Serum urate gene associations with incident gout, measured in the Framingham Heart Study, are modified by renal disease and not by body mass index

We hypothesized that serum urate-associated SNPs, individually or collectively, interact with BMI and renal disease to contribute to risk of incident gout. We measured the incidence of gout and associated comorbidities using the original and offspring cohorts of the Framingham Heart Study. We used direct and imputed genotypes for eight validated serum urate loci. We fit binomial regression models of gout incidence as a function of the covariates, age, type 2 diabetes, sex, and all main and interaction effects of the eight serum urate SNPs with BMI and renal disease. Models were also fit with a genetic risk score for serum urate levels which corresponds to the sum of risk alleles at the eight SNPs. Model covariates, age (P = 5.95E-06), sex (P = 2.46E-39), diabetes (P = 2.34E-07), BMI (P = 1.14E-11) and the SNPs, rs1967017 (P = 9.54E-03), rs13129697 (P = 4.34E-07), rs2199936 (P = 7.28E-03) and rs675209 (P = 4.84E-02) were all associated with incident gout. No BMI by SNP or BMI by serum urate genetic risk score interactions were statistically significant, but renal disease by rs1106766 was statistically significant (P = 6.12E-03). We demonstrated that minor alleles of rs1106766 (intergenic, INHBC) were negatively associated with the risk of incident gout in subjects without renal disease, but not for individuals with renal disease. These analyses demonstrate that a significant component of the risk of gout may involve complex interplay between genes and environment.

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.

Discovery of URAT1 SNPs and association between serum uric acid levels and URAT1

OBJECTIVES

Human urate transporter 1 (URAT1) is a member of the organic anion transporter family (SLC22A12) that primarily regulates the renal tubular reabsorption of uric acid. This case-control study was designed to analyse whether hURAT1 might also be a candidate gene for hyperuricaemia or hypouricaemia.

SETTING

We recruited 68 healthy volunteers and divided them into two groups: a normal uric acid group and a hyperuricaemia group. We analysed the sequence of the URAT1 gene and found five significant single nucleotide polymorphisms (SNPs). We then selected 900 male subjects from the 262,200 enrolled in the Korean Cancer Prevention Study-II (KCPS-II) cohort for further genetic analysis.

PARTICIPANTS

DNA samples from 36 individuals with normal uric acid (<4.5 mg/dL) and 32 individuals with hyperuricaemia (>8.5 mg/dL) were sequenced. Five significant SNPs (rs7929627, rs75786299, rs3825017, rs11602903 and rs121907892) were identified. We then chose 900 subjects from the KCPS-II cohort consisting of 450 subjects with normal uric acid (UA <4.1 mg/dL) and 450 subjects with hyperuricaemia (UA >8.7 mg/dL). The groups were matched by age, body mass index, metabolic syndrome and use of anti-hypertensive medication.

PRIMARY OUTCOME MEASURES

We compared the OR of the incidence of hyperuricaemia by URAT1 genotype.

RESULTS

The strongest association with hyperuricaemia was observed for rs75786299 (IVS3+11A/G) with an OR of 32.05. rs7929627 (IVS7-103A/G) and rs3825017 (N82N) showed an association with hyperuricaemia with ORs of 2.56 and 2.29, respectively. rs11602903 (788A/T) and rs121907892 (W258X) were negatively correlated with hyperuricaemia with ORs of 0.350 and 0.447, respectively. Individuals carrying the GATAG haplotype (n=32)-a relatively common variant consisting of rs7929627, rs75786299 and rs3825017-showed the highest risk for hyperuricaemia with an OR of 92.23 (p=9.55×10(-3)).

CONCLUSIONS

These results indicate that five newly described SNPs in the hURAT1 gene are significantly associated with uric acid level (4-2008-0318 and 4-2011-0277).

Association analysis between genetic variants in interleukin genes among different populations with hyperuricemia in Xinjiang Autonomous Region

