene might be one of the candidate genes that is responsible for the pathogenesis of Der f-specific IgE responsiveness.

Sex-stratified linkage analysis identifies a female-specific locus for IgE to cockroach in Costa Ricans

RATIONALE

The basis for gender influences on allergen-specific IgEs is unclear.

OBJECTIVES

To perform regular and sex-stratified genomewide linkage analyses of IgE to each of three allergens (Ascaris lumbricoides, Blatella germanica [German cockroach]), and Dermatophagoides pteronyssinus [dust mite]) and to conduct an association study of a candidate gene in a linked genomic region.

METHODS

Genomewide linkage analyses of allergen-specific IgEs were conducted in 653 members of eight large families of Costa Rican children with asthma. An analysis of the association between single-nucleotide polymorphisms in thymic stromal lymphopoietin (TSLP) and IgE measurements was conducted in 417 parent-child trios in Costa Rica. Significant results were replicated in 470 families of white children in the Childhood Asthma Management Program (CAMP).

MEASUREMENTS AND MAIN RESULTS

Among all subjects, there was suggestive evidence of linkage (LOD >/= 2.72) to IgE to Ascaris (on chromosome 7q) and IgE to dust mite (on chromosomes 7p and 12q). In a sex-stratified analysis, there was significant evidence of linkage to IgE to cockroach on chromosome 5q23 (peak LOD, 4.14 at 127 cM) in female subjects. TSLP is located within the 1.5 LOD-unit support interval for this linkage peak and has female-specific effects on lung disease in mice. In a sex-stratified analysis, the T allele of single-nucleotide polymorphism rs2289276 in TSLP was associated with reductions in IgE to cockroach (in Costa Rican girls) and total IgE (in girls in Costa Rica and in CAMP; P value for sex-by-genotype interaction, <0.01 in both studies).

CONCLUSIONS

Consistent with findings in murine models, a variant in TSLP may have female-specific effects on allergic phenotypes.

Recent advances in asthma genetics

There are over 100 genes that have been reported to be associated with asthma or related phenotypes. In 2006–2007 alone there were 53 novel candidate gene associations reported in the literature. Replication of genetic associations and demonstration of a functional mechanism for the associated variants are needed to confirm an asthma susceptibility gene. For most of the candidate genes there is little functional information. In a previous review by Hoffjan et al. published in 2003, functional information was reported for 40 polymorphisms and here we list another 22 genes which have such data. Some important genes such as filaggrin, interleukin-13, interleukin-17 and the cysteinyl leukotriene receptor-1 which not only were replicated by independent association studies but also have functional data are reviewed in this article.

[Asthma genetic factors]

Asthma is a chronic inflammatory airways disease, with a rising prevalence, particularly in childhood, and is considered an important public health problem. Its familial transmission is recognised, while the description and identification of the genes implicated in this disease are a challenge. In this revision paper the authors give a comprehensive explanation of the associated genes as well as the laboratorial methods that allow their identification.

Severity of childhood asthma and human leukocyte antigens type

We sought to learn if Class II HLA genes are associated with the severity of asthma in children. We examined a previously recruited cohort of 340 healthy children who had Class II HLA allele data available. We conducted a comprehensive review of their medical records to determine asthma status and, when present, its severity. We found that Class II HLA alleles, which were previously reported to have an association with asthma incidence, appear to have an association as well with asthma severity. These data support our hypothesis that both the incidence and severity of asthma are heritable and that HLA may play an important role in both development and severity of asthma. Because of limited statistical power, our study findings are subject to further investigation.

Childhood asthma and human leukocyte antigen type

Little is known about the relationship between human leukocyte antigen (HLA) class II genes and family history of asthma or atopy in relation to the incidence of childhood asthma. The objective of the study was to determine whether specific HLA class II genes (e.g., DRB1*03) are associated with asthma and whether such association explains the influences of family history of asthma or atopy on asthma incidence. A stratified random sample of 340 children who had HLA data available from the Rochester Family Measles Study cohort (n= 876) and a convenience sample of healthy children aged 5-12 years were the participants. We conducted comprehensive medical record reviews to determine asthma status of these children. The associations between the presence of specific HLA alleles and development of asthma and the role of family history of asthma or atopy in the association were evaluated by fitting Cox models. The cumulative incidence of asthma by 12 years of age among children who carry HLA DRB1*03 was 33%, compared to 24.2% among those who did not carry this allele. Adjusting for family history of asthma or atopy, gender, low birth weight, season of birth, HLA DRB1*04, and HLA DQB1*0302, the hazards ratio for HLA DRB1*03 carriers was 1.8 (95% confidence interval: 1.1-2.9, P= 0.020). We concluded that the HLA DRB1*03 allele is associated with asthma. However, the HLA class II gene does not explain the influences of family history of asthma or atopy on development of asthma. The mechanism underlying the association between asthma and HLA genes needs to be elucidated.

