Distribution and Characteristics of Hypouricemia within the Japanese General Population: A Cross-Sectional Study

Genotype and Phenotype of Renal Hypouricemia: A Single-Center Study from China

BACKGROUND

Renal hypouricemia (RHUC), a rare inherited disorder characterized by impaired uric acid reabsorption and subsequent profound hypouricemia, occurs mainly due to variants in SLC22A12 or SLC2A9. Only anecdotal cases and one small-scale RHUC screening study have been reported in the Chinese population.

METHODS

A total of 19 patients with RHUC from 17 unrelated families were recruited from our center. The medical history, clinical manifestations, biochemical exam, and clinical outcomes were collected. Next-generation sequencing-based targeted gene sequencing or whole exon sequencing was performed.

RESULTS

A total of 22 variants in SLC22A12 or SLC2A9 were found in 19 patients. The variant c.944G>A (p.W315X) in SLC2A9 was identified in three patients. Three variants c.165C>A (p.D55E), c.1549_1555delGAGACCC (p.E517Rfs*17), and c.1483T>C (p.W495R) in SLC22A12 and three variants c.1215+1G>A (splicing variant), c.643A>C (p.T215P), and c.227C>A (p.S76X) in SLC2A9 were novel. A proportion of 10 out of 19 patients presented with exercise-induced acute kidney injury (EIAKI). The renal outcome was favorable. Five patients had nephrolithiasis, in whom three had hypercalciuria.

CONCLUSION

The current study reported six novel variants in SLC22A12 and SLC2A9 genes of Chinese patients with RHUC. The variant c.944G>A (p.W315X) in SLC2A9 may be common in Chinese patients. EIAKI is the main clinical phenotype associated with RHUC in our cohort, with a favorable outcome. Hypercalciuria presented in some RHUC patients is a new finding.

Hypouricemia in the emergency department: A retrospective, single-center study

Backgrounds

Few studies have reported the prevalence and characteristics of hypouricemia in the emergency department (ED). We investigated the prevalence and characteristics of hypouricemia in the ED of a university-affiliated hospital in Japan.

Methods

This is a retrospective cross-sectional single-center study. All adult patients (18 years old or older) who had their serum uric acid (SUA) measured at the ED between 2011 and 2021 were included. Information collected included age, sex, SUA, and serum creatinine. Hypouricemia was defined as an SUA level ≦2.0 mg/dL.

Results

A total of 10,551 patients were included in the study. Fifty-one percent were male. The median SUA levels were significantly higher in men than in women (6.0 [4.8-7.4] vs. 4.7 [3.7-6.1], p < 0.001). The prevalence of hypouricemia was higher in women than in men (2.0% vs. 0.9%, p < 0.001). A possible cause of hypouricemia was identified in 88 patients. Malignancy and diabetes were the major possible cause of hypouricemia (p < 0.001).

Conclusion

The distribution of SUA levels and prevalence of hypouricemia differed significantly by sex and age in the ED. Malignancy was the leading cause of hypouricemia in the ED.

Association of serum uric acid with anemia in U.S. adults: a cross-sectional study using secondary data

BACKGROUND

High serum uric acid (SUA) is a risk factor of cardiovascular disease (CVD). Abnormal SUA have been correlated with a significant increase in mortality. Anemia is an independent predictor of mortality and CVD. To date, no study has investigated the relationship between SUA and anemia. Here, we explored the correlation between SUA and anemia in the American population.

METHODS

The cross-sectional study involved 9205 US adults from NHANES (2011-2014). The relationship between SUA and anemia was explored using multivariate linear regression models. Two-piecewise linear regression model, generalized additive models (GAM) and smooth curve fitting were performed to explore the non-linear relationships between SUA and anemia.

RESULTS

We found a U-shaped non-linear relationship between SUA and anemia. The inflection point of the SUA concentration curve was 6.2 mg/dL. The ORs (95% CIs) for anemia on the left and right of the inflection point were 0.86 (0.78-0.95) and 1.33 (1.16-1.52), respectively. The 95% CI of inflection point was 5.9-6.5 mg/dL. The findings showed that both genders presented a U-shaped correlation. Safe ranges of SUA in men and women were 6-6.5 and 4.3-4.6 mg/dL, respectively.

CONCLUSIONS

Both high and low SUA levels were correlated with increased risk of anemia, and a U-shaped relationship was observed between SUA and anemia.