To investigate whether functional variants of five interleukin genes (IL-1β, IL-10, IL-8, IL-18 and IL-18RAP) are associated with susceptibility to hyperuricemia among different nationalities (including Uygur, Kazak and Han populations) in the Xinjiang Autonomous Region of China. A total of 884 hyperuricemia patients and 1316 matched controls were recruited from the First Affiliated Hospital of Xinjiang Medical University in Urumqi. After genotyping of rs4073 in IL-8, rs16944 in IL-1, rs187238 in IL-18, rs1800871 in IL-10 and rs13015714 in IL-18RAP by TaqMan allele discrimination assays, an association analysis was performed using the χ(2) test as well as a genotype-phenotype analysis. For the Uygur population, IL-8 rs4073, IL-18 rs187238 and IL-18RAP rs130154 polymorphisms were all associated with hyperuricemia (P<0.001 by genotype and P=0.008, OR 0.802 by allele for IL-8; P=0.01 by genotype and P=0.006, OR 1.332 by allele for IL-18 rs187238; P=0.007 by genotype and P=0.005, OR 1.27 by allele for IL-18RAP rs130154). For the Kazak population, only IL-18 rs187238 showed statistical significance with hyperuricemia (P=0.002 by genotype and P=0.007, OR 1.823 by allele). However, no differences were found between the five SNPs and hyperuricemia among the Han population. This study demonstrated genetic polymorphisms of different interleukin genes related to hyperuricemia vary in different nationalities in the Xinjiang Autonomous Region because of different geographical environments. IL-8, IL-1RL1 and IL-18 might be involved in the development of hyperuricemia in the Uygur population, whereas only IL-18 might be involved in the Kazak population.

Autosomal dominant tubulointerstitial kidney disease: diagnosis, classification, and management--A KDIGO consensus report

Rare autosomal dominant tubulointerstitial kidney disease is caused by mutations in the genes encoding uromodulin (UMOD), hepatocyte nuclear factor-1β (HNF1B), renin (REN), and mucin-1 (MUC1). Multiple names have been proposed for these disorders, including 'Medullary Cystic Kidney Disease (MCKD) type 2', 'Familial Juvenile Hyperuricemic Nephropathy (FJHN)', or 'Uromodulin-Associated Kidney Disease (UAKD)' for UMOD-related diseases and 'MCKD type 1' for the disease caused by MUC1 mutations. The multiplicity of these terms, and the fact that cysts are not pathognomonic, creates confusion. Kidney Disease: Improving Global Outcomes (KDIGO) proposes adoption of a new terminology for this group of diseases using the term 'Autosomal Dominant Tubulointerstitial Kidney Disease' (ADTKD) appended by a gene-based subclassification, and suggests diagnostic criteria. Implementation of these recommendations is anticipated to facilitate recognition and characterization of these monogenic diseases. A better understanding of these rare disorders may be relevant for the tubulointerstitial fibrosis component in many forms of chronic kidney disease.

Effects of Xie-Zhuo-Chu-Bi-Fang on miR-34a and URAT1 and their relationship in hyperuricemic mice

ETHNOPHARMACOLOGICAL RELEVANCE

Xie-Zhuo-Chu-Bi-Fang (XZCBF) is an empirical formula that was developed based on the principles of traditional Chinese medicine, for the therapeutic purpose of treating hyperuricemia. XZCBF has been clinically utilized in the Department of Traditional Chinese Medicine at General Hospital of Guangzhou Military Command of PLA for many years and has exhibited favorable efficacy. The aim of the study is to evaluate the effects of XZCBF on the expression of uric acid transporter 1 (URAT1) and miR-34a in hyperuricemic mice and to determine, the correlation between the two expression levels.

MATERIALS AND METHODS

A hyperuricemic animal model was created by administering adenine and allantoxanic acid potassium salt to mice. The blood uric acid levels were measured in these model mice after treatment with XZCBF for 15 days. The potential targets of miR-34a were screened. The expression levels of miR-34a and URAT1 in the renal tissues collected from the model mice were determined by quantitative real-time polymerase chain reaction (qRT-PCR) analysis, and their correlation was further established by immunohistochemistry and in situ hybridization.

RESULTS

The uric acid levels in the model mice were significantly higher than those in the blank controls (P<0.05). These levels were significantly lower in the three groups receiving different doses of XZCBF (P<0.05), which was, in agreement with the downregulation of URAT1 and the upregulation of miR-34a in each group. The mRNA expression level of URAT1 was positively correlated with the concentration of uric acid but, negatively correlated with the expression level of miR-34a.

CONCLUSIONS

The ability of XZCBF to facilitate the excretion of uric acid and to lower its level in the model group was mediated by the upregulation of miR-34a and the inhibition of URAT1 mRNA expression, which suggests that XZCBF could be an option for the treatment of hyperuricemia in mice.

Synergism between asymmetric dimethylarginine (ADMA) and a genetic marker of uric acid in CKD progression

BACKGROUND & AIMS

We have recently reported that a polymorphism (rs734553) in a major urate transporter gene (GLUT9) is a strong predictor of incident renal events in stage 2-5 CKD patients implying that life-time exposure to high uric acid levels may be causally implicated in CKD progression. Since disturbed NO bioavailability is a major pathway whereby high uric may cause renal damage, we tested the interaction between the major endogenous inhibitor of NO synthase, asymmetric-dimethylargine (ADMA), and the rs734553 polymorphism for CKD progression in the same cohort.

