Primary hyperoxaluria

A case of failure to thrive secondary to primary hyperoxaluria type 1

Primary hyperoxaluria type 1 is a rare genetic condition characterized by oxalate deposition in the kidneys. We report findings of an 8-month old female presenting with failure to thrive, poor oral intake, and kidney stones resulting in the diagnosis of primary hyperoxaluria type 1. The patient exhibits a unique presentation without renal failure at the time of diagnosis suggesting a previously unreported comorbidity in early stages of disease.

Outcomes of liver-kidney transplantation in patients with primary hyperoxaluria: an analysis of the scientific registry of transplant recipients database

Background

Primary hyperoxaluria (PH) is an inherited disease lacking of hepatic oxalic acid metabolic enzymes which could lead to irreverisible renal damage. Currently, liver–kidney transplantation is a curative but highly invasive therapy used to treat patients with PH. However, limited studies have focused on combined liver–kidney transplantation (CLKT) and sequential liver and kidney transplantation (SLKT) in patients with PH.

Methods

The present study included 201 patients with PH who received both liver and kidney transplants and who were listed on the Scientific Registry of Transplant Recipients from 1987 to 2018. According to the liver–kidney transplant procedure, patients were separated into a CLKT group and a SLKT group. Patient demographics and transplant outcomes were assessed in each group.

Results

Compared with the SLKT group, The CLKT group got a worse pretransplant dialysis condition in both the proportion of patients under pretransplant dialysis (p = 0.048) and the duration of the pretransplant dialysis (p < 0.001). The SLKT group got higher human leukocyte antigen mismatch score of kidney donor (p < 0.001) and liver donor (p = 0.003). The CLKT group utilized higher proportion (98.9%) of organs from a single deceased donor, while the SLKT group utilized 75.0% of organs from deceased liver donors and only 35.0% of organs from deceased kidney donors (p < 0.001). Kidney function measured by serum creatinine concentration before liver transplantation (LT) or CLKT was similar (p = 0.305) between groups. Patient survival was not significantly different between the two groups (p = 0.717) and liver (p = 0.685) and kidney (p = 0.464) graft outcomes were comparable between the two groups.

Conclusions

SLKT seems to be an alternative option with strict condition for CLKT, further exploration about the SLKT is still required.

Etiologies, Clinical Features, and Outcome of Oxalate Nephropathy

Background

Oxalate nephropathy is a potentially underestimated cause of kidney failure characterized by massive deposition of calcium oxalate crystals in the renal parenchyma. The prevalence and modes of presentation of this entity are ill-defined.

Methods

Here we report on the largest consecutive series of cases of adult oxalate nephropathy diagnosed on native kidney biopsies from January 2010 to December 2018 in the UCLouvain Kidney Disease Network.

Results

We screened 2265 native kidney biopsies and identified 22 cases (1%) of oxalate nephropathy. Patients had a mean age at diagnosis of 61 years (±20) and presented either with acute on chronic kidney disease (CKD) (62%) or with acute kidney injury (AKI) (38%). Mean serum creatinine at biopsy was 8.0 ± 4.5 mg/dl. Kidney biopsies showed abundant calcium oxalate crystal deposits, associated with acute interstitial nephritis and tubular necrosis, and variable degrees of interstitial fibrosis and tubular atrophy. Chronic pancreatitis and gastric bypass were the most common causes of oxalate nephropathy (48%). During a mean follow-up of 29 months, half of the patients (52%) progressed to kidney failure, all within the month following diagnosis. Higher serum creatinine level at presentation and interstitial fibrosis and tubular atrophy score were associated with progression to kidney failure.

Conclusion

Oxalate nephropathy is the cause of kidney disease in 1% of consecutive native kidney biopsies and typically presents as acute on CKD or AKI. The prognosis of the disease is poor, with a high rate of kidney failure within the first month after the diagnosis.

Cycloserine enantiomers are reversible inhibitors of human alanine:glyoxylate aminotransferase: implications for Primary Hyperoxaluria type 1

Peroxisomal alanine:glyoxylate aminotransferase (AGT) is responsible for glyoxylate detoxification in human liver and utilizes pyridoxal 5'-phosphate (PLP) as coenzyme. The deficit of AGT leads to Primary Hyperoxaluria Type I (PH1), a rare disease characterized by calcium oxalate stones deposition in the urinary tract as a consequence of glyoxylate accumulation. Most missense mutations cause AGT misfolding, as in the case of the G41R, which induces aggregation and proteolytic degradation. We have investigated the interaction of wild-type AGT and the pathogenic G41R variant with d-cycloserine (DCS, commercialized as Seromycin), a natural product used as a second-line treatment of multidrug-resistant tuberculosis, and its synthetic enantiomer l-cycloserine (LCS). In contrast with evidences previously reported on other PLP-enzymes, both ligands are AGT reversible inhibitors showing inhibition constants in the micromolar range. While LCS undergoes half-transamination generating a ketimine intermediate and behaves as a classical competitive inhibitor, DCS displays a time-dependent binding mainly generating an oxime intermediate. Using a mammalian cellular model, we found that DCS, but not LCS, is able to promote the correct folding of the G41R variant, as revealed by its increased specific activity and expression as a soluble protein. This effect also translates into an increased glyoxylate detoxification ability of cells expressing the variant upon treatment with DCS. Overall, our findings establish that DCS could play a role as pharmacological chaperone, thus suggesting a new line of intervention against PH1 based on a drug repositioning approach. To a widest extent, this strategy could be applied to other disease-causing mutations leading to AGT misfolding.

Investigational Therapies for Primary Hyperoxaluria

Recent years have brought exciting new insights in the field of primary hyperoxaluria (PH), both on a basic research level as well as through the progress of novel therapeutics in clinical development. To date, very few supportive measures are available for patients suffering from PH, which, together with the severity of the disorder, make disease management challenging. Basic and clinical research and development efforts range from correcting the underlying gene mutations, preventing calcium oxalate crystal-induced kidney damage, to the administration of probiotics favoring the intestinal secretion of excess oxalate. In this review, current advances in the development of those strategies are presented and discussed.

Sulforaphane elicts dual therapeutic effects on Renal Inflammatory Injury and crystal deposition in Calcium Oxalate Nephrocalcinosis

Intrarenal calcium oxalate (CaOx) crystals induce renal tubular epithelial cells (TECs) injury and inflammation, which involve Toll-like receptor 4 (TLR4)/interferon regulatory factor 1 (IRF1) signaling. Additionally, infiltrating macrophages (Mϕs) might influence intrarenal CaOx crystals and CaOx-induced renal injury. Although the roles of nuclear factor erythroid 2-related factor 2 (Nrf2) in regulating inflammation and macrophage polarization are well characterized, its potential mechanisms in regulating CaOx nephrocalcinosis remain undefined.

