The value of isolated populations in genetic studies of allergic diseases.

Asthma and other IgE-mediated atopic disorders are extremely common in the population, with a consistent, but rather small, genetic component (lambda 3-5) in the inheritance of the disease. So far, genome-wide gene mapping studies in asthma-related traits have not achieved the same success as the positional cloning of genes for Mendelian diseases. Many disease predisposing alleles are believed to be involved in the development of these phenotypes, but at present we do not understand their genetic architecture. As a result of reduced allelic diversity and longer-range linkage disequilibrium compared with more mixed populations, isolated populations may offer a unique opportunity to model a simplified picture of these complex genetic events predisposing to common diseases, such as asthma, which demonstrate familial clustering, but do not follow a simple Mendelian mode of inheritance.(sib)