The genetics of bronchial asthma in children

Bronchial asthma is a chronic inflammatory disease based on an inappropriate stimulation of the immune system, for instance by environmental aeroallergens. It is characterised by bronchial hyperreactivity, reversible airway obstruction and mucus overproduction. During the last decades bronchial asthma has become the most common disease of childhood. Accordingly, many epidemiological and genetic studies have dealt with its origin. In fact, hundreds of genome-wide linkage analyses and association studies have identified several chromosomal regions harbouring asthma susceptibility genes like chromosome 2q, 5q, 6q, 11q, 12q and 13q. Also about 100 candidate genes for asthma have been described. However, not all of them have been confirmed in independent studies. Besides the genetic predisposition environmental factors play an important role in the development of allergic diseases. Studies predominantly performed in farmer children have shown that exposure to bacterial endotoxin early in life reduces the risk to develop asthma or atopy later on. Thus, recent studies focussed also on the interaction of genes variants with environmental factors which is summarised under the term genetic epidemiology. Further dissection of asthma genetics and its complex interaction with surrounding factors will hopefully help us in the development of new very specific drugs. In addition, the generation of a genetic risk profile for bronchial asthma should enable us for the first time to take well-directed preventive measurements early in live.

Haplotypes of surfactant protein C are associated with common paediatric lung diseases

Surfactant protein C is part of the surfactant complex lining up the alveoles and thereby inhibiting collapse of the airways. In addition it is involved in innate immune responses. Rare polymorphisms within surfactant protein C have been linked to sporadic paediatric lung diseases, like proteinosis or interstitial lung diseases. One study in the Finnish population described association of common polymorphisms with neonatal respiratory syndrome. Other common lung diseases have not yet been investigated for association with this gene. The aim of this study was to test surfactant protein C for association with bronchial asthma and with severe respiratory syncytial virus associated diseases in infancy. The two common amino acid variants Asn138Thr and Asn186Ser were genotyped on 322 children with asthma, 131 children with severe respiratory syncytial virus associated diseases and 270 controls. Statistical analyses of single polymorphisms made use of the Armitage's trend test; haplotypes were calculated with FAMHAP and FASTEHPLUS. Polymorphisms were in Hardy-Weinberg equilibrium and in tight linkage equilibrium in all populations. Single polymorphisms showed no association with the diseases, however, surfactant protein C haplotypes were associated with severe respiratory syncytial virus associated diseases (p = 0.013). Furthermore, an inverse haplotype distribution was found between children with asthma and respiratory syncytial virus infection (p = 0.00025). The results of our study might suggest opposing roles of surfactant Protein C in the genetic predisposition for respiratory syncytial virus associated diseases vs. asthma. The causal mechanism for this observation has still to be shown.

What are we learning from genetic cohort studies?

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

AluyMICB dimorphism within the class I region of the major histocompatibility complex is associated with asthma and airflow obstruction in the Busselton population

AIM

To examine the association between the Alu dimorphism within the first intron of the MICB gene and asthma and airflow obstruction. Background The highly polymorphic non-classical MHC class I polypeptide-related (MIC) genes, MICA and MICB, encode stress inducible glycoproteins, which are expressed on a variety of epithelial cells, including those of the lungs.

METHODS

AluyMICB genotyping was performed on 1109 subjects from the Busselton Health Study. From a standard questionnaire, 359 individuals indicated that they had been diagnosed by a doctor with asthma. Lung function was assessed by the forced expired volume in 1 second (FEV1) and expressed as a percent of the predicted value. Airflow obstruction was defined as FEV1<80% predicted.

RESULTS

In men, a dominant relationship was found between the AluyMICB DD genotype and asthma (P=0.006; chi2(2)=7.65). Furthermore, multivariate analysis adjusted for age, height, weight and body mass index (BMI) showed a relationship between DD genotype and asthma in men in a dominant model (odds ratio (OR)=1.97; 95% confidence interval (CI)=1.11-3.51; P=0.021). In women, an association was found between the AluyMICB II genotype and FEV1 percent predicted as a continuous variable (P=0.001). When adjusted for age and BMI, it showed a significant relationship between AluyMICB and airflow obstruction in a dominant model (OR=14.11%, 95% CI 3.29-60.57, P<0.001). However, no association was found between the AluyMICB II genotypes and airflow obstruction in men.

CONCLUSION

These findings suggest the possible involvement of a MHC class I gene in abnormal airway structure in women and airway function in men.

The synergistic effects of the IL-9 gene and environmental exposures on asthmatic Taiwanese families as determined by the transmission/disequilibrium test

Asthma occurs in genetically susceptible individuals in the presence of environmental factors. The interleukin-9 (IL-9) gene, one of the cytokine genes located on chromosome 5q31, plays an important role in the development of asthmatic syndrome by enhancing both T-cell and mast-cell function. This study investigated GT repeat polymorphism of the IL-9 gene and the gene-environment interactions, which may predispose individuals to asthma and atopy pathogenesis. In this study, we used the transmission/disequilibrium test (TDT) to investigate the relationship between asthma and the IL-9 gene by studying 123 parent-offspring trios and 91 siblings. For allele-specific TDT chi-squared test, allele 122 of the IL-9 gene showed significant association with asthmatics with specific IgE against house dust (HD) (P = 0.038). The additions of covariates to TDT to conduct the synergistic effects between the IL-9 gene and environmental factors into account were estimated by conditional logistic regression models. The odds ratio for transmission of allele 122 of the IL-9 gene was 1.23 (P = 0.28) for all asthmatic probands. There was slight increased interaction effect on asthma between transmission of allele 122 of IL-9 gene to offspring and who were exposed to the fur of pets (OR = 3.33, P = 0.047). We also detected elevated odds of transmission of allele 122 to atopic asthmatic probands (OR = 2.08, P = 0.03) and offspring with very high levels of serum IgE (> or = 800 IU mL(-1)). In conclusion, this study has found that the IL-9 gene was slightly associated with asthmatics who have positive specific IgE against Der p (or Der f) and house dust, when information on environmental factors was incorporated as effect modifiers.

