American Board of Internal Medicine Nephrology Procedure Requirements for Initial Certification: Time for a Change and Pursuing Consensus in the Nephrology Community

In 1988, the American Board of Internal Medicine (ABIM) defined essential procedural skills in nephrology, and candidates for ABIM certification were required to present evidence of possessing the skills necessary for placement of temporary dialysis vascular access, hemodialysis, peritoneal dialysis, and percutaneous renal biopsy. In 1996, continuous renal replacement therapy was added to the list of nephrology requirements. These procedure requirements have not been modified since 1996 while the practice of nephrology has changed dramatically. In March 2021, the ABIM Nephrology Board embarked on a policy journey to revise the procedure requirements for nephrology certification. With the guidance of nephrology diplomates, training program directors, professional and patient organizations, and other stakeholders, the ABIM Nephrology Board revised the procedure requirements to reflect current practice and national priorities. The approved changes include the Opportunity to Train standard for placement of temporary dialysis catheters, percutaneous kidney biopsies, and home hemodialysis which better reflects the current state of training in most training programs, and the new requirements for home dialysis therapies training will align with the national priority to address the underuse of home dialysis therapies. This perspective details the ABIM process for considering changes to the certification procedure requirements and how ABIM collaborated with the larger nephrology community in considering revisions and additions to these requirements.

Clinicopathologic Characteristics, Etiologies, and Outcome of Secondary Oxalate Nephropathy

OBJECTIVE

To report the clinicopathologic characteristics, prognostic indicators, prognosis, and transplant outcome of secondary oxalate nephropathy (ON).

PATIENTS AND METHODS

We performed a retrospective analysis of 113 consecutive patients with secondary ON diagnosed at Mayo Clinic in Rochester, Minnesota, between January 1, 2001, and March 1, 2023.

RESULTS

The incidence of secondary ON among all native biopsies from Mayo Clinic patients over the study period (n=11,617) was 0.97%. ON was attributed to enteric hyperoxaluria in 60% of the 113 patients (68; most commonly Roux-en-Y gastric bypass), excessive ingestion of foods high in oxalate or oxalate precursors in 23% (26) (most commonly vitamin C), and idiopathic in 17% (19). Most patients presented with acute kidney injury (AKI) (particularly in the ingestion group) or AKI on chronic kidney disease, and 53% (60 of 113) were diabetic. Calcium oxalate crystals were accompanied by acute tubular injury, inflammation, and interstitial fibrosis and tubular atrophy. Concurrent pathologic conditions were present in 53% of the patients (60 of 113), most commonly diabetic nephropathy. After a median follow-up of 36 months, 27% of the patients (30 of 112) had kidney recovery, 19% (21 of 112) had persistent kidney dysfunction, 54% (61 of 112) had development of kidney failure, and 29% (32 of 112) died. The mean kidney survival was worse for patients with a concurrent pathologic lesion (30 months vs 96 months for those without a concurrent pathologic lesion; P<.001). Independent predictors of kidney failure were the degree of interstitial fibrosis and tubular atrophy and nadir estimated glomerular filtration rate but not the degree of crystal deposition. After a median follow-up of 58 months in 23 patients who received kidney transplant, 4 had graft loss (due to ON in 3). The 2-, 5-, and 10-year graft survivals were 90% (18 of 20), 79% (11 of 14), and 50% (6 of 12).

CONCLUSION

ON is a rare cause of AKI or AKI on chronic kidney disease. Most patients have comorbid pathologic conditions, particularly diabetic nephropathy, which worsen the prognosis. Recurrence in the renal allograft and graft loss may occur if hyperoxaluria is not controlled.

Natural history of urine and plasma oxalate in children with primary hyperoxaluria type 1

BACKGROUND

Primary hyperoxaluria type 1 (PH1) is a rare, severe genetic disease causing increased hepatic oxalate production resulting in urinary stone disease, nephrocalcinosis, and often progressive chronic kidney disease. Little is known about the natural history of urine and plasma oxalate values over time in children with PH1.

METHODS

For this retrospective observational study, we analyzed data from genetically confirmed PH1 patients enrolled in the Rare Kidney Stone Consortium PH Registry between 2003 and 2018 who had at least 2 measurements before age 18 years of urine oxalate-to-creatinine ratio (Uox:cr), 24-h urine oxalate excretion normalized to body surface area (24-h Uox), or plasma oxalate concentration (Pox). We compared values among 3 groups: homozygous G170R, heterozygous G170R, and non-G170R AGXT variants both before and after initiating pyridoxine (B6).

RESULTS

Of 403 patients with PH1 in the registry, 83 met the inclusion criteria. Uox:cr decreased rapidly over the first 5 years of life. Both before and after B6 initiation, patients with non-G170R had the highest Uox:cr, 24-h Uox, and Pox. Patients with heterozygous G170R had similar Uox:cr to homozygous G170R prior to B6. Patients with homozygous G170R had the lowest 24-h Uox and Uox:cr after B6. Urinary oxalate excretion and Pox tend to decrease over time during childhood. eGFR over time was not different among groups.

CONCLUSIONS

Children with PH1 under 5 years old have relatively higher urinary oxalate excretion which may put them at greater risk for nephrocalcinosis and kidney failure than older PH1 patients. Those with homozygous G170R variants may have milder disease. A higher resolution version of the Graphical abstract is available as Supplementary information.

Mayo Clinic consensus report on membranous nephropathy: proposal for a novel classification

Membranous nephropathy (MN) is a pattern of injury caused by autoantibodies binding to specific target antigens, with accumulation of immune complexes along the subepithelial region of glomerular basement membranes. The past 20 years have brought revolutionary advances in the understanding of MN, particularly via the discovery of novel target antigens and their respective autoantibodies. These discoveries have challenged the traditional classification of MN into primary and secondary forms. At least 14 target antigens have been identified, accounting for 80%-90% of cases of MN. Many of the forms of MN associated with these novel MN target antigens have distinctive clinical and pathologic phenotypes. The Mayo Clinic consensus report on MN proposes a 2-step classification of MN. The first step, when possible, is identification of the target antigen, based on a multistep algorithm and using a combination of serology, staining of the kidney biopsy tissue by immunofluorescence or immunohistochemistry, and/or mass spectrometry methodology. The second step is the search for a potential underlying disease or associated condition, which is particularly relevant when knowledge of the target antigen is available to direct it. The meeting acknowledges that the resources and equipment required to perform the proposed testing may not be generally available. However, the meeting consensus was that the time has come to adopt an antigen-based classification of MN because this approach will allow for accurate and specific MN diagnosis, with significant implications for patient management and targeted treatment.