The Association Between Hypouricemia and Cardiometabolic Diseases: Analyzing Nationwide Data From Medical Checkup and Health Insurance Records

OBJECTIVES

The aims of this study were to evaluate the association between hypouricemia and cardiometabolic diseases, such as hypertension, dyslipidemia, and reduced kidney function, and to explore the sex-specific optimal range for serum uric acid (sUA) associated with the lowest risk for these diseases.

METHODS

In this cross-sectional study, we identified individuals with sUA data between April 2018 and March 2019 and recorded the frequency of cardiometabolic comorbidities according to sUA. Univariable and multivariable logistic regression analyses were performed for the overall population and after classifying by sex to assess the association between sUA and cardiometabolic comorbidities.

RESULTS

Among 796,508 individuals, a J-shaped association was observed between the sUA level and cardiometabolic diseases in the overall population. The adjusted odds ratios (95% confidence interval) for hypertension, dyslipidemia, and reduced renal function in individuals with sUA ≤1.0 mg/dL compared with those with sUA ranging between 2.1 and 3.0 mg/dL were 1.38 (1.13-1.69), 1.52 (1.30-1.78), and 2.17 (1.47-3.20), respectively. A J-shaped association between sUA and hypertension was observed only in women. The optimal range of sUA associated with the lowest risk for hypertension was assumed to be <6 mg/dL in men and 1-4 mg/dL in women. A J-shaped association between the sUA and dyslipidemia and reduced renal function was observed in both men and women. The optimal range of sUA for dyslipidemia and reduced renal function was approximately 2-5 mg/dL in men and 1-4 mg/dL in women.

CONCLUSIONS

Excess and extremely low uric acid levels may be related to an increased cardiometabolic risk.

Evaluation of the factors affecting long-term mortality in geriatric patients followed up in intensive care unit due to hospital-acquired pneumonia

Aging is a normal physiological process involving changes in the respiratory system, thereby causing an increased incidence of pulmonary infections such as hospital-acquired pneumonia (HAP). The primary aim of this study was to investigate the role of acute-phase reactants and inflammation-based biomarkers in predicting 90-day mortality in patients aged over 65 years who were hospitalized in the intensive care unit (ICU) due to HAP. Clinical records of patients aged ≥65 years who were diagnosed as having HAP and were followed up in ICU were retrospectively evaluated. One hundred and fifteen ICU patients (67.8% male, mean age 76.81 ± 7.480 years) were studied. Ninety-day mortality occurred in 43 (37.4%) patients. Red cell distribution (RDW, %), mean platelet volume (MPV, f/L), white blood cell count (WBC, 103/μL), C-reactive protein (CRP, mg/L), and procalcitonin (PCT, ng/mL) median values were 18.2 (13.7-35.6), 7.42 (5.66-11.2), 14.3 (3.21-40), 9.58 (0.12-32), 0.41 (0.05-100) in the group with 90-day mortality. In the Receiver Operator Characteristics Curve analysis, a WBC value 18.2 × 10ˆ3/μL predicted 90-day independent mortality with a sensitivity of 90.70% and specificity of 31.94% (P = .029). The results indicated that serum WBC level can be used for predicting long-term mortality and prognosis in HAP patients aged over 65 years. High WBC value was statistically significant in predicting 90-day independent mortality (P < .05).

Genetic Basis of the Epidemiological Features and Clinical Significance of Renal Hypouricemia

A genetic defect in urate transporter 1 (URAT1) is the major cause of renal hypouricemia (RHUC). Although RHUC is detected using a serum uric acid (UA) concentration <2.0 mg/dL, the relationship between the genetic state of URAT1 and serum UA concentration is not clear. Homozygosity and compound heterozygosity with respect to mutant URAT1 alleles are associated with a serum UA concentration of <1.0 mg/dL and are present at a prevalence of ~0.1% in Japan. In heterozygous individuals, the prevalence of a serum UA of 1.1−2.0 mg/dL is much higher in women than in men. The frequency of mutant URAT1 alleles is as high as 3% in the general Japanese population. The expansion of a specific mutant URAT1 allele derived from a single mutant gene that occurred in ancient times is reflected in modern Japan at a high frequency. Similar findings were reported in Roma populations in Europe. These phenomena are thought to reflect the ancient migration history of each ethnic group (founder effects). Exercise-induced acute kidney injury (EI-AKI) is mostly observed in individuals with homozygous/compound heterozygous URAT1 mutation, and laboratory experiments suggested that a high UA load on the renal tubules is a plausible mechanism for EI-AKI.

