Association analysis of the beta-3 adrenergic receptor Trp64Arg (rs4994) polymorphism with urate and gout.

The Arg64 allele of variant rs4994 (Trp64Arg) in the ß3-adrenergic receptor gene has been associated with increased serum urate and risk of gout. Our objective was to investigate the relationship of rs4994 with serum urate and gout in New Zealand European, Maori and Pacific subjects. A total of 1730 clinically ascertained gout cases and 2145 controls were genotyped for rs4994 by Taqman(®). Maori and Pacific subjects were subdivided into Eastern Polynesian (EP) and Western Polynesian (WP) sample sets. Publicly available genotype data from the Atherosclerosis Risk in Communities Study and the Framingham Heart Study were utilized for serum urate association analysis. Multivariate logistic and linear regression adjusted for potential confounders was carried out using R version 2.15.2. No significant association of the minor Arg64 (G) allele of rs4994 with gout was found in the combined Polynesian cohorts (OR = 0.98, P = 0.88), although there was evidence, after adjustment for renal disease, for association in both the WP (OR = 0.53, P = 0.03) and the lower Polynesian ancestry EP sample sets (OR = 1.86, P = 0.05). There was no evidence for association with gout in the European sample set (OR = 1.11, P = 0.57). However, the Arg64 allele was positively associated with urate in the WP data set (ß = 0.036, P = 0.004, P Corrected = 0.032). Association of the Arg64 variant with increased urate in the WP sample set was consistent with the previous literature, although the protective effect of this variant with gout in WP was inconsistent. This association provides an etiological link between metabolic syndrome components and urate homeostasis.

Positive association of tomato consumption with serum urate: support for tomato consumption as an anecdotal trigger of gout flares.

BACKGROUND: Gout is a consequence of an innate immune reaction to monosodium urate crystals deposited in joints. Acute gout attacks can be triggered by dietary factors that are themselves associated with serum urate levels. Tomato consumption is an anecdotal trigger of gout flares. This study aimed to measure the frequency of tomato consumption as a self-reported trigger of gout attacks in a large New Zealand sample set, and to test the hypothesis that tomato consumption is associated with serum urate levels. METHODS: Two thousand fifty one New Zealanders (of Maori, Pacific Island, European or other ancestry) with clinically-ascertained gout were asked about gout trigger foods. European individuals from the Atherosclerosis Risk In Communities (ARIC; n = 7517) Study, Cardiovascular Health Study (CHS; n = 2151) and Framingham Heart Study (FHS; n = 3052) were used to test, in multivariate-adjusted analyses, for association between serum urate and tomato intake. RESULTS: Seventy one percent of people with gout reported having ≥1 gout trigger food. Of these 20% specifically mentioned tomatoes, the 4(th) most commonly reported trigger food. There was association between tomato intake and serum urate levels in the ARIC, CHS and FHS combined cohort (ß = 0.66 µmolL(-1) increase in serum urate per additional serve per week; P = 0.006) - evident in both sexes (men: ß = 0.84 µmolL(-1), P = 0.035; women: ß = 0.59 µmolL (-1), P = 0.041). CONCLUSIONS: While our descriptive and observational data are unable to support the claim that tomato consumption is a trigger of gout attacks, the positive association between tomato consumption and serum urate levels suggests that the self-reporting of tomatoes as a dietary trigger by people with gout has a biological basis.

Influence of genetic variants on renal uric acid handling in response to frusemide: an acute intervention study.

OBJECTIVES: Genetic variation in the renal urate transporters SLC2A9 (GLUT9) and SLC22A11 (OAT4) has been reported to interact with diuretics to increase the risk of developing gout. The aim of this study was to determine whether variation in SLC2A9 or SLC22A11 influences acute renal handling of uric acid in response to frusemide. METHODS: Following an overnight fast, healthy participants (n=100) attended a study visit with oral intake of 40 mg frusemide. Blood and urine samples were obtained at baseline and 30, 60, 120 and 180 min after frusemide intake. The primary end point was change in fractional excretion of uric acid (FEUA). RESULTS: Following intake of frusemide, FEUA initially increased (mean (SD) change from baseline +1.9% (3.0%) at 60 min, p<0.001) and then decreased (mean (SD) change from baseline -1.5% (2.1%) at 180 min, p<0.001). A very small increase in serum urate was observed over the study period (mean (SD) change from baseline 0.007 (0.01) mmol/L at 180 min, p<0.001). The presence of the urate-lowering and gout-protective alleles for SLC2A9 (rs11942223 and rs13129697) and SLC22A11 (rs207826) did not significantly alter the FEUA following a frusemide load. At both 60 and 180 min, change in fractional excretion of sodium was independently associated with change in FEUA (standardised ß≥0.40, p<0.001). CONCLUSIONS: The tested variants in SLC2A9 and SLC22A11 do not influence acute changes in renal handling of uric acid in response to frusemide. TRIAL REGISTRATION NUMBER: ACTRN12614000871640; Results.

Association of SLC2A9 genotype with phenotypic variability of serum urate in pre-menopausal women.