Association of interleukin 18 (IL18) polymorphisms with specific IgE levels to mite allergens among asthmatic patients

BACKGROUND

Allergy is regarded as a multifactorial condition. Its onset and severity are influenced by both genetic and environmental factors. Identification of genetic factors involved in asthma development and related phenotypes is a major task in understanding the genetic background of asthma. The possible involvement of IL18 polymorphisms in asthma was examined in a Korean asthma cohort.

METHODS

Direct sequencing was performed to discover single-nucleotide polymorphisms (SNPs) in the IL18 gene. Single-base extension (SBE) method was employed for genotyping. Genotypic influence of IL18 was analysed using logistic and multiple-regression models.

RESULTS

Although no polymorphisms in the IL18 gene showed significant association with the risk of asthma development, analyses of the association with specific serum IgE levels to Dermatophagoides farinae (D.f.) and D. pteronyssinus (D.p.) among asthmatic patients revealed significant associations with two completely linked SNPs, i.e. -148G>C and +13925A>C(Ser35Ser) (P = 0.01-0.11 for D.f. and P = 0.005-0.11 for D.p.). Both C allele of -148G>C and C allele of +13925A>C showed gene dose-dependent effects on the levels of specific IgE. The lowest IgE levels in homozygotes of minor alleles (1.13 and 1.22 of D.f.; 1.38 and 1.33 of D.p., respectively), intermediate IgE levels in heterozygotes (1.60 and 1.70 of D.f.; 1.84 and 1.92 of D.p., respectively), and the highest levels in homozygotes for major allele (1.93 and 1.93 of D.f.; 2.24 and 2.24 of D.p., respectively), were found.

CONCLUSION

The genetic relevance of IL18 to specific IgE might offer an important step in understanding the genetic background of allergic diseases.

Genome screen in the French EGEA study: detection of linked regions shared or not shared by allergic rhinitis and asthma

In the sample of 295 French EGEA families with at least one asthmatic subject, a genome screen was conducted to identify potential linkage regions specific either to allergic rhinitis (AR) or to asthma as well as those shared by the two diseases. Two binary rhinitis phenotypes based on (1) diagnosis (ARbin1) and (2) symptoms (ARbin2) and a categorical ordered trait (ARcat) were considered. Asthma phenotype was based on answers to a standardized questionnaire plus the presence of bronchial hyper-responsiveness. Linkage analyses were conducted using the maximum likelihood binomial (MLB) method. These analyses provided potential evidence for linkage to three regions in the whole sample: 1p31 for the phenotype defined by ARbin2 plus asthma (P=0.00016), 2q32 for ARbin2 (P=0.00016) and 3p24-p14 for ARcat (P=0.001). Two other regions were detected in the subset of 185 families with at most one asthmatic sib: 9p22 and 9q22-q34 for ARbin1 (P=0.001 and 0.0007, respectively). No region showed evidence for linkage to asthma without being also linked to AR. While 1p31 may contain a genetic determinant common to asthma and AR, 2q32, 3p24-p14, 9p22 and 9q22-q34 are more likely to harbor genetic factors specific to AR.

Positionally cloned susceptibility genes in allergy and asthma

After several years of research to find asthma-susceptibility genes using genome-wide linkage scans and refined genetic mapping methods, four highly interesting candidate genes have recently been reported. Each of these genes represents a different functional class, and might point to a new pathway in the pathogenesis of asthma. Current research is focusing on confirming the genetic associations in diverse populations and understanding the biochemical functions of the proteins. These second-generation candidate genes for asthma susceptibility will stimulate much research, and might also enable the testing of multigenic models with sufficiently large sample sets.

Asthma genetics: pitfalls and triumphs

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

Clustering patterns of LOD scores for asthma-related phenotypes revealed by a genome-wide screen in 295 French EGEA families

A genome-wide scan for asthma phenotypes was conducted in the whole sample of 295 EGEA families selected through at least one asthmatic subject. In addition to asthma, seven phenotypes involved in the main asthma physiopathological pathways were considered: SPT (positive skin prick test response to at least one of 11 allergens), SPTQ score being the number of positive skin test responses to 11 allergens, Phadiatop (positive specific IgE response to a mixture of allergens), total IgE levels, eosinophils, bronchial responsiveness (BR) to methacholine challenge and %predicted FEV(1). Four regions showed evidence for linkage (P</=0.001): 6q14 for %FEV(1), 12p13 for IgE, 17q22-q24 for SPT and 21q21 for both SPTQ and %FEV(1). Nine other regions indicated smaller linkage signals (0.001<P</=0.005). While most of these regions have been reported by previous asthma and lung function screens, 6q14 appears to be a new region potentially linked to %FEV(1). To determine which of these various asthma phenotypes are more likely to share common genetic determinants, a principal component analysis was applied to the genome-wide LOD scores. This analysis revealed clustering of LODs for asthma, SPT and Phadiatop on one axis and clustering of LODs for %FEV(1), BR and SPTQ on the other, while LODs for IgE and eosinophils appeared to be independent from all other LODs. These results provide new insights into the potential sharing of genetic determinants by asthma-related phenotypes.