End Point Considerations for Clinical Trials in Enteric Hyperoxaluria

Enteric hyperoxaluria is a medical condition characterized by elevated urinary oxalate excretion due to increased gastrointestinal oxalate absorption. Causative features include fat malabsorption and/or increased intestinal permeability to oxalate. Enteric hyperoxaluria has long been known to cause nephrolithiasis and nephrocalcinosis, and, more recently, an association with CKD and kidney failure has been shown. Currently, there are no US Food and Drug Administration-approved therapies for enteric hyperoxaluria, and it is unclear what end points should be used to evaluate the efficacy of new drugs and biologics for this condition. This study represents work of a multidisciplinary group convened by the Kidney Health Initiative to review the evidence supporting potential end points for clinical trials in enteric hyperoxaluria. A potential clinical outcome is symptomatic kidney stone events. Potential surrogate end points include ( 1 ) an irreversible loss of kidney function as a surrogate for progression to kidney failure, ( 2 ) asymptomatic kidney stone growth/new stone formation observed on imaging as a surrogate for symptomatic kidney stone events, ( 3 ) urinary oxalate and urinary calcium oxalate supersaturation as surrogates for the development of symptomatic kidney stone events, and ( 4) plasma oxalate as a surrogate for the development of the clinical manifestations of systemic oxalosis. Unfortunately, because of gaps in the data, this Kidney Health Initiative workgroup was unable to provide definitive recommendations. Work is underway to obtain robust information that can be used to inform trial design and medical product development in this space.

Estimating glomerular filtration rate with new equations: can one size ever fit all?

Glomerular filtration rate (GFR) is thought to be the best overall indicator of kidney health. On an individual patient basis, a working knowledge of GFR is important to understand the future risk for chronic kidney disease (CKD) progression, enhanced risk for cardiovascular disease and death, and for optimal medical management including the dosing of certain drugs. Although GFR can be directly measured using exogenous compounds that are eliminated by the kidney, these methods are not scalable for repeated and routine use in clinical care. Thus, in most circumstances GFR is estimated, termed estimated GFR (eGFR), using serum biomarkers that are eliminated by the kidney. Of these, serum creatinine, and to a lesser extent cystatin C, are most widely employed. However, the resulting number is simply a population average for an individual of that age and sex with a given serum creatinine and/or cystatin C, while the range of potential GFR values is actually quite large. Thus, it is important to consider characteristics of a given patient that might make this estimate better or worse in a particular case. In some circumstances, cystatin C or creatinine might be the better choice. Ultimately it is difficult, if not impossible, to have an eGFR equation that performs equally well in all populations. Thus, in certain cases it might be appropriate to directly measure GFR for high consequence medical decision-making, such as approval for kidney donation or prior to certain chemotherapeutic regimens. In all cases, the eGFR thresholds of CKD stage should not be viewed as absolute numbers. Thus, clinical care should not be determined solely by CKD stage as determined by eGFR alone, but rather by the combination of an individual patient's likely kidney function together with their current clinical situation.

Assessing GFR With Proenkephalin

Introduction

In clinical practice, kidney (dys)function is monitored through creatinine-based estimations of glomerular filtration rate (eGFR: Modification of Diet in Renal Disease [MDRD], Chronic Kidney Disease Epidemiology Collaboration [CKD-EPI]). Creatinine is recognized as a late and insensitive biomarker of glomerular filtration rate (GFR). The novel biomarker proenkephalin (PENK) may overcome these limitations, but no PENK-based equation for eGFR is currently available. Therefore, we developed and validated a PENK-based equation to assess GFR.

Methods

In this international multicenter study in 1354 stable and critically ill patients, GFR was measured (mGFR) through iohexol or iothalamate clearance. A generalized linear model with sigmoidal nonlinear transfer function was used for equation development in the block-randomized development set. Covariates were selected in a data-driven fashion. The novel equation was assessed for bias, precision (mean ± SD), and accuracy (eGFR percentage within ±30% of mGFR, P30) in the validation set and compared with MDRD and CKD-EPI.

Results

Median mGFR was 61 [44-81] ml/min per 1.73 m2. In order of importance, PENK, creatinine, and age were included, and sex or race did not improve performance. The PENK-based equation mean ± SD bias of the mGFR was 0.5 ± 15 ml/min per 1.73 m2, significantly less compared with MDRD (8 ± 17, P < 0.001) and 2009 CKD-EPI (5 ± 17, P < 0.001), not reaching statistical significance compared with 2021 CKD-EPI (1.3 ± 16, P = 0.06). The P30 accuracy of the PENK-based equation was 83%, significantly higher compared with MDRD (68%, P < 0.001) and 2009 CKD-EPI (76%, P < 0.001), similar to 2021 CKD-EPI (80%, P = 0.13).

Conclusion

Overall, the PENK-based equation to assess eGFR performed better than most creatinine-based equations without using sex or race.

Mayo Clinic Consensus Report on Membranous Nephropathy: Proposal for a Novel Classification

Membranous nephropathy (MN) is a pattern of injury caused by autoantibodies binding to specific target antigens, with accumulation of immune complexes along the subepithelial region of glomerular basement membranes. The past 20 years have brought revolutionary advances in the understanding of MN, particularly via the discovery of novel target antigens and their respective autoantibodies. These discoveries have challenged the traditional classification of MN into primary and secondary forms. At least 14 target antigens have been identified, accounting for 80%-90% of cases of MN. Many of the forms of MN associated with these novel MN target antigens have distinctive clinical and pathologic phenotypes. The Mayo Clinic consensus report on MN proposes a 2-step classification of MN. The first step, when possible, is identification of the target antigen, based on a multistep algorithm and using a combination of serology, staining of the kidney biopsy tissue by immunofluorescence or immunohistochemistry, and/or mass spectrometry methodology. The second step is the search for a potential underlying disease or associated condition, which is particularly relevant when knowledge of the target antigen is available to direct it. The meeting acknowledges that the resources and equipment required to perform the proposed testing may not be generally available. However, the meeting consensus was that the time has come to adopt an antigen-based classification of MN because this approach will allow for accurate and specific MN diagnosis, with significant implications for patient management and targeted treatment.