Methods: We used a Gene Expression Omnibus dataset to analyze gene-expression profiles. Luciferase reporter, western blot, quantitative polymerase chain reaction, immunofluorescence staining, fluorescence in situ hybridization, positron emission tomography computed tomography imaging, flow cytometry, and chromatin immunoprecipitation assays were employed to study the mechanism of miR-93-TLR4/IRF1 regulation by Nrf2. Anti-inflammatory activity and regulation of macrophage polarization by Nrf2 were investigated in vitro and in vivo.

Results: We found that stone-mediated kidney inflammation significantly affected stone growth, and that sulforaphane attenuated CaOx nephrocalcinosis-induced kidney injury and renal CaOx crystals deposition. Additionally, Nrf2 levels significantly increased and negatively correlated with TLR4 and IRF1 levels in a mouse model of CaOx nephrocalcinosis following sulforaphane treatment. Moreover, Nrf2 suppressed TLR4 and IRF1 levels and decreased M1-macrophage polarization which induced by supernatants from COM-stimulated TECs in vitro. In terms of mechanism, transcription factor analyses, microRNA microarray, and chromatin immunoprecipitation assays showed that Nrf2 exhibited positive transcriptional activation of miR-93-5p. In addition, Luciferase reporter, qRT-PCR, and western blot validated that miR-93-5p targets TLR4 and IRF1 mRNA. Furthermore, suppressed miR-93-5p expression partially reversed Nrf2-dependent TLR4/IRF1 downregulation.

Conclusions: The results suggested that sulforaphane might promote M2Mϕ polarization and inhibit CaOx nephrocalcinosis-induced inflammatory injury to renal tubular epithelial cells via the Nrf2-miR-93-TLR4/IRF1 pathway in vitro and in vivo.

Plasma oxalate: comparison of methodologies

Measurement of oxalate in the blood is essential for monitoring primary hyperoxaluria patients with progressive renal impairment and on dialysis prior to transplantation. As no external quality assurance scheme is available for this analyte, we conducted a sample exchange scheme between six laboratories specifically involved with the investigation of primary hyperoxaluria to compare results. The methodologies compared were gas chromatography/mass spectrometry (GCMS), ion chromatography with mass spectrometry (ICMS), and enzymatic methods using oxalate oxidase and spectrophotometry. Although individual laboratories performed well in terms of reproducibility and linearity, there was poor agreement (absolute values) between centres as illustrated by a longer-term comparison of patient results from two of the participating laboratories. This situation was only partly related to differences in calibration and mainly reflected the lower recoveries seen with the ultrafiltration of samples. These findings lead us to conclude that longitudinal monitoring of primary hyperoxaluria patients with deteriorating kidney function should be performed by a single consistent laboratory and the methodology used should always be defined. In addition, plasma oxalate concentrations reported in registry studies and those associated with the risk of systemic oxalosis in published studies need to be interpreted in light of the methodology used. A reference method and external quality assurance scheme for plasma oxalate analysis would be beneficial.

Plasma Oxalate as a Predictor of Kidney Function Decline in a Primary Hyperoxaluria Cohort

This retrospective analysis investigated plasma oxalate (POx) as a potential predictor of end-stage kidney disease (ESKD) among primary hyperoxaluria (PH) patients. PH patients with type 1, 2, and 3, age 2 or older, were identified in the Rare Kidney Stone Consortium (RKSC) PH Registry. Since POx increased with falling estimated glomerular filtration rate (eGFR), patients were stratified by chronic kidney disease (CKD) subgroups (stages 1, 2, 3a, and 3b). POx values were categorized into quartiles for analysis. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) for risk of ESKD were estimated using the Cox proportional hazards model with a time-dependent covariate. There were 118 patients in the CKD1 group (nine ESKD events during follow-up), 135 in the CKD 2 (29 events), 72 in CKD3a (34 events), and 45 patients in CKD 3b (31 events). During follow-up, POx Q4 was a significant predictor of ESKD compared to Q1 across CKD2 (HR 14.2, 95% CI 1.8–115), 3a (HR 13.7, 95% CI 3.0–62), and 3b stages (HR 5.2, 95% CI 1.1–25), p < 0.05 for all. Within each POx quartile, the ESKD rate was higher in Q4 compared to Q1–Q3. In conclusion, among patients with PH, higher POx concentration was a risk factor for ESKD, particularly in advanced CKD stages.

The association of calcium oxalate deposition in kidney allografts with graft and patient survival

BACKGROUND

Whether calcium oxalate (CaOx) deposition in kidney allografts following transplantation (Tx) adversely affects patient outcomes is uncertain, as are its associated risk factors.

METHODS

We performed a retrospective cohort study of patients who had kidney allograft biopsies performed within 3 months of Tx at Brigham and Women's Hospital and examined the association of CaOx deposition with the composite outcome of death or graft failure within 5 years.

RESULTS

Biopsies from 67 of 346 patients (19.4%) had CaOx deposition. In a multivariable logistic regression model, higher serum creatinine [odds ratio (OR) = 1.28 per mg/dL, 95% confidence interval (CI) 1.15-1.43], longer time on dialysis (OR = 1.11 per additional year, 95% CI 1.01-1.23) and diabetes (OR = 2.26, 95% CI 1.09-4.66) were found to be independently associated with CaOx deposition. CaOx deposition was strongly associated with delayed graft function (DGF; OR = 11.31, 95% CI 5.97-21.40), and with increased hazard of the composite outcome after adjusting for black recipient race, donor type, time on dialysis before Tx, diabetes and borderline or acute rejection (hazard ratio 1.90, 95% CI 1.13-3.20).

CONCLUSIONS

CaOx deposition is common in allografts with poor function and portends worse outcomes up to 5 years after Tx. The extent to which CaOx deposition may contribute to versus result from DGF, however, cannot be determined based on our retrospective and observational data. Future studies should examine whether reducing plasma and urine oxalate prevents CaOx deposition in the newly transplanted kidney and whether this has an effect on clinical outcomes.

Bone Disease in Nephropathic Cystinosis: Beyond Renal Osteodystrophy

Patients with chronic kidney disease (CKD) display significant mineral and bone disorders (CKD-MBD) that induce significant cardiovascular, growth and bone comorbidities. Nephropathic cystinosis is an inherited metabolic disorder caused by the lysosomal accumulation of cystine due to mutations in the CTNS gene encoding cystinosin, and leads to end-stage renal disease within the second decade. The cornerstone of management relies on cysteamine therapy to decrease lysosomal cystine accumulation in target organs. However, despite cysteamine therapy, patients display severe bone symptoms, and the concept of “cystinosis metabolic bone disease” is currently emerging. Even though its exact pathophysiology remains unclear, at least five distinct but complementary entities can explain bone impairment in addition to CKD-MBD: long-term consequences of renal Fanconi syndrome, malnutrition and copper deficiency, hormonal disturbances, myopathy, and intrinsic/iatrogenic bone defects. Direct effects of both CTNS mutation and cysteamine on osteoblasts and osteoclasts are described. Thus, the main objective of this manuscript is not only to provide a clinical update on bone disease in cystinosis, but also to summarize the current experimental evidence demonstrating a functional impairment of bone cells in this disease and to discuss new working hypotheses that deserve future research in the field.

