Meta-analysis of 28,141 individuals identifies common variants within five new loci that influence uric acid concentrations

Validation of standard operating procedures in a multicenter retrospective study to identify -omics biomarkers for chronic low back pain

Chronic low back pain (CLBP) is one of the most common medical conditions, ranking as the greatest contributor to global disability and accounting for huge societal costs based on the Global Burden of Disease 2010 study.

Large genetic and -omics studies provide a promising avenue for the screening, development and validation of biomarkers useful for personalized diagnosis and treatment (precision medicine). Multicentre studies are needed for such an effort, and a standardized and homogeneous approach is vital for recruitment of large numbers of participants among different centres (clinical and laboratories) to obtain robust and reproducible results. To date, no validated standard operating procedures (SOPs) for genetic/-omics studies in chronic pain have been developed.

In this study, we validated an SOP model that will be used in the multicentre (5 centres) retrospective “PainOmics” study, funded by the European Community in the 7th Framework Programme, which aims to develop new biomarkers for CLBP through three different -omics approaches: genomics, glycomics and activomics.

The SOPs describe the specific procedures for (1) blood collection, (2) sample processing and storage, (3) shipping details and (4) cross-check testing and validation before assays that all the centres involved in the study have to follow.

Multivariate analysis revealed the absolute specificity and homogeneity of the samples collected by the five centres for all genetics, glycomics and activomics analyses.

The SOPs used in our multicenter study have been validated. Hence, they could represent an innovative tool for the correct management and collection of reliable samples in other large-omics-based multicenter studies.

Genetic risk scores, sex and dietary factors interact to alter serum uric acid trajectory among African-American urban adults

Serum uric acid (SUA), a causative agent for gout among others, is affected by both genetic and dietary factors, perhaps differentially by sex. We evaluated cross-sectional (SUAbase) and longitudinal (SUArate) associations of SUA with a genetic risk score (GRS), diet and sex. We then tested the interactive effect of GRS, diet and sex on SUA. Longitudinal data on 766 African-American urban adults participating in the Healthy Aging in Neighborhood of Diversity across the Lifespan study were used. In all, three GRS for SUA were created from known SUA-associated SNP (GRSbase (n 12 SNP), GRSrate (n 3 SNP) and GRStotal (n 15 SNP)). Dietary factors included added sugar, total alcohol, red meat, total fish, legumes, dairy products, caffeine and vitamin C. Mixed-effects linear regression models were conducted. SUAbase was higher among men compared with that among women, and increased with GRStotal tertiles. SUArate was positively associated with legume intake in women (γ=+0·14; 95 % CI +0·06, +0·22, P=0·001) and inversely related to dairy product intake in both sexes combined (γ=-0·042; 95 % CI -0·075, -0·009), P=0·010). SUAbase was directly linked to alcohol consumption among women (γ=+0·154; 95 % CI +0·046, +0·262, P=0·005). GRSrate was linearly related to SUArate only among men. Legume consumption was also positively associated with SUArate within the GRStotal's lowest tertile. Among women, a synergistic interaction was observed between GRSrate and red meat intake in association with SUArate. Among men, a synergistic interaction between low vitamin C and genetic risk was found. In sum, sex-diet, sex-gene and gene-diet interactions were detected in determining SUA. Further similar studies are needed to replicate our findings.

Recent advances in understanding and managing gout

Gout is the most common crystal arthropathy and the leading cause of inflammatory arthritis. It is associated with functional impairment and, for many, a diminished health-related quality of life. Numerous studies have demonstrated the impact of gout and its associated conditions on patient morbidity and mortality. Unfortunately, gout remains under-diagnosed and under-treated in the general community. Despite major advances in treatment strategies, as many as 90% of patients with gout are poorly controlled or improperly managed and their hyperuricemia and recurrent flares continue. The introduction of novel urate-lowering therapies, new imaging modalities, and a deeper understanding of the pathogenesis of gout raise the possibility of better gout care and improved patient outcomes. Here, we spotlight recent advances in the diagnosis and management of gout and discuss novel therapeutics in gout treatment.

Effects of multiple genetic loci on the pathogenesis from serum urate to gout

Gout is a common arthritis resulting from increased serum urate, and many loci have been identified that are associated with serum urate and gout. However, their influence on the progression from elevated serum urate levels to gout is unclear. This study aims to explore systematically the effects of genetic variants on the pathogenesis in approximately 5,000 Chinese individuals. Six genes (PDZK1, GCKR, TRIM46, HNF4G, SLC17A1, LRRC16A) were determined to be associated with serum urate (P_FDR < 0.05) in the Chinese population for the first time. ABCG2 and a novel gene, SLC17A4, contributed to the development of gout from hyperuricemia (OR = 1.56, P_FDR = 3.68E-09; OR = 1.27, P_FDR = 0.013, respectively). Also, HNF4G is a novel gene associated with susceptibility to gout (OR = 1.28, P_FDR = 1.08E-03). In addition, A1CF and TRIM46 were identified as associated with gout in the Chinese population for the first time (P_FDR < 0.05). The present study systematically determined genetic effects on the progression from elevated serum urate to gout and suggests that urate-associated genes functioning as urate transporters may play a specific role in the pathogenesis of gout. Furthermore, two novel gout-associated genes (HNF4G and SLC17A4) were identified.

The serum uric acid concentration is not causally linked to diabetic nephropathy in type 1 diabetes

Previous studies have shown a relationship between uric acid concentration and progression of renal disease. Here we studied causality between the serum uric acid concentration and progression of diabetic nephropathy in 3895 individuals with type 1 diabetes in the FinnDiane Study. The renal status was assessed with the urinary albumin excretion rate and estimated glomerular filtration rate (eGFR) at baseline and at the end of the follow-up. Based on previous genomewide association studies on serum uric acid concentration, 23 single nucleotide polymorphisms (SNPs) with good imputation quality were selected for the SNP score. This score was used to assess the causality between serum uric acid and renal complications using a Mendelian randomization approach. At baseline, the serum uric acid concentration was higher with worsening renal status. In multivariable Cox regression analyses, baseline serum uric acid concentration was not independently associated with progression of diabetic nephropathy over a mean follow-up of 7 years. However, over the same period, baseline serum uric acid was independently associated with the decline in eGFR. In the cross-sectional logistic regression analyses, the SNP score was associated with the serum uric acid concentration. Nevertheless, the Mendelian randomization showed no causality between uric acid and diabetic nephropathy, eGFR categories, or eGFR as a continuous variable. Thus, our results suggest that the serum uric acid concentration is not causally related to diabetic nephropathy but is a downstream marker of kidney damage.

Genome-wide methylation data mirror ancestry information

Background

Genetic data are known to harbor information about human demographics, and genotyping data are commonly used for capturing ancestry information by leveraging genome-wide differences between populations. In contrast, it is not clear to what extent population structure is captured by whole-genome DNA methylation data.

Results

We demonstrate, using three large-cohort 450K methylation array data sets, that ancestry information signal is mirrored in genome-wide DNA methylation data and that it can be further isolated more effectively by leveraging the correlation structure of CpGs with cis-located SNPs. Based on these insights, we propose a method, EPISTRUCTURE, for the inference of ancestry from methylation data, without the need for genotype data.

Conclusions

EPISTRUCTURE can be used to infer ancestry information of individuals based on their methylation data in the absence of corresponding genetic data. Although genetic data are often collected in epigenetic studies of large cohorts, these are typically not made publicly available, making the application of EPISTRUCTURE especially useful for anyone working on public data. Implementation of EPISTRUCTURE is available in GLINT, our recently released toolset for DNA methylation analysis at: http://glint-epigenetics.readthedocs.io.

Electronic supplementary material

The online version of this article (doi:10.1186/s13072-016-0108-y) contains supplementary material, which is available to authorized users.

