The case: a young man with acute kidney injury after exercise. The diagnosis: exercise induced acute kidney injury in hereditary renal hypouricemia

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.

Acute renal failure with severe loin pain and patchy renal ischemia after anaerobic exercise

BACKGROUND

There are two known types of exercise-induced acute renal failure. One is the long-known myoglobinuria-induced acute renal failure due to severe rhabdomyolysis, and the other is the recently recognized non-myoglobinuria-induced acute renal failure with mild rhabdomyolysis. Exercise-induced acute renal failure was first reported in 1982. Non-myoglobinuria-induced acute renal failure is associated with severe low back pain and patchy renal vasoconstriction, and it is termed post-exercise acute renal failure because it usually occurs hours after exercise. It is also called acute renal failure with severe loin pain and patchy renal ischemia after anaerobic exercise (ALPE).

AIM

To makes a significant contribution to medical literature as it presents a study that investigated a not-widely-known type of exercise-induced acute renal failure known as ALPE.

METHODS

We performed a database search selecting papers published in the English or Japanese language. A database search was lastly accessed on September 1, 2022. The results of this study were compared with those reported in other case series.

RESULTS

The study evaluated renal hypouricemia as a key risk factor of ALPE. The development of ALPE is due to the sum of risk factors such as exercise, hypouricemia, nonsteroidal anti-inflammatory drugs, vasopressors, and dehydration.

CONCLUSION

In conclusion, hypouricemia plays a key role in the development of ALPE and is often associated with anaerobic exercise. The development of ALPE is a result of the cumulative effects of risk factors such as exercise, hypouricemia, NSAIDs, vasopressors, and dehydration.

A novel mutation in a patient with familial renal hypouricemia type 2

INTRODUCTION

Hypouricemia may be caused by disorders leading to decreased UA production, oxidation of UA to allantoin by drugs or increased renal tubular loss of filtered UA, renal hypouricemia (RHUC). RHUC may be resulted from familial or acquired disorders. Familial RHUC cases are classified according to the gene affected as type 1 (SLC22A12 gene) and type 2 (SLC2A9). Clinical importance of RHUC entity is mainly determined by emerging of acute kidney injury (AKI) after strenuous exercise and urolithiasis.

CASE PRESENTATION

Here, we report a case of RHUC with increased fractional excretion of uric acid value of more than 100%, serum uric acid level of nearly zero, and exercise-induced AKI episodes clinically and a new unpublished homozygous (biallelic) mutation of c.1419+2T>G (IVS11+2T>G) in the SLC2A9 gene genetically for the first time to our knowledge.

CONCLUSION

Clinicians should be aware of this rare entity defined as hereditary RHUC in order to provide long term renoprotection by advisements like simple precautions such as avoiding severe exercises.

A novel mutation in a patient with familial renal hypouricemia type 2

INTRODUCTION

Hypouricemia may be caused by disorders leading to decreased UA production, oxidation of UA to allantoin by drugs or increased renal tubular loss of filtered UA, renal hypouricemia (RHUC). RHUC may be resulted from familial or acquired disorders. Familial RHUC cases are classified according to the gene affected as type 1 (SLC22A12 gene) and type 2 (SLC2A9). Clinical importance of RHUC entity is mainly determined by emerging of acute kidney injury (AKI) after strenuous exercise and urolithiasis.

CASE PRESENTATION

Here, we report a case of RHUC with increased fractional excretion of uric acid value of more than 100%, serum uric acid level of nearly zero, and exercise-induced AKI episodes clinically and a new unpublished homozygous (biallelic) mutation of c.1419+2T>G (IVS11+2T>G) in the SLC2A9 gene genetically for the first time to our knowledge.

CONCLUSION

Clinicians should be aware of this rare entity defined as hereditary RHUC in order to provide long term renoprotection by advisements like simple precautions such as avoiding severe exercises.

