Molecular scanning of the beta-3-adrenergic receptor gene in Pima Indians and Caucasians

Background The beta-3-adrenergic receptor (beta 3AR) stimulates lipolysis a nd thermogenesis in adipocytes. The Trp64Arg beta 3AR variant is associated in some, but not all, studies with an earlier onset of Type 2 diabetes mel litus and features of the insulin resistance syndrome. Functional studies a s to the role of the Trp64Arg variant have been inconclusive. Earlier studi es screened the beta 3AR gene in only ten obese, diabetic Pima Indians. Pot entially another yet to be identified polymorphism in the beta 3AR gene in linkage disequilibrium with the Trp64Arg polymorphism could explain the fin dings in the association and functional studies. Methods We scanned the beta 3AR gene in 20 diabetic Pima subjects and 20 Ca ucasian subjects using single stranded conformational polymorphism (SSCP) a nalysis. Variants were sequenced using dideoxy sequence analysis and furthe r characterized using allele specific oligonucleotide hybridization (ASO) a nd RNA template specific-polymerase chain reaction (RS-PCR) assays. Results We found a guanine to thymidine substitution in the first intron, 1 4 bases from the splice donor site in both groups. In virtually all subject s, only two haplotypes were detected, Trp64/g1856 and Arg64/t1856, indicati ng that the g1856t polymorphism is in linkage disequilibrium with the Trp64 Arg polymorphism. The g1856t substitution introduces a new consensus splice donor site which, if used, would encode a truncated protein. RNA levels of the two beta 3AR alleles were approximately equal in omental adipose tissu e of heterozygotes. No aberrantly spliced beta 3AR mRNA was detected, indic ating that the new consensus splice donor site is not used in vivo. Conclusion The g1856t polymorphism is in linkage disequilibrium with the Tr p64Arg variant, but does not appear to have a functional role. Copyright (C ) 1999 John Wiley & Sons, Ltd.