Abstract
Objective. The common polymorphism rs4994 [c. T387C, p. Trp64Arg (W64R)] of the lipolysis regulator beta-3-adrenergic receptor (ADRB3) was identified as a marker in the pathogenesis of hyperuricemia. As gout is characterized by elevated serum concentrations of uric acid, we investigated ADRB3 as a potential candidate for gout.
Methods. This was a prospective case-control study in a group of 421 male patients with gout and 312 gout-free male controls to genotype the single-nucleotide polymorphism rs4994 of ADRB3 gene.
Results. Our results showed that the C allele carrier confers a significantly higher risk for development of gout [chi-square = 4.91, df = 1, p = 0.027, OR 1.95 (adjusted by age, total cholesterol level, and body mass index), 95% CI 1.22–3.13 by dominant mode]. There was significantly higher uric acid level in carriers of the Arg64/Arg64 genotype in controls compared to non-carriers (480.5 mmol/l vs 315.0 mmol/l, respectively).
Conclusion. ADRB3 rs4994 polymorphism is a potential candidate for the pathogenesis of gout in a male Chinese population.
Gout is characterized by joint pain, inflammation, and painful tophi, and can result in joint destruction and disability if untreated1. Uric acid (UA) is the endproduct of purine metabolism in humans, and concentrations of it are primarily determined by endogenous metabolism and the rate of excretion and reabsorption in the kidney2.
The beta-3-adrenergic receptor (ADRB3), located on human chromosome 8p12–p11.2, is expressed predominantly in adipose tissue and is involved in the regulation of lipolysis and thermogenesis3. The direct potential for this gene is to promote obesity in humans; previous studies suggested that ADRB3-selective agonists had an antidiabetic effect in rodent models of obesity and diabetes4.
Trp64Arg (W64R, rs4994) variant was first reported by Walston and colleagues in Indians5. This single-nucleotide polymorphism has moreover been associated with obesity and insulin resistance6,7.
Genes responsible for insulin resistance could contribute to the development of hyperuricemia. Cross-sectional and case-control studies8,9,10 have suggested ADRB3 as a possible candidate for the development of hyperuricemia. This result suggested to us that ADRB3 may also be a potential candidate for development of gout, since hyperuricemia is characterized by elevated levels of UA, and a higher level of UA is the major cause of gout. Our objective was to assess the genetic association of rs4994 polymorphism in a Chinese Han male population.
MATERIALS AND METHODS
A total of 421 male patients with gout and 312 gout-free male controls were recruited from Qingdao University. We collected the clinical features from all the participants. The diagnosis of gout was based on the preliminary criteria for classification of gout of the American Rheumatism Association8 for use in either clinical settings or population-based epidemiology studies. The study protocol conformed to the ethical guidelines of the 1975 Declaration of Helsinki and was approved by the Ethics Committee of the National Research Institute for Family Planning.
Urea nitrogen in the urine was measured from all participants. We calculated the body mass index (BMI) to assess obesity. Hyperuricemia is defined as UA concentrations > 7 mg/dl. The rs4994 and its surrounding sequences in patients and controls were amplified by polymerase chain reaction (PCR) and PCR products were sequenced using an ABI 3730XL instrument (Applied Biosystems, Foster City, CA, USA) to perform genetic analysis.
Statistical analyses were carried out using SPSS version 13.0 (Stata, College Station, TX, USA). Differences between noncontiguous variables, genotype distribution, and allele frequency were tested by chi-square analysis. Student’s t test was used to compare clinical parameters between different genotypes. Significant differences between or among groups were indicated by a p value < 0.05.
RESULTS
The distributions of allele frequencies in patients with gout and controls were in Hardy-Weinberg equilibrium. The results showed that gout patients had significantly higher abnormal blood urea nitrogen levels, total cholesterol levels, blood glucose levels, obesity, hypertension, and hyperuricemia than controls (p < 0.05; Table 1).
There were significant differences in rs4994 genotypic and allelic frequencies between gout cases and controls (Table 2). Compared with controls, there was a higher Arg64/Arg64 genotype and Arg64 allele frequency of rs4994 polymorphism in the gout cases (2.4% vs 0.6% by genotype; 15.0% vs 10.6% by allele). The association to gout reached significance [chi-square = 4.91, df = 1, p = 0.027, OR 1.95 (adjusted by age, total cholesterol, and BMI), 95% CI 1.22–3.13 by dominant mode].
Compared with T allele carriers, there were significantly higher average uric acid levels in Arg64/Arg64 genotype carriers than in controls (480.5 mmol/l vs 315.0 mmol/l; p < 0.001, respectively).
DISCUSSION
The primary finding in our study was that men with ADRB3 Arg64 allele had a significantly higher risk of the incidence of gout than men with Trp64/Trp64 genotype.
Morcillo, et al demonstrated that W64R polymorphism of the ADRB3 gene predicted the risk of developing hyperuricemia in an adult population9. Studies in Chinese and Korean cohorts suggested that W64R polymorphism is possibly related to serum uric acid levels in populations of Asian subjects10,11. According to the results of our study, the carriers of the Arg64/Arg64 genotype had significantly higher serum uric acid levels than noncarriers.
W64R polymorphism is located at the first intracellular loop of ADRB3, considered to be extremely important for receptor movement and in subsequent coupling to the effector system. Therefore, the substitution at position 64 may lead to a lower activity of ADRB3 protein and induce a decrease in intracellular signal transduction leading to development of metabolic syndromes such as gout12.
We investigated the differences of allele and genotype distributions of the ADRB3 W64R polymorphism between 412 Chinese male patients with gout and 312 gout-free controls. ADRB3 rs4994 polymorphism is a potential candidate for the pathogenesis of gout in a male Chinese population.
Footnotes
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Supported by the National Basic Research Program of China (2010CB534902), the National Infrastructure Program of Chinese Genetic Resources (2006DKA21300), the National Natural Science Foundation of China (30570890), and the National Natural Science and Foundation of China (30871192).
- Accepted for publication September 10, 2010.