Fine mapping of genes underlying asthma and eosinophilia

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Asthma is the fourth most common chronic disease in Australia, and is increasing in incidence. Genetic factors are known to be important modifiers of disease risk, and several genes have been reported in the literature as being involved in either causing asthma or altering response to therapy. Immunoglobulin E (IgE) level and eosinophil count are two factors known to be increased in the blood of asthmatics. In two studies by our group, one of asthma in families, the other of healthy adolescent twins, we showed these measures to be genetically linked to two different regions in the genome. Closer examination of these regions found several genes that might be responsible for the linkage. In the present study, we plan to test which of these candidate genes actually causes elevated IgE level or eosinophil count. The approach is to compare the frequency of a putative gene in a child expressing that phenotype to that in their parents. Each child receives one copy of a gene from the father, and one from the mother, making up a complete genotype (two possibly different versions or alleles of the gene). Since each parent transmitted only one allele to the child, the remaining allele from each parent can be used to create a normal control genotype, that is guaranteed to come from the same ethnic background as the asthmatic child. Therefore, we will collect replacement blood samples in those familes where all the previously DNA has been used up in our earlier study. We will extract DNA, and measure the genotypes of parents and children at the 6 genes in our two regions that we think most likely to be involved in eosinophil count or IgE level. This family based test will allow us to decide which genes are genuinely associated with asthma in our population. We will also test if these genes interact with other genes thought to be asthma risk factors. Identification of novel genes involved in asthma will help understand and ultimately treat this condition.