Studying gene-environment interactions may elucidate the complex origins of atopic diseases but requires large study populations. Pooling data from several cohort studies may help but may also obscure findings. Gene-environment interactions in atopy development were studied and the benefits of pooling data were evaluated.Haplotype-tagging polymorphisms in the genes interleukin (IL)13 and CD14 were genotyped in 3,062 children from the following birth cohorts: the Prevention and Incidence of Asthma and Mite Allergy (PIAMA) study; the Prevention of Asthma in Children (PREVASC) study; and the Child, Parent, Health, Focus on Lifestyle and Predisposition (KOALA) study, and tested for association with total and specific immunoglobulin (Ig)E and interaction with tobacco smoke and pet exposure at ages 1, 2, 4 and 8 yrs by analysis of variance, Chi-squared tests and regression analyses.At all ages, in IL13, minor alleles of rs1295685 and rs20541 were significantly associated with elevated IgE levels in pooled analyses. In CD14, the rs2569190-TT and rs2569191-CC genotypes associated with lower IgE and decreased risk of sensitisation at 4 and 8 yrs in children exposed to pets, with an opposite effect in nonexposed children. Findings for IL13 and CD14 were comparable in separate cohorts.The present study indicates that atopy is importantly influenced by interleukin 13 at age 1-8 yrs and by CD14 in interaction with pet exposure at ages 4 and 8 yrs. Additionally, pooled data improved effect estimates and genetic effects could be detected in interaction with important environmental factors.

To cite this article: Reijmerink NE, Bottema RWB, Kerkhof M, Gerritsen J, Stelma FF, Thijs C, van Schayck CP, Smit HA, Brunekreef B, Koppelman GH, Postma DS. TLR‐related pathway analysis: novel gene–gene interactions in the development of asthma and atopy. Allergy 2010; 65: 199–207. Abstract Background:  The toll‐like receptor (TLR)‐related pathway is important in host defence and may be crucial in the development of asthma and atopy. Numerous studies have shown associations of TLR‐related pathway genes with asthma and atopy phenotypes. So far it has not been investigated whether gene–gene interactions in this pathway contribute to atopy and asthma development. Methods:  One hundred and sixty‐nine haplotype tagging single nucleotide polymorphisms (SNPs) of 29 genes (i.e. membrane and intracellular receptors, TLR4 or lipopolysaccharide‐binding/facilitating proteins, adaptors, interleukin‐1 receptor associated kinases, kinases, chaperone molecules, transcription factors and inhibitors) were analysed for single‐ and multilocus associations with atopy [total and specific immunglobulin E (IgE) at 1–2 and 6–8 years] and asthma (6–8 years). A total of 3062 Dutch children from the birth cohorts PIAMA, PREVASC and KOALA (Allergenic study) were investigated. Chi‐squared test, logistic regression and the data mining approach multifactor dimensionality reduction method (MDR) were used in analysis. Results:  Several genes in the TLR‐related pathway were associated with atopy and/or asthma [e.g. IL1RL1, BPI, NOD1, NOD2 and MAP3K7IP1]. Multiple, single associations were found with the phenotypes under study. MDR analysis showed novel, significant gene–gene interactions in association with atopy and asthma phenotypes (e.g. IL1RL1 and TLR4 with sIgE to indoor allergens and IRAK1, NOD1 and MAP3K7IP1 with asthma). Interestingly, gene–gene interactions were identified with SNPs that did not have an effect on their own. Conclusion:  Our unbiased approach provided suggestive evidence for interaction between several TLR‐related pathway genes important in atopy and/or asthma development and pointed to novel genes.

Background: Asthma and rhinitis may represent two manifestations of the same airway disease. Genetic research can increase our understanding of their common or distinct pathogenesis. IL13 and IL4R polymorphisms are associated with asthma and show gene-gene interaction in asthma. Their role in rhinitis has not been extensively studied. Methods: Association of IL13 and IL4R polymorphisms in relation to rhinitis, asthma, serum IgE and skin test response was studied in: (1) 188 trios ascertained through a proband with rhinitis who were clinically not affected by asthma; (2) 407 trios with an asthmatic proband, and (3) 118 asthma cases and 102 unrelated healthy controls using family-based association testing, logistic regression, and analysis of variance as appropriate. Gene-gene interaction was evaluated using logistic regression analysis. Results: IL13 C–1111T (rs1800925) was significantly associated with rhinitis and atopic phenotypes in rhinitis trios that were not affected by clinical asthma. IL13 Arg130Gln (rs20541) and G870A (rs1295685) were consistently associated with asthma and serum IgE in both asthma populations. IL4R Glu375Ala (rs1805011) and Ser411Leu (rs1805013) were associated with asthma in the asthma case-control population. Combining risk genotypes of IL13 Arg130Gln with IL4R Glu375Ala, and IL13 C–1111T with IL4R Ser478Pro yielded increased risks for asthma compared to their separate effects. Conclusion:IL13 polymorphisms were associated with asthma and rhinitis without clinical asthma; thus, these polymorphisms may constitute a common etiologic pathway for their development. In addition, the study replicates a previously reported interaction of IL13 and IL4R polymorphisms in asthma.

The association between occupational endotoxin exposure and wheeze in agricultural workers was significantly modified by genetic variants in CD14 and MD2. Our study suggests that carriers of the functional CD14/-260 C allele are more responsive to endotoxin exposure than T allele homozygotes.

This is the first study showing across three cohorts that X-chromosomal FOXP3 genotypes may contribute to development of sensitisation against egg and indoor allergens in girls in early childhood. In addition, an association with remission of sensitisation to food allergens existed in boys only.

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Environmental and genetic factors contribute to atopy development. High microbial exposure may confer a protective effect on atopy. Toll-like receptors (TLRs) bind microbial products and are important in activating the immune system.To assess whether interactions between microbial exposures and genes encoding TLRs (and related genes) result in atopy, genes, environmental factors and gene-environment interactions of 66 single-nucleotide polymorphisms (SNPs) of 12 genes (TLR 1-6, 9 and 10, CD14, MD2, lipopolysaccharide-binding protein (LBP) and Dectin-1), and six proxy parameters of microbial exposure (sibship size, pets (three different parameters), day-care and intrauterine and childhood tobacco smoke exposure) were analysed for association with atopic phenotypes in 3,062 Dutch children (the Allergenic study).The presence of two or more older siblings increased the risk of developing high total immunoglobulin (Ig)E levels at different ages. This risk increased further in children aged 1-2 yrs carrying the minor allele of TLR6 SNP rs1039559. Furthermore, novel two-and three-factor genegene and gene-environment interactions were found (e.g. between sibship size, day-care and LBP SNP rs2232596).Larger sibship size is associated with increased total IgE levels. Furthermore, complex two-and three-factor interactions exist between genes and the environment. The TLRs and related genes interact with proxy parameters of high microbial exposure in atopy development.