Characterization of a Compound Heterozygous SLC2A9 Mutation That Causes Hypouricemia

Renal hypouricemia is a rare genetic disorder. Hypouricemia can present as renal stones or exercise-induced acute renal failure, but most cases are asymptomatic. Our previous study showed that two recessive variants of SLC22A12 (p.Trp258*, pArg90His) were identified in 90% of the hypouricemia patients from two independent cohorts: the Korean genome and epidemiology study (KoGES) and the Korean Cancer Prevention Study (KCPS-II). In this work, we investigate the genetic causes of hypouricemia in the rest of the 10% of unsolved cases. We found a novel non-synonymous mutation of SLC2A9 (voltage-sensitive uric acid transporter) in the whole-exome sequencing (WES) results. Molecular dynamics prediction suggests that the novel mutation p.Met126Val in SLCA9b (p.Met155Val in SLC2A9a) hinders uric acid transport through a defect of the outward open geometry. Molecular analysis using Xenopus oocytes confirmed that the p.Met126Val mutation significantly reduced uric acid transport but does not affect the SLC2A9 protein expression level. Our results will shed light on a better understanding of SLC2A9-mediated uric acid transport and the development of a uric acid-lowering agent.

A Proposal for Practical Diagnosis of Renal Hypouricemia: Evidenced from Genetic Studies of Nonfunctional Variants of URAT1/SLC22A12 among 30,685 Japanese Individuals

BACKGROUND

Renal hypouricemia (RHUC) is characterized by a low serum uric acid (SUA) level and high fractional excretion of uric acid (FE_UA). Further studies on FE_UA in hypouricemic individuals are needed for a more accurate diagnosis of RHUC.

METHODS

In 30,685 Japanese health-examination participants, we genotyped the two most common nonfunctional variants of URAT1 (NFV-URAT1), W258X (rs121907892) and R90H (rs121907896), in 1040 hypouricemic individuals (SUA ≤ 3.0 mg/dL) and 2240 individuals with FE_UA data. The effects of NFV-URAT1 on FE_UA and SUA were also investigated using linear and multiple regression analyses.

RESULTS

Frequency of hypouricemic individuals (SUA ≤ 3.0 mg/dL) was 0.97% (male) and 6.94% (female) among 30,685 participants. High frequencies of those having at least one allele of NFV-URAT1 were observed in 1040 hypouricemic individuals. Furthermore, NFV-URAT1 significantly increased FE_UA and decreased SUA, enabling FE_UA and SUA levels to be estimated. Conversely, FE_UA and SUA data of hypouricemic individuals are revealed to be useful to predict the number of NFV-URAT1.

CONCLUSIONS

Our findings reveal that specific patterns of FE_UA and SUA data assist with predicting the number of nonfunctional variants of causative genes for RHUC, and can also be useful for practical diagnosis of RHUC even before genetic tests.

Coexistence of autosomal dominant polycystic kidney disease type 1 and hereditary renal hypouricemia type 2: A model of early-onset and fast cyst progression

Autosomal dominant polycystic kidney disease (ADPKD) is a heterogeneous inherited disease characterized by renal and extrarenal manifestations with progressive fluid-filled cyst development leading to end-stage renal disease. The rate of disease progression in ADPKD exhibits high inter- and intrafamilial variability suggesting involvement of modifier genes and/or environmental factors. Renal hypouricemia (RHUC) is an inherited disorder characterized by impaired tubular uric acid transport with severe complications, such as acute kidney injury and chronic kidney disease (CKD). However, the two disorders have distinct and well-delineated genetic, biochemical, and clinical findings. Only a few cases of coexistence of ADPKD and RHUC (type 1) in a single individual have been reported. We report a family with two members: an ADPKD 24-year-old female which presented bilateral renal cysts in utero and hypouricemia since age 5, and her mother with isolated hypouricemia. Next-generation sequencing identified two mutations in two genes PKD1 and SLC2A9 in this patient and one isolated SLC2A9 mutation in her mother, showing RHUC type 2, associated to CKD. The coexistence of these two disorders provides evidence of SLC2A9 variant could act as a modifier change, with synergistic actions, that could promote cystogenesis and rapid ADPKD progression. This is the first case of coexistence of PKD1 and SLC2A9 mutations treated with tolvaptan.