Polymorphic Variants of [[Beta].Sub.1] Adrenergic Receptor Gene (Ser49gly & Arg389gly) in Healthy Tamilian Volunteers (Report)
The [[beta].sub.1]-adrenergic receptor (ADRB1) belongs to the family of guanine nucleotide binding regulatory protein coupled receptors (GPCRs). ADRB1 is expressed in the heart and mediates the physiological effects of catecholamines like epinephrine and norepinephrine (1). The human [[beta].sub.1]-adrenergic receptor is encoded by an intronless gene with 45 aminoacids located on chromosome10q24-26 (2). Of the 73 polymorphisms of ADRB1 gene identified so far, 13 of these result in change of amino acid in the ADRB1 protein (3,4). Among these, two common functional polymorphic variants (Ser49Gly & Arg389Gly) have been identified and extensively studied. Firstly, substitution of nucleotide A [right arrow] G at 145th position resulted in the change of amino acid serine to glycine (5,6). This polymorphic variant is localized in the extracellular amino terminus (7). Secondly, the change of nucleotide C [right arrow] G at 1165 position resulted in the substitution of amino acid glycine for arginine. This polymorphic variant is localized in the intracellular cytoplasmic tail portion (5). In vitro studies had demonstrated that Arg389 of [[beta].sub.1]-adrenergic receptor was reported to have higher affinity in coupling with the Gs protein and increased signal transduction in the presence of agonist when compared to Gly389 polymorphic variant (8). The polymorphic variant Gly49 of [[beta].sub.1]-adrenergic receptor was shown to have an increased cell expression and affinity towards agonists which leads to desensitization and down-regulation of receptors in contrast to Ser49 (9). The Ser49Gly and Arg389Gly polymorphisms of the [[beta].sub.1]-adrenergic receptor gene are the most extensively studied which are known to influence several cardiovascular disorders. The frequency distribution of these polymorphisms varies with ethnicity. Several studies of diverse human population in Mexicans (10), Swedish (11), Chinese (12), Japanese (13), Caucasians (14) and African Americans (15) have been carried out to determine the prevalence of these genetic variants. To the best of our knowledge, there is no study reporting the genotype and allele frequencies of these two polymorphisms in any of the Indian population. Therefore, we studied the genotype and allele frequency of [[beta].sub.1]-adrenergic receptor gene polymorphisms (Ser49Gly and Arg389Gly) among the healthy volunteers in a South Indian Tamilian population.