Association of the interleukin-1 receptor antagonist gene with asthma

The interleukin-1 cluster on human chromosome 2q12-2q14 harbors various promising candidate genes for asthma and other inflammatory diseases. We conducted a systematic association study with single-nucleotide polymorphisms (SNPs) located in candidate genes situated in this cluster. Single-marker, two-locus and three-locus haplotype analysis of SNPs yielded several significant results (p < 0.05-0.0021) for the human IL1RN gene encoding the IL-1 receptor antagonist protein, an antiinflammatory cytokine that plays an important role in maintaining the balance between inflammatory and antiinflammatory cytokines. These findings were replicated and confirmed in an independent Italian family sample in which significant, although weaker, association with asthma was detected. A sequencing approach to the coding region of the human IL1RN gene revealed additional DNA variants, from which a selection was also associated with the disease in German and Italian samples. Calculation of the linkage disequilibrium for the human IL1RN gene showed strong linkage disequilibrium for nearly all analyzed SNPs. Further haplotype analysis indicated that six SNPs are sufficient for tagging all haplotypes with a prevalence of more than 1%. The most frequent haplotype constructed from these SNPs was 1.4-fold overtransmitted in the German family sample.

Fine-scale mapping of type I allergy candidate loci suggests central susceptibility genes on chromosomes 3q, 4q and Xp

BACKGROUND

Type I allergy globally affects an increasing number of individuals with the consequence of considerable personal morbidity and socio-economic costs. Identification of disease susceptibility genes would render enormous medical perspectives in terms of improved diagnosis, treatment and prevention. Like for other complex disorders, achievement of the knowledge necessary depends on confirmation of reported genomic candidate regions.

METHODS

We performed a two-stage fine-scale linkage analysis in 11 selected candidate regions on chromosome 3p, 3q, 4p, 4q, 5q, 6p, 9p, 12q, 12qter, 18q and Xp. We analysed 97 polymorphic markers in 424 individuals from 100 sib-pair families and evaluated the data for five phenotypes: Allergic asthma, atopic dermatitis, allergic rhinitis and total and specific immunoglobulin E.

RESULTS

The highest maximum likelihood scores (MLS) were obtained on chromosomes 3q (MLS = 2.69), 4p (MLS = 2.34), 4q (MLS = 2.75), 6p (MLS = 2.22), 12qter (MLS = 2.15) and Xp (MLS = 2.23). All five phenotypes showed MLS >/= 2 in one or more of the candidate regions.

CONCLUSIONS

Susceptibility genes in the 3q, 4q and Xp regions may play a central role in the inheritance of allergic disease, as positive results were obtained for all five phenotypes in these three regions.

Allergic rhinitis and polymorphisms of the interleukin 1 gene complex

BACKGROUND

Allergic rhinitis is a chronic inflammatory disease with a genetic background. Inflammatory reactions are regulated by cytokines. Cytokine genes are polymorphic and have been implicated as candidate genes in allergy.

OBJECTIVES

To study the significance of the interleukin 1 (IL-1) gene complex in allergic rhinitis.

METHODS

Population-based, cross-sectional study. We studied the polymorphisms of 3 IL-1 gene complex genes, IL1A (+4845G>T), IL1B (-511 degrees C>T), and IL1RN (variable number of tandem repeats; IVS2, 86 bp, duplicates 2 to 5), in patients with allergic rhinitis. The study group consisted of 405 nonasthmatic individuals of whom 56 had allergic rhinitis.

RESULTS

The genotype distribution differed significantly in all cytokine genes studied between subjects with and without allergic rhinitis. The difference was mainly due to an increased number of IL1A allele G homozygotes (67.9% vs 43.2%; odds ratio [OR], 2.8; 95% confidence interval [CI], 1.5-5.1), IL1B heterozygotes (72.2% vs 47.4%; OR, 2.8; 95% CI, 1.5-5.3), and IL1RN allele 2 homozygotes (18.5% vs 7.5%; OR, 2.8; 95% CI, 1.3-6.2) in allergic rhinitis. Haplotype analysis revealed a significant difference in the distribution of IL-1 gene complex haplotypes between subjects with and without allergic rhinitis (P = 0.005, 10 df).

CONCLUSIONS

The IL-1 gene complex polymorphism is strongly associated with allergic rhinitis in nonasthmatic individuals.

Positional cloning of a novel gene influencing asthma from chromosome 2q14

Asthma is a common disease in children and young adults. Four separate reports have linked asthma and related phenotypes to an ill-defined interval between 2q14 and 2q32 (refs. 1-4), and two mouse genome screens have linked bronchial hyper-responsiveness to the region homologous to 2q14 (refs. 5,6). We found and replicated association between asthma and the D2S308 microsatellite, 800 kb distal to the IL1 cluster on 2q14. We sequenced the surrounding region and constructed a comprehensive, high-density, single-nucleotide polymorphism (SNP) linkage disequilibrium (LD) map. SNP association was limited to the initial exons of a solitary gene of 3.6 kb (DPP10), which extends over 1 Mb of genomic DNA. DPP10 encodes a homolog of dipeptidyl peptidases (DPPs) that cleave terminal dipeptides from cytokines and chemokines, and it presents a potential new target for asthma therapy.

