Reference
Complete the bibliographic reference for the article according to AJE format.

Small KM, Wagoner LE, Levin AM, et al. Synergistic polymorphisms of beta1- and alpha2C-adrenergic receptors and the risk of congestive heart failure. N Engl J Med 2002;347:1135-42.

Category of HuGE information
Specify the types of information (from the list below) available in the article:

1. Prevalence of gene variant
2. Gene-disease association
3. Gene-environment interaction
4. Gene-gene interaction
5. Genetic test evaluation/
   monitoring

Study hypotheses or purpose
The authors study hypotheses or main purpose for conducting the study

Hypothesis:  The authors postulated that combination of the α_2cDel322-325 and β₁Arg389 receptor variants would predispose persons to heart failure.

Gene(s)
Identification of the following:

1. Gene name
2. Chromosome location
3. Gene product/function
4. Alleles
5. OMIM #

1. Gene name: ADRA2C, Alpha 2C adrenergic receptor
2. Chromosome location: 4p16.3-p15
3. Gene product/function:

   Relative to other subtypes, alpha 2C adrenergic receptor gene (ARDA2C) expression predominates in heart, lung, aorta, spleen, kidney, adrenal gland, cerebral cortex and cerebellum (1) . In transfected Chinese hamster ovary cells, the Del 322-325 variant had decreased high affinity agonist binding compared with wild type, indicating impaired formation of agonist-receptor-G protein complex. In these cells, the receptor coded by homozygous variant was associated with reduced inhibition of inositol phosphates and reduced agonist-promoted activation of  mitogen-activated protein (MAP) kinase. Thus, loss of function was observed in several signal transduction cascades (2) . The variant may alter the therapeutic effects of clozapine (an atypical neuroleptic useful for treatment-resistant schizophrenia) and clonidine (prescribed for Tourette syndrome, attention deficit hyperactivity disorder (ADHD), and hyperactivity associated with autism, and used to treat hypertension) (3) .

   
   
4. Alleles: In-frame 12 nucleic acid deletion (Del 322-325) encoding a receptor lacking four amino acids (Gly-Ala-Gly-Pro) in third intracellular loop (2) .
5. OMIM #: *104250

1. Gene name: ADRB1, Beta 1 adrenergic receptor
2. Chromosome location: 10q25
3. Gene product/function: In transfected Chinese hamster fibroblasts, the Arg389 receptor displayed greater stimulation of adenylyl cyclase activities by isoproterenol, and increased agonist-promoted [35S]GTPgammaS binding than the Gly389 receptor. Thus, the variant alters receptor-Gs interaction with functional signal transduction consequences (4).
   
   In the heart, Beta 1 adrenergic receptor is the predominant beta-adrenergic receptor subtype. It is expressed on monocytes of the atria and ventricles, where they act to increase the force and frequency of contraction in response to sympathetic stimulation.
4. Alleles: Cytosine substitution for guanine at nucleotide 1165, altering the encoded amino acid from Gly to Arg at amino acid position 389 in C-terminal intracellular G-protein coupling domain. (The former previously considered as human wild type (4).
5. OMIM #: *109630

Environmental factor(s)
Identification of the major environmental factors studied (infectious, chemical, physical, nutritional, and behavioral)

None

Health outcome(s)
Identification of the major health outcome(s) studied

Congestive heart failure

1. Case-control
2. Cohort 
3. Cross-sectional
4. Descriptive or case series
5. Clinical trial
6. Population screening

1. Disease case definition
2. Exclusion criteria
3. Gender
4. Race/ethnicity
5. Age
6. Time period
7. Geographic location
8. Number of participants (% of total eligible)

1. Disease case definition: Left ventricular ejection fraction <35%; heart failure of New York Heart Association class II, III, or IV; diagnosis of either (i) idiopathic dilated cardiomyopathy or (ii) ischemic cardiomyopathy.
2. Exclusion criteria:Heart failure from primary valvular disease, myocarditis, or obstructive or hypertrophic cardiomyopathies.
3. Sex: Men and women
4. Race/Ethnicity: 78 blacks, 81 whites
5. Age: 20-79 years
6. Time period: January 2, 1999- January 2, 2001
7. Geographic location: greater Cincinnati area
8. Number of participants: 159