Outpatient Antibiotic Use is Not Associated with an Increased Risk of First-Time Symptomatic Kidney Stones

SIGNIFICANCE STATEMENT

Antibiotics modify human microbiomes and may contribute to kidney stone risk. In a population-based case-control study using 1247 chart-validated first-time symptomatic kidney stone formers and 4024 age- and sex-matched controls, the risk of kidney stones was transiently higher during the first year after antibiotic use. However, this risk was no longer evident after adjustment for comorbidities and excluding participants with prior urinary symptoms. Findings were consistent across antibiotic classes and the number of antibiotic courses received. This suggests that antibiotics are not important risk factors of kidney stones. Rather, kidney stones when they initially cause urinary symptoms are under-recognized, resulting in antibiotic use before a formal diagnosis of kidney stones ( i.e. , reverse causality).

BACKGROUND

Antibiotics modify gastrointestinal and urinary microbiomes, which may contribute to kidney stone formation. This study examined whether an increased risk of a first-time symptomatic kidney stone episode follows antibiotic use.

METHODS

A population-based case-control study surveyed 1247 chart-validated first-time symptomatic kidney stone formers with a documented obstructing or passed stone (cases) in Olmsted County, Minnesota, from 2008 to 2013 and 4024 age- and sex-matched controls. All prescriptions for outpatient oral antibiotic use within 5 years before the onset of symptomatic stone for the cases and their matched controls were identified. Conditional logistic regression estimated the odds ratio (OR) of a first-time symptomatic kidney stone across time after antibiotic use. Analyses were also performed after excluding cases and controls with prior urinary tract infection or hematuria because urinary symptoms resulting in antibiotic prescription could have been warranted because of undiagnosed kidney stones.

RESULTS

The risk of a symptomatic kidney stone was only increased during the 1-year period after antibiotic use (unadjusted OR, 1.31; P = 0.001), and this risk was attenuated after adjustment for comorbidities (OR, 1.16; P = 0.08). After excluding cases and controls with prior urinary symptoms, there was no increased risk of a symptomatic kidney stone during the 1-year period after antibiotic use (unadjusted OR, 1.04; P = 0.70). Findings were consistent across antibiotic classes and the number of antibiotic courses received.

CONCLUSIONS

The increased risk of a first-time symptomatic kidney stone with antibiotic use seems largely due to both comorbidities and prescription of antibiotics for urinary symptoms. Under-recognition of kidney stones that initially cause urinary symptoms resulting in antibiotic use may explain much of the perceived stone risk with antibiotics ( i.e. , reverse causality).

Performance of Nuclear Magnetic Resonance-Based Estimated Glomerular Filtration Rate in a Real-World Setting

An accurate estimate of glomerular filtration rate (eGFR) is essential for proper clinical management, especially in patients with kidney dysfunction. This prospective observational study evaluated the real-world performance of the nuclear magnetic resonance (NMR)-based GFR_NMR equation, which combines creatinine, cystatin C, valine, and myo-inositol with age and sex. We compared GFR_NMR performance to that of the 2021 CKD-EPI creatinine and creatinine-cystatin C equations (CKD-EPI_2021Cr and CKD-EPI_2021CrCys), using 115 fresh routine samples of patients scheduled for urinary iothalamate clearance measurement (mGFR). Median bias to mGFR of the three eGFR equations was comparably low, ranging from 0.4 to 2.0 mL/min/1.73 m². GFR_NMR outperformed the 2021 CKD-EPI equations in terms of precision (interquartile range to mGFR of 10.5 vs. 17.9 mL/min/1.73 m² for GFR_NMR vs. CKD-EPI_2021CrCys; p = 0.01) and accuracy (P15, P20, and P30 of 66.1% vs. 48.7% [p = 0.007], 80.0% vs. 60.0% [p < 0.001] and 95.7% vs. 86.1% [p = 0.006], respectively, for GFR_NMR vs. CKD-EPI_2021CrCys). Clinical parameters such as etiology, comorbidities, or medications did not significantly alter the performance of the three eGFR equations. Altogether, this study confirmed the utility of GFR_NMR for accurate GFR estimation, and its potential value in routine clinical practice for improved medical care.

The Site and Type of CLCN5 Genetic Variation Impact the Resulting Dent Disease-1 Phenotype

Introduction

Dent disease is an X-linked recessive disorder associated with low molecular weight proteinuria (LMWP), nephrocalcinosis, kidney stones, and kidney failure in the third to fifth decade of life. It consists of Dent disease 1 (DD1) (60% of patients) because of pathogenic variants in the CLCN5 gene and Dent disease 2 (DD2) with changes in OCRL.

Methods

Retrospective review of 162 patients from 121 different families with genetically confirmed DD1 (82 different pathogenic variants validated using American College of Medical Genetics [ACMG] guidelines). Clinical and genetic factors were compared using observational statistics.

Results

A total of 110 patients had 51 different truncating (nonsense, frameshifting, large deletions, and canonical splicing) variants, whereas 52 patients had 31 different nontruncating (missense, in-frame, noncanonical splicing, and stop-loss) changes. Sixteen newly described pathogenic variants were found in our cohort. Among patients with truncating variants, lifetime stone events positively correlated with chronic kidney disease (CKD) evolution. Patients with truncating changes also experienced stone events earlier in life and manifested a higher albumin excretion rate than the nontruncating group. Nevertheless, neither age of nephrocalcinosis nor CKD progression varied between the truncating versus nontruncating patients. A large majority of nontruncating changes (26/31; 84%) were clustered in the middle exons that encode the voltage ClC domain whereas truncating changes were spread across the protein. Variants associated with kidney failure were restricted to truncating (11/13 cases), plus a single missense variant previously shown to markedly reduce ClC-5 functional activity that was found in the other 2 individuals.

Conclusion

DD1 manifestations, including the risk of kidney stones and progression to kidney failure, may relate to the degree of residual ClC-5 function.

Characterization of Stone Events in Patients With Type 3 Primary Hyperoxaluria

PURPOSE

Hallmarks of primary hyperoxaluria type 3 are nephrolithiasis and hyperoxaluria. However, little is known about factors influencing stone formation in this disease. We characterized stone events and examined associations with urine parameters and kidney function in a primary hyperoxaluria type 3 population.

MATERIALS AND METHODS

We retrospectively analyzed clinical, and laboratory data of 70 primary hyperoxaluria type 3 patients enrolled in the Rare Kidney Stone Consortium Primary Hyperoxaluria Registry.

