Genome-wide association studies for discovery of genes involved in asthma

Asthma is the result of a complex interaction between environmental factors and genetic variants that confer susceptibility. Studies of the genetics of asthma have previously been conducted using linkage designs and candidate gene association studies. Recently, the association study design has been extended from specific candidate genes to an unbiased genome-wide approach: the genome-wide association study (GWAS). To date, there have been 12 GWAS to look for susceptibility loci for asthma and related traits. The first GWAS for asthma discovered a novel associated locus on chromosome 17q21 encompassing the genes ORMDL3, GSDMB and ZPBP2. None of these genes would have been selected in a candidate association study based on current knowledge of the functions of these genes. Nevertheless, this finding has been consistently replicated in independent populations of European ancestry and also in other ethnic groups. Thus, chromosome 17q21 seems to be a true asthma susceptibility locus. Other genes that were identified in more than one GWAS are IL33, RAD50, IL1RL1 and HLA-DQB1. Additional novel susceptibility genes identified in a single study include DENND1BI and IL2RB. Discovering the causal mechanism behind these associations is likely to yield great insights into the development of asthma. It is likely that further meta-analyses of asthma GWAS data from existing international consortia will uncover more novel susceptibility genes and further increase our understanding of this disease.