ABCG2 and PKD2 polymorphisms correlate with gout-related metabolic indices in Chinese Han and Tibetan populations

Gout is a complex inflammation disease resulting from an increase in serum uric acid (SUA), which is one of the most common forms of inflammatory arthritis worldwide. Identification of the genetic factors of gout could be paramount contribution to early prevention of gout. Recent evidence suggests that heredity and metabolic syndrome contribute to gout development. ATP-binding cassette, sub-family G (ABCG2) and PKD2 may play a role in gout progression in Chinese and Han populations. A total of 455 patients (139 Han, 316 Tibetan) with gout and 627 healthy control subjects (309 Han, 318 Tibetan) were recruited for a case-control association study. Analysis of variance was used to evaluate the impact of polymorphism on gout based on metabolism indicators. Polymorphisms of the ABCG2 and PKD2 genes affected multiple risk factors for gout progression. Significant differences in alkaline phosphatase (AKP), high-density lipoproteins (HDL-C) and total bilirubin (TBIL) levels were detected between different genotypic groups with ABCG2 polymorphisms rs4693924, rs2622621, rs17731799 and rs3114020. In addition, significant differences in AKP, HDL-C and glutamic oxalacetic transaminase (AST) levels were detected between different genotypic groups with the PKD2 polymorphisms rs2728104, rs2728099 and rs2728121 in Chinese Han and Tibetan populations. Our results provided significant evidence for the potential relationships among ABCG2, PKD2 polymorphisms correlate with gout related metabolic indices in Chinese Han and Tibetan populations.

A novel mode of operation of SLC22A11: Membrane insertion of estrone sulfate versus translocation of uric acid and glutamate

Estrone sulfate alias estrone-3-sulfate (E3S) is considerably larger and much more hydrophobic than typical substrates of SLC22 transporters. It is puzzling that many otherwise unrelated transporters have been reported to transport E3S. Here we scrutinized the mechanism of transport of E3S by SLC22A11 (alias OAT4), by direct comparison with uric acid (UA), an important physiological substrate. Heterologous expression of SLC22A11 in human 293 cells gave rise to a huge unidirectional efflux of glutamate (Glu) and aspartate, as determined by LC-MS/MS. The uptake of E3S was 20-fold faster than the uptake of UA. Yet, the outward transport of Glu was inhibited by extracellular E3S, but not by UA. The release of E3S after preloading was trans-stimulated by extracellular dehydroepiandrosterone sulfate (DHEAS), but neither by UA nor 6-carboxyfluorescein (6CF). The equilibrium accumulation of E3S was enhanced 3-fold by replacement of chloride with gluconate, but the opposite effect was observed for UA. These results establish that SLC22A11 provides entirely different transport mechanisms for E3S and UA. Therefore, E3S must not be used as a substitute for UA to assay the function of SLC22A11. In equilibrium accumulation experiments, the transporter-mediated uptake was a linear function of the concentration of UA and 6CF. By contrast, in the same concentration range the graph for E3S was hyperbolic. This suggests that SLC22A11 inserts E3S into a small volume with limited capacity, the plasma membrane. Our data support the notion that the reverse process, extraction from the membrane, is also catalyzed by the carrier.

Uric acid transporters hiding in the intestine

CONTEXT

Hyperuricaemia is known as an abnormally increased uric acid level in the blood. Although it was observed many years ago, since uric acid excretion via the intestine pathway accounted for approximately one-third of total elimination of uric acid, the molecular mechanism of 'extra-renal excretion' was poorly understood until the finding of uric acid transporters.

OBJECTIVE

The objective of this study was to gather all information related to uric acid transporters in the intestine and present this information as a comprehensive and systematic review article.

METHODS

A literature search was performed from various databases (e.g., Medline, Science Direct, Springer Link, etc.). The key terms included uric acid, transporter and intestine. The period for the search is from the 1950s to the present. The bibliographies of papers relating to the review subject were also searched for further relevant references.

RESULTS

The uric acid transporters identified in the intestine are discussed in this review. The solute carrier (SLC) transporters include GLUT9, MCT9, NPT4, NPT homolog (NPT5) and OAT10. The ATP binding cassette (ABC) transporters include ABCG2 (BCRP), MRP2 and MRP4. Bacterial transporter YgfU is a low-affinity and high-capacity transporter for uric acid.

CONCLUSION

The present review may be helpful for further our understanding of hyperuricaemia and be of value in designing future studies on novel therapeutic pathways.

Fructose suppresses uric acid excretion to the intestinal lumen as a result of the induction of oxidative stress by NADPH oxidase activation

BACKGROUND

A high intake of fructose increases the risk for hyperuricemia. It has been reported that long-term fructose consumption suppressed renal uric acid excretion and increased serum uric acid level. However, the effect of single administration of fructose on excretion of uric acid has not been clarified.

METHODS

We used male Wistar rats, which were orally administered fructose (5g/kg). Those rats were used in each experiment at 12h after administration.

RESULTS

Single administration of fructose suppressed the function of ileal uric acid excretion and had no effect on the function of renal uric acid excretion. Breast cancer resistance protein (BCRP) predominantly contributes to intestinal excretion of uric acid as an active homodimer. Single administration of fructose decreased BCRP homodimer level in the ileum. Moreover, diphenyleneiodonium (DPI), an inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox), recovered the suppression of the function of ileal uric acid excretion and the Bcrp homodimer level in the ileum of rats that received single administration of fructose.

CONCLUSIONS

Single administration of fructose decreases in BCRP homodimer level, resulting in the suppression the function of ileal uric acid excretion. The suppression of the function of ileal uric acid excretion by single administration of fructose is caused by the activation of Nox. The results of our study provide a new insight into the mechanism of fructose-induced hyperuricemia.

Natural Products Improving Hyperuricemia with Hepatorenal Dual Effects

This review aims to put forth an overview of natural products reducing uric acid level with hepatorenal dual effects. The prevalence of hyperuricemia increased rapidly in recent years and has closely interdependent relationship with other metabolic disorders. Current therapeutically used drugs including a few uricostatic and uricosuric chemical drugs are proved efficient to control serum uric acid level. However, their side effects as well as contraindication in some cases with liver, kidney injury, or other conditions frequently limit their clinic application. More attention thus has been paid to natural products as an alternative means in treating hyperuricemia. Many natural products have been proved efficient in downregulating uric acid level, among which some can improve hyperuricemia with hepatorenal dual effects. It means these natural products can regulate both the production and the excretion of uric acid by targeting the key metabolic enzymes mainly in liver or uric acid transporters in kidneys. Thus, these natural products could have stronger efficacy and broader application, which may be developed for the treatment of hyperuricemia in clinic.

Mechanism of high affinity inhibition of the human urate transporter URAT1

Gout is caused by elevated serum urate levels, which can be treated using inhibitors of the uric acid transporter, URAT1. We exploited affinity differences between the human and rat transporters to map inhibitor binding sites in URAT1. Human-rat transporter chimeras revealed that human URAT1 serine-35, phenylalanine-365 and isoleucine-481 are necessary and sufficient to provide up to a 100-fold increase in affinity for inhibitors. Moreover, serine-35 and phenylalanine-365 are important for high-affinity interaction with the substrate urate. A novel URAT1 binding assay provides support for direct interaction with these amino acids; thus, current clinically important URAT1 inhibitors likely bind the same site in URAT1. A structural model suggests that these three URAT1 residues are in close proximity potentially projecting within the channel. Our results indicate that amino acids from several transmembrane segments functionally cooperate to form a high-affinity URAT1 inhibitor binding site that, when occupied, prevents substrate interactions.

Association of DNA methyltransferase polymorphisms with susceptibility to primary gouty arthritis

Gouty arthritis is the most common type of inflammatory and immune disease, and the prevalence and incidence of gout increases annually. Genetic variations in the DNA methyltransferases (DNMTs) gene have not, to the best of our knowledge, been reported to influence gene expression and to participate in the pathogenesis of gout. The aim of the present study was to investigate whether the DNMT1, DNMT3A and DNMT3B polymorphisms contribute to gout susceptibility. These polymorphisms were screened for in 336 gout patients and 306 healthy control subjects (from a South China population) for association with gout. The distribution frequencies of DNMT1 rs2228611 AA genotype (P=0.007) and A allele (P=0.002; odds ratio=1.508, 95% confidence interval=1.158-1.964) were found to be significantly increased in the gout patients when compared with those in the healthy control subjects. The rs1550117 in DNMT3A and rs2424913 in DNMT3B exhibited no significant associations with gout susceptibility between the patients and control subjects. These results demonstrated that the DNMT1 rs2228611 polymorphism may be involved in the pathogenesis of gout, while DNMT3A rs1550117 and DNMT3B rs2424913 did not show any obvious significance in the current study; thus, may not be used as risk factors to predict the susceptibility to gout. However, further studies are required to investigate the functions and regulatory mechanism of the polymorphisms of DNMTs in gout.