RESULTS

Kidney stones occurred in 65/70 primary hyperoxaluria type 3 patients (93%). Among the 49 patients with imaging available, the median (IQR) number of stones was 4 (2, 5), with largest stone 7 mm (4, 10) at first imaging. Clinical stone events occurred in 62/70 (89%) with median number of events per patient 3 (2, 6; range 1-49). Age at first stone event was 3 years (0.99, 8.7). Lifetime stone event rate was 0.19 events/year (0.12, 0.38) during follow-up of 10.7 (4.2, 26.3) years. Among 326 total clinical stone events, 139 (42.6%) required surgical intervention. High stone event rates persisted for most patients through the sixth decade of life. Analysis was available for 55 stones: pure calcium oxalate accounted for 69%, with mixed calcium oxalate and phosphate in 22%. Higher calcium oxalate supersaturation was associated with increased lifetime stone event rate after adjusting for age at first event (IRR [95%CI] 1.23 [1.16, 1.32]; P < .001). By the fourth decade, estimated glomerular filtration rate was lower in primary hyperoxaluria type 3 patients than the general population.

CONCLUSIONS

Stones impose a lifelong burden on primary hyperoxaluria type 3 patients. Reducing urinary calcium oxalate supersaturation may reduce event frequency and surgical intervention.

Tissue Inhibitor Metalloproteinase-2 and Insulin-Like Growth Factor Binding Protein-7 Kinetics Following Exposure to High-Dose Methotrexate

Urinary TIMP2×IGFBP7 (uTIMP2×IGFBP7) concentrations experienced a rapid and sustained decline after high-dose methotrexate (MTX) exposure. uTIMP2×IGFBP7 kinetics and concentrations after high-dose MTX exposure demonstrated no utility in predicting AKI.

Nedosiran in primary hyperoxaluria subtype 3: results from a phase I, single-dose study (PHYOX4)

Nedosiran is an N-acetyl-D-galactosamine (GalNAc)-conjugated RNA interference agent targeting hepatic lactate dehydrogenase (encoded by the LDHA gene), the putative enzyme mediating the final step of oxalate production in all three genetic subtypes of primary hyperoxaluria (PH). This phase I study assessed the safety, pharmacokinetics (PK), and pharmacodynamics (PD) of subcutaneous nedosiran in patients with PH subtype 3 (PH3) and an estimated glomerular filtration rate  ≥ 30 mL/min/1.73 m2. Single-dose nedosiran 3 mg/kg or placebo was administered in a randomized (2:1), double-blinded manner. Safety/tolerability, 24-h urinary oxalate (Uox) concentrations, and plasma nedosiran concentrations were assessed. The main PD endpoint was the proportion of participants achieving a > 30% decrease from baseline in 24-h Uox at two consecutive visits. Six participants enrolled in and completed the study (nedosiran, n = 4; placebo, n = 2). Nedosiran was well-tolerated and lacked safety concerns. Although the PD response was not met, 24-h Uox excretion declined 24.5% in the nedosiran group and increased 10.5% in the placebo group at Day 85. Three of four nedosiran recipients had a > 30% reduction in 24-h Uox excretion during at least one visit, and one attained near-normal (i.e., ≥ 0.46 to < 0.60 mmol/24 h; ≥ 1.0 to < 1.3 × upper limit of the normal reference range) 24-h Uox excretion from Day 29 to Day 85. Nedosiran displayed predictable plasma PK. The acceptable safety and trend toward Uox-lowering after single-dose nedosiran treatment enables further clinical development of nedosiran in patients with PH3 who currently have no viable therapeutic options. A plain language summary is available in the supplementary information.

Impact of race-independent equations on estimating glomerular filtration rate for the assessment of kidney dysfunction in liver disease

BACKGROUND

Altered hemodynamics in liver disease often results in overestimation of glomerular filtration rate (GFR) by creatinine-based GFR estimating (eGFR) equations. Recently, we have validated a novel eGFR equation based on serum myo-inositol, valine, and creatinine quantified by nuclear magnetic resonance spectroscopy in combination with cystatin C, age and sex (GFR_NMR). We hypothesized that GFR_NMR could improve chronic kidney disease (CKD) classification in the setting of liver disease.

RESULTS

We conducted a retrospective multicenter study in 205 patients with chronic liver disease (CLD), comparing the performance of GFR_NMR to that of validated CKD-EPI eGFR equations, including eGFRcr (based on creatinine) and eGFRcr-cys (based on both creatinine and cystatin C), using measured GFR as reference standard. GFR_NMR outperformed all other equations with a low overall median bias (-1 vs. -6 to 4 ml/min/1.73 m² for the other equations; p < 0.05) and the lowest difference in bias between reduced and preserved liver function (-3 vs. -16 to -8 ml/min/1.73 m² for other equations). Concordant classification by CKD stage was highest for GFR_NMR (59% vs. 48% to 53%) and less biased in estimating CKD severity compared to the other equations. GFR_NMR P30 accuracy (83%) was higher than that of eGFRcr (75%; p = 0.019) and comparable to that of eGFRcr-cys (86%; p = 0.578).

CONCLUSIONS

Addition of myo-inositol and valine to creatinine and cystatin C in GFR_NMR further improved GFR estimation in CLD patients and accurately stratified liver disease patients into CKD stages.

Precision nephrology identified tumor necrosis factor activation variability in minimal change disease and focal segmental glomerulosclerosis

The diagnosis of nephrotic syndrome relies on clinical presentation and descriptive patterns of injury on kidney biopsies, but not specific to underlying pathobiology. Consequently, there are variable rates of progression and response to therapy within diagnoses. Here, an unbiased transcriptomic-driven approach was used to identify molecular pathways which are shared by subgroups of patients with either minimal change disease (MCD) or focal segmental glomerulosclerosis (FSGS). Kidney tissue transcriptomic profile-based clustering identified three patient subgroups with shared molecular signatures across independent, North American, European, and African cohorts. One subgroup had significantly greater disease progression (Hazard Ratio 5.2) which persisted after adjusting for diagnosis and clinical measures (Hazard Ratio 3.8). Inclusion in this subgroup was retained even when clustering was limited to those with less than 25% interstitial fibrosis. The molecular profile of this subgroup was largely consistent with tumor necrosis factor (TNF) pathway activation. Two TNF pathway urine markers were identified, tissue inhibitor of metalloproteinases-1 (TIMP-1) and monocyte chemoattractant protein-1 (MCP-1), that could be used to predict an individual's TNF pathway activation score. Kidney organoids and single-nucleus RNA-sequencing of participant kidney biopsies, validated TNF-dependent increases in pathway activation score, transcript and protein levels of TIMP-1 and MCP-1, in resident kidney cells. Thus, molecular profiling identified a subgroup of patients with either MCD or FSGS who shared kidney TNF pathway activation and poor outcomes. A clinical trial testing targeted therapies in patients selected using urinary markers of TNF pathway activation is ongoing.