Urinary monocyte chemoattractant protein 1 associated with calcium oxalate crystallization in patients with primary hyperoxaluria

Background

Patients with primary hyperoxaluria (PH) often develop kidney stones and chronic kidney disease. Noninvasive urine markers reflective of active kidney injury could be useful to gauge the effectiveness of ongoing treatments.

Methods

A panel of biomarkers that reflect different nephron sites and potential mechanisms of injury (clusterin, neutrophil gelatinase-associated lipocalin (NGAL), 8-isoprostane (8IP), monocyte-chemoattractant protein 1(MCP-1), liver-type fatty acid binding protein (L-FABP), heart-type fatty acid binding protein (H-FABP), and osteopontin (OPN)) were measured in 114 urine specimens from 30 PH patients over multiple visits. Generalized estimating equations were used to assess associations between biomarkers and 24 h urine excretions, calculated proximal tubular oxalate concentration (PTOx), and eGFR.

Results

Mean (±SD) age at first visit was 19.5 ± 16.6 years with an estimated glomerular filtration rate (eGFR) of 68.4 ± 21.0 ml/min/1.73m². After adjustment for age, sex, and eGFR, a higher urine MCP-1 concentration and MCP-1/creatinine ratio was positively associated with CaOx supersaturation (SS). Higher urine NGAL and NGAL/creatinine as well as OPN and OPN/creatinine were associated with higher eGFR. 8IP was negatively associated with PTOx and urinary Ox, but positively associated with CaOx SS.

Conclusion

In PH patients greater urine MCP-1 and 8IP excretion might reflect ongoing collecting tubule crystallization, while greater NGAL and OPN excretion may reflect preservation of kidney mass and function. CaOx crystals, rather than oxalate ion may mediate oxidative stress in hyperoxaluric conditions. Further studies are warranted to determine whether urine MCP-1 excretion predicts long term outcome or is altered in response to treatment.

Targeting kidney inflammation as a new therapy for primary hyperoxaluria?

The primary hyperoxalurias (PHs) are inborn errors of glyoxylate metabolism characterized by endogenous oxalate overproduction in the liver, and thus elevated urinary oxalate excretion. The urinary calcium-oxalate (CaOx) supersaturation and the continuous renal accumulation of insoluble CaOx crystals yield a progressive decline in renal function that often ends with renal failure. In PH Type 1 (AGXT mutated), the most frequent and severe condition, patients typically progress to end-stage renal disease (ESRD); in PH Type 2 (GRHPR mutated), 20% of patients develop ESRD, while only one patient with PH Type 3 (HOGA1 mutated) has been reported with ESRD so far. Patients with ESRD undergo frequent maintenance (haemo)dialysis treatment, and finally must receive a combined liver-kidney transplantation as the only curative treatment option available in PH Type 1. In experimental models using oxalate-enriched chow, CaOx crystals were bound to renal tubular cells, promoting a pro-inflammatory environment that led to fibrogenesis in the renal parenchyma by activation of a NACHT, LRR and PYD domains-containing protein 3 (NALP3)-dependent inflammasome in renal dendritic cells and macrophages. Chronic fibrogenesis progressively impaired renal function. Targeting the inflammatory response has recently been suggested as a therapeutic strategy to treat not only oxalate-induced crystalline nephropathies, but also those characterized by accumulation of cystine and urate in other organs. Herein, we summarize the pathogenesis of PH, revising the current knowledge of the CaOx-mediated inflammatory response in animal models of endogenous oxalate overproduction. Furthermore, we highlight the possibility of modifying the NLRP3-dependent inflammasome as a new and complementary therapeutic strategy to treat this severe and devastating kidney disease.

Liver Transplantation Outcome in Iranian Patients with Primary Hyperoxaluria; Risks and Perspectives

Background: Primary hyperoxaluria (PH) is an autosomal genetic disorder characterized by abnormal glycosylate metabolism. Objectives: The aim of the present study was to assess post-transplant complications and survival of patients with PH who underwent either liver transplantation (LT) or simultaneous liver-kidney transplantation. Methods: 18 patients with established PH diagnosis who underwent LT or simultaneous liver-kidney transplantation in the Transplantation Center of Shiraz, Iran, were included. Demographic and clinical data were collected by reviewing clinical documents and interviews by the patients. The patients were prospectively followed up for the occurrence of the intended outcomes. The data was analyzed by SPSS 18 software. Results: 12 patients (66.7%) were male, and six patients (33.3%) were female with the age range of 3 to 32 years (mean age, 18.89 ± 7.42 years). The patients’ weight ranged from 13 to 73 kg (mean weight, 47.39 ± 17.18 kg). Polyuria was the most common clinical presentation (11/18), and end-stage renal disease and hemodialysis were noted in 13 and 12 patients pre-transplantation, respectively. Hepatic arterial thrombosis, biliary complications, infections, and graft rejection comprised the most frequent post-transplant complications. Of 18 patients, seven patients (38.9%) died due to various complications during one year after transplant. Based on the Kaplan-Meier analysis, the survival rate was 61.1% at the end of the study. The mean survival time was 46.25 ± 18.6 months. The patients succumbed to the disease died within 3 to 320 days (mean, 61.57 days) post-surgery. Conclusions: LT seems an effective intervention in prevention of kidney failure in patients with PH.

Bone oxaloma-a localized manifestation of bone oxalosis

Oxalosis is a metabolic disorder characterized by the accumulation of calcium oxalate deposits in various organ systems. Bone oxalosis is a systemic manifestation of oxalosis, in which calcium oxalate deposits accumulate in the skeletal system. This report describes a 69-year-old female patient who presented with right hip pain and was later found to have an osseous mass-like lesion in the right proximal femur, with radiographic findings resembling those of a benign bone tumor. CT-guided biopsy and surgical biopsy showed that the mass had pathologic findings typical of bone oxalosis. Because the patient had no predisposing factors for systemic oxalosis and had no hyperoxalemia or hyperoxaluria, she could be diagnosed with localized bone oxalate deposition disease or bone oxaloma rather than bone oxalosis. This is the first report of this clinical entity to present as a benign-appearing bone mass and without any predisposing systemic causes.

Inhibitors of Calcium Oxalate Crystallization for the Treatment of Oxalate Nephropathies

Calcium oxalate (CaOx) crystal-induced nephropathies comprise a range of kidney disorders, for which there are no efficient pharmacological treatments. Although CaOx crystallization inhibitors have been suggested as a therapeutic modality already decades ago, limited progress has been made in the discovery of potent molecules with efficacy in animal disease models. Herein, an image-based machine learning approach to systematically screen chemically modified myo-inositol hexakisphosphate (IP6) analogues is utilized, which enables the identification of a highly active divalent inositol phosphate molecule. To date, this is the first molecule shown to completely inhibit the crystallization process in the nanomolar range, reduce crystal-cell interactions, thereby preventing CaOx-induced transcriptomic changes, and decrease renal CaOx deposition and kidney injury in a mouse model of hyperoxaluria. In conclusion, IP6 analogues based on such a scaffold may represent a new treatment option for CaOx nephropathies.