METHODS & RESULTS

Over a 29 ± 11 months follow-up the risk for incident renal events was higher in patients harboring the risk allele of the polymorphism (T) as compared to those without the risk allele (HR: 2.35, 95% CI: 1.25-4.42, P = 0.008) (p = 0.01). Similarly, patients with ADMA > median value had an increased risk for the same outcome (HR: 1.37, 95% CI: 1.06-1.76, P = 0.016). Interaction analysis showed a strong amplification by ADMA of the risk for renal events associated to the T allele because in adjusted (P = 0.016) and bootstrapping validated (P = 0.020) analyses the risk excess associated to this allele was progressively higher across increasing ADMA levels.

CONCLUSIONS

The rs734553 polymorphism, the strongest genetic marker of uric acid levels discovered so far, interacts with ADMA in determining the risk for CKD progression in CKD patients. This synergic interaction conforms to biological knowledge indicating that disturbed NO bio-availability is a critical pathway whereby life time exposure to high uric acid may engender renal damage.

Partial HPRT Deficiency with a Novel Mutation of the HPRT Gene in Combination with Four Previously Reported Variants Associated with Hyperuricemia

A 15-year-old boy was referred to our department due to gout. The laboratory findings showed hyperuricemia with a decreased erythrocyte hypoxanthine phosphoribosyl transferase (HPRT) activity. The HPRT cDNA sequence was revealed to be 206A>T, which has not been previously reported. In addition, direct sequencing of genomic DNA showed the patient to possess four variants reported to be associated with hyperuricemia. This is the first case report of partial HPRT deficiency due to a novel HPRT mutation accompanied by variants associated with hyperuricemia. Combination treatment consisting of benzbromarone and febuxostat had a significant effect in reducing the urate level in our patient.

Uromodulin retention in thick ascending limb of Henle's loop affects SCD1 in neighboring proximal tubule: renal transcriptome studies in mouse models of uromodulin-associated kidney disease

Uromodulin-associated kidney disease (UAKD) is a hereditary progressive renal disease which can lead to renal failure and requires renal replacement therapy. UAKD belongs to the endoplasmic reticulum storage diseases due to maturation defect of mutant uromodulin and its retention in the enlarged endoplasmic reticulum in the cells of the thick ascending limb of Henle's loop (TALH). Dysfunction of TALH represents the key pathogenic mechanism of UAKD causing the clinical symptoms of this disease. However, the molecular alterations underlying UAKD are not well understood. In this study, transcriptome profiling of whole kidneys of two mouse models of UAKD, Umod^A227T and Umod^C93F, was performed. Genes differentially abundant in UAKD affected kidneys of both Umod mutant lines at different disease stages were identified and verified by RT-qPCR. Additionally, differential protein abundances of SCD1 and ANGPTL7 were validated by immunohistochemistry and Western blot analysis. ANGPTL7 expression was down-regulated in TALH cells of Umod mutant mice which is the site of the mutant uromodulin maturation defect. SCD1 was expressed selectively in the S3 segment of proximal tubule cells, and SCD1 abundance was increased in UAKD affected kidneys. This finding demonstrates that a cross talk between two functionally distinct tubular segments of the kidney, the TALH segment and the S3 segment of proximal tubule, exists.

Gout: a review of nonmodifiable and modifiable risk factors

Gout is a common inflammatory arthritis triggered by the crystallization of uric acid within the joints. Gout affects millions worldwide and has an increasing prevalence. Recent research has been carried out to better qualify and quantify the risk factors predisposing individuals to gout. These can largely be broken into nonmodifiable risk factors, such as gender, age, race, and genetics, and modifiable risk factors, such as diet and lifestyle. Increasing knowledge of factors predisposing certain individuals to gout could potentially lead to improved preventive practices. This review summarizes the nonmodifiable and modifiable risk factors associated with development of gout.

Apolipoprotein E gene polymorphisms are associated with primary hyperuricemia in a Chinese population

Objective

Primary hyperuricemia, an excess of uric acid in the blood, is a major public health problem. In addition to the morbidity that is attributable to gout, hyperuricemia is also associated with metabolic syndrome, hypertension, and cardiovascular disease. This study aims to assess the genetic associations between Apolipoprotein E (APOE) polymorphisms and hyperuricemia in a Chinese population.