Measuring copeptin, a surrogate for vasopressin in patients with hypertension - Can it identify those who are volume Responsive?

BACKGROUND

Among hypertensive patients, plasma renin activity is lower and the response to diuretic monotherapy greater in volume responsive hypertensive patients. We hypothesized that hormones influencing extracellular volume such as vasopressin / antidiuretic hormone (ADH) might permit the development of a simple test to identify those with volume-related hypertension. Such a test might be of particular benefit to the Black population which is purported to have a higher incidence of volume-related and responsive hypertension. Thus, using copeptin, a surrogate marker for ADH, we studied if there were differences in this hormone between those with and without volume responsive hypertension.

METHODS

Serum copeptin was measured in biobanked blood samples from the Genetic Epidemiology of Responses to Antihypertensives (GERA) I study and analyzed with other variables from the study dataset.

RESULTS

There was no relationship between PRA and copeptin values nor could the response in blood pressure be predicted by the copeptin values. However, baseline copeptin levels were higher in Black than in White subjects (7.5 pmol/L vs 5.4 pmol/L, P < 0.001) while plasma sodium and calculated plasma osmolality were slightly lower in keeping with the concept that Black subjects have more volume-related hypertension. In addition, after hydrochlorothiazide (HCTZ), copeptin was significantly lower in Black (6.2 pmol/L, P = 0.004) but unchanged in White subjects (5.2 pmol/L, P = 0.901) and there were also changes in sodium.

CONCLUSION

The current study suggests differences in ADH physiology between hypertensive Black and White patients. However, the use of copeptin to identify volume responsive patients could not be confirmed.

Lumasiran for Advanced Primary Hyperoxaluria Type 1: Phase 3 ILLUMINATE-C Trial

RATIONALE & OBJECTIVE

Lumasiran reduces urinary and plasma oxalate (POx) in patients with primary hyperoxaluria type 1 (PH1) and relatively preserved kidney function. ILLUMINATE-C evaluates the efficacy, safety, pharmacokinetics, and pharmacodynamics of lumasiran in patients with PH1 and advanced kidney disease.

STUDY DESIGN

Phase 3, open-label, single-arm trial.

SETTING & PARTICIPANTS

Multinational study; enrolled patients with PH1 of all ages, estimated glomerular filtration rate ≤45 mL/min/1.73 m² (if age ≥12 months) or increased serum creatinine level (if age <12 months), and POx ≥20 μmol/L at screening, including patients with or without systemic oxalosis.

INTERVENTION

Lumasiran administered subcutaneously; 3 monthly doses followed by monthly or quarterly weight-based dosing.

OUTCOME

Primary end point: percent change in POx from baseline to month 6 (cohort A; not receiving hemodialysis at enrollment) and percent change in predialysis POx from baseline to month 6 (cohort B; receiving hemodialysis at enrollment). Pharmacodynamic secondary end points: percent change in POx area under the curve between dialysis sessions (cohort B only); absolute change in POx; percent and absolute change in spot urinary oxalate-creatinine ratio; and 24-hour urinary oxalate adjusted for body surface area.

RESULTS

All patients (N = 21; 43% female; 76% White) completed the 6-month primary analysis period. Median age at consent was 8 (range, 0-59) years. For the primary end point, least-squares mean reductions in POx were 33.3% (95% CI, -15.2% to 81.8%) in cohort A (n = 6) and 42.4% (95% CI, 34.2%-50.7%) in cohort B (n = 15). Improvements were also observed in all pharmacodynamic secondary end points. Most adverse events were mild or moderate. No patient discontinued treatment or withdrew from the study. The most commonly reported lumasiran-related adverse events were injection-site reactions, all of which were mild and transient.

LIMITATIONS

Single-arm study without placebo control.

CONCLUSIONS

Lumasiran resulted in substantial reductions in POx with acceptable safety in patients with PH1 who have advanced kidney disease, supporting its efficacy and safety in this patient population.

FUNDING

Alnylam Pharmaceuticals.

TRIAL REGISTRATION

Registered at ClinicalTrials.gov with study number NCT04152200 and at EudraCT with study number 2019-001346-17.

PLAIN-LANGUAGE SUMMARY

Primary hyperoxaluria type 1 (PH1) is a rare genetic disease characterized by excessive hepatic oxalate production that frequently causes kidney failure. Lumasiran is an RNA interference therapeutic that is administered subcutaneously for the treatment of PH1. Lumasiran has been shown to reduce oxalate levels in the urine and plasma of patients with PH1 who have relatively preserved kidney function. In the ILLUMINATE-C study, the efficacy and safety of lumasiran were evaluated in patients with PH1 and advanced kidney disease, including a cohort of patients undergoing hemodialysis. During the 6-month primary analysis period, lumasiran resulted in substantial reductions in plasma oxalate with acceptable safety in patients with PH1 complicated by advanced kidney disease.

Dietary Assessment of Lithogenic Factors in Plant-Based Meat Products

Introduction: Patients who form kidney stones are typically advised to limit intake of nondairy animal protein. Plant-based meat products may be a processed substitute protein source for these patients and have recently gained popularity because of health concerns, increased retail availability, decreased environmental impact, and meat supply shortages during the COVID-19 pandemic. Despite these perceived benefits and tangential association with whole food plant-based diets, the potential lithogenic risks associated with these products are not well characterized. Methods: The U.S. Department of Agriculture database was queried with a sample of plant-based meat products widely available to U.S. consumers. Nutrient profile data were compiled and compared with animal protein data using standardized serving sizes. Primary protein sources were identified using verified ingredient lists. Oxalate content was extrapolated based on dietary data sources. Results: A total 47 plant-based meat products (16 beef, 11 pork, 10 chicken, and 10 seafood) were analyzed. Compared with their respective animal protein, most products contained on average fewer calories (plant-based beef 77%, pork 94%, chicken 86%, and seafood 83%) and less protein (plant-based beef 68%, pork 96%, chicken 53%, and seafood 54%). Most products used soy protein as the primary protein source (55%). Soy-based beef contained the highest average oxalate content (18 mg per serving), whereas soy-based seafood contained the lowest (7 mg). The most common non-soy protein source was pea protein (30%), containing trace amounts of oxalate. Sodium content was higher in most plant-based products overall (72%) and in each category (plant-based beef 109%, pork 128%, chicken 100%, and seafood 148%). Calcium content was higher (plant-based beef 317%, pork 144%, chicken 291%, and seafood 295%) compared with animal protein. Conclusions: Most plant-based meat products consist of protein sources that are, relative to animal protein sources, higher in oxalate, sodium, and calcium. Stone-forming patients should be counseled about the potential lithogenic risk of these processed products.

