Genetic And Environmental Factors In Childhood Respiratory Health

Environmental Health Sciences

Investigators

Linked publications & trials

Abstract

The primary project is a family study of genetic susceptibility to asthma in a highly ozone exposed population, Mexico City. This study uses the case-parent triad design. We have had several interesting results in the past year. S-nitrosothiols are potent endogenous bronchodilators depleted in asthmatic airway lining fluid. S-nitrosoglutathione reductase (GSNOR) catalyzes the metabolism of S-nitrosoglutathione (GSNO) and controls intracellular levels of S-nitrosothiols. Recent work has shown that GSNOR knockout mice have increased lung S-nitrosothiol levels and are thus protected from airway hyperresponsiveness after methacholine or allergen challenge. We therefore examined polymorphisms in GSNOR in relation to childhood asthma in our Mexico City study. We found association with several tagging single nucleotide polymorphisms in GSNOR and childhood asthma but not with the degree of atopy. These results are what would be predicted from the mouse studies. This is the first study to examine GSNOR variants in relatio to respiratory disease and it is currently being followed up by other investigators. In follow-up of inbred mouse studies which have found TNF alpha to be a likely susceptibility gene in respiratory responses to asthma, we examined tagging SNPs across TNF and the adjacent LTA gene, including functional SNPs in the promoter. We found a modest association of borderline statistical significance between two TNF promoter SNPs and childhood asthma. When we stratified by parent smoking, we found a stronger association among children with smoking parents. We believe that this finding of a stronger association with the genetic variant in the lower exposed population makes sense given the previous literature. TNF expression is strongly influenced by exposure to both ozone and tobacoo smoke. Given that the Mexico City population is highly exposed to ozone, the modest genetic contribution to variation in TNF expression may be more easily detected among children without co-exposure to another inducer, tobacco smoke. This year, we also examined the association of SNPs in transforming growth factor beta (TGFB1) and asthma risk. There is strong biologic basis for the importance of this gene in asthma but most previous studies have been relatively small and thus results are inconsistent. We found consistent associations between functionally important SNPs in TGFB1 and asthma risk. This finding provides substantial support for the importance of TGFB1 in asthma. The result was subsequently corroborated by another large study of childhood asthma. [unreadable] [unreadable] Although a substantial body of evidence supports a protective effect of breastfeeding on early childhood wheezing, some recent studies suggest that breastfeeding may be deleterious with respect to later childhood asthma and some early atopic phenotypes. However, these findings were often seen in data subsets in studies underpowered for such analyses. Because of the public concern about whether breastfeeding might increase asthma incidence, we examined the relation between breastfeeding and several objective measures of atopy and asthma in later childhoodin the ALSPAC birth cohort in the UK. This is the largest study to date with prospective data on breastfeeding and objective measures of atopy and bronchial hyperresponsiveness. We found no evidence that breastfeeding has deleterious effects on any outcome. A major benefit of this study is the large sample size which give substantial power, even upon stratification by other factors such as maternal atopy. Furthermore, the prospective data collection enabled us to address potential reverse causation, whereby early manifestations of asthma phenotypes might influence the duration of breastfeeding. This possible bias has been only rarely examined. Although we did find evidence that mothers of infants with wheezing in the first few months of life breast fed these children longer, using a Bayesian analysis we did not find evidence for bias in the association between breastfeeding and asthma phenotypes. We believe that these findings are strong evidence that breastfeeding is not a risk factor for childhood asthma and should reassure pregnant mothers and their physicians regarding this practice. The work has been submitted to a journal. [unreadable] [unreadable] Various investigators in the Epidemiology Branch have established a collaboration with the Norwegian Mother and Child Cohort (called MoBa), a population based cohort of 100,000 pregnant women in Norway who are being followed until their children reach adulthood. I have established a collaboration with the asthma group in Norway around gene-environment interaction and epigenetics. NIEHS/DIR partially supports the MoBa study with the goal of enabling such add-on studies. I have been working on analyses of early childhood outcomes with the MoBa investigators and we are planning follow-up of the children as they turn seven years of age to enable high quality studies of asthma phenotypes.