Renal hypouricemia (RHUC) is a pathological condition characterized by extremely low serum urate and overexcretion of urate in the kidney; this inheritable disorder is classified into type 1 and type 2 based on causative genes encoding physiologically-important urate transporters, URAT1 and GLUT9, respectively; however, research on RHUC type 2 is still behind type 1. We herein describe a typical familial case of RHUC type 2 found in a Slovak family with severe hypouricemia and hyperuricosuria. Via clinico-genetic analyses including whole exome sequencing and in vitro functional assays, we identified an intronic GLUT9 variant, c.1419+1G>A, as the causal mutation that could lead the expression of p.Gly431GlufsTer28, a functionally-null variant resulting from exon 11 skipping. The causal relationship was also confirmed in another unrelated Macedonian family with mild hypouricemia. Accordingly, non-coding regions should be also kept in mind during genetic diagnosis for hypouricemia. Our findings provide a better pathogenic understanding of RHUC and pathophysiological importance of GLUT9.

• Keywords
• RHUC, genetic disorder, renal urate handling, splicing variant, urate,
• Publication type
• Journal Article MeSH

Renal hypouricemia (RHUC) is caused by an inherited defect in the main reabsorption system of uric acid, SLC22A12 (URAT1) and SLC2A9 (GLUT9). RHUC is characterized by a decreased serum uric acid concentration and an increase in its excreted fraction. Patients suffer from hypouricemia, hyperuricosuria, urolithiasis, and even acute kidney injury. We report clinical, biochemical, and genetic findings in a cohort recruited from the Košice region of Slovakia consisting of 27 subjects with hypouricemia and relatives from 11 families, 10 of whom were of Roma ethnicity. We amplified, directly sequenced, and analyzed all coding regions and exon-intron boundaries of the SLC22A12 and SLC2A9 genes. Sequence analysis identified dysfunctional variants c.1245_1253del and c.1400C>T in the SLC22A12 gene, but no other causal allelic variants were found. One heterozygote and one homozygote for c.1245_1253del, nine heterozygotes and one homozygote for c.1400C>T, and two compound heterozygotes for c.1400C>T and c.1245_1253del were found in a total of 14 subjects. Our result confirms the prevalence of dysfunctional URAT1 variants in Roma subjects based on analyses in Slovak, Czech, and Spanish cohorts, and for the first time in a Macedonian Roma cohort. Although RHUC1 is a rare inherited disease, the frequency of URAT1-associated variants indicates that this disease is underdiagnosed. Our findings illustrate that there are common dysfunctional URAT1 allelic variants in the general Roma population that should be routinely considered in clinical practice as part of the diagnosis of Roma patients with hypouricemia and hyperuricosuria exhibiting clinical signs such as urolithiasis, nephrolithiasis, and acute kidney injury.

• Keywords
• Roma, SLC22A12, URAT1, ethnic specificity, renal hypouricemia,
• Publication type
• Journal Article MeSH

Urate transporters, which are located in the kidneys, significantly affect the level of uric acid in the body. We looked at genetic variants of genes encoding the major reabsorption proteins GLUT9 (SLC2A9) and URAT1 (SLC22A12) and their association with hyperuricemia and gout. In a cohort of 250 individuals with primary hyperuricemia and gout, we used direct sequencing to examine the SLC22A12 and SLC2A9 genes. Identified variants were evaluated in relation to clinical data, biochemical parameters, metabolic syndrome criteria, and our previous analysis of the major secretory urate transporter ABCG2. We detected seven nonsynonymous variants of SLC2A9. There were no nonsynonymous variants of SLC22A12. Eleven variants of SLC2A9 and two variants of SLC22A12 were significantly more common in our cohort than in the European population (p = 0), while variants p.V282I and c.1002+78A>G had a low frequency in our cohort (p = 0). Since the association between variants and the level of uric acid was not demonstrated, the influence of variants on the development of hyperuricemia and gout should be evaluated with caution. However, consistent with the findings of other studies, our data suggest that p.V282I and c.1002+78A>G (SLC2A9) reduce the risk of gout, while p.N82N (SLC22A12) increases the risk.

