Asthma treatment with inhaled steroids demonstrates significant between-person variability. Genetic variation could contribute to this response to inhaled glucocorticosteroids. Difficulties in ...performing genetic association studies are well known. We designed a test and validation strategy to assess steroid pathway candidate genes. One hundred thirty-one single nucleotide polymorphisms in 14 candidate genes in the steroid pathway were genotyped in an 8-week clinical trial of 470 adults with moderate to severe asthma. We then validated our findings in a second population of individuals with childhood asthma in a 4-year clinical trial of inhaled corticosteroids and a third population of adults with asthma. One gene, corticotrophin-releasing hormone receptor 1 (CRHR1, NM_004382), demonstrated multiple single nucleotide polymorphism associations within each of the three populations. The approach of a test and multiple replication populations is a valuable strategy in asthma pharmacogenetics, which can insure valid association findings.
Background Childhood asthma is a complex disease with known heritability and phenotypic diversity. Although an earlier onset has been associated with more severe disease, there has been no ...genome-wide association study of the age of onset of asthma in children. Objective We sought to identify genetic variants associated with earlier onset of childhood asthma. Methods We conducted the first genome-wide association study of the age of onset of childhood asthma among participants in the Childhood Asthma Management Program (CAMP) and used 3 independent cohorts from North America, Costa Rica, and Sweden for replication. Results Two single nucleotide polymorphisms (SNPs) were associated with earlier onset of asthma in the combined analysis of CAMP and the replication cohorts: rs9815663 (Fisher P = 2.31 × 10−8 ) and rs7927044 ( P = 6.54 × 10−9 ). Of these 2 SNPs, rs9815663 was also significantly associated with earlier asthma onset in an analysis including only the replication cohorts. Ten SNPs in linkage disequilibrium with rs9815663 were also associated with earlier asthma onset (2.24 × 10−7 < P < 8.22 × 10−6 ). Having 1 or more risk alleles of the 2 SNPs of interest (rs9815663 and rs7927044) was associated with lower lung function and higher asthma medication use during 4 years of follow-up in CAMP. Conclusions We have identified 2 SNPs associated with earlier onset of childhood asthma in 4 independent cohorts.
Asthma is the leading serious pediatric chronic illness in the United States, affecting 7.1 million children. The prevalence of asthma in children under 4 years of age has increased dramatically in ...the last 2 decades. Existing evidence suggests that this increase in prevalence derives from early environmental exposures acting on a pre-existing asthma-susceptible genotype. We studied the origins of asthma susceptibility in developing lung in rat strains that model the distinct phenotypes of airway hyperresponsiveness (Fisher rats) and atopy (brown Norway BN rats). Postnatal BN rat lungs showed increased epithelial proliferation and tracheal goblet cell hyperplasia. Fisher pups showed increased lung resistance at age 2 weeks, with elevated neutrophils throughout the postnatal period. Diverse transcriptomic signatures characterized the distinct respiratory phenotypes of developing lung in both rat models. Linear regression across age and strain identified developmental variation in expression of 1,376 genes, and confirmed both strain and temporal regulation of lung gene expression. Biological processes that were heavily represented included growth and development (including the T Box 1 transcription factor Tbx5, the epidermal growth factor receptor Egfr, the transforming growth factor beta-1-induced transcript 1 Tgfbr1i1), extracellular matrix and cell adhesion (including collagen and integrin genes), and immune function (including lymphocyte antigen 6 (Ly6) subunits, IL-17b, Toll-interacting protein, and Ficolin B). Genes validated by quantitative RT-PCR and protein analysis included collagen III alpha 1 Col3a1, Ly6b, glucocorticoid receptor and Importin-13 (specific to the BN rat lung), and Serpina1 and Ficolin B (specific to the Fisher lung). Innate differences in patterns of gene expression in developing lung that contribute to individual variation in respiratory phenotype are likely to contribute to the pathogenesis of asthma.
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