Characterising a healthy adult with a rare HAO1 knockout to support a therapeutic strategy for primary hyperoxaluria

By sequencing autozygous human populations, we identified a healthy adult woman with lifelong complete knockout of HAO1 (expected ~1 in 30 million outbred people). HAO1 (glycolate oxidase) silencing is the mechanism of lumasiran, an investigational RNA interference therapeutic for primary hyperoxaluria type 1. Her plasma glycolate levels were 12 times, and urinary glycolate 6 times, the upper limit of normal observed in healthy reference individuals (n = 67). Plasma metabolomics and lipidomics (1871 biochemicals) revealed 18 markedly elevated biochemicals (>5 sd outliers versus n = 25 controls) suggesting additional HAO1 effects. Comparison with lumasiran preclinical and clinical trial data suggested she has <2% residual glycolate oxidase activity. Cell line p.Leu333SerfsTer4 expression showed markedly reduced HAO1 protein levels and cellular protein mis-localisation. In this woman, lifelong HAO1 knockout is safe and without clinical phenotype, de-risking a therapeutic approach and informing therapeutic mechanisms. Unlocking evidence from the diversity of human genetic variation can facilitate drug development.

End Points for Clinical Trials in Primary Hyperoxaluria

Patients with primary hyperoxaluria experience kidney stones from a young age and can develop progressive oxalate nephropathy. Progression to kidney failure often develops over a number of years, and is associated with systemic oxalosis, intensive dialysis, and often combined kidney and liver transplantation. There are no therapies approved by the Food and Drug Association. Thus, the Kidney Health Initiative, in partnership with the Oxalosis and Hyperoxaluria Foundation, initiated a project to identify end points for clinical trials. A workgroup of physicians, scientists, patients with primary hyperoxaluria, industry, and United States regulators critically examined the published literature for clinical outcomes and potential surrogate end points that could be used to evaluate new treatments. Kidney stones, change in eGFR, urine oxalate, and plasma oxalate were the strongest candidate end points. Kidney stones affect how patients with primary hyperoxaluria feel and function, but standards for measurement and monitoring are lacking. Primary hyperoxaluria registry data suggest that eGFR decline in most patients is gradual, but can be unpredictable. Epidemiologic data show a strong relationship between urine oxalate and long-term kidney function loss. Urine oxalate is reasonably likely to predict clinical benefit, due to its causal role in stone formation and kidney damage in CKD stages 1-3a, and plasma oxalate is likely associated with risk of systemic oxalosis in CKD 3b-5. Change in slope of eGFR could be considered the equivalent of a clinically meaningful end point in support of traditional approval. A substantial change in urine oxalate as a surrogate end point could support traditional approval in patients with primary hyperoxaluria type 1 and CKD stages 1-3a. A substantial change in markedly elevated plasma oxalate could support accelerated approval in patients with primary hyperoxaluria and CKD stages 3b-5. Primary hyperoxaluria type 1 accounts for the preponderance of available data, thus heavily influences the conclusions. Addressing gaps in data will further facilitate testing of promising new treatments, accelerating improved outcomes for patients with primary hyperoxaluria.

[Nephrolithiasis: From mechanisms to preventive medical treatment]

Renal lithiasis is a frequent pathology (prevalence ranging from 10 to 12% in France) and a recurrent condition. It is associated with chronic kidney disease and is responsible for 2 to 3% of cases of end-stage renal disease, especially if it is associated with nephrocalcinosis and/or is part of a monogenic disease (1.6% of lithiasis in adults, including 1% of cystinuria). In order to understand the pathophysiology of the nephrolithiasis, the analysis of stones (morphological and by infrared spectrophotometry) as well as a minimal biological evaluation including crystalluria must be carried out. Calcium nephrolithiasis is the most common form (more than 80%). Its preventive medical treatment relies on simple hygienic dietetics: non-alkaline hyperdiuresis greater than 2liters/day, normalization of calcium intakes (1g/day to be distributed over the three meals), restriction of sodium intakes (6g/day) and of protein intakes (0.8-1g/kg of theoretical weight/day), and avoidance of foods rich in oxalate. If there is a hypercalciuria (greater than 0.1mmol/kg of theoretical weight/day with normal calcium intakes), its mechanism should be explored with an oral calcium load test. In the absence of primary hyperparathyroidism, thiazide diuretics can be prescribed, taking care to prevent hypokalemia and iatrogenic hypocitraturia. The treatment of uric acid lithiasis includes alkaline hyperdiuresis (urinary pH 6.2 to 6.8). Allopurinol is only justified if the urinary excretion of uric acid exceeds 4mmol/day. With a well-managed medical treatment, more than 80% of recurrent lithiasis can be stopped, making nephrolithiasis one of the kidney diseases the more accessible to the preventive medical treatment.

Calciphylaxis or vascular oxalosis?

We report the case of a 31-year-old female with primary hyperoxaluria type 1 with end-stage kidney disease who developed severe peripheral vascular disease leading to limb amputation initially thought to be secondary to calciphylaxis. However, polarized review of the pathologic specimen revealed calcium oxalate deposition in the lumen of blood vessels. This unusual presentation of systemic oxalosis demonstrates the adverse consequences of elevations of serum oxalate in patients with hyperoxaluria and that levels can acutely worsen with abrupt onset of kidney failure.

Induction of retinopathy by fibrillar oxalate assemblies

The formation of metabolite fibrillar assemblies represents a paradigm shift in the study of human metabolic disorders. Yet, direct clinical relevance has been attributed only to metabolite crystals. A notable example for metabolite crystallization is calcium oxalate crystals observed in various diseases, including primary hyperoxaluria. We unexpectedly observed retinal damage among young hyperoxaluria patients in the absence of crystals. Exploring the possible formation of alternative supramolecular organizations and their biological role, here we show that oxalate can form ordered fibrils with no associated calcium. These fibrils inflict intense retinal cytotoxicity in cultured cells. A rat model injected with oxalate fibrils recaptures patterns of retinal dysfunction observed in patients. Antibodies purified from hyperoxaluria patient sera recognize oxalate fibrils regardless of the presence of calcium. These findings highlight a new molecular basis for oxalate-associated disease, and to our knowledge provide the first direct clinical indication for the pathogenic role of metabolite fibrillar assemblies.

Oxalobacter formigenes treatment combined with intensive dialysis lowers plasma oxalate and halts disease progression in a patient with severe infantile oxalosis

BACKGROUND

Infantile oxalosis, the most devastating form of primary hyperoxaluria type 1 (PH1), often leads to end-stage renal disease (ESRD) during the first weeks to months of life.