Methods

A total of 770 subjects (356 hyperuricemic cases and 414 normouricemic controls) were recruited from the Ningxia Hui Autonomous Region, China. A physical examination was performed and fasting blood was collected for biochemical tests, including determination of the levels of serum lipid, creatinine, and uric acid. Multi-ARMS PCR was applied to determine the APOE genotypes, followed by an investigation of the distribution of APOE genotypes and alleles frequencies in the controls and cases.

Results

The frequencies of the APOE-ε2ε3 genotype (17.70% vs. 10.39%, P = 0.003) and the APOE-ε2 allele (10.53% vs. 5.80%, P = 0.001) were significantly higher in the hyperuricemic group than in the normouricemic group. Furthermore, male cases were more likely to have the APOE-ε2ε3 genotype and APOE-ε2 allele, compared with male controls. In both Han and Hui subjects, cases were more likely to have the APOE-ε2ε3 genotype and the APOE-ε2 allele compared with controls. Furthermore, multivariate logistic regression showed that carriers of the APOE-ε2ε3 genotype (P = 0.001, OR = 2.194) and the ε2 allele (P = 0.001, OR = 2.099) were significantly more likely to experience hyperuricemia than carriers of the ε3/ε3 genotype and the ε3 allele after adjustment for sex, body mass index (BMI), diastolic blood pressure (DBP), triglyceride (TG), low density lipoprotein cholesterol (LDL-C), creatinine (Cr) and fasting blood glucose(FBG).

Conclusions

The APOE-ε2ε3 genotype and the APOE-ε2 allele are associated with serum uric acid levels in Chinese subjects, indicating that individuals carrying the APOE-ε2 allele have a higher risk of hyperuricemia than non-carriers.

Complex analysis of urate transporters SLC2A9, SLC22A12 and functional characterization of non-synonymous allelic variants of GLUT9 in the Czech population: no evidence of effect on hyperuricemia and gout

Objective

Using European descent Czech populations, we performed a study of SLC2A9 and SLC22A12 genes previously identified as being associated with serum uric acid concentrations and gout. This is the first study of the impact of non-synonymous allelic variants on the function of GLUT9 except for patients suffering from renal hypouricemia type 2.

Methods

The cohort consisted of 250 individuals (150 controls, 54 nonspecific hyperuricemics and 46 primary gout and/or hyperuricemia subjects). We analyzed 13 exons of SLC2A9 (GLUT9 variant 1 and GLUT9 variant 2) and 10 exons of SLC22A12 by PCR amplification and sequenced directly. Allelic variants were prepared and their urate uptake and subcellular localization were studied by Xenopus oocytes expression system. The functional studies were analyzed using the non-parametric Wilcoxon and Kruskall-Wallis tests; the association study used the Fisher exact test and linear regression approach.

Results

We identified a total of 52 sequence variants (12 unpublished). Eight non-synonymous allelic variants were found only in SLC2A9: rs6820230, rs2276961, rs144196049, rs112404957, rs73225891, rs16890979, rs3733591 and rs2280205. None of these variants showed any significant difference in the expression of GLUT9 and in urate transport. In the association study, eight variants showed a possible association with hyperuricemia. However, seven of these were in introns and the one exon located variant, rs7932775, did not show a statistically significant association with serum uric acid concentration.

Conclusion

Our results did not confirm any effect of SLC22A12 and SLC2A9 variants on serum uric acid concentration. Our complex approach using association analysis together with functional and immunohistochemical characterization of non-synonymous allelic variants did not show any influence on expression, subcellular localization and urate uptake of GLUT9.

Familial juvenile hyperuricemic nephropathy 1 (FJHN1)

Familial juvenile hyperuricemic nephropathy 1 (FJHN1) is an autosomal dominant disorder characterized by decreased urinary excretion of urate and hyperuricemia, followed by the development of chronic interstitial nephritis most often leading to progressive renal failure and death in middle age. We report a case of FJHN1 presenting as chronic tophaceous gout, hypertension, renal failure and a family history suggestive of autosomal dominant inheritance, for its rarity.

Trp64Arg (rs4994) polymorphism of β3-adrenergic receptor gene is associated with hyperuricemia in a Chinese male population

BACKGROUND

β3-Adrenergic receptor (β3-AR) gene is associated with insulin resistance and may affect serum uric acid levels. Our aim was to determine the possible association between β3-AR gene Trp64Arg polymorphism (rs4994) and hyperuricemia in a Chinese male population.

