A pathway-based association study reveals variants from Wnt signalling genes contributing to asthma susceptibility

BACKGROUND

Genetic susceptibility to asthma is currently linked to a handful of genes which have a limited ability to predict the overall disease risk, suggesting the existence of many other genes involved in disease development. Accumulated evidence from association studies in genes related by biological pathways could reveal novel asthma genes.

OBJECTIVE

To reveal novel asthma susceptibility genes by means of a pathway-based association study.

METHODS

Based on summary data from a previous a genomewide association study (GWAS) of asthma, we first identified significant biological pathways using a gene-set enrichment analysis. We then mapped all tested single nucleotide polymorphisms (SNPs) on the genes contributing to significant pathways and prioritized those with a disproportionate number of nominal significant associations for further studies. For those prioritized genes, association studies were performed for selected SNPs in independent case-control samples (n = 1765) using logistic regression models, and results were meta-analysed with those from the GWAS.

RESULTS

Two biological processes were significantly enriched: the cytokine-cytokine receptor interaction (P = 0.002) and the Wnt signalling (P = 0.012). From the 417 genes interacting in these two pathways, 10 showed an excess of nominal associations, including a known asthma susceptibility locus (encoding SMAD family member 3) and other novel candidate genes. From the latter, association studies of 14 selected SNPs evidenced replication in a locus near the frizzled class receptor 6 (FZD6) gene (P = 9.90 × 10^-4 ), which had a consistent direction of effects with the GWAS findings (meta-analysed odds ratio = 1.49; P = 5.87 × 10^-6 ) and was in high linkage disequilibrium with expression quantitative trait loci in lung tissues.

CONCLUSIONS AND CLINICAL RELEVANCE

This study revealed the importance of two biological pathways in asthma pathogenesis and identified a novel susceptibility locus near Wnt signalling genes.

Assessing the validity of asthma associations for eight candidate genes and age at diagnosis effects

BACKGROUND

Before the advent of genome-wide association studies (GWAS), ADAM33, ADRB2, CD14, MS4A2 (alias FCER1B), IL13, IL4, IL4R, and TNF constituted the most replicated non-HLA candidate genes with asthma and related traits. However, except for the IL13-IL4 region, none of these genes have been found in close proximity of genome-wide significant hits among GWAS for asthma or related traits. Here we aimed to assess the reproducibility of these asthma associations and to test if associations were more evident considering the effect of age at diagnosis.

METHODOLOGY/PRINCIPAL FINDINGS

We systematically evaluated 286 common single nucleotide polymorphisms (SNPs) of these 8 genes in a sample of 1,865 unrelated Spanish individuals (606 asthmatics and 1,259 controls). We found that variants at MS4A2, IL4R and ADAM33 genes demonstrated varying association effects with the age at diagnosis of asthma, with 10 SNPs showing study-wise significance after the multiple comparison adjustment. In addition, in silico replication with GWAS data supported the association of IL4R.

CONCLUSIONS/SIGNIFICANCE

Our results support the important role of MS4A2, IL4R and ADAM33 genes in asthma and/or atopy susceptibility. However, additional studies in larger samples sets are needed to firmly implicate these genes in asthma susceptibility, and also to identify the causal variation underlying the associations found.

Contact urticaria caused by heat-sensitive raw fish allergens

Patients allergic to fish usually present with skin reactions after handling raw fish. Less frequently, these reactions are seen without symptoms after oral intake, often in chefs and food handlers. We have attempted to explain the skin selectivity of such reactions in a 36-year-old woman with contact urticaria after handling raw fish. We obtained aqueous extracts of raw and cooked fish (sole and hake) for in vivo (prick test) and in vitro (SDS-PAGE, IgE Immunoblot) tests. Prick-by-prick test, 20-min closed patch test, rub test with fresh and cooked fish (sole, hake and cod) and specific IgE (CAP-system) to sole, cod and hake were performed. The strength of positive reaction to raw fish was greater than to cooked fish on both prick and prick-by-prick testing. Rub tests showed positive responses only to raw fish. Specific IgEs to sole (45 KU/l), hake (66.9 KU/l) and cod (18.7 KU/l) were obtained. IgE immunoblot recognized 3 antigens of 25, 48, 56 kDa in raw sole and 1 of 42 kDa in raw hake extracts. No IgE binding was observed with the cooked extracts or control sera. Our findings strongly suggest a Type-I hypersensitivity to fish. Immunoblot analyses demonstrated a loss of specific IgE binding to cooked extracts. We have reported a case of contact urticaria caused by heat-sensitive raw-fish allergens in a patient who probably became sensitized via the cutaneous route.