Research article

Multiple interactions between the alpha_2C- and beta₁-adrenergic receptors influence heart failure survival

Sharon LR Kardia¹ , Reagan J Kelly¹ , Mehdi A Keddache² , Bruce J Aronow² , Gregory A Grabowski² , Harvey S Hahn³ , Karen L Case³ , Lynne E Wagoner³ , Gerald W Dorn II^3,4 and Stephen B Liggett⁵

¹  Department of Epidemiology, School of Public Health, University of Michigan, 109 Observatory St., Ann Arbor, MI 48109-2029 USA

²  Cincinnati Children's Hospital Medical Center, Cincinnati, OH USA

³  Department of Internal Medicine, University of Cincinnati, Cincinnati, OH USA

⁴  Center for Pharmacogenomics, Washington University School of Medicine, St Louis, MO 63110 USA

⁵  Department of Medicine, Cardiopulmonary Genomics Program, University of Maryland, 20 Penn St., HSF-II, Baltimore, MD 21201-1075 USA

author email corresponding author email

BMC Medical Genetics 2008, 9:93doi:10.1186/1471-2350-9-93

Published:	23 October 2008

Abstract

Background

Persistent stimulation of cardiac β₁-adrenergic receptors by endogenous norepinephrine promotes heart failure progression. Polymorphisms of this gene are known to alter receptor function or expression, as are polymorphisms of the α_2C-adrenergic receptor, which regulates norepinephrine release from cardiac presynaptic nerves. The purpose of this study was to investigate possible synergistic effects of polymorphisms of these two intronless genes (ADRB1 and ADRA2C, respectively) on the risk of death/transplant in heart failure patients.

Methods

Sixteen sequence variations in ADRA2C and 17 sequence variations in ADRB1 were genotyped in a longitudinal study of 655 white heart failure patients. Eleven sequence variations in each gene were polymorphic in the heart failure cohort. Cox proportional hazards modeling was used to identify polymorphisms and potential intra- or intergenic interactions that influenced risk of death or cardiac transplant. A leave-one-out cross-validation method was utilized for internal validation.

Results

Three polymorphisms in ADRA2C and five polymorphisms in ADRB1 were involved in eight cross-validated epistatic interactions identifying several two-locus genotype classes with significant relative risks ranging from 3.02 to 9.23. There was no evidence of intragenic epistasis. Combining high risk genotype classes across epistatic pairs to take into account linkage disequilibrium, the relative risk of death or transplant was 3.35 (1.82, 6.18) relative to all other genotype classes.

Conclusion

Multiple polymorphisms act synergistically between the ADRA2C and ADRB1 genes to increase risk of death or cardiac transplant in heart failure patients.