• Keywords
• SLC22A12, SLC2A9, gout, hyperuricemia, sequencing, urate transporters,
• Publication type
• Journal Article MeSH

BACKGROUND: Renal hypouricemia is a rare heterogeneous inherited disorder characterized by impaired tubular uric acid transport with severe complications, such as acute kidney injury and nephrolithiasis. Type 1 is caused by a loss-of-function mutation in the SLC22A12 gene (URAT1), while type 2 is caused by defects in the SLC2A9 gene (GLUT9). METHODS AND RESULTS: In this article we present clinical, biochemical and molecular genetics of two Czech patients. The serum uric acid in the probands was 57 and 98 µmol/l and expressed as an increase in the fractional excretion of uric acid (40 and 18 %). The sequencing analysis of SLC22A12 and SLC2A9 revealed novel variants p.R92C and p.R203C in URAT1 and p.G72D in GLUT9. Functional studies were performed for these novel variants and for previously reported variants p.I118HfsX27, p.G216R and p.N333S in GLUT9 responsible for renal hypouricemia in three probands from Czech Republic and United Kingdom. Functional studies showed significantly decreased urate uptake for all variants. However, urate uptake of GLUT9 variants prepared for both isoforms were not significantly different. CONCLUSIONS: This is the first complex function characterization of non-synonymous allelic variants in patients with renal hypouricemia regarding both GLUT9 isoforms. Our finding of defects in the SLC2A9 and SLC22A12 genes show the following: renal hypouricemia is not restricted to East Asia populations; urate uptake of GLUT9 variants prepared for both isoforms were not significantly different; renal hypouricemia type 2 has more wide clinical variability than type 1; the phenotypic severity of renal hypouricemia is not correlated with results of functional characterizations of URAT1 and GLUT9 variants.

• Keywords
• GLUT9, Renal hypouricemia, SLC22A12, SLC2A9, URAT1, Uric acid transporters,
• MeSH
• Child MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Urinary Calculi genetics   MeSH
• DNA Mutational Analysis MeSH
• Organic Anion Transporters genetics   MeSH
• Organic Cation Transport Proteins genetics   MeSH
• Glucose Transport Proteins, Facilitative genetics   MeSH
• Renal Tubular Transport, Inborn Errors genetics   MeSH
• Xenopus MeSH
• Animals MeSH
• Check Tag
• Child MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Case Reports MeSH
• Names of Substances
• Organic Anion Transporters MeSH
• Organic Cation Transport Proteins MeSH
• Glucose Transport Proteins, Facilitative MeSH
• SLC22A12 protein, human MeSH Browser
• SLC2A9 protein, human MeSH Browser

Renal hypouricemia is a rare heterogeneous inherited disorder characterized by impaired tubular uric acid transport with severe complications, such as acute kidney injury. Type 1 and 2 are caused by loss-of-function mutations in the SLC22A12 and SLC2A9 gene, respectively. A cohort of 881 randomly chosen ethnic Roma from two regions in Eastern Slovakia and two regions in the Czech Republic participated. Genomic DNA was isolated from buccal swabs and/or from blood samples. The c.1245_1253del and c.1400C>T genotypes were determined using polymerase chain reaction with allele-specific primers in a multiplex arrangement and/or direct sequencing of exon 7 and 9. Allele frequencies and genotypes were tested for Hardy-Weinberg equilibrium using the Chi-square test. 25 subjects were heterozygous and three were homozygous for the c.1245_1253del, while 92 subjects were heterozygous and two were homozygous for the c.1400C>T. Moreover, two participants were compound heterozygotes. Frequencies of the c.1245_1253del and c.1400C>T variants were 1.87 and 5.56 %, respectively. Our finding confirms an uneven geographical and ethnic distribution of SLC22A12 mutant variants. We found that the c.1245_1253del and c.1400C>T variants were present in the Czech and Slovak Roma population at unexpectedly high frequencies. Renal hypouricemia should be kept in mind during differential diagnostic on Roma patients with low serum uric acid concentrations.