Lesinurad, a novel, oral compound for gout, acts to decrease serum uric acid through inhibition of urate transporters in the kidney

Background

Excess body burden of uric acid promotes gout. Diminished renal clearance of uric acid causes hyperuricemia in most patients with gout, and the renal urate transporter (URAT)1 is important for regulation of serum uric acid (sUA) levels. The URAT1 inhibitors probenecid and benzbromarone are used as gout therapies; however, their use is limited by drug–drug interactions and off-target toxicity, respectively. Here, we define the mechanism of action of lesinurad (Zurampic®; RDEA594), a novel URAT1 inhibitor, recently approved in the USA and Europe for treatment of chronic gout.

Methods

sUA levels, fractional excretion of uric acid (FE_UA), lesinurad plasma levels, and urinary excretion of lesinurad were measured in healthy volunteers treated with lesinurad. In addition, lesinurad, probenecid, and benzbromarone were compared in vitro for effects on urate transporters and the organic anion transporters (OAT)1 and OAT3, changes in mitochondrial membrane potential, and human peroxisome proliferator-activated receptor gamma (PPARγ) activity.

Results

After 6 hours, a single 200-mg dose of lesinurad elevated FE_UA 3.6-fold (p < 0.001) and reduced sUA levels by 33 % (p < 0.001). At concentrations achieved in the clinic, lesinurad inhibited activity of URAT1 and OAT4 in vitro, did not inhibit GLUT9, and had no effect on ABCG2. Lesinurad also showed a low risk for mitochondrial toxicity and PPARγ induction compared to benzbromarone. Unlike probenecid, lesinurad did not inhibit OAT1 or OAT3 in the clinical setting.

Conclusion

The pharmacodynamic effects and in vitro activity of lesinurad are consistent with inhibition of URAT1 and OAT4, major apical transporters for uric acid. Lesinurad also has a favorable selectivity and safety profile, consistent with an important role in sUA-lowering therapy for patients with gout.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1107-x) contains supplementary material, which is available to authorized users.

Epidermal growth factor gene is a newly identified candidate gene for gout

Chromosome 4q25 has been identified as a genomic region associated with gout. However, the associations of gout with the genes in this region have not yet been confirmed. Here, we performed two-stage analysis to determine whether variations in candidate genes in the 4q25 region are associated with gout in a male Chinese Han population. We first evaluated 96 tag single nucleotide polymorphisms (SNPs) in eight inflammatory/immune pathway- or glucose/lipid metabolism-related genes in the 4q25 region in 480 male gout patients and 480 controls. The SNP rs12504538, located in the elongation of very-long-chain-fatty-acid-like family member 6 gene (Elovl6), was found to be associated with gout susceptibility (P_adjusted = 0.00595). In the second stage of analysis, we performed fine mapping analysis of 93 tag SNPs in Elovl6 and in the epidermal growth factor gene (EGF) and its flanking regions in 1017 male patients gout and 1897 healthy male controls. We observed a significant association between the T allele of EGF rs2298999 and gout (odds ratio = 0.77, 95% confidence interval = 0.67–0.88, P_adjusted = 6.42 × 10⁻³). These results provide the first evidence for an association between the EGF rs2298999 C/T polymorphism and gout. Our findings should be validated in additional populations.

Assessment of genetic polymorphisms associated with hyperuricemia or gout in the Hmong

AIM

Hyperuricemia commonly causes gout. Minnesota Hmong exhibit a two- to fivefold higher prevalence of gout versus non-Hmong. To elucidate a possible genomic contribution to this disparity, prevalence of risk alleles for hyperuricemia in Hmong was compared with European (CEU) and Han-Chinese (CHB).

METHODS

In total, 235 Hmong were genotyped for eight SNPs representing five candidate genes (SLC22A12, SLC2A9, ABCG2, SLC17A1 and PDZK1).

RESULTS

The frequency of seven out of eight risk alleles in the Hmong was significantly different than CEU; six higher and one with lower prevalence. The frequency of three out of eight risk alleles in the Hmong was significantly different than CHB; two higher and one with lower prevalence.

CONCLUSION

Hyperuricemia risk alleles are more prevalent in the Hmong than CEU and HB.

Common variant of PDZ domain containing 1 (PDZK1) gene is associated with gout susceptibility: A replication study and meta-analysis in Japanese population

PDZ domain containing 1 (PDZK1) is a scaffold protein that organizes a transportsome and regulates several transporters' functions including urate and drug transporters. Therefore, PDZK1 in renal proximal tubules may affect serum uric acid levels through PDZK1-binding renal urate transporters. Two previous studies in Japanese male population reported that a PDZK1 single nucleotide polymorphism (SNP), rs12129861, was not associated with gout. In the present study, we performed a further association analysis between gout and rs12129861 in a different large-scale Japanese male population and a meta-analysis with previous Japanese population studies. We genotyped rs12129861 in 1210 gout cases and 1224 controls of a Japanese male population by TaqMan assay. As a result, we showed that rs12129861 was significantly associated with gout susceptibility (P = 0.016, odds ratio [OR] = 0.80, 95% confidence interval [CI] 0.67-0.96). The result of the meta-analysis among Japanese populations also showed a significant association (P = 0.013, OR = 0.85, 95%CI 0.75-0.97). Our findings show the significant association between gout susceptibility and common variant of PDZK1 which reportedly regulates the functions of urate transporters in the urate transportsome.

Modulation of Glucokinase Regulatory Protein: A Double-Edged Sword?

The continuous search for drugs targeting type 2 diabetes mellitus (T2DM) has led to the identification of small molecules that disrupt the binding between glucokinase and glucokinase regulatory protein (GKRP). Although mice studies are encouraging, it will take years before these disruptors can be introduced to T2DM patients. Recently, genome-wide association studies (GWASs) have shown that variants in the gene encoding GKRP protect against T2DM and kidney disease but predispose to gout, nonalcoholic fatty liver disease, and dyslipidemia. These genetic data, together with previous experience with systemic and hepatospecific glucokinase activators, provide insight into the anticipated efficacy and safety of small-molecule disruptors in humans. Interestingly, they suggest that the opposite--enhanced GKRP-glucokinase binding--could be beneficial in selected patients.

Histological characterization of orphan transporter MCT14 (SLC16A14) shows abundant expression in mouse CNS and kidney

BACKGROUND

MCT14 (SLC16A14) is an orphan member of the monocarboxylate transporter (MCT) family, also known as the SLC16 family of secondary active transmembrane transporters. Available expression data for this transporter is limited, and in this paper we aim to characterize MCT14 with respect to tissue distribution and cellular localization in mouse brain.

RESULTS

Using qPCR, we found that Slc16a14 mRNA was highly abundant in mouse kidney and moderately in central nervous system, testis, uterus and liver. Using immunohistochemistry and in situ hybridization, we determined that MCT14 was highly expressed in excitatory and inhibitory neurons as well as epithelial cells in the mouse brain. The expression was exclusively localized to the soma of neurons. Furthermore, we showed with our phylogenetic analysis that MCT14 most closely relate to the aromatic amino acid- and thyroid-hormone transporters MCT8 (SLC16A2) and MCT10 (SLC16A10), in addition to the carnitine transporter MCT9 (SLC16A9).

CONCLUSIONS

We provide here the first histological mapping of MCT14 in the brain and our data are consistent with the hypothesis that MCT14 is a neuronal aromatic-amino-acid transporter.

Association between serum uric acid related genetic loci and diabetic kidney disease in the Chinese type 2 diabetes patients

AIM

We aimed to investigate the association between uric acid related genetic loci and DKD susceptibility in type 2 diabetes patients.

METHODS

Seventeen single nucleotide polymorphisms (SNPs) from thirteen loci related to serum uric acid were genotyped in 2,892 type 2 diabetes patients. Associations between SNPs and uric acid, SNPs and quantitative traits related to DKD or its susceptibility were evaluated.

