Renal hypouricemia in school-aged children: screening of serum uric acid level before physical training

J-shaped Relationship Between Chronic Kidney Disease and Serum Uric Acid Levels: A Cross-sectional Study on the Korean Population

Objective

Both hypouricemia and hyperuricemia are reportedly associated with reduced kidney function This study investigated the association between uric acid levels and the risk of reduced renal function in men and women.

Methods

We conducted a cross-sectional study using data from a government-funded health examinee cohort of a Korean genome and epidemiological study A total of 172,970 participants (58,981 men, 113,989 women) aged 40∼79 years were included A logistic regression test was performed, and the odds ratio (OR) and 95% confidence interval (CI) were calculated to examine the relationship between stratified uric acid levels and the frequency of chronic kidney disease.

Results

As the uric acid level increased, the risk of reduced renal function increased Moreover, for uric acid levels ≤20 mg/dL, the risk of reduced renal function was higher than that of the reference group Among the total, man, and woman groups, a statistically significant association was observed in men (OR 171, 95% CI 0945∼3111, OR 5003, 95% CI 1405∼17809, and OR 1377, 95% CI 0696∼2724, respectively).

Conclusion

The OR of reduced renal function according to uric acid levels formed a J-shaped curve in both genders.

Prevalence and possible causes of hypouricemia at a tertiary care hospital

BACKGROUND/AIMS

We aimed to investigate the prevalence and possible causes of hypouricemia in the Korean population and to compare our findings with published results of other populations.

METHODS

We examined the serum uric acid levels of 30,757 subjects who had their uric acid values measured at least once during a 1-year period. All individuals with hypouricemia (serum uric acid < 2.0 mg/dL, n = 424) were reviewed with respect to medical drug history and concomitant diseases previously identified as being associated with hypouricemia.

RESULTS

The prevalence of hypouricemia was 4.14% (299/7,223) among inpatients and 0.53% (125/23,534) among outpatients, for an overall prevalence of 1.39% (424/30,757). Possible causes associated with hypouricemia were found to be solid or hematologic malignancies (n = 86), diabetes mellitus (n = 56), and therapeutic drugs (n = 29). The medications were allopurinol (n = 11), angiotensin II receptor blockers (n = 10), salicylates (n = 6), febuxostat (n = 1), and warfarin (n = 1). In the remaining 226 individuals, the cause of hypouricemia was not identified.

CONCLUSIONS

Hypouricemia is relatively common in the Korean population compared to those of other countries. The possible causes associated with hypouricemia are related to underlying diseases and medications.

Recurrent exercise-induced acute renal failure in a young Pakistani man with severe renal hypouricemia and SLC2A9 compound heterozygosity

Background

Familial renal hypouricemia (RHUC) is a hereditary disease characterized by hypouricemia, high renal fractional excretion of uric acid (FE-UA) and can be complicated by acute kidney failure and nephrolithiasis. Loss-of-function mutations in the SLC22A12 gene cause renal hypouricemia type 1 (RHUC1), whereas renal hypouricemia type 2 (RHUC2) is caused by mutations in the SLC2A9 gene.

Case presentation

We describe a 24-year-old Pakistani man who was admitted twice to our hospital for severe exercise-induced acute renal failure (EIARF), abdominal pain and fever; he had very low serum UA levels (0.2 mg/dl the first time and 0.09 mg/dl the second time) and high FE-UA (200% and 732% respectively), suggestive of RHUC. Mutational analyses of both urate transporters revealed a new compound heterozygosity for two distinct missense mutations in the SLC2A9 gene: p.Arg380Trp, already identified in heterozygosity, and p.Gly216Arg, previously found in homozygosity or compound heterozygosity in some RHUC2 patients. Compared with previously reported patients harbouring these mutations, our proband showed the highest FE-UA levels, suggesting that the combination of p.Arg380Trp and p.Gly216Arg mutations most severely affects the renal handling of UA.

Conclusions

The clinical and molecular findings from this patient and a review of the literature provide new insights into the genotype-phenotype correlation of this disorder, supporting the evidence of an autosomal recessive inheritance pattern for RHUC2. Further investigations into the functional properties of GLUT9, URAT1 and other urate transporters are required to assess their potential research and clinical implications.