1. Control selection criteria
2. Matching variables
3. Exclusion criteria
4. Gender
5. Race/ethnicity
6. Age
7. Time period
8. Geographic location
9. Number of participants (% of total eligible)

1. Control selection criteria: Apparently healthy persons (as assessed by questionnaire) recruited before voluntary blood donation and by newspaper advertisements
2. Matching variables: None
3. Exclusion criteria: Related to other controls; History or symptoms of cardiovascular disease; Taking medications for long periods
4. Sex: Not specified
5. Race/Ethnicity: 84 blacks, 105 whites
6. Age: Not specified
7. Time period: Not specified
8. Geographic location: greater Cincinnati area
9. Number of participants: 189

1. Environmental factor
2. Exposure assessment
3. Exposure definition
4. Number of participants with exposure data (% of total eligible)

N/A

1. Gene
2. DNA source
3. Methodology
4. Number of participants genotyped (% of total eligible) 

1. Gene: ARDA2C
2. DNA source: peripheral blood
3. Methodology: method of Small et al. (5)
4. Number of participants genotyped: not specified

1. Gene: ADRB1
2. DNA source: peripheral blood
3. Methodology: method of Small et al. (5)
4. Number of participants genotyped: not specified

1. Prevalence of gene variant
2. Gene-disease association
3. Gene-environment interaction
4. Gene-gene interaction
5. Genetic test evaluation/
   monitoring

1. Prevalence of gene variants: see attached Table 1 & Table 2 Study under review shaded in green.
2. Gene-disease associations:  see attached Table 3
3. Gene-gene interaction: see attached Table 5

The authors concluded that α_2cDel322-325 and β₁₁Arg389 receptor variants act synergistically to increase the risk for heart failure in blacks. Genotyping at these two loci may be useful for identifying persons at risk for heart failure or its progression who may be candidates for early preventive measures.

Selection of subjects

• The study base of case- and control-subjects may not be the same. No data are presented on participation rates of potentially eligible cases or for the blood donors (this would not have been possible to determine for persons who responded to newspaper advertisements).
• Comparison of the genotype distribution between the two types of controls would have been helpful.
• The control distributions of genotypes for both polymorphisms are in Hardy-Weinberg equilibrium and appear to be similar to those in other reports (most of which are not population-based studies)
• A strength of the study is that the possible effect of stratification was investigated by comparing 9 short-tandem repeat markers between cases and controls. No evidence of stratification was observed.
• A further strength is that among participating case-subjects, a survivor effect was investigated. The results did not suggest such an effect.
• A substantially higher proportion of white case-subjects (60.5%) than black case-subjects (33.3%) were on beta-blockers at the start of the study (Table 1 of the journal report). If either genotype, or the combination of genotypes, affected response to beta-blocker therapy, this might have differentially selected persons potentially eligible to participate in the study by ethnic group.

Analysis of interaction

• The biologic argument for an interaction specifically between the two variants investigated in this study is not strong.
• There appears to be some dependence between the genotypes in the population at risk of the disease. The control-only odds ratio in all subjects is 0.37; in blacks, 0.39; and in whites, 84/0. This would have inflated the estimate of interaction. (The case-only odds ratios were 0.83, 2.09, and 0.88 respectively)
• Subgroup analysis by ethnic group appears justified, but the existence of an a priori hypothesis that the interaction would be found only in one group is not clear (otherwise the study might have been done only in one group)
• As with so many studies of this type, statistical power was limited.

• The finding with ARDA2C is novel; no other studies have been published about cardiovascular outcomes and this variant
• ARDB1 has been investigated in relation to a number of cardiovascular outcomes. The results are inconsistent.