• Keywords
• Acute kidney injury, Renal hypouricemia, SLC22A12, URAT1,
• MeSH
• Genetic Testing methods   MeSH
• Humans MeSH
• Urinary Calculi genetics   MeSH
• Polymerase Chain Reaction methods   MeSH
• Organic Anion Transporters genetics   MeSH
• Organic Cation Transport Proteins genetics   MeSH
• Retrospective Studies MeSH
• Roma genetics   MeSH
• Renal Tubular Transport, Inborn Errors genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Multicenter Study MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Czech Republic MeSH
• Slovakia MeSH
• Names of Substances
• Organic Anion Transporters MeSH
• Organic Cation Transport Proteins MeSH
• SLC22A12 protein, human MeSH Browser

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.

• MeSH
• Alleles MeSH
• White People MeSH
• Biological Transport MeSH
• Gout genetics   pathology   MeSH
• Adult MeSH
• Gene Expression MeSH
• Gene Frequency MeSH
• Hyperuricemia genetics   pathology   MeSH
• Polymorphism, Single Nucleotide * MeSH
• Middle Aged MeSH
• Humans MeSH
• Organic Anion Transporters genetics   MeSH
• Organic Cation Transport Proteins genetics   MeSH
• Glucose Transport Proteins, Facilitative genetics   MeSH
• Aged MeSH
• Case-Control Studies MeSH
• Animals MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Male MeSH
• Aged MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Czech Republic MeSH
• Names of Substances
• Organic Anion Transporters MeSH
• Organic Cation Transport Proteins MeSH
• Glucose Transport Proteins, Facilitative MeSH
• SLC22A12 protein, human MeSH Browser
• SLC2A9 protein, human MeSH Browser

OBJECTIVE: Uric acid is the end product of purine metabolism in humans, and increased serum uric acid concentrations lead to gout. The objective of the current study was to identify factors that are independently associated with serum uric acid concentrations in a cohort of Czech control individuals. METHODS: The cohort consisted of 589 healthy subjects aged 18-65 years. We studied the associations between the serum uric acid concentration and the following: (i) demographic, anthropometric and other variables previously reported to be associated with serum uric acid concentrations; (ii) the presence of metabolic syndrome and the levels of metabolic syndrome components; and (iii) selected genetic variants of the MTHFR (c.665C>T, c.1286A>C), SLC2A9 (c.844G>A, c.881G>A) and ABCG2 genes (c.421C>A). A backward model selection procedure was used to build two multiple linear regression models; in the second model, the number of metabolic syndrome criteria that were met replaced the metabolic syndrome-related variables. RESULTS: The models had coefficients of determination of 0.59 and 0.53. The serum uric acid concentration strongly correlated with conventional determinants including male sex, and with metabolic syndrome-related variables. In the simplified second model, the serum uric acid concentration positively correlated with the number of metabolic syndrome criteria that were met, and this model retained the explanatory power of the first model. Moderate wine drinking did not increase serum uric acid concentrations, and the urate transporter ABCG2, unlike MTHFR, was a genetic determinant of serum uric acid concentrations. CONCLUSION: Metabolic syndrome, moderate wine drinking and the c.421C>A variant in the ABCG gene are independently associated with the serum uric acid concentration. Our model indicates that uric acid should be clinically monitored in persons with metabolic syndrome.