CASE-DIAGNOSIS

Here, we report the outcome of the therapeutic use of Oxalobacter formigenes (Oxabact OC5; OxThera AB, Stockholm, Sweden) in a female infant with PH1 who exhibited severely elevated plasma oxalate (Pox) levels, pronounced nephrocalcinosis, anuretic end-stage renal disease, and retinal oxalate deposits. Following the diagnosis of PH1 at an age of 8 weeks, a combined regimen of daily peritoneal dialysis, daily pyridoxine treatment and hemodialysis (3 times a week) was unable to reduce the pronounced hyperoxalemia. After the addition of Oxalobacter formigenes therapy to the otherwise unchanged treatment regimen, Pox levels first stabilized and subsequently declined from 130 μmol/L to around 80 μmol/L. Nephrocalcinosis and retinal deposits stabilized. Oxalobacter formigenes treatment was well-tolerated and no related adverse events were observed. The patient showed nearly age-appropriate growth and development and received successful combined liver-kidney transplantation at the age of two years.

CONCLUSIONS

Treatment with O. formigenes combined with intensive dialysis led to reduction of Pox, stabilization of systemic oxalosis, and improvement in the clinical disease course. O. formigenes treatment may be an option for reduction of oxalosis in infantile patients with insufficient response to conservative treatments until combined liver-kidney transplantation can be performed.

Stiripentol fails to lower plasma oxalate in a dialysis-dependent PH1 patient

BACKGROUND

Primary hyperoxaluria type 1 (PH1) is a multisystemic metabolic disorder caused by an excessive production of oxalate by the liver. The majority of patients presenting in early infancy have end-stage renal disease (ESRD). While awaiting the results of sRNAi trials, the current standard treatment is combined liver-kidney transplantation. Recently, Stiripentol has been reported as a promising drug in the treatment of primary hyperoxaluria by reducing urinary oxalate (U_Ox). Stiripentol is an anti-convulsive drug used in the treatment of children suffering from Dravet syndrome. It causes blockage of the last step in oxalate production by inhibition of hepatic lactate dehydrogenase 5 (LDH5).

CASE

We administered Stiripentol as compassionate use in an anuric infant with dialysis-dependent PH1 over a period of 4 months. Although achieving plasma concentrations of Stiripentol that were recently reported to lower U_Ox excretion, we did not observe significant reduction to plasma oxalate concentrations (P_Ox).

CONCLUSION

We conclude that Stiripentol may not be useful to reduce P_Ox in PH patients with advanced chronic kidney disease (CKD), but larger studies are needed to confirm this finding.

Pre-, post- or no acidification of urine samples for calcium analysis: does it matter?

Background Measuring 24 h-urine calcium concentration is essential to evaluate calcium metabolism and excretion. Manufacturers recommend acidifying the urine before a measurement to ensure calcium solubility, but the literature offers controversial information on this pre-analytical treatment. The objectives of the study were (1) to compare pre-acidification (during urine collection) versus post-acidification (in the laboratory), and (2) to evaluate the impact of acidification on urinary calcium measurements in a large cohort. Methods We evaluated the effects of pre- and post-acidification on 24-h urine samples collected from 10 healthy volunteers. We further studied the impact of acidification on the calcium results for 567 urine samples from routine laboratory practice, including 46 hypercalciuria (≥7.5 mmol/24 h) samples. Results Calciuria values in healthy volunteers ranged from 0.6 to 12.5 mmol/24 h, and no statistical significance was found between non-acidified, pre-acidified and post-acidified conditions. A comparison of the values (ranging from 0.21 to 29.32 mmol/L) for 567 urine samples before and after acidification indicated 25 samples (4.4%) with analytical differences outside limits of acceptance. The bias observed for these deviant values ranged from -3.07 to 1.32 mmol/L; no patient was re-classified as hypercalciuric after acidification, and three patients with hypercalciuria were classified as normocalciuric after acidification. These three deviant patients represent 6.5% of hypercalciuric patients. Conclusions Our results indicate that pre- and post-acidification of urine is not necessary prior to routine calcium analysis.

Oxalate retinopathy is irreversible despite early combined liver-kidney transplantation in primary hyperoxaluria type 1

In primary hyperoxaluria type 1 (PH1), systemic oxalate deposition (oxalosis) in end-stage renal disease (ESRD) is associated with high morbidity and mortality, particularly in children with infantile oxalosis (IO). Combined liver and kidney transplantation (CLKT) is the only curative treatment option in these patients. After CLKT, systemic oxalosis decreases continuously, although only insufficient data are available regarding oxalate retinopathy (ROx), leading to severe visual impairment. We analyzed long-term follow-up data of ROx in 13 patients undergoing CLKT for PH1 at our center between 1998 and 2018. Age at transplantation was 1.3-14.2 years, including nine patients with IO. We performed visual acuity testing, slit lamp investigation, funduscopy, fundus photography, and spectral-domain optical coherence tomography (SD-OCT) imaging. Severe (grade 2-4) ROx was present in all nine children with IO but not in the four patients developing ESRD in adolescence. A significant negative correlation was found between age at onset of ESRD and grade of ROx (r = -0.66; P < .001). Notably, follow-up assessment after CLKT demonstrated no regression of ROx after a median of 5.3 years (range 0.6-14). The data show that despite early CLKT in IO, ROx is irreversible and the concomitant visual deterioration occurs prior to transplantation.

Subclinical myocardial disease in patients with primary hyperoxaluria and preserved left ventricular ejection fraction: a two-dimensional speckle-tracking imaging study

BACKGROUND

Primary hyperoxaluria (PH) is characterized by progressive chronic kidney disease (CKD) and systemic oxalate deposition. Myocardial dysfunction might be present early in the course of the disease. However, this hypothesis has not yet been tested in the PH population. Therefore, we aimed to determine whether strain imaging using two-dimensional speckle tracking echocardiography (2D-STE) might detect subclinical myocardial disease in otherwise asymptomatic PH patients.

METHODS

Prospective study of pediatric and adolescent PH patients with preserved LV ejection fraction (LV EF) and without renal replacement therapy. Subjects underwent conventional echocardiography and 2D-STE. Global (GLS) and segmental peak systolic LV longitudinal strain (LS) measurements were obtained. Data were compared with age- and gender-matched controls, and Z-scores were calculated as appropriate.

RESULTS

Fifteen PH patients (age 14.1 ± 5.9 years; 13/15 in CKD stages 1-2) were studied. Although LV EF was preserved (63 ± 6%) in patients, GLS was significantly impaired (GLS - 17.1 ± 2.2% vs - 22.4 ± 1.9%, p < 0.001). This was mainly due to decreased LS values in the apical segments (p < 0.05). Echocardiographic indices of ventricular wall thickness were significantly increased in patients compared to controls (all p < 0.03). GLS correlated significantly with Z-scores of diastolic interventricular wall thickness (r = - 0.57, p = 0.025) and moderately with serum creatinine levels (r = 0.53, p = 0.044). No correlation was found between GLS and blood pressure measurements.