Prevalence of inherited changes of uric acid levels in kidney dysfunction including stage 5 D and T: a systematic review

Background/aims

Familial juvenile hereditary nephropathy (FJHN) is characterized by hyperuricemia due to severely impaired urinary excretion of urate. Hereditary renal hypouricemia is an inborn error of membrane transport. Because studies of inherited tubulopathy is rare, prevalence and diagnosis of these inherited tubulopathy increase with genetic testing.The aim of this study is to investigate prevalence of clinical features, biochemical profiles, and genetic analysis of patients with changes in serum uric acid levels in inherited tubulopathy.

Main body

The paper has written based on searching PubMed and Google Scholar to identify potentially relevant articles or abstracts. In this retrospective study, a total 65 patients with changes of serum uric acid levels and kidney dysfunction were investigated. Clinical features, laboratory data at initial presentation, management, and outcomes were collected. Forty studies (65 participants) included in this review. The mean ± SD of age of study patients in inherited tubulointerstitial kidney disease was 25.29 ± 14.69 years. Mean ± SD age of patients at time of diagnosis in inherited renal hypouricemia was 18.83 ± 10.59 years. Correlation between exon region in mutated UMOD, SLC22A12, and SLC2A9 genes and serum uric acid levels were assessed and revealed significant statistical correlation between exon region of SLC2A9 mutation and serum uric acid levels. Prevalence of progression to end-stage kidney disease in patients with inherited tubulointerstitial kidney disease and inherited renal hypouricemia were assessed 20% and 2.5%, respectively. There was nephrolithiasis in two patients (2/25, 8%) with inherited renal hypouricemia.

Conclusions

This study shows that UMOD and SLC22A12 gene mutations were responsible for majority of autosomal-dominant tubulointerstitial kidney disease and inherited renal hypouricemia, respectively.

Exercise-Induced Acute Kidney Injury in a Police Officer with Hereditary Renal Hypouricemia

Hereditary renal hypouricemia is characterized by hypouricemia with hyper-uric acid clearance due to a defect in renal tubular transport. Patients with hereditary renal hypouricemia have a higher risk of exercise-induced acute kidney injury (EAKI) and reduced kidney function. Although the best preventive measure is avoiding exercise, there are many kinds of jobs that require occupational exercise. A 27-year-old male police officer suffered from stage 3 AKI after performing a 20-m multistage shuttle run test. His mother had previously been diagnosed as having renal hypouricemia at another facility. The patient had reported having hypouricemia during a health check at a previous police station, but his serum uric acid concentration was within the normal range at our hospital. After treatment, he recovered from EAKI and exhibited low serum uric acid and hyper-uric acid clearance. Since the patient desired to continue his career requiring strenuous exercise, it was difficult to establish a preventive plan against the recurrence of EAKI. Patients with hereditary renal hypouricemia who must undergo strenuous occupational anaerobic exercise are at higher risk of developing EAKI than other workers. The risks of EAKI among patients with hypouricemia should be considered when undergoing physical occupational training.

Amplicon targeted resequencing for SLC2A9 and SLC22A12 identified novel mutations in hypouricemia subjects

Background

To identify potential causative mutations in SLC2A9 and SLC22A12 that lead to hypouricemia or hyperuricemia (HUA).

Methods

Targeted resequencing of whole exon regions of SLC2A9 and SLC22A12 was performed in three cohorts of 31 hypouricemia, 288 HUA and 280 normal controls.

Results

A total of 84 high‐quality variants were identified in these three cohorts. Eighteen variants were nonsynonymous or in splicing region, and then included in the following association analysis. For common variants, no significant effects on hypouricemia or HUA were identified. For rare variants, six single nucleotide variations (SNVs) p.T21I and p.G13D in SLC2A9, p.W50fs, p.Q382L, p.V547L and p.E458K in SLC22A12, occurred in totally six hypouricemia subjects and were absent in HUA and normal controls. Allelic and genotypic frequency distributions of the six SNVs differed significantly between the hypouricemia and normal controls even after multiple testing correction, and p.G13D in SLC2A9 and p.V547L in SLC22A12 were newly reported. All these mutations had no significant effects on HUA susceptibility, while the gene‐based analyses substantiated the significant results on hypouricemia.