• MeSH
• ATP Binding Cassette Transporter, Subfamily G, Member 2 MeSH
• ATP-Binding Cassette Transporters blood   genetics   MeSH
• Adult MeSH
• Gene Expression MeSH
• Polymorphism, Single Nucleotide * MeSH
• Cohort Studies MeSH
• Uric Acid blood   MeSH
• Middle Aged MeSH
• Humans MeSH
• Metabolic Syndrome blood   genetics   pathology   MeSH
• Methylenetetrahydrofolate Reductase (NADPH2) blood   genetics   MeSH
• Adolescent MeSH
• Models, Genetic MeSH
• Neoplasm Proteins blood   genetics   MeSH
• Alcohol Drinking blood   genetics   pathology   MeSH
• Glucose Transport Proteins, Facilitative blood   genetics   MeSH
• Regression Analysis MeSH
• Aged MeSH
• Sex Factors MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Male MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• ATP Binding Cassette Transporter, Subfamily G, Member 2 MeSH
• ATP-Binding Cassette Transporters MeSH
• ABCG2 protein, human MeSH Browser
• Uric Acid MeSH
• Methylenetetrahydrofolate Reductase (NADPH2) MeSH
• MTHFR protein, human MeSH Browser
• Neoplasm Proteins MeSH
• Glucose Transport Proteins, Facilitative MeSH
• SLC2A9 protein, human MeSH Browser

Renal hypouricemia (RHUC) is a heterogeneous inherited disorder characterized by impaired tubular uric acid (UA) transport with severe complications, such as acute kidney injury (AKI). Type 1 is caused by a loss-of-function mutation in the SLC22A12 gene (URAT1), type 2 in the SLC2A9 gene (GLUT9). This article describes three Czech families with RHUC type 1. The serum UA in the probands was 0.9, 1.1 and 0.5 mg/dl and expressed as an increase in the fractional excretion of UA (48, 43 and 39%). The sequencing analysis of SLC22A12 revealed three novel variants: p.G366R, p.T467M and a deletion p.L415_G417del. A detailed metabolic investigation in proband C for progressive visual failure supported suspicion of neuronal ceroid lipofuscinosis type 7 conditioned by the mutation in the MFSD8 gene. Functional studies showed significantly decreased urate uptake and a mis-localized URAT1 signal in p.G366R, p.L415_G417del and p.T467M. Furthermore, colocalization studies showed accumulation of URAT1 protein in the endoplasmic reticulum. The findings suggest that loss-of-function mutations cause RHUC via loss of UA absorption partly by protein misfolding. However, they do not necessarily lead to AKI and a possible genotype-phenotype correlation was not proposed. Furthermore, results confirm an uneven geographical and ethnic distribution of SLC22A12 variants; the p.L415_G417del mutation predominates in the Roma ethnic group in the Czech Republic.

• MeSH
• Absorption MeSH
• Acute Kidney Injury diagnosis   etiology   genetics   MeSH
• Alleles * MeSH
• Child MeSH
• Adult MeSH
• Endoplasmic Reticulum metabolism   MeSH
• Gene Frequency * MeSH
• Heterozygote MeSH
• Uric Acid urine   MeSH
• Humans MeSH
• Membrane Transport Proteins genetics   MeSH
• Urinary Calculi complications   diagnosis   ethnology   genetics   MeSH
• Mutation * MeSH
• Neuronal Ceroid-Lipofuscinoses diagnosis   etiology   genetics   MeSH
• Organic Anion Transporters genetics   metabolism   MeSH
• Organic Cation Transport Proteins genetics   metabolism   MeSH
• Pedigree MeSH
• Roma genetics   MeSH
• Renal Tubular Transport, Inborn Errors complications   diagnosis   ethnology   genetics   MeSH
• Xenopus MeSH
• Animals MeSH
• Check Tag
• Child MeSH
• Adult MeSH
• Humans MeSH
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Case Reports MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Czech Republic MeSH
• Names of Substances
• Uric Acid MeSH
• Membrane Transport Proteins MeSH
• MFSD8 protein, human MeSH Browser
• Organic Anion Transporters MeSH
• Organic Cation Transport Proteins MeSH
• SLC22A12 protein, human MeSH Browser