CONCLUSIONS

Subclinical myocardial disease is already present early in the course of disease in PH patients with preserved LV EF and some degree of renal dysfunction, but without overt systemic oxalosis. Current recommendations to screen only PH patients with advanced CKD for cardiac disease should be revised accordingly.

Diet and Adaptive Evolution of Alanine-Glyoxylate Aminotransferase Mitochondrial Targeting in Birds

Adaptations to different diets represent a hallmark of animal diversity. The diets of birds are highly variable, making them an excellent model system for studying adaptive evolution driven by dietary changes. To test whether molecular adaptations to diet have occurred during the evolution of birds, we examined a dietary enzyme alanine-glyoxylate aminotransferase (AGT), which tends to target mitochondria in carnivorous mammals, peroxisomes in herbivorous mammals, and both mitochondria and peroxisomes in omnivorous mammals. A total of 31 bird species were examined in this study, which included representatives of most major avian lineages. Of these, 29 have an intact mitochondrial targeting sequence (MTS) of AGT. This finding is in stark contrast to mammals, which showed a number of independent losses of the MTS. Our cell-based functional assays revealed that the efficiency of AGT mitochondrial targeting was greatly reduced in unrelated lineages of granivorous birds, yet it tended to be high in insectivorous and carnivorous lineages. Furthermore, we found that proportions of animal tissue in avian diets were positively correlated with mitochondrial targeting efficiencies that were experimentally determined, but not with those that were computationally predicted. Adaptive evolution of AGT mitochondrial targeting in birds was further supported by the detection of positive selection on MTS regions. Our study contributes to the understanding of how diet drives molecular adaptations in animals, and suggests that caution must be taken when computationally predicting protein subcellular targeting.

Nine novel HOGA1 gene mutations identified in primary hyperoxaluria type 3 and distinct clinical and biochemical characteristics in Chinese children

BACKGROUND

Primary hyperoxaluria type 3 (PH3) is characterized by mutations in the 4-hydroxy-2-oxoglutarate aldolase (HOGA1) gene. PH3 patients are thought to present with a less severe phenotype than PH1 and PH2 patients. However, the clinical characteristics of PH3 patients have yet to be defined in sufficient detail. The aims of this study were to report HOGA1 mutations of PH3 in Chinese children, and to analyze the genotype and clinical characteristics of these PH3 patients.

METHODS

Genetic analysis (targeted gene panel-based and/or whole-exome sequencing) of HOGA1 was performed in 52 patients with a high suspicion of PH3, and DNA was obtained from the patient and both the parents. The clinical, biochemical, and genetic data of these 12 patients identified with HOGA1 mutations were subsequently retrospectively reviewed.

RESULTS

These 12 patients were identified with HOGA1 mutation. The median onset of clinical symptoms was 18.25 (range 5-38) months. In total, 14 different mutations were identified including 9 novel mutations in these 12 patients with PH3. All of these 12 patients initially presented with urolithiasis, and 3 patients among them comorbid urinary tract infection (UTI) as another initial symptom. Ten patients experienced hyperoxaluria (average oxalate 0.77 mmol/1.73 m²/24h). In contrast, urine calcium excretion was normal in 8 patients and 2 patients with hypercalciuria (urine calcium > 4 mg/kg/24 h). At the time of diagnosis, estimated GFR was 155.6 ml/min per 1.73 m², and at last follow-up time (17.3 months later from diagnosis on average), estimated GFR was 157.5 ml/min per 1.73 m². To date, none of the patients has impaired renal function based on and progressed to ESRD.

CONCLUSIONS

We found that PH3 was significantly diagnosed in our urolithiasis patients during childhood. Nine novel HOGA1 mutations were identified in association with PH3, which provide a first-line investigation in Chinese PH3 patients. The eGFR was normal in all children with PH3. This finding is in contrast to the early impairment of renal function in PH1 and PH2.

The Ocular Phenotype in Primary Hyperoxaluria Type 1

PURPOSE

To investigate ophthalmic features in a large group of patients with primary hyperoxaluria type 1 (PH1) and to determine the relation between ocular involvement and systemic disease severity.

DESIGN

Retrospective, cross-sectional, multicenter study of the OxalEurope Registry Network.

METHODS

Sixty-eight patients with PH1 were included. Infantile PH1 was diagnosed in 12 patients, and non-infantile PH1 was diagnosed in 56 patients (17 with end-stage renal disease). Ophthalmic examination included best corrected visual acuity (BCVA) testing and multimodal retinal imaging, including fundus photography and optical coherence tomography (OCT). In selected cases, fundus autofluorescence imaging was performed.

RESULTS

All eyes (n = 24) of infantile PH1 patients revealed severe retinal alterations and oxalate deposits, including macular crystals and hyperpigmentations (n = 9, 38%), and subretinal fibrosis (n = 15, 63%) with (n = 7, 47%) or without (n = 8; 53%) associated chronic retinal edema. In 9 eyes (38%, all with subretinal fibrosis), BCVA was significantly reduced (<20/50 Snellen equivalent). In contrast, all eyes (n = 112) of patients with non-infantile PH1 had a BCVA in the normal range (median, 20/20). Only 6 patients with non-infantile disease (11%, all with end-stage renal disease) showed mild, likely PH1-related retinal features. These deposits appeared as focal hyperreflective subretinal lesions on OCT imaging and were hyperautofluorescent on autofluorescence images.

CONCLUSIONS

Severe ocular alterations occur in infantile cases, whereas mild or no ocular alterations are typical in non-infantile PH1 patients. The natural history of (sub)retinal oxalate deposits, the pathogenesis of subretinal fibrosis, and exact factors influencing the overall severity of ocular disease manifestation remain to be determined.

Patients with primary hyperoxaluria type 2 have significant morbidity and require careful follow-up

Primary hyperoxaluria type 2 is a rare inherited disorder of glyoxylate metabolism causing nephrocalcinosis, renal stone formation and ultimately kidney failure. Previously, primary hyperoxaluria type 2 was considered to have a more favorable prognosis than primary hyperoxaluria type 1, but earlier reports are limited by low patient numbers and short follow up periods. Here we report on the clinical, genetic, and biochemical findings from the largest cohort of patients with primary hyperoxaluria type 2, obtained by a retrospective record review of genetically confirmed cases in the OxalEurope registry, a dataset containing 101 patients from eleven countries. Median follow up was 12.4 years. Median ages at first symptom and diagnosis for index cases were 3.2 years and 8.0 years, respectively. Urolithiasis was the most common presenting feature (82.8% of patients). Genetic analysis revealed 18 novel mutations in the GRHPR gene. Of 238 spot-urine analyses, 23 (9.7%) were within the normal range for oxalate as compared to less than 4% of 24-hour urine collections. Median intra-individual variation of 24-hour oxalate excretion was substantial (34.1%). At time of review, 12 patients were lost to follow-up; 45 of the remaining 89 patients experienced chronic kidney disease stage 2 or greater and 22 patients had reached stage 5. Median renal survival was 43.3 years, including 15 kidney transplantations in 11 patients (1 combined with liver transplantation). Renal outcome did not correlate with genotype, biochemical parameters or initially present nephrocalcinosis. Thus, primary hyperoxaluria type 2 is a disease with significant morbidity. Accurate diagnosis by 24-hour urine analysis and genetic testing are required with careful follow-up.