Associations between total serum IgE levels and the 6 potentially functional variants within the genes IL4, IL13, and IL4RA in German children: the German Multicenter Atopy Study

BACKGROUND

Increased total serum IgE levels are a common characteristic of atopic disorders. Six potentially functional variants, including C-590T in the IL4 gene, C-1055T and Arg130Gln in the IL13 gene, and Ile50Val, Ser478Pro, and Gln551Arg in the IL4RA gene, have been evaluated for their involvement in the control of total serum IgE levels and related atopic disorders, but the results of these studies have been inconsistent.

OBJECTIVE

We examined whether these 6 variants had genotypic effects on total serum IgE levels in 823 unrelated German children from a large infant cohort, the German Multicenter Atopy Study.

METHODS

Marginal effect models were used for the analyses of the repeated IgE measurements. Weighted linear regression and family-based tests of association were performed to minimize the possibility of spurious effects caused by selection bias or confounding on the basis of ethnic background.

RESULTS

There are significant associations between increased total serum IgE levels and 2 variants in the IL13 gene (P <.005 and.0002 for Arg130Gln and C-1055T, respectively). These genetic effects are unlikely to be due to solely linkage disequilibrium between 2 polymorphisms, population stratification, or nonrepresentative samples. In addition, exposure to maternal smoking appears to modify the above effects on total serum IgE levels. However, no statistical association was observed between this quantitative phenotype and the other 4 variants examined.

CONCLUSION

These findings suggest that variants C-1055T and Arg130Gln of the IL13 gene might play an important role on total serum IgE production in this study population.

Positional cloning of a quantitative trait locus on chromosome 13q14 that influences immunoglobulin E levels and asthma

Atopic or immunoglobulin E (IgE)-mediated diseases include the common disorders of asthma, atopic dermatitis and allergic rhinitis. Chromosome 13q14 shows consistent linkage to atopy and the total serum IgE concentration. We previously identified association between total serum IgE levels and a novel 13q14 microsatellite (USAT24G1; ref. 7) and have now localized the underlying quantitative-trait locus (QTL) in a comprehensive single-nucleotide polymorphism (SNP) map. We found replicated association to IgE levels that was attributed to several alleles in a single gene, PHF11. We also found association with these variants to severe clinical asthma. The gene product (PHF11) contains two PHD zinc fingers and probably regulates transcription. Distinctive splice variants were expressed in immune tissues and cells.

A new gene for asthma: would you ADAM and Eve it?

Recently, a novel gene was reported to underlie asthma. Linkage to the short arm of chromosome 20 in a genome screen was followed by positive tests of association that centre on the gene for a membrane-anchored zinc-dependent metalloproteinase known as ADAM33. The domain structure of the ADAM33 protein gives capabilities of proteolysis, adhesion, cell fusion and intracellular signalling. Although its function is at present unknown, these potential actions of ADAM33 provide many possibilities for further research.

Genetic analyses in asthma: current concepts and future directions

Asthma is a complex genetic disorder with a heterogeneous phenotype, largely attributed to the interactions among many genes and between these genes and the environment. Numerous loci and candidate genes have been reported to show linkage and association of asthma and the asthma-associated phenotypes, atopy, elevated immunoglobulin E (IgE) levels, and bronchial hyper-responsiveness to alleles of microsatellite markers and single nucleotide polymorphisms (SNPs) within specific cytokine/chemokine, and IgE regulating genes. While many studies reporting these observations are compelling, only one asthma gene conferring high risk has been mapped. In this review, we present studies that support linkage and/or associations to the various genetic loci and genes in asthma. The first genome-wide scan for linkage to quantitative traits underlying asthma identified linkage on chromosome 4q, 6, 7, 11q, 13q and 16. A genome scan in American families from three racial groups revealed linkage to chromosome 2q, 5q, 6p, 12q, 13q and 14q. A two-stage scan in Hutterite families from the US found linkage on chromosome 5q, 12q, 19q and 21q. A screen in German families identified linkage to asthma on chromosome 2q, 6p, 9 and 12q and a two-stage genome scan in French families found replicated linkage on chromosomes 1p, 12q and 17q. A study of asthma in Finland showed linkage to high IgE on 7q14. Apart from a European linkage study of 199 families with atopic dermatitis, which demonstrated significant linkage to chromosome 3q21, three other studies have reported linkage results of genome-wide significance, including a linkage study in 175 Icelandic asthma families (14q24), a study in 533 Chinese families with bronchial hyper-responsiveness (chromosome 2) and a study in 47 Japanese families with mite-sensitive atopic asthma (5q31), suggesting that these regions may harbor genes contributing to the development of asthma and allergies. While significant progress has been made in the field of asthma genetics in the past decade, the clinical implications of the genes and genetic variations within the numerous candidate asthma genes that have been found to associate with the expression of the asthmatic phenotype, remain undetermined.