METHODS

A total of 410 hyperuricemic and 420 normouricemic male subjects were genotyped in this study. The genotypic and allelic frequencies were compared between the two groups. Body mass index (BMI), waist to hip ratio (WHR), systolic blood pressure (SBP), diastolic blood pressure (DBP), serum uric acid, urea nitrogen, creatinine, triglyceride, total cholesterol, low-density lipoprotein-cholesterol (LDL-C), high-density lipoprotein-cholesterol (HDL-C) and fasting plasma glucose (FPG) were determined.

RESULTS

The frequencies of CC genotype and C allele for Trp64Arg polymorphism were higher in hyperuricemic group than in normouricemic group (p<0.01 and p<0.05, respectively). In both hyperuricemic and normouricemic groups, subjects with mutated C allele of Trp64Arg polymorphism showed significantly higher average uric acid levels than TT genotype carriers (p<0.01 and p<0.01, respectively). Univariate and multivariate logistic regression showed that carrier of mutated C allele of Trp64Arg polymorphism was significantly associated with hyperuricemia occurrence (p=0.003, OR=1.587, 95% CI 1.175-2.145 and p=0.003, OR=1.676, 95% CI 1.051-3.617).

CONCLUSIONS

Trp64Arg polymorphism was associated with hyperuricemia in a Chinese male population and should be an independent risk factor for hyperuricemia.

Unilateral hypoplastic kidney - a novel highly penetrant feature of familial juvenile hyperuricaemic nephropathy

BACKGROUND

Familial juvenile hyperuricaemic nephropathy is a rare inherited nephropathy with genetic heterogeneity. Categorised by genetic defect, mutations in uromodulin (UMOD), renin (REN) and hepatocyte nuclear factor-1β (HNF-1β) genes as well as linkage to chromosome 2p22.1-21 have previously been identified. Knowledge of the genetics of this phenotype has provided important clues to developmental pathways in the kidney.

CASE PRESENTATION

We report a novel phenotype, with the typical features of hyperuricemia and renal deterioration, but with the additional unexpected feature of unilateral renal hypoplasia. Mutation analyses of the existing known genes and genetic loci were negative indicating a new monogenic cause. Interestingly two cousins of the index case did not share the latter feature, suggesting a modifier gene effect.

CONCLUSION

Unilateral renal hypo/aplasia is usually sporadic and relatively common, with no genetic cause to date identified. This reported pedigree reveals the possibility that a new, unknown renal developmental gene may be implicated in the FJHN phenotype.

Wild-type uromodulin prevents NFkB activation in kidney cells, while mutant uromodulin, causing FJHU nephropathy, does not

BACKGROUND

Uromodulin (Tamm-Horsfall protein) is the most abundant urinary protein in healthy individuals. Despite 60 years of research, its physiological role remains rather elusive. Familial juvenile hyperuricemic nephropathy and medullary cystic kidney disease Type 2 are autosomal dominant tubulointerstitial nephropathies characterized by gouty arthritis and progressive renal insufficiency, caused by uromodulin (UMOD) mutations. The aim of this study was to compare the cellular effects of mutant and wild-type UMOD.

METHODS

Wild-type UMOD cDNA was cloned from human kidney cDNA into pcDNA3 expression vector. A mutant UMOD construct, containing the previously reported mutation, V273, was created by in vitro mutagenesis. Transient and stable transfection studies were performed in human embryonic kidney cells and mouse distal convoluted tubular cells, respectively. Expression was evaluated by reverse transcription polymerase chain reaction (RT-PCR), western blot and immunofluorescence. Oligosaccharide cleavage by glycosidases was performed to characterize different forms of UMOD. Nuclear translocation of P65 and degradation of IκBα and IRAK1 in response to interleukin (IL)-1β were used to evaluate the effects of wild-type and mutant UMOD on the IL-1R-NFκB pathway.

RESULTS

The mutant protein was shown to be retained in the endoplasmic reticulum and was not excreted to the cell medium, as opposed to the wild-type protein. NFκB activation in cells expressing mutant UMOD was similar to that of untransfected cells. In contrast, cells over-expressing wild-type UMOD showed markedly reduced NFκB activation.

CONCLUSION

Our findings suggest that UMOD may have a physiologic function related to its inhibitory effect on the NFκB pathway.

Late diagnosis of Lesch-Nyhan disease variant

A 30-year-old man was referred for investigation and management of hyperuricaemia. History included recurrent nephrolithiasis and chronic gout with poor response to medical management. Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) enzyme activity was investigated and found to be deficient confirming the diagnosis of Lesch-Nyhan disease. Hyperuricaemia was treated with allopurinol. To prevent nephrolithiasis, the patient was instructed to avoid dehydration and aim for a minimum urine output of 2 L/day. Urinary alkalinisation with potassium citrate was started. The patient was referred for genetic counselling. This case discusses the genetics, pathophysiology, clinical manifestations, diagnosis and management of HGPRT deficiency.

