Summary Background Exhaled nitric oxide (Fe NO ) is a biomarker for eosinophilic inflammation in the airways and for responsiveness to corticosteroids in asthmatics. Objective We sought to identify in adults the genetic determinants of fractional exhaled nitric oxide (Fe NO ) levels and to assess whether environmental and disease‐related factors influence these associations. Methods We performed a genome‐wide association study of Fe NO through meta‐analysis of two independent discovery samples of European ancestry: the outbred EGEA study (French Epidemiological study on the Genetics and Environment of Asthma, N = 610 adults) and the Hutterites ( N = 601 adults), a founder population living on communal farms. Replication of main findings was assessed in adults from an isolated village in Sardinia (Talana study, N = 450). We then investigated the influence of asthma, atopy and tobacco smoke exposure on these genetic associations, and whether they were also associated with Fe NO values in children of the EAGLE ( EA rly Genetics & Lifecourse Epidemiology, N = 8858) consortium. Results We detected a common variant in RAB 27A (rs2444043) associated with Fe NO that reached the genome‐wide significant level ( P = 1.6 × 10 −7 ) in the combined discovery and replication adult data sets. This SNP belongs to member of RAS oncogene family ( RAB 27A ) and was associated with an expression quantitative trait locus for RAB 27A in lymphoblastoid cell lines from asthmatics. A second suggestive locus (rs2194437, P = 8.9 × 10 −7 ) located nearby the sodium/calcium exchanger 1 ( SLC 8A1 ) was mainly detected in atopic subjects and influenced by inhaled corticosteroid use. These two loci were not associated with childhood Fe NO values. Conclusions and Clinical Relevance This study identified a common variant located in RAB 27A gene influencing Fe NO levels specifically in adults and with a biological relevance to the regulation of Fe NO levels. This study provides new insight into the biological mechanisms underlying Fe NO levels in adults.

BACKGROUND:HLA-G is a non-classical HLA with important immunomodulatory roles in pregnancy. A polymorphism in the promoter region, -725G, was previously associated with sporadic miscarriage in women who were unselected with respect to reproductive history. In this study, the transcription levels of different HLA-G promoter haplotypes were examined to determine whether the miscarriage-associated -725G allele influences transcription.METHODS:Five naturally occurring promoter haplotypes and three variant haplotypes created by site-directed mutagenesis were sub-cloned into luciferase expression vectors and transfected into JEG-3 cells. Expression levels of these eight haplotypes were examined in cultured cells before and after treatment with interferon-beta (IFN-beta), cytosine-5-DNA methyltransferase (M. SssI) and 5-aza-2'-deoxycytidine. Differences in expression levels between haplotypes were determined by analysis of variance (ANOVA).RESULT:Promoter haplotypes with the miscarriage-associated -725G allele were expressed at significantly higher levels in all culture conditions compared with otherwise identical haplotypes that had a -725C or -725T allele.CONCLUSION:Variation in the HLA-G promoter region influences transcription rates. Contrary to expectations, increased expression of HLA-G may be disadvantageous in some pregnancies.

A genome-wide screen for asthma and atopy susceptibility alleles conducted in the Hutterites, a founder population of European descent, reported evidence of linkage with a short tandem repeat polymorphism (STRP) within the type I interferon (IFN) gene cluster on chromosome 9p21. The goal of this study was to identify variation within the IFN gene cluster that influences susceptibility to asthma and atopic phenotypes. We screened approximately 25 kb of sequence, including the flanking sequence of all 15 functional genes and the single coding exon in 12, in Hutterites representing different IFNA-STRP genotypes. We identified 78 polymorphisms, and genotyped 40 of these (in 14 genes) in a large Hutterite pedigree. Modest associations (0.003<P<0.05) with asthma, bronchial hyper-responsiveness (BHR), and atopy were observed with individual variants or genes, spanning the entire 400 kb region. However, pairwise combinations of haplotypes between genes showed highly significant associations with different phenotypes (P<10(-5)) that were localized to specific pairs of genes or regions of this cluster. These results suggest that variation in multiple genes in the type I IFN cluster on 9p22 contribute to asthma and atopy susceptibility, and that not all genes contribute equally to all phenotypes.

Asthma affects nearly 14 million people worldwide and has been steadily increasing in frequency for the past 50 years. Although environmental factors clearly influence the onset, progression, and severity of this disease, family and twin studies indicate that genetic variation also influences susceptibility. Linkage of asthma and related phenotypes to chromosome 6p21 has been reported in seven genome screens, making it the most replicated region of the genome. However, because many genes with individually small effects are likely to contribute to risk, identification of asthma susceptibility loci has been challenging. In this study, we present evidence from four independent samples in support of HLA-G as a novel asthma and bronchial hyperresponsiveness susceptibility gene in the human leukocyte antigen region on chromosome 6p21, and we speculate that this gene might contribute to risk for other inflammatory diseases that show linkage to this region.