Clinical and functional characterization of URAT1 variants

Idiopathic renal hypouricaemia is an inherited form of hypouricaemia, associated with abnormal renal handling of uric acid. There is excessive urinary wasting of uric acid resulting in hypouricaemia. Patients may be asymptomatic, but the persistent urinary abnormalities may manifest as renal stone disease, and hypouricaemia may manifest as exercise induced acute kidney injury. Here we have identified Macedonian and British patients with hypouricaemia, who presented with a variety of renal symptoms and signs including renal stone disease, hematuria, pyelonephritis and nephrocalcinosis. We have identified heterozygous missense mutations in SLC22A12 encoding the urate transporter protein URAT1 and correlate these genetic findings with functional characterization. Urate handling was determined using uptake experiments in HEK293 cells. This data highlights the importance of the URAT1 renal urate transporter in determining serum urate concentrations and the clinical phenotypes, including nephrolithiasis, that should prompt the clinician to suspect an inherited form of renal hypouricaemia.

Recurrent EIARF and PRES with severe renal hypouricemia by compound heterozygous SLC2A9 mutation

Renal hypouricemia (RHU) is a hereditary disease that predisposes affected people to exercise-induced acute renal failure (EIARF). In most patients with RHU, the disorder is caused by loss-of-function mutations in SLC22A12 (solute carrier family 22, member 12), which encodes urate transporter 1 (URAT1). Patients with RHU without any mutations in the URAT1 gene were recently found to have a mutation in the glucose transporter 9 (GLUT9) gene (SLC2A9 [solute carrier family 2, member 9]). Central nervous system complications seem to be rare in patients with RHU with SLC22A12 mutations. Here, we report the case of a girl with severe RHU (serum urate: 5.9 μmol/L [0.1 mg/dL]) associated with recurrent EIARF in whom the disease was caused by a compound heterozygous mutation in SLC2A9, a nonsense mutation in the paternal allele (p.G207X in exon 7), and a large duplication (c.1-2981_1204+16502) in the maternal allele detected by reverse-transcription polymerase chain reaction (PCR), semiquantitative PCR, long PCR, and direct sequencing. The episodes of EIARF were complicated by posterior reversible encephalopathy syndrome (PRES), which suggested a relationship between PRES and GLUT9 or severe hypouricemia. This is the second report of mutations of both alleles of SLC2A9 that resulted in severe hypouricemia. Our findings indicate that even a nonsense mutation responsible for the heterozygous status of SLC2A9 did not cause severe hypouricemia, and they lend support to previous speculation that mutations of both SLC2A9 alleles cause severe hypouricemia. Our case shows that GLUT9, unlike URAT1, may play a specific role in exercise-induced PRES.

Non-urate transporter 1-related renal hypouricemia and acute renal failure in an Israeli-Arab family

Idiopathic renal hypouricemia (IRHU) is a rare hereditary disease, predisposing the individual to exercise-induced acute renal failure (EIARF) and nephrolithiasis, and it is characterized by increased clearance of renal uric acid. Most of the described patients are Japanese, who have loss-of-function mutations in the SLC22A12 gene coding for the human urate transporter 1 (URAT1) gene. An 18-year-old youth, who was admitted for EIARF due to IRHU, and six consanguineous Israeli-Arab family members were included in the study. The family members were tested for fractional excretion of uric acid and molecular analysis of the URAT1 gene. Four family members, including the proband, had very low levels of blood uric acid and high rate of fractional excretion (FE urate> 100%) of uric acid. Genetic analysis of the affected family members did not reveal a mutation in the coding regions and intron-exon boundaries of SCL22A12. Haplotype analysis excluded SCL22A12 involvement in the pathogenesis, suggesting a different gene as a cause of the disease. We herein describe the first Israeli-Arab family with IRHU. A non-URAT1 genetic defect that causes decreased reabsorption or, more probably, increased secretion of uric acid, induces IRHU. Further studies are required in order to elucidate the genetic defect.