The Genetics of Asthma and Chromosome 13

The incidence of allergic asthma has increased greatly over the last thirty years, reaching epidemic proportions in many westemi~ed countries. Family and twin bas~d studies have shown there is a significant genetic component to asthma susceptibility. Great effort has been spent to identify the genes and polymorphisms underlying atopic . asthma, both by candidate gene studies and genome-wide linkage analysis folIowed by positional cloning. Evidence from linkage analysis studies indicated that one such susceptibility locus resides at chromosome 13q14. Subsequent association between a microsatellite and total serum IgE levels, a quantitative phenotype of asthma, was identified. The work presented in this study details the identification of an asthma susceptibility gene and the determination of possible roles for polymorphisms within it that could lead to disease. A detailed single nucleotide polymorphism (SNP) map of the region was created. The strongest association was located within the gene PHF11 and extended into the two flanking genes SETDB2 and RCBTBI. No nonsynonymous polymorphisms were identified within PHF11, therefore a functional role.in transcription factor binding was investigated for the three most associated. SNPs within this gene. In addition, d8exl, a polymorphism associated with total IgE levels and located within the first exon of SETDB2, was also included. The putative function of SETDB2 indicates it may have a role in asthma and additional evidence indicates that a combined SETDB2-PHF11 mRNA may exist. Electrophoretic mobility shift assays (EMSAs) revealed alIele specific protein binding for d8exl and the PHFll SNP b5_3. Supershift experiments identified one b5_3 band as being due to Oct-l and/or SRY binding, while the alIele-specific bands of d8exl were due to YYl and SRY transcription factor binding. As these polymorphisms affected binding allelespecificalIy, it was investigated whether this led to an imbalance of the alleles in the mRNA in heterozygous individuals using alIelotyping. The results indicated a small overall skew in favour of one allele for each polymorphism across the population examined. Biallelic preferential expression was also observed and some individuals showed extreme imbalance in the alleles pre~ent in the mRNA. Multiple linear regression revealed that between 20% and 40% of the variation in expression of the alleles could be explained by the haplotypes of individuals. PHFll is to date one of six asthma susceptibility genes identified by whole genome linkage mapping and positional cloning. In addition, the gene SETDB2 .within the same region may also play a role in the disease. Evidence for a functional role of polymorphisms on transcription efficiency has ~en found. This indicates a possible mechanism by which polymorphisms within these genes could result in their misregulation. This in tum could result in increased susceptibility to asthma. Further work must be performed to confirm the effect of these polymorphisms upon gene expression and identify the role played by these genes within the alIergic pathway.EThOS - Electronic Theses Online ServiceGBUnited Kingdo