RESULTS

In this study, uric acid showed a strong association with DKD (OR=1.006, p<0.0001). GCKR rs780094, SLC2A9 rs11722228, SLC2A9 rs3775948, ABCG2 rs2231142, SLC22A12 rs505802 and NRXN2 rs506338 were positively associated with serum uric acid (p=3.79E-05, 0.0002, 2.04E-10, 2.23E-09, 0.0018 and 0.0015, respectively). SLC2A9 rs11722228 and SF1 rs606458 were significantly associated with DKD (OR=0.864, p=0.0440; OR=1.223, p=0.0038). SLC2A9 rs3775948 and ABCG2 rs2231142 were associated with DKD marginally (OR=0.878, p=0.0506; OR=0.879, p=0.0698). SLC2A9 rs11722228, SLC2A9 rs3775948, ABCG2 rs2231142 and SF1 rs606458 were significantly associated with the estimated glomerular filtration rate (p=0.0005, 0.0006, 0.0003, and 0.0424, respectively).

CONCLUSIONS

Our study indicated that the uric acid related alleles of SLC2A9 rs11722228, SLC2A9 rs3775948, ABCG2 rs2231142 might affect DKD susceptibility and possibly through non-uric acid pathway in the Chinese people with type 2 diabetes.

Selecting instruments for Mendelian randomization in the wake of genome-wide association studies

Mendelian randomization (MR) studies typically assess the pathogenic relevance of environmental exposures or disease biomarkers, using genetic variants that instrument these exposures. The approach is gaining popularity-our systematic review reveals a greater than 10-fold increase in MR studies published between 2004 and 2015. When the MR paradigm was first proposed, few biomarker- or exposure-related genetic variants were known, most having been identified by candidate gene studies. However, genome-wide association studies (GWAS) are now providing a rich source of potential instruments for MR analysis. Many early reviews covering the concept, applications and analytical aspects of the MR technique preceded the surge in GWAS, and thus the question of how best to select instruments for MR studies from the now extensive pool of available variants has received insufficient attention. Here we focus on the most common category of MR studies-those concerning disease biomarkers. We consider how the selection of instruments for MR analysis from GWAS requires consideration of: the assumptions underlying the MR approach; the biology of the biomarker; the genome-wide distribution, frequency and effect size of biomarker-associated variants (the genetic architecture); and the specificity of the genetic associations. Based on this, we develop guidance that may help investigators to plan and readers interpret MR studies.

Common UCP2 variants contribute to serum urate concentrations and the risk of hyperuricemia

Elevated serum urate, which is regulated at multiple levels including genetic variants, is a risk factor for gout and other metabolic diseases. This study aimed to investigate the association between UCP2 variants and serum urate as well as hyperuricemia in a Chinese population. In total, 4332 individuals were genotyped for two common UCP2 variants, -866G/A and Ala55Val. These loci were not associated either serum urate level or with a risk of hyperuricemia in the total group of subjects. However, in females, -866G/A and Ala55Val were associated with a lower serum urate (P = 0.006 and 0.014, seperately) and played a protective role against hyperuricemia (OR = 0.80, P = 0.018; OR = 0.79, P = 0.016). These associations were not observed in the males. After further stratification, the two loci were associated with serum urate in overweight, but not underweight females. The haplotype A-T (-866G/A-Ala55Val) was a protective factor for hyperuricemia in the female subgroup (OR = 0.80, P = 0.017). This present study identified a novel gene, UCP2, that influences the serum urate concentration and the risk of hyperuricemia, and the degree of association varies with gender and BMI levels.

Urate Handling in the Human Body

Elevated serum urate concentration is the primary cause of gout. Understanding the processes that affect serum urate concentration is important for understanding the etiology of gout and thereby understanding treatment. Urate handing in the human body is a complex system including three major processes: production, renal elimination, and intestinal elimination. A change in any one of these can affect both the steady-state serum urate concentration as well as other urate processes. The remarkable complexity underlying urate regulation and its maintenance at high levels in humans suggests that this molecule could potentially play an interesting role other than as a mere waste product to be eliminated as rapidly as possible.

Additive composite ABCG2, SLC2A9 and SLC22A12 scores of high-risk alleles with alcohol use modulate gout risk

The aim of the present study was to evaluate the contribution of urate transporter genes and alcohol use to the risk of gout/tophi. Eight variants of ABCG2, SLC2A9, SLC22A12, SLC22A11 and SLC17A3 were genotyped in male individuals in a case-control study with 157 gout (33% tophi), 106 asymptomatic hyperuricaemia and 295 control subjects from Taiwan. The multilocus profiles of the genetic risk scores for urate gene variants were used to evaluate the risk of asymptomatic hyperuricaemia, gout and tophi. ABCG2 Q141K (T), SLC2A9 rs1014290 (A) and SLC22A12 rs475688 (C) under an additive model and alcohol use independently predicted the risk of gout (respective odds ratio for each factor=2.48, 2.03, 1.95 and 2.48). The additive composite Q141K, rs1014290 and rs475688 scores of high-risk alleles were associated with gout risk (P<0.0001). We observed the supramultiplicative interaction effect of genetic urate scores and alcohol use on gout and tophi risk (P for interaction=0.0452, 0.0033). The synergistic effect of genetic urate score 5-6 and alcohol use indicates that these combined factors correlate with gout and tophi occurrence.

Serum uric acid and the risk of cardiovascular and renal disease

Substantial evidence suggests that chronic hyperuricemia is an independent risk factor for hypertension, metabolic syndrome, chronic kidney disease (CKD) and cardiovascular diseases. This highlights the need for greater attention to serum uric acid levels when profiling patients, and suggests that the threshold above which uricemia is considered abnormal is 6  mg/dl, in light of the available evidence. Another important question is whether lowering serum uric acid can improve cardiovascular and renal outcomes, and what therapeutic mechanism of action could provide more clinical benefits to patients; the available literature shows a trend toward improvement associated with administration of urate-lowering drugs, in particular for the xanthine oxidase inhibitors. The demonstrated efficacy of urate-lowering therapy on outcomes other than gout flares leads to the consideration that treatment may be beneficial even in the absence of overt gout when hyperuricemia accompanies other clinical conditions, such as urate deposition, advanced CKD or cardiovascular risk factors.

SHEsisPlus, a toolset for genetic studies on polyploid species

Currently, algorithms and softwares for genetic analysis of diploid organisms with bi-allelic markers are well-established, while those for polyploids are limited. Here, we present SHEsisPlus, the online algorithm toolset for both dichotomous and quantitative trait genetic analysis on polyploid species (compatible with haploids and diploids, too). SHEsisPlus is also optimized for handling multiple-allele datasets. It's free, open source and also designed to perform a range of analyses, including haplotype inference, linkage disequilibrium analysis, epistasis detection, Hardy-Weinberg equilibrium and single locus association tests. Meanwhile, we developed an accurate and efficient haplotype inference algorithm for polyploids and proposed an entropy-based algorithm to detect epistasis in the context of quantitative traits. A study of both simulated and real datasets showed that our haplotype inference algorithm was much faster and more accurate than existing ones. Our epistasis detection algorithm was the first try to apply information theory to characterizing the gene interactions in quantitative trait datasets. Results showed that its statistical power was significantly higher than conventional approaches. SHEsisPlus is freely available on the web at http://shesisplus.bio-x.cn/. Source code is freely available for download at https://github.com/celaoforever/SHEsisPlus.

Analysis of ABCG2 and other urate transporters in uric acid homeostasis in chronic kidney disease: potential role of remote sensing and signaling

Background

In the setting of chronic kidney disease (CKD), altered extra-renal urate handling may be necessary to regulate plasma uric acid. The Remote Sensing and Signaling Hypothesis (Nigam S. What do drug transporters really do? Nat Rev Drug Discov 2015; 14: 29–44) suggests that multispecific solute carrier (SLC) and ATP-binding cassette (ABC) drug transporters in different tissues are part of an inter-organ communication system that maintains levels of urate and other metabolites after organ injury.