Conclusion

Our study first presents a comprehensive mutation spectrum of hypouricemia in a large Chinese cohort.

Unexpected high plasma xanthine oxidoreductase activity in female subjects with low levels of uric acid

Hypouricemia is a high-risk factor of exercise-induced acute kidney injury (EIAKI) probably through a lack of an antioxidant effect of uric acid. Xanthine oxidoreductase (XOR) is an enzyme that catalyzes the formation of uric acid from hypoxanthine and xanthine, leading to an increase in superoxide and reactive oxygen species. Activation of XOR has been proposed to promote oxidative stress-related tissue injury. We measured plasma XOR activity by a sensitive and accurate assay using a combination of liquid chromatography and triple quadrupole mass spectrometry in subjects with relatively low levels of uric acid (≤4.0 mg/dL) who were recruited from 627 subjects (male/female: 292/335) in the Tanno-Sobetsu Study, a population-based cohort. The numbers of subjects with uric acid ≤4.0 mg/dL, ≤3.0 mg/dL and ≤2.0 mg/dL were 72 (11.5%, male/female: 5/67), 13 (2.1%, all females) and 2 (0.3%, both females), respectively. Plasma XOR activities in 5 male subjects were below the median value of the 292 male subjects. In 12 (17.9%) of the 67 female subjects with uric acid ≤4.0 mg/dL, plasma XOR activities were above the upper quartile value of the 335 female subjects. Eleven of the 12 female subjects with high plasma XOR activity and a low uric acid level had liver dysfunction and/or insulin resistance. In conclusion, unexpected high plasma XOR activities were found in some female subjects with relatively low levels of uric acid. Measurement of plasma XOR activity may help to identify hypouricemic patients with a high risk for EIAKI.

Renal hypouricemia caused by novel compound heterozygous mutations in the SLC22A12 gene: a case report with literature review

Background

Renal hypouricemia (RHUC) is a heterogeneous genetic disorder that is characterized by decreased serum uric acid concentration and increased fractional excretion of uric acid. Previous reports have revealed many functional mutations in two urate transporter genes, SLC22A12 and/or SLC2A9, to be the causative genetic factors of this disorder. However, there are still unresolved patients, suggesting the existence of other causal genes or new mutations. Here, we report an RHUC patient with novel compound heterozygous mutations in the SLC22A12 gene.

Case presentation

A 27-year-old female presenting with recurrent hypouricemia during routine checkups was referred to our hospital. After obtaining the patient’s consent, both the patient and her healthy parents were analyzed using whole-exome sequencing (WES) and Sanger sequencing to discover and validate causal mutations, respectively. The prioritization protocol of WES screened out two mutations of c.269G > A/p.R90H and c.1289_1290insGG/p.M430fsX466, which are both located in the SLC22A12 gene, in the patient. Sanger sequencing further confirmed that the patient’s heterozygous c.269G > A/p.R90H mutation, which has been reported previously, derived from her mother, and the heterozygous c.1289_1290insGG/p.M430fsX466 mutation, which was found for the first time, derived from her father. p.R90H, which is highly conserved among different species, may decrease the stability of this domain and was considered to be almost damaging in silicon analysis. p.M430fsX466 lacks the last three transmembrane domains, including the tripeptide motif (S/T)XΦ (X = any amino acid and Φ = hydrophobic residue), at the C-terminal, which interact with scaffolding protein PDZK1 and thus will possibly lead to weak functioning of urate transport through the disruption of the “transporter complex” that is formed by URAT1 and PDZK1.