Serum myo-inositol and valine improve metabolomic-based estimated glomerular filtration rate among kidney transplant recipients

BACKGROUND

Close monitoring of glomerular filtration rate (GFR) is essential for the management of patients post kidney transplantation. Measured GFR (mGFR), the gold standard, is not readily accessible in most centers. Furthermore, the performance of new estimated GFR (eGFR) equations based upon creatinine and/or cystatin C have not been validated in kidney transplant patients. Here we evaluate a recently published eGFR equation using cystatin C, creatinine, myo-inositol and valine as measured by nuclear magnetic resonance (eGFRNMR).

METHODS

Residual sera was obtained from a cohort of patients with clinically ordered iothalamate renal clearance mGFR (n = 602). Kidney transplant recipients accounted for 220 (37%) of participants.

RESULTS

Compared to mGFR, there was no significant bias for eGFRcr or eGFRNMR, while eGFRcr-cys significantly underestimated mGFR. P30 values were similar for all eGFR. P15 was significantly higher for eGFRNMR compared to eGFRcr, while the P15 for eGFRcr-cys only improved among patients without a kidney transplant. Agreement with mGFR CKD stages of <15, 30, 45, 60, and 90 ml/min/1.73 m2 was identical for eGFRcr and eGFRcr-cys (61.8%, both cases) while eGFRNMR was significantly higher (66.4%) among patients with a kidney transplant.

CONCLUSION

The 2021 CKD-EPI eGFRcr and eGFRcr-cys have similar bias, P15, and agreement while eGFRNMR more closely matched mGFR with the strongest improvement among kidney transplant recipients.

Nuclear Magnetic Resonance Metabolomic Profiling and Urine Chemistries in Incident Kidney Stone Formers Compared with Controls

BACKGROUND

The urine metabolites and chemistries that contribute to kidney stone formation are not fully understood. This study examined differences between the urine metabolic and chemistries profiles of first-time stone formers and controls.

METHODS

High-resolution 1H-nuclear magnetic resonance (NMR) spectroscopy-based metabolomic analysis was performed in 24-hour urine samples from a prospective cohort of 418 first-time symptomatic kidney stone formers and 440 controls. In total, 48 NMR-quantified metabolites in addition to 12 standard urine chemistries were assayed. Analysis of covariance was used to determine the association of stone former status with urine metabolites or chemistries after adjusting for age and sex and correcting for the false discovery rate. Gradient-boosted machine methods with nested cross-validation were applied to predict stone former status.

RESULTS

Among the standard urine chemistries, stone formers had lower urine oxalate and potassium and higher urine calcium, phosphate, and creatinine. Among NMR urine metabolites, stone formers had lower hippuric acid, trigonelline, 2-furoylglycine, imidazole, and citrate and higher creatine and alanine. A cross-validated model using urine chemistries, age, and sex yielded a mean AUC of 0.76 (95% CI, 0.73 to 0.79). A cross-validated model using urine chemistries, NMR-quantified metabolites, age, and sex did not meaningfully improve the discrimination (mean AUC, 0.78; 95% CI, 0.75 to 0.81). In this combined model, among the top ten discriminating features, four were urine chemistries and six NMR-quantified metabolites.

CONCLUSIONS

Although NMR-quantified metabolites did not improve discrimination, several urine metabolic profiles were identified that may improve understanding of kidney stone pathogenesis.

GeoBioMed perspectives on kidney stone recurrence from the reactive surface area of SWL-derived particles

Shock wave lithotripsy (SWL) is an effective and commonly applied clinical treatment for human kidney stones. Yet the success of SWL is counterbalanced by the risk of retained fragments causing recurrent stone formation, which may require retreatment. This study has applied GeoBioMed experimental and analytical approaches to determine the size frequency distribution, fracture patterns, and reactive surface area of SWL-derived particles within the context of their original crystal growth structure (crystalline architecture) as revealed by confocal autofluorescence (CAF) and super-resolution autofluorescence (SRAF) microscopy. Multiple calcium oxalate (CaOx) stones were removed from a Mayo Clinic patient using standard percutaneous nephrolithotomy (PCNL) and shock pulse lithotripsy (SPL). This produced approximately 4-12 mm-diameter PCNL-derived fragments that were experimentally treated ex vivo with SWL to form hundreds of smaller particles. Fractures propagated through the crystalline architecture of PCNL-derived fragments in a variety of geometric orientations to form rectangular, pointed, concentrically spalled, and irregular SWL-derived particles. Size frequency distributions ranged from fine silt (4-8 μm) to very fine pebbles (2-4 mm), according to the Wentworth grain size scale, with a mean size of fine sand (125-250 μm). Importantly, these SWL-derived particles are smaller than the 3-4 mm-diameter detection limit of clinical computed tomography (CT) techniques and can be retained on internal kidney membrane surfaces. This creates clinically undetectable crystallization seed points with extremely high reactive surface areas, which dramatically enhance the multiple events of crystallization and dissolution (diagenetic phase transitions) that may lead to the high rates of CaOx kidney stone recurrence after SWL treatment.