Association of plasma uric acid with ischaemic heart disease and blood pressure: mendelian randomisation analysis of two large cohorts

OBJECTIVES

To assess the associations between both uric acid levels and hyperuricaemia, with ischaemic heart disease and blood pressure, and to explore the potentially confounding role of body mass index.

DESIGN

Mendelian randomisation analysis, using variation at specific genes (SLC2A9 (rs7442295) as an instrument for uric acid; and FTO (rs9939609), MC4R (rs17782313), and TMEM18 (rs6548238) for body mass index).

SETTING

Two large, prospective cohort studies in Denmark.

PARTICIPANTS

We measured levels of uric acid and related covariables in 58,072 participants from the Copenhagen General Population Study and 10,602 from the Copenhagen City Heart Study, comprising 4890 and 2282 cases of ischaemic heart disease, respectively.

MAIN OUTCOME

Blood pressure and prospectively assessed ischaemic heart disease.

RESULTS

Estimates confirmed known observational associations between plasma uric acid and hyperuricaemia with risk of ischaemic heart disease and diastolic and systolic blood pressure. However, when using genotypic instruments for uric acid and hyperuricaemia, we saw no evidence for causal associations between uric acid, ischaemic heart disease, and blood pressure. We used genetic instruments to investigate body mass index as a potentially confounding factor in observational associations, and saw a causal effect on uric acid levels. Every four unit increase of body mass index saw a rise in uric acid of 0.03 mmol/L (95% confidence interval 0.02 to 0.04), and an increase in risk of hyperuricaemia of 7.5% (3.9% to 11.1%).

CONCLUSION

By contrast with observational findings, there is no strong evidence for causal associations between uric acid and ischaemic heart disease or blood pressure. However, evidence supports a causal effect between body mass index and uric acid level and hyperuricaemia. This finding strongly suggests body mass index as a confounder in observational associations, and suggests a role for elevated body mass index or obesity in the development of uric acid related conditions.

[Effect of total saponin of Dioscorea on chronic hyperuricemia and expression of URAT1 in rats]

OBJECTIVE

To study the preventive and therapeutic effects of total saponin of Dioscorea (TSD) on chronic hyperuricemia, and its effect on urate transporter 1 (URAT1) in rats.

METHOD

Ninety male rats were randomly divided into 6 groups: the normal group, the model group, TSD high-, medium- and low-dose (300, 100, 30 mg x kg(-1)) groups and the benzbromarone (10 mg x kg(-1)) group. Potassium oxonate and ethambutol were adopted to establish the chronic hyperuricemia model Since the third week, all the rats were intragastrically administered with drugs for 4 weeks, once a day, in order to determine their uric acid in serum and urine, uric acid excretion and xanthine oxidase (XOD). URAT1 mRNA and URAT1 protein expression in rat renal tubular cells were determined by RT-PCR and immunohistochemistry method respectively.

RESULT

Serum uric acid level of the model group increased significantly, while uric acid excretion decreased, with high expressions of renal URAT1 mRNA and URAT1 protein. TSD could dose-dependently reduce the serum uric acid level of chronic hyperuricemia rats, increase the concentration of uric acid and uric acid excretion in urine, and reduce renal URAT1 mRNA and URAT1 protein expression. Its effects were similar with that of benzbromarone, but with no significant effect on XOD and urinary volume of chronic hyperuricemia rats.

CONCLUSION

TSD has an obvious effect of anti-hyperuricemia It may reduce the reabsorption of uric acid by inhibiting the high expression of rat renal URAT1.

Type of uromodulin mutation and allelic status influence onset and severity of uromodulin-associated kidney disease in mice