Genetics and genomics of asthma and allergic diseases

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

A major susceptibility gene for asthma maps to chromosome 14q24

Asthma is a complex genetic disorder with a heterogeneous phenotype, largely attributed to the interactions among many genes and between these genes and the environment. Numerous loci and candidate genes have been reported to show linkage and association to asthma and atopy. Although some studies reporting these observations are compelling, no gene has been mapped that confers a sufficiently high risk of asthma to meet the stringent criteria for genomewide significance. Using 175 extended Icelandic families that included 596 patients with asthma, we performed a genomewide scan with 976 microsatellite markers. The families were identified by cross-matching a list of patients with asthma from the Department of Allergy/Pulmonary Medicine of the National University Hospital of Iceland with a genealogy database of the entire Icelandic nation. We detected linkage of asthma to chromosome 14q24, with an allele-sharing LOD score of 2.66. After we increased the marker density within the locus to an average of one microsatellite every 0.2 cM, the LOD score rose to 4.00. We designate this locus "asthma locus one" (AS1). Taken together, these results provide evidence of a novel susceptibility gene for asthma on chromosome 14q24.

Associations of Fc epsilon R1-beta polymorphisms with immunoglobin E antibody responses to common inhalant allergens in a rural population

BACKGROUND

Polymorphisms within the beta subunit of the high-affinity receptor for IgE (Fc epsilon R1-beta ) on chromosome 11q13 have been related to atopy and asthma and the lymphotoxin alpha (LT alpha) gene on chromosome 6 is implicated in asthma.

OBJECTIVE

To elucidate the association of polymorphisms in the Fc epsilon R1-beta and LT alpha genes to IgE responses and asthma in a family-orientated rural population.

METHODS

A total of 461 adult farmers, who participated in an epidemiological follow-up study on respiratory symptoms among farmers on the Swedish island of Gotland, were examined. The traits assessed included serum total IgE, IgE antibody responses to 21 common inhalant allergens and asthma.

RESULTS

The 237G mutation was only detected in seven persons. Atopy was found to be associated with the RsaI-ex7 AB-genotype (OR = 1.9; P = 0.04). The RsaI-ex7 B allele had a significant influence on IgE responses to pollens and dust mites (OR = 5.5; P = 0.03 and OR = 5.2; P = 0.049, respectively). The influence of this allele was stronger when the association towards single dust mite species (Lepidoglyphus destructor) was estimated (OR = 7.1, P = 0.03) and the association increased even more when the major allergen of L. destructor (rLep d 2) was analysed (OR = 11.2, P = 0.02). These associations were independent of sex, age and smoking, and the estimates of RsaI-in2 independent of RsaI-ex7. RsaI-in2, RsaI-ex7 and LT alpha genotypes were unassociated with total serum IgE. No significant difference in the distribution of RsaI-in2, RsaI-ex7 and LT alpha genotypes was found among subjects with atopy or asthma compared to healthy controls.

CONCLUSION

This study supports the notion that polymorphisms in the Fc epsilon R1-beta gene have significant effects on IgE responsiveness. Secondly, dust mites in rural populations influence the expression of genes on chromosome 11q13.

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.

Oligogenic approaches to the predisposition of asthma in ethnically diverse populations

Using the genome-wide screening data of the Collaborative Study on the Genetics of Asthma (CSGA) (226 families, 1,461 genotyped subjects, 323 marker loci) and Hutterite studies (129 families, 690 genotyped subjects, 365 marker loci), we applied a genetic similarity function in order to quantify the inter-individual genetic distances d(xi,xj) between feature vectors xi, xj made up by the allelic patterns of subjects i,j with respect to loci li, l2,..., ln. Based on this similarity function, we structurally decomposed the genetic diversity of the CSGA population in order to address the question of ethnicity-related asthma vulnerability for genetically homogenous CSGA subgroups. The question of ethnicity-independent asthma vulnerability was investigated with all CSGA families as training and the Hutterite families as replication samples. We evaluated the between-sib similarities, which were expected to deviate from "0.5" in affected sib pairs if the region of interest contained markers close to disease-causing genes. The reference value 0.5 was derived by determining the parent-offspring similarities, which are always 0.5, irrespective of the affection status of parents and offspring. We found 18 vulnerability loci on chromosomes 1, 3, 4, 5, 6, 8, 12, 13, and 14, which were remarkably reproducible in the CSGA and the Hutterite data and constituted an ethnicity-independent oligogenic model.

Positive association to IgE levels and a physical map of the 13q14 atopy locus

Linkage of atopy and associated traits to a locus on chromosome 13q14 has been identified by several studies in diverse populations. We have previously shown the putative atopy gene to be contained within an interval of approximately 5 Mb flanked by D13S328 and D13S1269 and centred on D13S273. We have now extended this work using a top-down approach to physical mapping. A YAC contig was constructed covering the D13S328 and D13S1269 interval. Thirty-one ESTs were mapped to the contig. We constructed a BAC and PAC contig flanking D13S273 by approximately 750 kb in either direction. The interval contained 27 of the 31 ESTS from the YAC contig. Seven previously unknown microsatellites were recovered and then typed in two subject panels. A positive association between the total serum Immunoglobulin E concentration and the novel USAT24G1 microsatellite was discovered (P(corrected)<0.005) and replicated in a second panel of families. The discovery of a region of positive association within the BAC/PAC contig will permit identification of the atopy gene from this locus.

Asthma genetics

Asthma is the most common chronic childhood disease in developed nations and is a complex disease that has high social and economic costs. Asthma and its associated intermediate phenotypes are under a substantial degree of genetic control. Identifying the genes underlying asthma offers a means of better understanding its pathogenesis, with the promise of improving preventive strategies, diagnostic tools, and therapies. A number of chromosomal regions containing genes influencing asthma and atopy have been identified consistently by different groups, and a role for several candidate genes has been established.