Metabolite Repair Enzymes Control Metabolic Damage in Glycolysis

Hundreds of metabolic enzymes work together smoothly in a cell. These enzymes are highly specific. Nevertheless, under physiological conditions, many perform side-reactions at low rates, producing potentially toxic side-products. An increasing number of metabolite repair enzymes are being discovered that serve to eliminate these noncanonical metabolites. Some of these enzymes are extraordinarily conserved, and their deficiency can lead to diseases in humans or embryonic lethality in mice, indicating their central role in cellular metabolism. We discuss how metabolite repair enzymes eliminate glycolytic side-products and prevent negative interference within and beyond this core metabolic pathway. Extrapolating from the number of metabolite repair enzymes involved in glycolysis, hundreds more likely remain to be discovered that protect a wide range of metabolic pathways.

Crystal deposition triggers tubule dilation that accelerates cystogenesis in polycystic kidney disease

The rate of disease progression in autosomal-dominant (AD) polycystic kidney disease (PKD) exhibits high intra-familial variability suggesting that environmental factors may play a role. We hypothesized that a prevalent form of renal insult may accelerate cystic progression and investigated tubular crystal deposition. We report that calcium oxalate (CaOx) crystal deposition led to rapid tubule dilation, activation of PKD-associated signaling pathways, and hypertrophy in tubule segments along the affected nephrons. Blocking mTOR signaling blunted this response and inhibited efficient excretion of lodged crystals. This mechanism of "flushing out" crystals by purposefully dilating renal tubules has not previously been recognized. Challenging PKD rat models with CaOx crystal deposition, or inducing calcium phosphate deposition by increasing dietary phosphorous intake, led to increased cystogenesis and disease progression. In a cohort of ADPKD patients, lower levels of urinary excretion of citrate, an endogenous inhibitor of calcium crystal formation, correlated with increased disease severity. These results suggest that PKD progression may be accelerated by commonly occurring renal crystal deposition which could be therapeutically controlled by relatively simple measures.

A Short Review on the Relationships Between Nephrolithiasis and Myocardial Infarction

The interaction between organs is a crucial part of modern medicine. As a very prerequisite to manage a disease, practitioners should have a full awareness of the related organs. Kidney and heart are two vital organs that are closely interconnected in various fields. These two organs have a lot of common risk factors for making a person unhealthy; therefore, if you prevent the disease in one of them, the other's morbidity might be alleviated as well. Among them, nephrolithiasis and myocardial infarction (MI) have more risk factors in common, and both could be fatal. Also, these two diseases are important regarding the prevalence, incidence, and burden of disease. Some studies confirm the relationship between MI and nephrolithiasis; however, further researches are needed to discover the exact direction of their relationship. The present review aims to explain the mechanism of MI and nephrolithiasis; clarify the relationship between these two disease based on physiological, pathological, and clinical studies; and propose some solutions for the prevention and treatment of such diseases.

The experience of combined and sequential liver and kidney transplantation from a single living donor in patients with primary hyperoxaluria type 1

LKT is the only effective treatment for PH1 because it replaces both the source (liver) and the target (kidney) of the disease. Most studies report on LKT in patients with PH1 from deceased donors. This study reports on five patients who underwent LKT from a single living  donor between April 2017 and March 2018. Combined LKT was performed for 1 patient and sequential LKT for the remainder. The median age of the patients at the time of diagnosis and transplantation was 5.5 (0.3-18) and 10 (6-21) years, respectively. All patients received left lateral liver segment transplantation, except one patient who received right liver lobe transplantation. No liver graft loss was observed, and liver function tests were stable at the final evaluation of all patients. Renal function tests of the patients were also stable at the final assessment, except for the young adult patient. None of the patients suffered from acute rejection. One patient died at the second month following liver transplantation due to severe pneumonia and sepsis. This study concludes that combined or sequential LKT from a single living donor can be safely performed and provides encouraging results for even the youngest and smallest patients with PH1.

Reduction in urinary oxalate excretion in mouse models of Primary Hyperoxaluria by RNA interference inhibition of liver lactate dehydrogenase activity

The Primary Hyperoxaluria's (PH) are rare autosomal recessive disorders characterized by elevated oxalate production. PH patients suffer recurrent calcium oxalate kidney stone disease, and in severe cases end stage renal disease. Recent evidence has shown that RNA interference may be a suitable approach to reduce oxalate production in PH patients by knocking down key enzymes involved in hepatic oxalate synthesis. In the current study, wild type mice and mouse models of PH1 (AGT KO) and PH2 (GR KO) were treated with siRNA that targets hepatic LDHA. Although siRNA treatment substantially reduced urinary oxalate excretion [75%] in AGT KO animals, there was a relatively modest reduction [32%] in GR KO animals. Plasma and liver pyruvate levels significantly increased with siRNA treatment and liver organic acid analysis indicated significant changes in a number of glycolytic and TCA cycle metabolites, consistent with the known role of LDHA in metabolism. However, siRNA dosing data suggest that it may be possible to identify a dose that limits changes in liver organic acid levels, while maintaining a desired effect of reducing glyoxylate to oxalate synthesis. These results suggest that RNAi mediated reduction of hepatic LDHA may be an effective strategy to reduce oxalate synthesis in PH, and further analysis of its metabolic effects should be explored. Additional studies should also clarify in GR KO animals whether there are alternate enzymatic pathways in the liver to create oxalate and whether tissues other than liver contribute significantly to oxalate production.

LncRNA-miRNA-mRNA expression variation profile in the urine of calcium oxalate stone patients

Background

To explore long-non-coding RNA (lncRNA), microRNA (miRNA) and messenger RNA (mRNA) expression profiles and their biological functions in the urine samples in calcium oxalate (CaOx) patients.

Methods

Five CaOx kidney stone patients were recruited in CaOx stone group and six healthy people were included as control group, whose midstream morning urine was collected before the patients were given any medicine on admission. After total RNA was extracted from urine, microarray of miRNA, mRNA and lncRNA were applied to explore their expression variation. Gene ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed to reveal the gene functions of the dysregulated lncRNA-associated competing endogenous RNA (ceRNA) network. Quantitative real-time PCR were performed on HK-2 cells treated with sodium oxalate (NaOx) to further screen out the differentially expression profiles of these RNAs.

