Genetic And Environmental Factors In Childhood Respiratory Health

主要项目是对墨西哥城高度臭氧暴露人群哮喘遗传易感性的家庭研究。本研究采用个案-父母三元组设计。在过去的一年里，我们在这项研究中的工作主要集中在使用Illumina 55万单核苷酸多态性平台对这些样本进行全基因组基因分型。我们最近收到了完整的数据集，并在进行分析之前进行了广泛的数据质量控制。因为NIEHS以前没有人做过类似的分析，我们必须开发新的分析方法和开发计算资源来执行这些分析的专业知识。我们还获得了具有全基因组关联研究经验的各种外部合作者的帮助。此外，我们正在参与NHLBI最近建立的一个合作小组，以结合迄今为止所有美国研究中已经产生的全基因组关联数据。这将使每个研究能够克服样本量的限制，并提供方便的跨研究结果的复制。评估从以前的研究中出现的候选基因是很重要的。在开始我们的全基因组基因型之前，我们检查了与一个通过定位克隆（GPRA）鉴定的哮喘基因的关联。我们没有发现与这个基因有明确的联系，仔细研究以前的文献，似乎这个基因在关联研究中并没有得到一致的复制。虽然有几位作者报道了正复制，但在研究中缺乏与相同snp和单倍型的关联，并且几乎肯定存在正发表偏倚，这并不能为复制提供强有力的证据。这项工作发表于去年（Wu et al., 2008）。

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. In the past year our work in this study has focused on whole genome genotyping of these samples using the Illumina 550,000 single nucleotide polymorphism platform. We recently received the complete data set and have been doing the extensive data quality control needed before we can run analyses. Because no one at NIEHS has previously done similar analyses, we have had to develop expertise in new analytic methods and in developing computing resources to perform these analyses. We have also enlisted the assistance of various outside collaborators with experience in genome wide association studies. In addition, we are participating in a collaborative group recently established by NHLBI to combine genome wide association data already generated from all US studies to date. This will enable each study to overcome sample size limitations and also provide convenient replication of results across studies. It is important to evaluate candidate genes that have emerged from previous studies. Prior to beginning our whole genome genotype, we examined associations with an asthma gene that had been identified by positional cloning (GPRA). We found no clear association with this gene and in looking closely at the previous literature, it does not appear that this gene has replicated consistently in association studies. Although positive replication has been reported by several authors, the lack of association with the same SNPs and haplotypes across studies and the near certainty of positive publication bias do not give strong evidence for replication. This work was published in the past year (Wu et al., 2008). Increasing evidence suggest the importance of pregnancy and early life factors in the etiology of asthma and allergy in childhood. Various investigators in the Epidemiology Branch have established a collaboration with the Norwegian Mother and Child Cohort (called MoBa), a population based cohort of approximately 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. In the current year we have had two of these publication accepted. In addition, I have been working closely with the Norwegian investigators to develop follow-up of the children at age seven. At this age, asthma can be reliably identified. We developed and pilot tested a follow-up questionnaire for mailing to parents of children who have turned seven. The first pilot study identified an acceptable response rate. We will revise the questionnaire based on subject and data manager feedback and will next test the feasibility of offering a web-based alternative to the paper questionnaire to decrease costs for follow-up of the entire cohort. We also plan to validate self-reports of asthma by linking to the new Norwegian prescription registry. To further validate these outcome and obtain later childhood asthma phenotypes we are planning clinical evaluation of subsets of the children based on their responses to the seven year mailed questionnaire. These follow-up activities will form the basis for high quality, well powered studies of interactions between genetics/epigenetics and the environment. In the past year we have identified a novel association between higher intake of folate in pregnancy and increased incidence of some early respiratory outcomes in the children (manuscript under review). This finding is an important motivation to follow the children to age seven to examine possible associations with asthma. In addition, this finding has motivated us to begin developing studies of epigenetic changes as a function of maternal levels of folate and other methyl donors during pregnancy. With my input, Dr. Siri Haberg has obtained Norwegian funding to come to NIEHS to work with me during a postdoctoral year to develop this project. While the MoBa study will yield important data on early life factors in asthma, as explained above, this is a long term project to be pursued as the children mature. To examine important questions regarding early life factors in asthma, I developed a collaboration with a birth cohort in the UK of approximately 14,000 children called ALSPAC. 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 sometimes 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 childhood in the ALSPAC study. 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 published in the past year and featured with a commentary by the journal because of the public health importance of the findings (Elliot et al., 2008). I have also been working with Dr. Darryl Zeldin and others on analyses of data collected with NIEHS intramural funding within the National Health Examination Survey (NHANES) 2005-2006. I am collaborating on analyses of obesity as a risk factor for asthma and allergy and plan to pursue analyses of air pollution and allergen levels as these data become available.