Uromodulin-associated kidney disease (UAKD) is a dominant heritable renal disease in humans which is caused by mutations in the uromodulin (UMOD) gene and characterized by heterogeneous clinical appearance. To get insights into possible causes of this heterogeneity of UAKD, we describe the new mutant mouse line Umod(C93F), leading to disruption of a putative disulfide bond which is also absent in a known human UMOD mutation, and compare the phenotype of this new mouse line with the recently published mouse line Umod(A227T). In both mutant mouse lines, which were both bred on the C3H background, the Umod mutations cause a gain-of-toxic function due to a maturation defect of the mutant uromodulin leading to a dysfunction of thick ascending limb of Henle's loop (TALH) cells of the kidney. Umod mutant mice exhibit increased plasma urea and Cystatin levels, impaired urinary concentration ability, reduced fractional excretion of uric acid and nephropathological alterations including uromodulin retention in TALH cells, interstitial fibrosis and inflammatory cell infiltrations, tubular atrophy and occasional glomerulo- und tubulocystic changes, a phenotype highly similar to UAKD in humans. The maturation defect of mutant uromodulin leads to the accumulation of immature uromodulin in the endoplasmic reticulum (ER) and to ER hyperplasia. Further, this study was able to demonstrate for the first time in vivo that the severity of the uromodulin maturation defect as well as onset and speed of progression of renal dysfunction and morphological alterations are strongly dependent on the particular Umod mutation itself and the zygosity status.

Association of TLR4 Gene rs2149356 polymorphism with primary gouty arthritis in a case-control study

Background

The toll-like receptor (TLR)4-interleukin1β (IL1β) signaling pathway is involved in the monosodium urate (MSU)-mediated inflammation. The aim of this present study was to determine whether the TLR4 gene rs2149356 SNP is associated with gouty arthritis (GA) susceptibility and whether rs2149356 SNP impacts the TLR4-IL1β signaling pathway molecules expression.

Methods and Findings

The rs2149356 SNP was detected in 459 GA patients and 669 control subjects (containing 459 healthy and 210 hyperuricemic subjects). Peripheral blood mononuclear cells (PBMCs) TLR4 mRNA and serum IL1β were measured in different genotype carriers, and correlations between TLR4 gene SNP and TLR4 mRNA, IL1β were investigated. The frequencies of the genotype and allele were significantly different between the GA and control groups (P<0.01, respectively). The TT genotype was associated with a significantly increased risk of GA (OR = 1.88); this finding was not influenced by making adjustments for the components of possible confounders (adjusted OR = 1.96). TLR4 mRNA and IL1β were significantly increased in the TT genotype from acute GA patients (P<0.05, respectively), and lipids were significantly different among three genotypes in the GA patients (P<0.05, respectively).

Conclusions

The TLR4 gene rs2149356 SNP might be associated with GA susceptibility, and might participate in regulating immune, inflammation and lipid metabolism. Further studies are required to confirm these findings.

Can genetics aggravate the health of isolated and remote populations? The case of gout, hyperuricaemia and osteoarthritis in Dalmatia

INTRODUCTION

The aim of this study was to investigate whether genetics may be considered an additional risk factor for health in isolated and remote populations, compared with their populations of origin. In this study, two remote island population samples from Croatia (from the islands of Vis and the Korcula) were compared with mainland controls from the coastal city of Split. The analyses focused on gout, hyperuricaemia and osteoarthritis, as examples of complex, multifactorial diseases.

METHODS

A total of 3006 examinees from all three sites in Dalmatia, Croatia were included in the descriptive part of the study, within a large-scale project of 10,001 Dalmatians. Additionally, a subset of 2428 subjects was genotyped and information on three genomic loci was used in this study. All three loci belong to SLC2A9 gene, considered to have a major role in the regulation of serum uric acid concentration (rs6449213, rs1014290 and rs737267).

RESULTS

There was a much a higher prevalence of gout in the isolated populations compared with the mainland sample (3.3% in Vis, 2.2% in Korcula and 1.7% in Split, after age standardization). Furthermore, standardized prevalence of hyperuricaemia (defined as serum uric acid ≥403 mmol/L) was 9.9% in Vis, 5.6% in Korcula and 6.1% in Split. Analysis of the allele frequencies for the three loci of SLC2A9 suggested that in all three instances the prevalence of deleterious genotypes was highest in Vis, followed by Korcula, which had higher or comparable prevalence to the city of Split. Multivariate analysis, adjusted for the main confounder effects indicated that those on the island of Vis, which has the higher degree of isolation, had significantly higher odds ratio for both hyperuricaemia (odds ratio 1.90 95% confidence intervals [1.36-2.64]) and osteoarthritis, but not gout (3.37 [2.14-5.32]). The difference between Split and Korcula included only greater odds for osteoarthritis (1.92 [1.20-3.06]).

CONCLUSIONS

Isolated and remote populations that maintain a sufficient level of genetic isolation may suffer not only from consequences of geographic and social isolation, but their population genetic structure may also further contribute to poorer health status and outcomes.

