Dr. Ober and colleagues characterized the 5p-linked BHR susceptibility locus in the inbred Hutterites by positional cloning and replicating these findings in outbred, ethnically diverse populations. They examined single nucleotide polymorphisms (SNPs) spaced about 10 kb apart in each gene, and assessed the evidence for over transmission to affected offspring with each SNP and SNP haplotypes. Associations in the Hutterites were replicated in two outbred samples (a Caucasian sample from Germany, and an African American sample from Chicago). The functional effects of associated variants were assessed by in vitro assays as well as by genotype-phenotype studies in outbred samples that had been evaluated for asthma and atopy phenotypes. Identifying asthma or BHR susceptibility loci may identify novel pathways in asthma pathogenesis, thereby allowing for the development of new therapies and intervention strategies for these common diseases.