Antoaneta A. Toncheva

Polymorphisms related to ORMDL3 are associated with asthma susceptibility, alterations in transcriptional regulation of ORMDL3, and changes in TH2 cytokine levels.

BACKGROUND Chromosome 17q21, harboring the orosomucoid 1-like 3 (ORMDL3) gene, has been consistently associated with childhood asthma in genome-wide association studies. OBJECTIVE We investigated genetic variants in and around ORMDL3 that can change the function of ORMDL3 and thus contribute to asthma susceptibility. METHODS We performed haplotype analyses and fine mapping of the ORMDL3 locus in a cross-sectional (International Study of Asthma and Allergies in Childhood Phase II, n = 3557 total subjects, n = 281 asthmatic patients) and case-control (Multicenter Asthma Genetics in Childhood Study/International Study of Asthma and Allergies in Childhood Phase II, n = 1446 total subjects, n = 763 asthmatic patients) data set to identify putative causal single nucleotide polymorphisms (SNPs) in the locus. Top asthma-associated polymorphisms were analyzed for allele-specific effects on transcription factor binding and promoter activity in vitro and gene expression in PBMCs after stimulation ex vivo. RESULTS Two haplotypes (H1 and H2) were significantly associated with asthma in the cross-sectional (P = 9.9 × 10(-5) and P = .0035, respectively) and case-control (P = 3.15 × 10(-8) and P = .0021, respectively) populations. Polymorphisms rs8076131 and rs4065275 were identified to drive these effects. For rs4065275, a quantitative difference in transcription factor binding was found, whereas for rs8076131, changes in upstream stimulatory factor 1 and 2 transcription factor binding were observed in vitro by using different cell lines and PBMCs. This might contribute to detected alterations in luciferase activity paralleled with changes in ORMDL3 gene expression and IL-4 and IL-13 cytokine levels ex vivo in response to innate and adaptive stimuli in an allele-specific manner. Both SNPs were in strong linkage disequilibrium with asthma-associated 17q21 SNPs previously related to altered ORMDL3 gene expression. CONCLUSION Polymorphisms in a putative promoter region of ORMDL3, which are associated with childhood asthma, alter transcriptional regulation of ORMDL3, correlate with changes in TH2 cytokines levels, and therefore might contribute to the childhood asthma susceptibility signal from 17q21.

A polymorphism in the TH2 locus control region is associated with changes in DNA methylation and gene expression

Genomewide association and epigenetic studies found a region within the RAD50 gene on chromosome 5q31 to be associated with total serum IgE levels and asthma. In mice, this region harbors a locus control region for nearby TH2 cytokines, which is characterized by four Rad50 DNase I hypersensitive sites (RHS4–7). Among these, RHS7 seems to have the strongest impact on TH2 differentiation. We investigated whether within the human homolog of RHS7, functional polymorphisms exist, which could affect DNA methylation or gene expression in the 5q31 locus and might have an influence on asthma status or IgE regulation.

Childhood asthma is associated with mutations and gene expression differences of ORMDL genes that can interact.

Genomewide association studies identified ORMDL3 as a plausible asthma candidate gene. ORMDL proteins regulate sphingolipid metabolism and ceramide homeostasis and participate in lymphocyte activation and eosinophil recruitment. Strong sequence homology between the three ORMDL genes and ORMDL protein conservation among different species suggest that they may have shared functions. We hypothesized that if single nucleotide polymorphisms (SNPs) in ORMDL3 alter its gene expression and play a role in asthma, variants in ORMDL1 and ORMDL2 might also be associated with asthma.

Genetic variants in Protocadherin-1, bronchial hyper-responsiveness, and asthma subphenotypes in German children

To cite this article: Toncheva AA, Suttner K, Michel S, Klopp N, Illig T, Balschun T, Vogelberg C, von Berg A, Bufe A, Heinzmann A, Laub O, Rietschel E, Simma B, Frischer T, Genuneit J, von Mutius E, Kabesch M. Genetic variants in Protocadherin‐1, bronchial hyper‐responsiveness, and asthma subphenotypes in German children. Pediatr Allergy Immunol 2012.

6q12 and 11p14 variants are associated with postnatal exhaled nitric oxide levels and respiratory symptoms

Background: Exhaled nitric oxide (eNO) is a biomarker of airway inflammation and seems to precede respiratory symptoms, such as asthma, in childhood. Identifying genetic determinants of postnatal eNO levels might aid in unraveling the role of eNO in epithelial function or airway inflammation and disease. Objective: We sought to identify genetic determinants of early postnatal eNO levels and subsequent respiratory symptoms during the first year of life. Methods: Within a population‐based birth cohort, eNO levels were measured in healthy term infants aged 5 weeks during quiet tidal breathing in unsedated sleep. We assessed associations of single nucleotide polymorphisms with eNO levels in a genome‐wide association study and subsequent symptoms of lower respiratory tract infections during the first year of life and asked whether this was modified by prenatal and early‐life environmental factors. Results: We identified thus far unknown determinants of infant eNO levels: rs208515 (P = 3.3 × 10−8), which is located at 6q12, probably acting in “trans” and explaining 10.3% of eNO level variance, and rs1441519 (P = 1.6 × 10−6), which is located at 11p14, potentially affecting nitric oxide synthase 3 (NOS3) expression, as shown by means of in vitro functional analyses. Moreover, the 6q12 locus was inversely associated with subsequent respiratory symptoms (P < .05) and time to recovery after first respiratory symptoms during the first year of life (P < .05). Conclusion: The identification of novel genetic determinants of infant eNO levels might implicate that postnatal eNO metabolism in healthy infants before first viral infections and sensitization is related to mechanisms other than those associated with asthma, atopy, or increased risk thereof later in life.

Asthmatic farm children show increased CD3+ CD8low T-cells compared to non-asthmatic farm children

Several studies report an important role of CD8+ cytotoxic T-cells in atopy. Farm children show protection against atopy development, partly explained by CD4+ T-cell subtypes. Additional effects of CD8+ T-cells are unknown being investigated in this study within the PASTURE/EFRAIM birth cohort in PBMCs from farming and non-farming 6-year-old (N = 76) German children. CD3+ CD8+ CD25+ T-cells were analyzed by flow cytometry. Genotyping of 17q21 locus-SNPs associated with childhood asthma was performed. No differences in CD8+ T-cell subsets were seen between farmers and non-farmers regardless of asthma. Among farm children, asthmatics displayed increased CD3+ CD8low(CD25+) T-cells compared to non-asthmatics. Asthmatic farm children exhibited a lower PI-induced stimulatory capacity of CD3+ CD8low(CD25+) cells and a lower IFN-γ secretion than non-asthmatic farm children. Among farm children with GSDMB and ORMDL3 risk alleles, asthmatics displayed higher CD3+ CD8low cells than non-asthmatics. Our data indicates a specific role of CD8low T-cells in asthmatic farm children.