ALDH16A1 is a novel non-catalytic enzyme that may be involved in the etiology of gout via protein-protein interactions with HPRT1

Gout, a common form of inflammatory arthritis, is strongly associated with elevated uric acid concentrations in the blood (hyperuricemia). A recent study in Icelanders identified a rare missense single nucleotide polymorphism (SNP) in the ALDH16A1 gene, ALDH16A1*2, to be associated with gout and serum uric acid levels. ALDH16A1 is a novel and rather unique member of the ALDH superfamily in relation to its gene and protein structures. ALDH16 genes are present in fish, amphibians, protista, bacteria but absent from archaea, fungi and plants. In most mammalian species, two ALDH16A1 spliced variants (ALDH16A1, long form and ALDH16A1_v2, short form) have been identified and both are expressed in HepG-2, HK-2 and HK-293 human cell lines. The ALDH16 proteins contain two ALDH domains (as opposed to one in the other members of the superfamily), four transmembrane and one coiled-coil domains. The active site of ALDH16 proteins from bacterial, frog and lower animals contain the catalytically important cysteine residue (Cys-302); this residue is absent from the mammalian and fish orthologs. Molecular modeling predicts that both the short and long forms of human ALDH16A1 protein would lack catalytic activity but may interact with the hypoxanthine-guanine phosphoribosyltransferase (HPRT1) protein, a key enzyme involved in uric acid metabolism and gout. Interestingly, such protein-protein interactions with HPRT1 are predicted to be impaired for the long or short forms of ALDH16A1*2. These results lead to the intriguing possibility that association between ALDH16A1 and HPRT1 may be required for optimal HPRT activity with disruption of this interaction possibly contributing to the hyperuricemia seen in ALDH16A1*2 carriers.

[Uromodulin - can it be a new marker of kidney damage?]

Uromodulin (Tamm-Horsfall protein) is the most abundant protein excreted in the urine under physiological conditions. It is exclusively produced in the kidney and secreted into the urine via proteolytic cleavage. Its biological function is stillnot fully understood. Uromodulin has been linked to waterl electrolyte balance and to kidney innate immunity. Also, studies in knockout mice demonstrated that it has a protective role against urinary tract infections and renal stone formation. Mutations in the gene encoding uromodulin lead to rare autosomal dominant diseases, collectively referred to as uromodulin-associated kidney diseases. They are characterized by progressive tubulointerstitial damage, impaired urinary concentrating ability, hyperuricemia, renal cysts, and progressive renal failure. Novel in vivo studies point at intracellular accumulation of mutant uromodulin as a key primary event in the disease pathogenesis. Recently, genome-wide association studies identified uromodulin as a risk factor for chronic kidney disease (CKD) and hypertension, and suggested that the level of uromodulin in the urine could represent a useful biomarker for the development of CKD.

Association and interaction effect between VEGF receptor-2 (VEGFR-2) gene polymorphisms and dietary pattern on blood uric acid in Malays and Indians

INTRODUCTION

Gout and hyperuricaemia attributed to genetic and lifestyle factors have been associated with several chronic diseases. This study aimed to determine the association and interaction effects between vascular endothelial growth factor receptor-2 (VEGFR-2) gene polymorphisms (rs1870377 and rs2071559) and dietary patterns on blood uric acid in Malay and Indian adults.

METHODS

Dietary intakes of 153 Malays and 177 Indians were obtained using a food frequency questionnaire for the construction of dietary patterns using factor analysis. Genotyping of rs1870377 and rs2071559 was performed by real-time PCR using TaqMan probes. Anthropometric measurements, body mass index (BMI) and blood pressure and biomarkers, uric acid, glycated haemoglobin A1c (HbA1c), and blood lipids were determined.

RESULTS

There were significant differences in the mean values for HbA1c (41 +/- 12 vs 45 +/- 8 mmol/mol, p < 0.001) and blood lipids levels (p < 0.05) between Malays and Indians. Significant correlations were obtained between uric acid with selected blood lipids (p < 0.05) and BMI in Malays (r = 0.362, p < 0.001) and Indians (r = 0.212, p < 0.01). Four dietary patterns were extracted from dietary intakes of all subjects: 'Vegetables diet'; 'Fruits diet' (FD); 'Animal protein and rice diet'; and 'Fast foods and preserved foods diet'. There were no significant associations between dietary patterns (p = 0.054-0.609) and VEGFR-2 gene polymorphisms (p = 0.348-0.778) with uric acid. In Malay subjects, the interaction of rs2071559 and FD had a borderline effect (p = 0.05) on blood uric acid after adjusting for potential confounders.

CONCLUSION

The associations and gene-diet interactions involving VEGFR-2 gene polymorphisms and FD on uric acid provide new information on gout and hyperuricaemia risks in Malays.