Interactions between genes and environmental factors in asthma and atopy: new developments

Asthma and associated phenotypes are complex traits most probably caused by an interaction of multiple disease susceptibility genes and environmental factors. Major achievements have occurred in identifying chromosomal regions and polymorphisms in candidate genes linked to or associated with asthma, atopic dermatitis, IgE levels and response to asthma therapy. The aims of this review are to explain the methodology of genetic studies of multifactorial diseases, to summarize chromosomal regions and polymorphisms in candidate genes linked to or associated with asthma and associated traits, to list genetic alterations that may alter response to asthma therapy, and to outline genetic factors that may render individuals more susceptible to asthma and atopy due to environmental changes.

Allergic rhinitis--a total genome-scan for susceptibility genes suggests a locus on chromosome 4q24-q27

Allergic rhinitis is a common disease of complex inheritance and is characterised by mucosal inflammation caused by allergen exposure. The genetics of closely related phenotypes such as asthma, atopy and to some extend atopic dermatitis has attracted attention in recent years. Genetic reports of allergic rhinitis on the contrary have as yet been most sparse. To identify candidate regions holding genes for allergic rhinitis we performed a total genome-scan on affected sib-pair families. From 100 Danish sib-pair families selected for allergy, families containing sib-pairs matching a phenotype definition of both clinical allergic rhinitis and confirmed specific allergy were chosen. Thirty-three affected sib-pair families qualified for the scan that was undertaken using 446 microsatellite markers. Non-parametric linkage results were obtained from MAPMAKER/SIBS computer program. The study revealed one major candidate region on chromosome 4q24-q27 (LOD=2.83) and eight minor candidate regions 2q12-q33, 3q13, 4p15-q12, 5q13-q15, 6p24-p23, 12p13, 22q13, and Xp21 (LOD=1.04-1.63) likely to contain susceptibility genes for allergic rhinitis. Our findings did not support a previous report of linkage of allergic rhinitis to chromosome 12q14-q24 but they added positive evidence to the asthma and atopy candidate regions 2q33 and 6p23. Further identification of the specific genes involved in allergic rhinitis will give opportunities for improved diagnosis and treatment.

Indication of linkage and genetic heterogeneity of asthma according to age at onset on chromosome 7q in 107 French EGEA families

It is generally believed that an early age at the onset of disease is associated with a stronger genetic component. Our aim here was to investigate both linkage and genetic heterogeneity of asthma, the latter corresponding to different genotype relative risks of a putative linked gene according to age at onset of asthma. This analysis was conducted in 107 French EGEA families with at least two asthmatic siblings, considering 157 markers that were part of our previous genome screen, using the TTS (the Triangle Test Statistic) which has been developed to detect both linkage and intra-sibpair genetic heterogeneity. This test has been applied to 38 asthmatic sib-pairs discordant for age at the onset of asthma. To confirm the existence of genetic heterogeneity, we also used the predivided sample test (PST) which compares the IBD (identity by descent) distribution of marker alleles between asthmatic sib-pairs concordant (67) and discordant (38) for the age at onset. The cutoff point used for the age at onset was 4 years, the median age at onset in our sample of asthmatic sibs. Linkage and genetic heterogeneity for a region located on chromosome 7q (at 109 cM from pter) were indicated by both tests, TTS (P=0.005, P>0.5 after correction for multiple testing) and PST (P=0.0001, 0.015 after correction). These results suggest a genetic factor on 7q involved in asthma with genotype relative risks differing according to age at onset of disease.

Current concepts on the genetics of asthma

Asthma is a complex genetic disorder with variable phenotype, largely attributed to the interactions of the environment and multiple genes, each potentially having small effects. Numerous asthma and atopy loci have been reported in studies demonstrating associations and/or linkage of the asthma-associated phenotypes, atopy, elevated IgE levels, and bronchial hyperresponsiveness to alleles of microsatellite markers and single nucleotide polymorphisms within specific cytokine/chemokine and IgE regulating genes. Although the studies reporting these observations are compelling, most of them lack statistical power. This review compiles the evidence that supports linkage and associations to the various genetic loci and candidate genes. Whereas significant progress has been made in the field of asthma genetics in the past decade, the roles of the genes and genetic variations within the numerous candidate asthma genes that have been found to associate with the expression of the asthmatic phenotype remain to be determined.

IgE in unselected like-sexed monozygotic and dizygotic twins at birth and at 6 to 9 years of age: high but dissimilar genetic influence on IgE levels

BACKGROUND

IgE is a major determinant of allergic disease. Twin analysis of serum levels of IgE has been carried out previously in children and adults with heritability estimates of 30% to 70% on the basis of ANOVA.

OBJECTIVE

This study included the analysis of serum IgE in a population of 126 twins, 27 monozygotic pairs and 36 dizygotic pairs, studied at birth (cord blood [CB] IgE) and consecutively at the age of 6 to 9 years of age (serum IgE).

METHODS

IgE was determined by means of RIA. ANOVA, correlation analysis, and structural equation modeling by maximal likelihood analysis was used for genetic analysis.

