Genetic associations with asthma and virus-induced wheezing: a systematic review.

Various wheezing phenotypes can be identified based on differences in natural histories, risk factors and responses to treatment. In epidemiologic studies, atopic asthma or virus-induced wheezing can be discriminated by the presence or the absence of sensitization to allergens. Children with asthma have been shown to present lower levels of lung function. Patients with viral respiratory infections evolve from normal lung function to enhanced airway reactivity. The objective of this study was to identify genes and polymorphisms associated with different wheezing phenotypes. Using data obtained from the Genetic Association Database, we systematically reviewed studies on genes and polymorphisms that have been associated with virus-induced wheezing or atopic asthma. The research was carried out in February of 2009. Genes associated with the studied outcomes in more than three studies were included in the analysis. We found that different genes and loci have been associated with virus-induced wheezing or atopic asthma. Virus-induced wheezing has frequently been associated with IL-8 polymorphisms, whereas atopic asthma and atopy have frequently been associated with Th2 cytokine gene (CD14 and IL-13) polymorphisms on chromosome 5. This review provides evidence that different wheezing disorders in childhood can be differently affected by genetic variations, considering their role on airway inflammation and atopy. Future studies of genetic associations should consider the different wheezing phenotypes in infancy. In addition, stratified analyses for atopy can be useful for elucidating the mechanisms of the disease.