Methods

Data from the Chronic Renal Insufficiency Cohort (CRIC; n = 3598) were used to study associations between serum uric acid and single nucleotide polymorphisms (SNPs) on the following uric acid transporters: ABCG2 (BRCP), SLC22A6 (OAT1), SLC22A8 (OAT3), SLC22A10 (OAT5), SLC22A11 (OAT4), SLC22A12 (URAT1), SLC22A13 (OAT10), SLC17A1-A3 (NPTs), SLC2A9 (GLUT9), ABCC2 (MRP2) and ABCC4 (MRP4). Regression models, controlling for principal components age, gender and renal function, were run separately for those of European (EA) and African ancestry (AA), and P-values corrected for multiple comparisons. A twin cohort with participants of EA and normal renal function was used for comparison.

Results

Among those of EA in CRIC, statistically significant signals were observed for SNPs in ABCG2 (rs4148157; beta-coefficient = 0.68; P = 4.78E-13) and SNPs in SLC2A9 (rs13125646; beta-coefficient = −0.30; P = 1.06E-5). Among those of AA, the strongest (but not statistically significant) signals were observed for SNPs in SLC2A9, followed by SNPs in ABCG2. In the twin study (normal renal function), only SNPs in SLC2A9 were significant (rs4481233; beta-coefficient=−0.45; P = 7.0E-6). In CRIC, weaker associations were also found for SLC17A3 (NPT4) and gender-specific associations found for SLC22A8 (OAT3), SLC22A11 (OAT4), and ABCC4 (MRP4).

Conclusions

In patients of EA with CKD (CRIC cohort), we found striking associations between uric acid and SNPs on ABCG2, a key transporter of uric acid by intestine. Compared with ABCG2, SLC2A9 played a much less significant role in this subset of patients with CKD. SNPs in other SLC (e.g. SLC22A8 or OAT3) and ABC (e.g. ABCC4 or MRP4) genes appear to make a weak gender-dependent contribution to uric acid homeostasis in CKD. As renal urate transport is affected in the setting of declining kidney function, extra-renal ABCG2 appears to play a compensatory role—a notion consistent with animal studies and the Remote Sensing and Signaling Hypothesis. Overall, the data indicate how different urate transporters become more or less important depending on renal function, ethnicity and gender. Therapies focused on enhancing ABCG2 urate handling may be helpful in the setting of CKD and hyperuricemia.

Genome-wide association study of clinically defined gout identifies multiple risk loci and its association with clinical subtypes

OBJECTIVE

Gout, caused by hyperuricaemia, is a multifactorial disease. Although genome-wide association studies (GWASs) of gout have been reported, they included self-reported gout cases in which clinical information was insufficient. Therefore, the relationship between genetic variation and clinical subtypes of gout remains unclear. Here, we first performed a GWAS of clinically defined gout cases only.

METHODS

A GWAS was conducted with 945 patients with clinically defined gout and 1213 controls in a Japanese male population, followed by replication study of 1048 clinically defined cases and 1334 controls.

RESULTS

Five gout susceptibility loci were identified at the genome-wide significance level (p<5.0×10(-8)), which contained well-known urate transporter genes (ABCG2 and SLC2A9) and additional genes: rs1260326 (p=1.9×10(-12); OR=1.36) of GCKR (a gene for glucose and lipid metabolism), rs2188380 (p=1.6×10(-23); OR=1.75) of MYL2-CUX2 (genes associated with cholesterol and diabetes mellitus) and rs4073582 (p=6.4×10(-9); OR=1.66) of CNIH-2 (a gene for regulation of glutamate signalling). The latter two are identified as novel gout loci. Furthermore, among the identified single-nucleotide polymorphisms (SNPs), we demonstrated that the SNPs of ABCG2 and SLC2A9 were differentially associated with types of gout and clinical parameters underlying specific subtypes (renal underexcretion type and renal overload type). The effect of the risk allele of each SNP on clinical parameters showed significant linear relationships with the ratio of the case-control ORs for two distinct types of gout (r=0.96 [p=4.8×10(-4)] for urate clearance and r=0.96 [p=5.0×10(-4)] for urinary urate excretion).

CONCLUSIONS

Our findings provide clues to better understand the pathogenesis of gout and will be useful for development of companion diagnostics.

A causal relationship between uric acid and diabetic macrovascular disease in Chinese type 2 diabetes patients: A Mendelian randomization analysis

BACKGROUND

As the association between uric acid and macrovascular disease has been heavily debated, we aimed to confirm whether there is a causal relationship between uric acid and diabetic macrovascular disease through Mendelian randomization analysis.

METHODS

In 3207 type 2 diabetes patients, seventeen SNPs (single nucleotide polymorphisms) related to uric acid were genotyped. A weighted GRS (genetic risk score) was calculated using selected SNPs and the strength of their effects on uric acid levels. Diabetic macrovascular disease was diagnosed through vascular ultrasound, magnetic resonance imaging or other clinical evidence. Associations of diabetic macrovascular disease with uric acid and weighted GRS were evaluated separately.

RESULTS

In total participants and among females, the prevalence of diabetic macrovascular disease was significantly higher in hyperuricemic group than in normouricemic group, and uric acid was associated with diabetic macrovascular disease (OR=1.068, p=0.0349; OR=1.122, p=0.0158). The prevalence of diabetic macrovascular disease increased with the weighted GRS in a J-shaped manner for the females. The weighted GRS was positively correlated with uric acid in total population, male patients and female patients (β=0.203, p<0.0001; β=0.255, p<0.0001; β=0.142, p<0.0001, respectively). The weighted GRS was significantly associated with diabetic macrovascular disease in female patients (OR=1.184, p=0.0039). Among females, the observed association between weighted GRS and diabetic macrovascular disease was greater than predicted.

CONCLUSIONS

Using the uric acid-related weighted GRS as an instrumental variable for Mendelian randomization analysis, our study provided an evidence for causal relationship between uric acid and diabetic macrovascular disease in Chinese females with type 2 diabetes mellitus.

No causal effect of serum urate on bone-related outcomes among a population of postmenopausal women and elderly men of Chinese Han ethnicity--a Mendelian randomization study

SUMMARY

We conducted a Mendelian randomization analysis to assess the effect of serum uric acid on bone-related outcomes using a weighted urate transporter genetic risk score as the instrumental variable. The results showed no significance. Our study identified no evidence of a causal role between uric acid and bone-related outcomes.

INTRODUCTION

Observational studies have associated elevated levels of serum uric acid (SUA) with increasing bone mineral density (BMD) and a lowered prevalence of osteoporotic fractures (OFs) in postmenopausal women and elderly men. However, due to unmeasured confounding variables, these observational studies have not provided insight into the causal relationship between SUA and bone-related outcomes. Our aim was to evaluate the effect of SUA on bone-related outcomes using Mendelian randomization.

METHODS

We recruited 1322 Chinese Han individuals (214 elderly men and 1108 postmenopausal women) from the Shanghai area in China. Mendelian randomization using a two-stage least-squares regression method was conducted with SUA as the exposure variable, a weighted urate transporter genetic risk score as the instrumental variable, and all-site BMD, bone turnover markers, and levels of 25-hydroxyvitamin D3 [25(OH)D], serum calcium (Ca), serum phosphorus (P), and parathyroid hormone (PTH) as outcome variables.

RESULTS

Strong associations between SUA and bone-related outcomes were observed in an ordinary observational analysis (lumbar spine: beta = 0.122, p < 0.0001; hip: beta = 0.104, p < 0.0001; femoral neck: beta = 0.108, p < 0.0001). However, the Mendelian randomization analysis showed no evidence for a causal association of SUA with BMD (lumbar spine: beta = 0.385, p = 0.257; hip: beta = 0.191, p = 0.499; femoral neck: beta = 0.194, p = 0.533). Similar results were found between SUA and other bone-related phenotypes.

CONCLUSIONS

Our study identified no evidence of a causal role between SUA and bone-related outcomes, although strong associations in an observational analysis were observed in a population of postmenopausal women and elderly men.

