Genetic variation within the beta1-adrenergic receptor gene results in haplotype-specific expression phenotypes.
Résumé
Cardiac beta1-adrenergic receptor (beta1AR) responsiveness in heart failure exhibits interindividual variation that may be attributable to polymorphisms of the intronless beta1AR gene. We sought to ascertain the polymorphisms of the full-length gene and the specific combinations of polymorphisms (haplotypes) in two reference populations. Using whole-gene transfections, we established the impact of beta1AR polymorphisms, within the context of haplotypes, on receptor expression. Fifteen polymorphisms within the 6.1-kb gene with allele frequencies > or =0.05 were found in the 5'-flanking and coding regions, but none in the 3'UTR. These were organized into six common haplotypes. Ethnic-specific and cosmopolitan polymorphisms and haplotypes were noted. Whole-gene transfections of A431 cells revealed an association between haplotype and expression, with as much as twofold differences in expression. Phenotypes clustered into three groups, representing high (two haplotypes), intermediate (three haplotypes), and low (one haplotype) expression. We conclude that the beta1AR gene is highly polymorphic and is commonly found in six haplotypic forms in the population. Receptor expression varies by haplotype, which provides the foundation for cardiovascular association studies with enhanced predictive power using beta1AR haplotypes, or haplotype expression clusters, as compared with individual polymorphisms.