Differences of Uric Acid Transporters Carrying Extracellular Vesicles in the Urine from Uric Acid and Calcium Stone Formers and Non-Stone Formers

Background: Low urine pH and volume are established risk factors for uric acid (UA) stone disease (UASD). Renal tubular epithelial cells exposed to an acidic pH and/or UA crystals can shed extracellular vesicles (EVs) into the tubular fluid, and these EVs may be a pathogenic biomarker of UASD. Methods: Urinary EVs bearing UA transporters (SLC2A9, SLC17A3, SLC22A12, SLC5A8, ABCG2, and ZNF365) were quantified in urine from UA stone formers (UASFs), calcium stone formers (CSFs), and age-/sex-matched non-stone formers (NSFs) using a standardized and published method of digital flow cytometry. Results: Urinary pH was lower (p < 0.05) and serum and urinary UA were greater (p < 0.05) in UASFs compared with NSFs. Urinary EVs carrying SLC17A3 and SLC5A8 were lower (p < 0.05) in UASFs compared with NSFs. Urinary EVs bearing SLC2A9, SLC22A12, SLC5A8, ABCG2, and ZNF365 were lower (p < 0.05) in CSFs than UASFs, while excretion of SLC17A3-bearing EVs did not differ between groups. Conclusion: EVs bearing specific UA transporters might contribute to the pathogenesis of UASD and represent non-invasive pathogenic biomarkers for calcium and UA stone risk.

Estimated GFR Slope Across CKD Stages in Primary Hyperoxaluria Type 1

RATIONALE & OBJECTIVE

Primary hyperoxaluria type 1 (PH1) is an autosomal recessive disorder of glyoxylate metabolism that results in early-onset kidney stone disease, nephrocalcinosis, and kidney failure. There is an unmet need for reliable markers of disease progression to test effectiveness of new treatments for patients with PH. In this study, we assessed the rate of estimated glomerular filtration rate (eGFR) decline across chronic kidney disease (CKD) glomerular filtration rate (GFR) categories (CKD G2-G5) in a cohort of patients with PH1.

STUDY DESIGN

Retrospective observational study.

SETTING & PARTICIPANTS

Patients with PH1 enrolled in the Rare Kidney Stone Consortium (RKSC) registry who did not have kidney failure at diagnosis and who had at least 2 eGFR values recorded from within 1 month of diagnosis until their last contact date or incident kidney failure event.

PREDICTORS

CKD GFR category, baseline patient and laboratory characteristics.

OUTCOME

Annualized rate of eGFR decline.

ANALYTICAL APPROACH

Generalized estimating equations and linear regression were used to evaluate the associations between CKD GFR category, baseline patient and laboratory characteristics, and annual change in eGFR during follow-up.

RESULTS

Compared with the slope in CKD G2 (-2.3 mL/min/1.73 m2 per year), the mean annual eGFR decline was nominally steeper in CKD G3a (-5.3 mL/min/1.73 m2 per year) and statistically significantly more rapid in CKD G3b and G4 (-14.7 and -16.6 mL/min/1.73 m2 per year, respectively). In CKD G2, older age was associated with a more rapid rate of eGFR decline (P = 0.01). A common PH1-causing variant of alanine glyoxylate aminotransferase, a glycine to arginine substitution at amino acid 170 (G170R), appeared to be associated with less severe annual decline in eGFR.

LIMITATIONS

Data at regular time points were not available for all patients due to reliance on voluntary reporting in a retrospective rare disease registry.

CONCLUSIONS

The eGFR decline was not uniform across CKD GFR categories in this PH1 population, with a higher rate of eGFR decline in CKD G3b and G4. Thus, CKD GFR category needs to be accounted for when analyzing eGFR change in the setting of PH1.

Dietary Risk Factors for Incident and Recurrent Symptomatic Kidney Stones

OBJECTIVE

To compare dietary factors between incident symptomatic stone formers and controls, and among the incident stone formers, to determine whether dietary factors were predictive of symptomatic recurrence.

PATIENTS AND METHODS

We prospectively recruited 411 local incident symptomatic kidney stone formers (medical record validated) and 384 controls who were seen at Mayo Clinic in Minnesota or Florida between January 1, 2009, and August 31, 2018. Dietary factors were based on a Viocare, Inc, food frequency questionnaire administered during a baseline in-person study visit. Logistic regression compared dietary risk factors between incident symptomatic stone formers and controls. Incident stone formers were followed up for validated symptomatic recurrence in the medical record. Cox proportional hazards models estimated risk of symptomatic recurrence with dietary factors. Analyses adjusted for fluid intake, energy intake, and nondietary risk factors.

RESULTS

In fully adjusted analyses, lower dietary calcium, potassium, caffeine, phytate, and fluid intake were all associated with a higher odds of an incident symptomatic kidney stone. Among incident stone formers, 73 experienced symptomatic recurrence during a median 4.1 years of follow-up. Adjusting for body mass index, fluid intake, and energy intake, lower dietary calcium and lower potassium intake were predictive of symptomatic kidney stone recurrence. With further adjustment for nondietary risk factors, lower dietary calcium intake remained a predictor of recurrence, but lower potassium intake only remained a predictor of recurrence among those not taking thiazide diuretics or calcium supplements.

CONCLUSION

Enriching diets in stone formers with foods high in calcium and potassium may help prevent recurrent symptomatic kidney stones.

NMRpQuant: an automated software for large scale urinary total protein quantification by one-dimensional 1H NMR profiles

SUMMARY

1H nuclear magnetic resonance (NMR) spectroscopy is an established bioanalytical technology for metabolic profiling of biofluids in both clinical and large-scale population screening applications. Recently, urinary protein quantification has been demonstrated using the same 1D 1H NMR experimental data captured for metabolic profiling. Here, we introduce NMRpQuant, a freely available platform that builds on these findings with both novel and further optimized computational NMR approaches for rigorous, automated protein urine quantification. The results are validated by interlaboratory comparisons, demonstrating agreement with clinical/biochemical methodologies, pointing at a ready-to-use tool for routine protein urinalyses.

AVAILABILITY AND IMPLEMENTATION

NMRpQuant was developed on MATLAB programming environment. Source code and Windows/macOS compiled applications are available at https://github.com/pantakis/NMRpQuant, and working examples are available at https://doi.org/10.6084/m9.figshare.18737189.v1.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Randomized Placebo-Controlled Trial of Reloxaliase in Enteric Hyperoxaluria

Reloxaliase in Enteric HyperoxaluriaPatients with enteric hyperoxaluria received reloxaliase or placebo with food for 4 weeks. Urinary oxalate excretion decreased from 83.2 to 67.4 mg/24 hr during weeks 1 to 4 with reloxaliase compared with 84.2 to 78.1 mg/24 hr with placebo (P=0.004). Adverse events occurred for 69% of reloxaliase-treated patients versus 53% of those receiving placebo.