Genome wide association study of uric acid in Indian population and interaction of identified variants with Type 2 diabetes

Abnormal level of Serum Uric Acid (SUA) is an important marker and risk factor for complex diseases including Type 2 Diabetes. Since genetic determinant of uric acid in Indians is totally unexplored, we tried to identify common variants associated with SUA in Indians using Genome Wide Association Study (GWAS). Association of five known variants in SLC2A9 and SLC22A11 genes with SUA level in 4,834 normoglycemics (1,109 in discovery and 3,725 in validation phase) was revealed with different effect size in Indians compared to other major ethnic population of the world. Combined analysis of 1,077 T2DM subjects (772 in discovery and 305 in validation phase) and normoglycemics revealed additional GWAS signal in ABCG2 gene. Differences in effect sizes of ABCG2 and SLC2A9 gene variants were observed between normoglycemics and T2DM patients. We identified two novel variants near long non-coding RNA genes AL356739.1 and AC064865.1 with nearly genome wide significance level. Meta-analysis and in silico replication in 11,745 individuals from AUSTWIN consortium improved association for rs12206002 in AL356739.1 gene to sub-genome wide association level. Our results extends association of SLC2A9, SLC22A11 and ABCG2 genes with SUA level in Indians and enrich the assemblages of evidence for SUA level and T2DM interrelationship.

The effects of URAT1/SLC22A12 nonfunctional variants, R90H and W258X, on serum uric acid levels and gout/hyperuricemia progression

Urate transporter 1 (URAT1/SLC22A12), a urate transporter gene, is a causative gene for renal hypouricemia type 1. Among several reported nonsynonymous URAT1 variants, R90H (rs121907896) and W258X (rs121907892) are frequent causative mutations for renal hypouricemia. However, no case-control study has evaluated the relationship between gout and these two variants. Additionally, the effect size of these two variants on serum uric acid (SUA) levels remains to be clarified. Here, 1,993 primary gout patients and 4,902 health examination participants (3,305 males and 1,597 females) were genotyped with R90H and W258X. These URAT1 variants were not observed in any gout cases, while 174 subjects had the URAT1 variant in 2,499 health examination participants, respectively (P = 8.3 × 10⁻⁴⁶). Moreover, in 4,902 health examination participants, the URAT1 nonfunctional variants significantly reduce the risk of hyperuricemia (P = 6.7 × 10⁻¹⁹; risk ratio = 0.036 in males). Males, having 1 or 2 nonfunctional variants of URAT1, show a marked decrease of 2.19 or 5.42 mg/dl SUA, respectively. Similarly, females, having 1 or 2 nonfunctional variants, also evidence a decrease of 1.08 or 3.89 mg/dl SUA, respectively. We show that URAT1 nonfunctional variants are protective genetic factors for gout/hyperuricemia, and also demonstrated the sex-dependent effect size of these URAT1 variants on SUA (P for interaction = 1.5 × 10⁻¹²).

Association of ABCG2 rs2231142-A allele and serum uric acid levels in male and obese individuals in a Han Taiwanese population

BACKGROUND/PURPOSE

Recent studies suggest that hyperuricemia is a potential risk factor for cardiovascular disease (CVD). Hyperuricemia is highly heritable and is associated with sex and body weight. Previous genome-wide association studies have found that the ABCG2 single nucleotide polymorphism (SNP) rs2231142 is an important genetic factor for increased uric acid (UA) levels, and the degree of association between rs2231142 and hyperuricemia is affected by both sex and ethnicity. This investigation aimed to analyze the association between ABCG2 polymorphisms and UA levels, as well as their interactions with sex and obesity in Taiwanese.

METHODS

Two genetic polymorphisms around the ABCG2 gene were genotyped in 459 patients.

RESULTS

After adjusting for clinical covariates, the rs2231142 SNP was found significantly associated with UA levels using a dominant inheritance model. Patients carrying the rs2231142-A allele had a higher frequency of hyperuricemia than those with the rs2231142-CC allele. Subgroup analysis revealed an association of rs2231142 with UA levels in male or obese patients, and there was no association in nonobese female patients.

CONCLUSION

The rs2231142 SNP is associated with serum UA levels and hyperuricemia in Taiwanese patients and it occurs predominantly in male or obese patients. Hyperuricemia might be controlled differently by sex and obesity.

The Power of Serum Uric Acid in Predicting Metabolic Syndrome Diminishes With Age in an Elderly Chinese Population

OBJECTIVES

Although serum uric acid (sUA) is not a criterion for diagnosing metabolic syndrome (MetS), many studies have identified a positive association between sUA and MetS in patients of various ages and ethnicities. This association has not been fully established in the very elderly.

DESIGN

Cross-sectional and longitudinal study.

SETTING AND PARTICIPANTS

A total of 18,906 Chinese elderly aged 65 and older undergoing routine health checkups in Taiwan were enrolled.

MEASUREMENTS

Modified Adult Treatment Panel III criteria were used to define MetS. All participants were further divided into nine groups with gender specification according to age (the young-old, 65 to 74; old-old, 75 to 84; and oldest-old, 85 and over) and sUA concentration tertile (males: sUAG1, <5.7 mg/dL; sUAG2, 5.7-6.7 mg/dL; and sUAG3, > 6.7 mg/dL; females: sUAG1, <4.9 mg/dL; sUAG2, 4.9-5.9 mg/dL; and sUAG3, > 5.9 mg/dL). A cross-sectional study was first performed to determine the correlation between sUA and MetS and its components. A longitudinal study then excluded subjects with MetS at baseline to explore the risk of MetS according to sUA levels in 3 age groups.

RESULTS

In the cross-sectional study, we observed a graded, positive association between sUA and MetS components that diminished after age 75. Subjects with higher sUA levels had higher odds ratios (OR) for the occurrence of MetS in the young-old and old-old groups of both sexes (P<0.001) except sUAG2 males in the old-old group. However, the association diminished with age and only a higher OR was observed in sUAG2 males in the oldest-old group (OR, 3.38; 95% CI, 1.11-10.30; P = 0.032). In the longitudinal study, the Kaplan-Meier plot showed that higher sUA levels were associated with a higher risk of MetS in the young-old group of both genders (P < 0.001 sUAG3 vs. sUAG1 and sUAG2). Cox regression analysis further confirmed these results (young-old group: sUAG3 HR, 1.90; 95% CI, 1.42-2.54; P < 0.001; old-old group males: HR, 2.20; 95% CI, 1.04-4.65; P = 0.039; young-old females: HR, 1.83; 95% CI, 1.38 - 2.43; P < 0.001).

CONCLUSIONS

Higher sUA levels in the young-old group of Chinese elderly were associated with a higher risk of developing MetS. sUA levels are thus regarded as a potential tool for early diagnosis of MetS. However, this association diminished in those over 75 years of age.

Twenty-eight loci that influence serum urate levels: analysis of association with gout

OBJECTIVES

Twenty-eight genetic loci are associated with serum urate levels in Europeans. Evidence for association with gout at most loci is absent, equivocal or not replicated. Our aim was to test the loci for association with gout meeting the American College of Rheumatology gout classification criteria in New Zealand European and Polynesian case-control sample sets.

METHODS

648 European cases and 1550 controls, and 888 Polynesian (Ma¯ori and Pacific) cases and 1095 controls were genotyped. Association with gout was tested by logistic regression adjusting for age and sex. Power was adequate (>0.7) to detect effects of OR>1.3.

RESULTS

We focused on 24 loci without previous consistent evidence for association with gout. In Europeans, we detected association at seven loci, one of which was the first report of association with gout (IGF1R). In Polynesian, association was detected at three loci. Meta-analysis revealed association at eight loci-two had not previously been associated with gout (PDZK1 and MAF). In participants with higher Polynesian ancestry, there was association in an opposing direction to Europeans at PRKAG2 and HLF (HLF is the first report of association with gout). There was obvious inconsistency of gout association at four loci (GCKR, INHBC, SLC22A11, SLC16A9) that display very similar effects on urate levels.

CONCLUSIONS

We provide the first evidence for association with gout at four loci (IGF1R, PDZK1, MAF, HLF). Understanding why there is lack of correlation between urate and gout effect sizes will be important in understanding the aetiology of gout.

Predicting allopurinol response in patients with gout

AIMS

The primary aim of this research was to predict the allopurinol maintenance doses required to achieve the target plasma urate of ≤0.36 mmol l(-1) .

METHODS

A population analysis was conducted in nonmem using oxypurinol and urate plasma concentrations from 133 gout patients. Maintenance dose predictions to achieve the recommended plasma urate target were generated.