Conclusions

We report a Chinese patient with RHUC, which was caused by compound heterozygous mutations of the SLC22A12 gene, using WES and Sanger sequencing for the first time. Mutation-induced structural instability or malfunction of the urate transporter complex may be the main mechanisms for this hereditary disorder.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0595-8) contains supplementary material, which is available to authorized users.

Posterior reversible encephalopathy syndrome in a postpartum hemorrhagic woman without hypertension: A case report

RATIONALE

Posterior reversible encephalopathy syndrome (PRES), which diagnosis is based on clinical symptoms and radiological features, is a neurotoxic disease characterized by a set of clinical manifestations, such as seizure, headache, visual, and/or consciousness disturbance. It is the first case of PRES followed by postpartum hemorrhage (PPH) without underlying disease.

PATIENT CONCERNS

A 37-year-old healthy woman had PPH after caesarean section. Six days after delivery, headache occurred suddenly, followed by episodes of clonus seizure.

DIAGNOSES

Brain computed tomography showed ischemic stroke. However, magnetic resonance imaging revealed characteristics consistent with PRES.

INTERVENTIONS

The patient received phenytoin for seizure control.

OUTCOMES

Seizure was under good control over the following days. Three months later, repeated magnetic resonance imaging showed complete remission.

LESSONS

PRES may be triggered by PPH and is not necessarily secondary to typical predisposing factors such as hypertension or pre/eclampsia. Hormone fluctuation, increased blood pressure variation, and massive blood transfusion may be contributed to the development of PRES in our case. Also, it is necessary to rule out those life-threatening diseases, such as cavernoma hemorrhage, cerebral venous thrombosis, and ischemic stroke before the diagnosis of PRES.

A young patient of hereditary renal hypouricaemia presenting with exercise-induced rhabdomyolysis and acute kidney injury

Hereditary renal hypouricaemia (HRH) is a genetic disorder commonly associated with exercise-induced acute kidney injury (AKI). We report the case of a 19-year-old man who was admitted to hospital with exercise-induced AKI and who was subsequently shown to have HRH. We believe this to be the first description of a case of HRH co-presenting with rhabdomyolysis.

Effects of voluntary wheel running on the kidney at baseline and after ischaemia-reperfusion-induced acute kidney injury: a strain difference comparison

Exercise-induced vascular endothelial adaptations in the kidney are not well understood. Therefore, we investigated the impact of voluntary wheel running (VWR) on the abundance of endothelial nitric oxide synthase (eNOS) and extracellular superoxide dismutase (EC SOD), in kidney and lung, and other SOD isoforms and total antioxidant capacity (TAC), in kidney. We also determined whether VWR influences susceptibility to acute kidney injury (AKI). Male Sprague-Dawley and Fisher 344 rats, VWR or sedentary for 12 weeks, were subjected to AKI (uninephrectomy (UNX) and 35 min of left kidney ischaemia-24 h reperfusion, IR). We measured glomerular filtration rate (GFR) and renal plasma flow (RPF), and analysed renal structural injury. Running was comparable between strains and VWR reduced body weight. In Sprague-Dawley rats, VWR reduced eNOS and EC SOD, but increased Mn SOD in kidney. Similar changes were seen after 6 weeks of VWR in Sprague-Dawley rats. In Fisher 344 rats, VWR increased eNOS, all SOD isoforms and TAC in kidney. Both strains increased eNOS and EC SOD in lung with VWR. Compared to UNX alone, UNX-IR injury markedly reduced renal function for both strains; however, in the Sprague-Dawley rats, VWR exacerbated falls in GFR and RPF due to UNX-IR, whereas in the Fisher 344 rats, GFR was unaffected by VWR. Some indices of renal structural injury due to UNX-IR tended to be worse in SD vs. F344. Our study demonstrates that genetic background influences the effect of exercise on kidney eNOS and EC SOD, which in turn influence the susceptibility to AKI.

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.