The SLC2A9 gene, that encodes a renal uric acid reuptake transporter, has genetic variants that explain ∼3% of variance in urate levels. There are previous reports of non-additive interaction between SLC2A9 genotype and environmental factors which influence urate control. Therefore, our aim was to further investigate the general phenomenon that such non-additive interactions contribute to genotype-specific association with variance at SLC2A9. Data from 14135 European individuals were used in this analysis. The measure of variance was derived from a ranked inverse normal transformation of residuals obtained by regressing known urate-influencing factors (sex, age, and body mass index) against urate. Variant rs6449173 showed the most significant effect on serum urate variance at SLC2A9 (P = 7.9 × 10(-14)), which was maintained after accounting for the effect on average serum urate levels (P = 0.022). Noting the stronger effect in a sub-cohort that consisted of pre-menopausal women and younger men, the participants were stratified into males and pre-menopausal and post-menopausal women. This revealed a strong effect on variance in pre-menopausal women (P = 3.7 × 10(-5)) with a weak effect in post-menopausal women (P = 0.032) and no effect in men (P = 0.22). The T-allele of rs6449173, which associates with increased urate levels, was associated with the greater variance in urate. There was a non-additive interaction between rs6449173 genotype and female gender in control of serum urate levels that was driven by a greater increase in urate levels associated with the T-allele in women. Female hormones, and/or other factors they influence or are associated with (such as iron levels, temperature, testosterone) interact with SLC2A9 genotype in women to determine urate levels. The association of SLC2A9 with greater variance in pre-menopausal women may reflect the cyclical changes resulting from menstruation.

Mendelian randomization provides no evidence for a causal role of serum urate in increasing serum triglyceride levels.

BACKGROUND: Triglycerides and their lipoprotein transport molecules are risk factors for heart disease. Observational studies have associated elevated levels of serum urate (SU) with triglycerides and risk of heart disease. However, owing to unmeasured confounding, observational studies do not provide insight into the causal relationship between SU and triglyceride. The aim of this study was to test for a causal role of SU in increasing triglyceride using Mendelian randomization that accounts for unmeasured confounding. METHODS AND RESULTS: Subjects were of European ancestry from the atherosclerosis risk in communities (n=5237) and Framingham heart (n=2971) studies. Mendelian randomization by the 2-stage least squares regression method was done with SU as the exposure, a uric acid transporter genetic risk score as instrumental variable, and triglyceride as the outcome. In ordinary linear regression, SU was significantly associated with triglyceride levels (ß=2.69 mmol/L change in triglyceride per mmol/L increase in SU). However, Mendelian randomization-based estimation showed no evidence for a direct causal association of SU with triglyceride concentration-there was a nonsignificant 1.01 mmol/L decrease in triglyceride per mmol/L increase in SU attributable to the genetic risk score (P=0.21). The reverse analysis using a triglyceride genetic risk score provided evidence of a causal role for triglyceride in raising urate in men (P(Corrected)=0.018). CONCLUSIONS: These data provide no evidence for a causal role for SU in raising triglyceride levels, consistent with a previous Mendelian randomization report of no association between SU and ischemic heart disease.

Association analysis of the SLC22A11 (organic anion transporter 4) and SLC22A12 (urate transporter 1) urate transporter locus with gout in New Zealand case-control sample sets reveals multiple ancestral-specific effects.

INTRODUCTION: There is inconsistent association between urate transporters SLC22A11 (organic anion transporter 4 (OAT4)) and SLC22A12 (urate transporter 1 (URAT1)) and risk of gout. New Zealand (NZ) Maori and Pacific Island people have higher serum urate and more severe gout than European people. The aim of this study was to test genetic variation across the SLC22A11/SLC22A12 locus for association with risk of gout in NZ sample sets. METHODS: A total of 12 single nucleotide polymorphism (SNP) variants in four haplotype blocks were genotyped using TaqMan® and Sequenom MassArray in 1003 gout cases and 1156 controls. All cases had gout according to the 1977 American Rheumatism Association criteria. Association analysis of single markers and haplotypes was performed using PLINK and Stata. RESULTS: A haplotype block 1 SNP (rs17299124) (upstream of SLC22A11) was associated with gout in less admixed Polynesian sample sets, but not European Caucasian (odds ratio; OR = 3.38, P = 6.1 × 10-4; OR = 0.91, P = 0.40, respectively) sample sets. A protective block 1 haplotype caused the rs17299124 association (OR = 0.28, P = 6.0 × 10-4). Within haplotype block 2 (SLC22A11) we could not replicate previous reports of association of rs2078267 with gout in European Caucasian (OR = 0.98, P = 0.82) sample sets, however this SNP was associated with gout in Polynesian (OR = 1.51, P = 0.022) sample sets. Within haplotype block 3 (including SLC22A12) analysis of haplotypes revealed a haplotype with trans-ancestral protective effects (OR = 0.80, P = 0.004), and a second haplotype conferring protection in less admixed Polynesian sample sets (OR = 0.63, P = 0.028) but risk in European Caucasian samples (OR = 1.33, P = 0.039). CONCLUSIONS: Our analysis provides evidence for multiple ancestral-specific effects across the SLC22A11/SLC22A12 locus that presumably influence the activity of OAT4 and URAT1 and risk of gout. Further fine mapping of the association signal is needed using trans-ancestral re-sequence data.