RESULTS

The urate response was best described by a direct effects model. Renal function, diuretic use and body size were found to be significant covariates. Dose requirements increased approximately 2-fold over a 3-fold range of total body weight and were 1.25-2 fold higher in those taking diuretics. Renal function had only a modest impact on dose requirements.

CONCLUSIONS

Contrary to current guidelines, the model predicted that allopurinol dose requirements were determined primarily by differences in body size and diuretic use. A revised guide to the likely allopurinol doses to achieve the target plasma urate concentration is proposed.

A genetic marker of hyperuricemia predicts cardiovascular events in a meta-analysis of three cohort studies in high risk patients

INTRODUCTION

The strongest genetic marker of uric acid levels, the rs734553 SNP in the GLUT9 urate transporter gene, predicts progression to kidney failure in CKD patients and associates with systolic BP and carotid intima media thickness in family-based studies.

METHODS

Since genes are transmitted randomly (Mendelian randomization) we used this gene polymorphism as an unconfounded research instrument to further explore the link between uric acid and cardiovascular disease (cardiovascular death, and non-fatal myocardial infarction and stroke) in a meta-analysis of three cohort studies formed by high risk patients (MAURO: 755 CKD patients; GHS: 353 type 2 diabetics and coronary artery disease and the TVAS: 119 patients with myocardial infarction).

RESULTS

In separate analyses of the three cohorts, the incidence rate of CV events was higher in patients with the rs734553 risk (T) allele (TT/GT) than in those without (GG patients) and the HR in TT/GT patients in the three cohorts (range 1.72-2.14) coherently signaled an excessive cardiovascular risk with no heterogeneity (I2 = 0.01). The meta-analytical estimate (total number of patients, n = 1227; total CV events, n = 222) of the HR for the combined end-point in TT/GT patients was twice higher (pooled HR: 2.04, 95% CI: 1.11-3.75, P = 0.02) than in GG homozygotes.

CONCLUSIONS

The T allele of the rs734553 polymorphism in the GLUT9 gene predicts a doubling in the risk for incident cardiovascular events in patients at high cardiovascular risk. Findings in this study are compatible with the hypothesis of a causal role of hyperuricemia in cardiovascular disease in high risk conditions.

Evolutionary context for the association of γ-globin, serum uric acid, and hypertension in African Americans

Background

Hyperuricemia and associated cardio-metabolic disorders are more prevalent in African Americans than in European Americans. We used genome-wide admixture mapping and association testing to identify loci with ancestry effects on serum uric acid levels.

Methods

We analyzed 1,976 African Americans from Washington, D.C, including 1,322 individuals from 328 pedigrees and 654 unrelated individuals, enrolled in the Howard University Family Study. We performed admixture mapping and genome-wide association testing using ~800 k autosomal single-nucleotide polymorphisms (SNPs). We performed fine mapping by dense genotyping. We assessed functionality by a combination of bioinformatic annotation, reporter gene assays, and gel shift experiments. We also analyzed 12,641 individuals enrolled in the National Health and Nutrition Examination Survey.

Results

We detected a genome-wide significant locus on chromosome 11p15.4 at which serum uric acid levels increased with increasing African ancestry, independent of kidney function. Fine-mapping identified two independent signals in the β-globin locus. The ancestral allele at SNP rs2855126, located upstream of the hemoglobin, gamma A gene HBG1, was associated with increased serum uric acid levels and higher expression of a reporter gene relative to the derived allele. Hyperuricemia was associated with increased risk of hypertension in 3,767 African Americans (Odds Ratio = 2.48, p = 2.71 × 10^− 19).

Conclusions

Given that increased expression of γ-globin leads to increased levels of fetal hemoglobin which confers protection against malaria, we hypothesize that evolution in Africa of protection against malaria may have occurred at the cost of increased serum uric acid levels, contributing to the high rates of hyperuricemia and associated cardio-metabolic disorders observed in African Americans.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-015-0249-z) contains supplementary material, which is available to authorized users.

Genetic variants of SLC17A1 are associated with cholesterol homeostasis and hyperhomocysteinaemia in Japanese men

Hyperuricaemia is an undisputed and highly predictive biomarker for cardiovascular risk. SLC17A1, expressed in the liver and kidneys, harbours potent candidate single nucleotide polymorphisms that decrease uric acid levels. Therefore, we examined SLC17A1 polymorphisms (rs1165196, rs1179086, and rs3757131), which might suppress cardiovascular risk factors and that are involved in liver functioning, via a large-scale pooled analysis of the Japanese general population in a cross-sectional study. Using data from the Japan Multi-Institutional Collaborative Cohort Study, we identified 1842 participants of both sexes, 35–69-years-old, having the requisite data, and analysed their SLC17A1 genotypes. In men, logistic regression analyses revealed that minor alleles in SLC17A1 polymorphisms (rs1165196 and rs3757131) were associated with a low-/high-density lipoprotein cholesterol ratio >2.0 (rs1165196: odds ratio [OR], 0.703; 95% confidence interval [CI], 0.536–0.922; rs3757131: OR, 0.658; 95% CI, 0.500–0.866), and with homocysteine levels of >10.0 nmol/mL (rs1165196: OR, 0.544; 95% CI, 0.374–0.792; rs3757131: OR, 0.509; 95% CI, 0.347–0.746). Therefore, these polymorphisms had dominant negative effects on cholesterol homeostasis and hyperhomocysteinaemia, in men, independent of alcohol consumption, physical activity, or daily energy and nutrition intake. Thus, genetic variants of SLC17A1 are potential biomarkers for altered cholesterol homeostasis and hyperhomocysteinaemia in Japanese men.

Prognostic Role of Serum Levels of Uric Acid in Amyotrophic Lateral Sclerosis

Background and Purpose

It has been suggested that oxidative stress is one of the pathomechanisms underlying amyotrophic lateral sclerosis (ALS), and thus antioxidants such as uric acid (UA) that could reduce oxidative stress might be beneficial in the prevention or treatment of this disease. The objective of this study was to prospectively investigate serum UA levels in Korean ALS patients and to relate them to disease progression.

Methods

ALS patients and healthy controls who were individually well-matched for sex, age, and body mass index (BMI) underwent blood testing for serum UA levels, and analyzed whether UA levels were correlated with the disease status of the patients, as defined by the ALS Functional Rating Scale-Revised (ALSFRS-R).

Results

The study included 136 ALS patients and 136 matched controls. The UA level was lower in the ALS patients (4.50±1.17 mg/dL, mean±SD) than in the controls (5.51±1.22 mg/dL; p<0.001). Among the ALS patients, the level of UA acid was inversely correlated with the rate of disease progression (decrease in ALSFRS-R score). Kaplan-Meier analysis revealed that a better survival rate was more strongly correlated with top-tertile levels of serum UA than with bottom-tertile levels (log-rank test: p=0.035).

Conclusions

ALS patients had lower serum UA levels than did healthy individuals. UA levels in ALS were negatively correlated with the rate of disease progression and positively associated with survival, suggesting that UA levels contribute to the progression of ALS. UA levels could be considered a biomarker of disease progression in the early phase in ALS patients.

Integration of Genome-Wide SNP Data and Gene-Expression Profiles Reveals Six Novel Loci and Regulatory Mechanisms for Amino Acids and Acylcarnitines in Whole Blood

Profiling amino acids and acylcarnitines in whole blood spots is a powerful tool in the laboratory diagnosis of several inborn errors of metabolism. Emerging data suggests that altered blood levels of amino acids and acylcarnitines are also associated with common metabolic diseases in adults. Thus, the identification of common genetic determinants for blood metabolites might shed light on pathways contributing to human physiology and common diseases. We applied a targeted mass-spectrometry-based method to analyze whole blood concentrations of 96 amino acids, acylcarnitines and pathway associated metabolite ratios in a Central European cohort of 2,107 adults and performed genome-wide association (GWA) to identify genetic modifiers of metabolite concentrations. We discovered and replicated six novel loci associated with blood levels of total acylcarnitine, arginine (both on chromosome 6; rs12210538, rs17657775), propionylcarnitine (chromosome 10; rs12779637), 2-hydroxyisovalerylcarnitine (chromosome 21; rs1571700), stearoylcarnitine (chromosome 1; rs3811444), and aspartic acid traits (chromosome 8; rs750472). Based on an integrative analysis of expression quantitative trait loci in blood mononuclear cells and correlations between gene expressions and metabolite levels, we provide evidence for putative causative genes: SLC22A16 for total acylcarnitines, ARG1 for arginine, HLCS for 2-hydroxyisovalerylcarnitine, JAM3 for stearoylcarnitine via a trans-effect at chromosome 1, and PPP1R16A for aspartic acid traits. Further, we report replication and provide additional functional evidence for ten loci that have previously been published for metabolites measured in plasma, serum or urine. In conclusion, our integrative analysis of SNP, gene-expression and metabolite data points to novel genetic factors that may be involved in the regulation of human metabolism. At several loci, we provide evidence for metabolite regulation via gene-expression and observed overlaps with GWAS loci for common diseases. These results form a strong rationale for subsequent functional and disease-related studies.