RESULTS

Structural equation modeling by maximal likelihood analysis showed the best-fitting model to be the AE model (A for additive genetic variance and E for environmental variance) both at birth and later in childhood. The estimated heritability was 0.92 (95% CI, 0.84-0.95) for CB IgE and 0.78 (95% CI, 0.60-0.87) for serum IgE. The correlation between CB IgE and serum IgE was 0.04.

CONCLUSIONS

The study demonstrated a higher genetic dependency of serum IgE than previously recognized. The low correlation between the IgE levels at birth and later in childhood suggested that different effector mechanisms may be operating at different ages.

IL4-R1 (5q31-q33) and FcepsilonRI-betaca (11q13) markers and atopy: a case/control study in a spanish population

BACKGROUND

Rhinoconjunctivitis and bronchial asthma are atopic diseases with a high prevalence in the Canary Islands (Spain). Given that the most prevalent allergen is the house-dust mite Dermatophagoides pteronyssinus, early detection of genetically susceptible subjects would allow the application of preventive measures. The objective was to investigate the possible association of IL4-R1 (chromosome 5q31-q33) and FcepsilonRI-betaca (chromosome 11q13) markers with the atopic disease in our population.

METHODS

We performed a case/control study in which patients were recruited on the basis of diagnosis of rhinoconjunctivitis and/or bronchial asthma, and positive skin prick test to D. pteronyssinus. Analysis of IL4-R1 and FcepsilonRI-betaca microsatellites was carried out by PCR and electrophoresis in acrylamide gels.

RESULTS

We have not found evidence of association between IL4-R1 and FcepsilonRI-betaca markers and atopic disease in our population. In addition, these markers have shown a high percentage of homozygosis.

CONCLUSIONS

IL4-R1 and FcepsilonRI-betaca markers have not proved to be useful genetic markers for linkage or association studies in our population.

A high-density genetic map of the chromosome 13q14 atopy locus

Atopy describes a syndrome of immunoglobulin E (IgE)-mediated allergy that underlies asthma and infantile eczema. We have previously identified a locus on chromosome 13q14 that is linked to atopy and to the total serum immunoglobulin A concentration. We have therefore made a saturation genetic map of the region by typing 59 polymorphic microsatellite loci on chromosome 13q. Multipoint linkage analysis identified a 1-LOD support unit for the location of the atopy locus with a 7.5-cM region flanked by the loci D13S328 and D13S1269. The peak of linkage was at locus D13S161 with a nonparametric -log of P score of approximately 4.5. Parent of origin effects were present, with linkage primarily observed to paternally derived alleles. The genetic map of this region provides a basis for the effective identification of the chromosome 13 atopy gene.

Genome screen for asthma and related phenotypes in the French EGEA study

A genome-wide search was conducted in 107 nuclear families with at least two siblings with asthma, as part of the French EGEA study. A two-stage analysis strategy was applied to the 107 families divided into two independent subsets of 46 and 61 families, where all regions detected in the first set of families were tested for replication in the second set. In addition, all regions reported by published genome scans in different populations were examined in the total sample. A total of 254 markers were typed in the first set of families and 70% of them in the second set. Linkage was investigated by model-free methods for asthma and four asthma-related phenotypes: bronchial responsiveness (BR), skin test response, total immunoglobulin E (IgE) levels, and eosinophil count. The two-stage analysis led to the detection of three regions: 11p13 for IgE, 12q24 for eosinophils, and 17q12-21 for asthma and skin tests. Among the regions reported by published genome screens, seven were found in the 107 French EGEA families: three being already detected by the two-stage analysis, 11p13 (p = 0.005), 12q24 (p = 0.0008), and 17q12-21 (p = 0.001), and four additional ones, 1p31 (p = 0.005) for asthma, 11q13 (p = 0.006) for IgE, 13q31 (p = 0.001) for eosinophils, and 19q13 (p = 0.02) for BR.

A European study on the genetics of mite sensitization

BACKGROUND

Sensitization to mite allergens represents a prominent feature of atopy and an important predictor of bronchial asthma.

OBJECTIVE

It was the intention of this study to define genetic loci linked to mite sensitization because these could represent the genetic basis of the important atopic component of asthma.

METHODS

We studied a multiethnic white population of 99 families, including 224 sib pairs sensitized to Dermatophagoides pteronyssinus. A genome-wide candidate-region search was performed that covered potential asthma and atopy regions.

RESULTS

As for nonparametric linkage (NPL) analysis, 14 of the candidate regions showed evidence for linkage (NPL > 2.0), and 4 of them showed prominent linkage (NPL > 3.0). However, there were substantial ethnic differences. Maximizing the LOD score analysis identified candidate regions with suspected dominant and recessive mode of inheritance. Furthermore, genetic imprinting models provided significant evidence for linkage in the 8p23 region and revealed potential maternal imprinting. The regions found are distinct to those in asthma searches that have been found to be linked to asthma, as well to other inflammatory diseases. In addition, we could not find linkage to the HLA region. By different cutoff points of the phenotype definition, the IL cluster showed evidence of being linked to the degree of sensitization rather than to sensitization per se.

CONCLUSION

The results indicate that the genetic basis of the atopic component of asthma is different from that of the inflammatory component. Furthermore, it seems reasonable to assume that specific sensitizations are influenced by distinct genetic variants leading to their initiation versus those leading to their enhancement.