Results

A total of nine miRNAs, 883 mRNAs and 1002 lncRNAs were differentially expressed in urine of CaOx patients compared with normal population. GO analysis revealed that most of mRNAs from ceRNA network were enriched in terms of respiratory burst, regulation of mitophagy, and protein kinase regulator activity. KEGG pathway analysis of these genes related to ceRNA network highlight their critical role in pentose phosphate pathway, glyoxylate and dicarboxylate metabolism, and Janus kinase/signal transducer and activator of transcription (JAK-STAT) signaling pathway. Five miRNAs (miR-6796-3p, miR-30d-5p, miR-3192–3p, miR-518b and miR-6776-3p), four mRNAs (NT5E, CDH4, CLEC14A, CCNL1) and six lncRNAs (lnc-TIGD1L2–3, lnc-KIN-1, lnc-FAM72B-4, lnc-EVI5L-1, lnc-SERPINI1–2, lnc-MB-6) from the HK-2 cells induced by NaOx were consistent with the expression changes of microarray results.

Conclusion

The differential expressed miRNAs, mRNAs and lncRNAs may be associated with numerous variations of the signaling pathways or regulation of metabolism and kinase activity, providing potential biomarkers for early diagnosis of urolithiasis and new basis for further research of urolithiasis mechanism.

Electronic supplementary material

The online version of this article (10.1186/s12920-019-0502-y) contains supplementary material, which is available to authorized users.

Stiripentol protects against calcium oxalate nephrolithiasis and ethylene glycol poisoning

Increased urinary oxalate excretion (hyperoxaluria) promotes the formation of calcium oxalate crystals. Monogenic diseases due to hepatic enzymes deficiency result in chronic hyperoxaluria, promoting end-stage renal disease in children and young adults. Ethylene glycol poisoning also results in hyperoxaluria promoting acute renal failure and frequently death. Stiripentol is an antiepileptic drug used to treat children affected by Dravet syndrome, possibly by inhibiting neuronal lactate dehydrogenase 5 isoenzyme. As this isoenzyme is also the last step of hepatic oxalate production, we hypothesized that Stiripentol would potentially reduce hepatic oxalate production and urine oxalate excretion. In vitro, Stiripentol decreased in a dose-dependent manner the synthesis of oxalate by hepatocytes. In vivo, Stiripentol oral administration reduced significantly urine oxalate excretion in rats. Stiripentol protected kidneys against calcium oxalate crystal deposits in acute ethylene glycol intoxication and chronic calcium oxalate nephropathy models. In both models, Stiripentol improved significantly renal function. Patients affected by Dravet syndrome and treated with Stiripentol had a lower urine oxalate excretion than control patients. A young girl affected by severe type I hyperoxaluria received Stiripentol for several weeks: urine oxalate excretion decreased by two-thirds. Stiripentol is a promising potential therapy against genetic hyperoxaluria and ethylene glycol poisoning.

Association of Urinary Oxalate Excretion With the Risk of Chronic Kidney Disease Progression

IMPORTANCE

Oxalate is a potentially toxic terminal metabolite that is eliminated primarily by the kidneys. Oxalate nephropathy is a well-known complication of rare genetic disorders and enteric hyperoxaluria, but oxalate has not been investigated as a potential contributor to more common forms of chronic kidney disease (CKD).

OBJECTIVE

To assess whether urinary oxalate excretion is a risk factor for more rapid progression of CKD toward kidney failure.

DESIGN, SETTING, AND PARTICIPANTS

This prospective cohort study assessed 3123 participants with stages 2 to 4 CKD who enrolled in the Chronic Renal Insufficiency Cohort study from June 1, 2003, to September 30, 2008. Data analysis was performed from October 24, 2017, to June 17, 2018.

EXPOSURES

Twenty-four-hour urinary oxalate excretion.

MAIN OUTCOMES AND MEASURES

A 50% decline in estimated glomerular filtration rate (eGFR) and end-stage renal disease (ESRD).

RESULTS

This study included 3123 participants (mean [SD] age, 59.1 [10.6] years; 1414 [45.3%] female; 1423 [45.6%] white). Mean (SD) eGFR at the time of 24-hour urine collection was 42.9 (16.8) mL/min/1.73 m2. Median urinary excretion of oxalate was 18.6 mg/24 hours (interquartile range [IQR], 12.9-25.7 mg/24 hours) and was correlated inversely with eGFR (r = -0.13, P < .001) and positively with 24-hour proteinuria (r = 0.22, P < .001). During 22 318 person-years of follow-up, 752 individuals reached ESRD, and 940 individuals reached the composite end point of ESRD or 50% decline in eGFR (CKD progression). Higher oxalate excretion was independently associated with greater risks of both CKD progression and ESRD: compared with quintile 1 (oxalate excretion, <11.5 mg/24 hours) those in quintile 5 (oxalate excretion, ≥27.8 mg/24 hours) had a 33% higher risk of CKD progression (hazard ratio [HR], 1.33; 95% CI, 1.04-1.70) and a 45% higher risk of ESRD (HR, 1.45; 95% CI, 1.09-1.93). The association between oxalate excretion and CKD progression and ESRD was nonlinear and exhibited a threshold effect at quintiles 3 to 5 vs quintiles 1 and 2. Higher vs lower oxalate excretion (at the 40th percentile) was associated with a 32% higher risk of CKD progression (HR, 1.32; 95% CI, 1.13-1.53) and 37% higher risk of ESRD (HR, 1.37; 95% CI, 1.15-1.63). Results were similar when treating death as a competing event.

CONCLUSIONS AND RELEVANCE

Higher 24-hour urinary oxalate excretion may be a risk factor for CKD progression and ESRD in individuals with CKD stages 2 to 4.

Whole-Exome Sequencing Enables a Precision Medicine Approach for Kidney Transplant Recipients

BACKGROUND

Whole-exome sequencing (WES) finds a CKD-related mutation in approximately 20% of patients presenting with CKD before 25 years of age. Although provision of a molecular diagnosis could have important implications for clinical management, evidence is lacking on the diagnostic yield and clinical utility of WES for pediatric renal transplant recipients.

METHODS

To determine the diagnostic yield of WES in pediatric kidney transplant recipients, we recruited 104 patients who had received a transplant at Boston Children's Hospital from 2007 through 2017, performed WES, and analyzed results for likely deleterious variants in approximately 400 genes known to cause CKD.

RESULTS

By WES, we identified a genetic cause of CKD in 34 out of 104 (32.7%) transplant recipients. The likelihood of detecting a molecular genetic diagnosis was highest for patients with urinary stone disease (three out of three individuals), followed by renal cystic ciliopathies (seven out of nine individuals), steroid-resistant nephrotic syndrome (nine out of 21 individuals), congenital anomalies of the kidney and urinary tract (ten out of 55 individuals), and chronic glomerulonephritis (one out of seven individuals). WES also yielded a molecular diagnosis for four out of nine individuals with ESRD of unknown etiology. The WES-related molecular genetic diagnosis had implications for clinical care for five patients.

CONCLUSIONS

Nearly one third of pediatric renal transplant recipients had a genetic cause of their kidney disease identified by WES. Knowledge of this genetic information can help guide management of both transplant patients and potential living related donors.