Associations between interleukin and interleukin receptor gene polymorphisms and risk of gout

Gout is a self-limiting, auto-inflammatory arthritis induced by the deposition of monosodium urate crystals in the synovial fluid and periarticular tissues. The aim of this study was to investigate the associations between genetic variants in the interleukin (IL) and interleukin receptor (ILR) genes IL-33, IL-1RL1, IL-23R, and signal transducer and activator of transcription 4 (STAT4) and susceptibility to gout in Chinese Han male individuals. The genetic distributions of rs3939286 in IL-33, rs13015714 in IL-1RL1, rs10889677 in IL-23R, and rs7574865 in STAT4 were detected in 1100 men with gout and 1227 ethnically matched controls, using Taqman allelic discrimination real-time polymerase chain reaction (PCR). Differences in these polymorphisms between the groups were investigated using χ(2) tests. The genotype-phenotype relationship among gout patients was tested by analysis of variance. There was a significant difference in genotypic frequencies of IL-23R rs10889677 between gout patients and controls (χ(2) = 81.386, P < 0.001). However, there were no significant differences in distributions of the other polymorphisms between the groups. Our results revealed that the rs10889677 variant in IL-23R may be involved in the development of gout in Chinese Han male individuals. However, further studies in other ethnic groups are needed to confirm these results.

Serum uric acid level as a risk factor for acute kidney injury in hospitalized patients: a retrospective database analysis using the integrated medical information system at Kochi Medical School hospital

BACKGROUND AND OBJECTIVES

Recent studies have shown that both low and high levels of serum uric acid (SUA) before cardiovascular surgery are independent risk factors for postoperative acute kidney injury (AKI). However, these studies were limited by their small sample sizes. Here, we investigated the association between SUA levels and AKI by performing a retrospective database analysis of almost 30 years of data from 81,770 hospitalized patients.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENT

Hospitalized patients aged ≥18 years were retrospectively enrolled. AKI was diagnosed according to the Kidney Disease: Improving Global Outcomes 2012 Clinical Practice Guideline (KDIGO) criteria. Multivariate logistic regression analyses were performed to investigate the independent association between SUA levels and the incidence of AKI. SUA levels were treated as categorical variables because the relationship between SUA and the incidence of AKI has been suggested to be J-shaped or U-shaped. In addition to stratified SUA levels, we considered kidney function and related comorbidities, medications, and procedures performed prior to AKI onset as possible confounding risk factors.

RESULTS

The final study cohort included 59,219 adult patients. Adjusted odds ratios of AKI incidence were higher in both the high- and low-SUA strata. Odds ratios tended to become larger in the higher range of SUA levels in women than in men. Additionally, this study showed that AKI risk was elevated in patients with SUA levels ≤7 mg/dL. An SUA level >7 mg/dL is considered the point of initiation of uric acid crystallization.

CONCLUSIONS

SUA level could be an independent risk factor for AKI development in hospitalized patients. Additionally, our results might suggest that intervention to lower SUA levels is necessary, even in cases of moderate elevation that does not warrant hyperuricemia treatment. Results also showed that SUA levels that require attention are lower for women than for men.

Transcriptome-based reconstructions from the murine knockout suggest involvement of the urate transporter, URAT1 (slc22a12), in novel metabolic pathways

URAT1 (slc22a12) was identified as the transporter responsible for renal reabsorption of the medically important compound, uric acid. However, subsequent studies have indicated that other transporters make contributions to this process, and that URAT1 transports other organic anions besides urate (including several in common with the closely related multi-specific renal organic anion transporters, OAT1 (slc22a6) and OAT3 (slc22a8)). These findings raise the possibility that urate transport is not the sole physiological function of URAT1. We previously characterized mice null for the murine ortholog of URAT1 (mURAT1; previously cloned as RST), finding a relatively modest decrement in urate reabsorptive capacity. Nevertheless, there were shifts in the plasma and urinary concentrations of multiple small molecules, suggesting significant metabolic changes in the knockouts. Although these molecules remain unidentified, here we have computationally delineated the biochemical networks consistent with transcriptomic data from the null mice. These analyses suggest alterations in the handling of not only urate but also other putative URAT1 substrates comprising intermediates in nucleotide, carbohydrate, and steroid metabolism. Moreover, the analyses indicate changes in multiple other pathways, including those relating to the metabolism of glycosaminoglycans, methionine, and coenzyme A, possibly reflecting downstream effects of URAT1 loss. Taken together with the available substrate and metabolomic data for the other OATs, our findings suggest that the transport and biochemical functions of URAT1 overlap those of OAT1 and OAT3, and could contribute to our understanding of the relationship between uric acid and the various metabolic disorders to which it has been linked.

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URAT1 handles multiple substrates suggesting functions beyond urate transport

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We determined metabolic constraints of gene expression changes in URAT1 null mice

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These suggest URAT1 involvement in multiple bioenergtic and biosynthetic pathways

Polymorphisms in GCKR, SLC17A1 and SLC22A12 were associated with phenotype gout in Han Chinese males: a case-control study

Background

Gout is a common arthritic disease resulting from elevated serum uric acid (SUA) level. A large meta-analysis including 28,141 individuals identified nine single nucleotide polymorphisms (SNPs) associated with altered SUA level in a Caucasian population. However, raised SUA level alone is not sufficient for the development of gout arthritis and most of these SNPs have not been studied in a Han Chinese population. Here, we performed a case–control association analysis to investigate the relationship between these SUA correlated SNPs and gout arthritis in Han Chinese.

Methods

A total of 622 ascertained gout p9atients and 917 healthy controls were genotyped. Genome-wide significant SNPs, rs12129861, rs780094, rs734553, rs742132, rs1183201, rs12356193, rs17300741 and rs505802 in the previous SUA study, were selected for our analysis.

Results

No deviation from the Hardy–Weinberg equilibrium was observed either in the case or control cohorts (corrected p > 0.05). Three SNPs, rs780094 (located in GCKR, corrected p = 1.78E⁻⁴, OR = 0.723), rs1183201 (located in SLC17A1, corrected p = 1.39E⁻⁷, OR = 0.572) and rs505802 (located in SLC22A12, corrected p = 0.007, OR = 0.747), were significantly associated with gout on allelic level independent of potential cofounding traits. While the remaining SNPs were not replicated. We also found significant associations of uric acid concentrations with these three SNPs (rs780094 in GCKR, corrected p = 3.94E⁻⁵; rs1183201 in SLC17A1, corrected p = 0.005; rs505802 in SLC22A12, corrected p = 0.003) and of triglycerides with rs780094 (located in GCKR, corrected p = 2.96E⁻⁴). Unfortunately, SNP-SNP interactions for these three significant SNPs were not detected (rs780094 vs rs1183201, p = 0.402; rs780094 vs rs505802, p = 0.434; rs1183201 vs rs505802, p = 0.143).

Conclusions

Three SUA correlated SNPs in Caucasian population, rs780094 in GCKR, rs1183201 in SLC17A1 and rs505802 in SLC22A12 were confirmed to be associated with gout arthritis and uric acid concentrations in Han Chinese males. Considering genetic differences among populations and complicated pathogenesis of gout arthritis, more validating tests in independent populations and relevant functional experiments are suggested in future.