New therapeutics for primary hyperoxaluria type 1

PURPOSE OF REVIEW

Primary hyperoxaluria type 1 (PH1) is a rare genetic disorder that causes hepatic overproduction of oxalate and, often, nephrocalcinosis, nephrolithiasis, chronic kidney disease, and kidney failure. The purpose of the review is to provide an update on current emerging therapies for the treatment of PH1.

RECENT FINDINGS

Use of ribonucleic acid interference (RNAi) therapeutics that target the liver to block production of key enzymes along pathways that generate oxalate is a promising approach. Available evidence supports the efficacy of both Lumasiran (targeting glycolate oxidase) and Nedosiran (targeting hepatic lactate dehydrogenase (LDHa)) to reduce urinary oxalate excretion in PH1. The efficacy of alternative approaches including stiripentol (an anticonvulsant drug that also targets LDHa), lanthanum (a potential gastrointestinal oxalate binder), and Oxalobacter formigenes (a bacterium that can degrade oxalate within the gastrointestinal tract and may also increase its secretion from blood) are all also under study. Genetic editing tools including clustered regularly interspaced short palindromic repeats/Cas9 are also in preclinical study as a potential PH1 therapeutic.

SUMMARY

Novel treatments can reduce the plasma oxalate concentration and urinary oxalate excretion in PH1 patients. Thus, it is possible these approaches will reduce the need for combined kidney and liver transplantation to significantly decrease the morbidity and mortality of affected patients.

Primary hyperoxaluria type 1: novel therapies at a glance

Primary hyperoxaluria type 1 (PH1) is a rare and severe autosomal recessive disease of oxalate metabolism, resulting from a mutation in the AGXT gene that encodes the hepatic peroxisomal enzyme alanine–glyoxylate aminotransferase (AGT). Until recently, treatment of PH1 was supportive, consisting of intensive hyperhydration, use of crystallization inhibitors (citrate and neutral phosphorus), in a subset of responsive PH1 patients’ pharmacologic doses of vitamin B6 (pyridoxine), and kidney and liver transplantation when patients progressed to kidney failure. Treatment approaches have been similar for PH2 caused by mutations in hepatic glyoxylate reductase/hydroxypyruvate reductase (GR/HPR), although pyridoxine does not have any benefit in this group. PH3 is caused by mutations of mitochondrial 4-hydroxy-2-oxoglutarate aldolase (HOGA1) and was the most recently described. Kidney failure appears less common in PH3, although kidney stones occur as frequently as in PH1 and PH2. Oxalate metabolism in the liver is complex. Novel therapies based on RNA interference (RNAi) have recently emerged to modulate these pathways, designed to deplete substrate for enzymes upstream and decrease/avoid oxalate production. Two hepatic enzymes have been targeted to date in PH: glycolate oxidase (GO) with lumasiran and lactate dehydrogenase A (LDH-A) with nedosiran. Lumasiran was approved for the treatment of PH1 in 2020 by both the European Medicines Agency and the Food and Drug Administration, whilst clinical trials with nedosiran are ongoing. Results with the two RNAi therapies demonstrate a significant reduction of urinary oxalate excretion in PH1 patients, but long-term data on efficacy (preservation of kidney function, decreased stone events) and safety remain to be established. Nevertheless, the hepatically targeted RNAi approach represents a potential ‘game changer’ in the field of PH1, bringing hope to families and patients that they may be able to avoid liver and/or kidney transplantation in the future and suffer fewer stone events, perhaps with less strict therapeutic regimens. Pharmacological compounds directly inhibiting GO or LDH are also under development and could be of special interest in developing countries where RNAi therapies may not be readily available in the near future. Approaches to manipulate the intestinal microbiome with a goal to increase oxalate degradation or to stimulate secretion of oxalate into the intestine from plasma are also under development. Overall, we appear to be entering a new phase of PH treatment, with an array of promising approaches emerging that will need optimization and evaluation to establish long-term efficacy and safety.

The genetics of kidney stone disease and nephrocalcinosis

Kidney stones (also known as urinary stones or nephrolithiasis) are highly prevalent, affecting approximately 10% of adults worldwide, and the incidence of stone disease is increasing. Kidney stone formation results from an imbalance of inhibitors and promoters of crystallization, and calcium-containing calculi account for over 80% of stones. In most patients, the underlying aetiology is thought to be multifactorial, with environmental, dietary, hormonal and genetic components. The advent of high-throughput sequencing techniques has enabled a monogenic cause of kidney stones to be identified in up to 30% of children and 10% of adults who form stones, with ~35 different genes implicated. In addition, genome-wide association studies have implicated a series of genes involved in renal tubular handling of lithogenic substrates and of inhibitors of crystallization in stone disease in the general population. Such findings will likely lead to the identification of additional treatment targets involving underlying enzymatic or protein defects, including but not limited to those that alter urinary biochemistry.

Nephrotoxin Exposure in the 3 Years following Hospital Discharge Predicts Development or Worsening of Chronic Kidney Disease among Acute Kidney Injury Survivors

INTRODUCTION

Survivors of acute kidney injury (AKI) are at high risk of progression to chronic kidney disease (CKD), for which drugs may be a modifiable risk factor.

METHODS

We conducted a population-based cohort study of Olmsted County, MN residents who developed AKI while hospitalized between January 1, 2006, and December 31, 2014, using Rochester Epidemiology Project data. Adults with a hospitalization complicated by AKI who survived at least 90 days after AKI development were included. Medical records were queried for prescription of potentially nephrotoxic medications over the 3 years after discharge. The primary outcome was de novo or progressive CKD defined by either a new diagnosis code for CKD or ≥30% decline in estimated glomerular filtration rate from baseline. The composite of CKD, AKI readmission, or death was also evaluated.

RESULTS

Among 2,461 AKI survivors, 2,140 (87%) received a potentially nephrotoxic medication during the 3 years following discharge. When nephrotoxic medication use was analyzed in a time-dependent fashion, those actively prescribed at least one of these drugs experienced a significantly higher risk of de novo or progressive CKD (HR 1.38: 95% CI: 1.24, 1.54). Similarly, active potentially nephrotoxic medication use predicted a greater risk of the composite endpoint of CKD, AKI readmission, or death within 3 years of discharge (HR 1.41: 95% CI: 1.28, 1.56).

CONCLUSION

In this population-based cohort study, AKI survivors actively prescribed one or more potentially nephrotoxic medications were at significantly greater risk for de novo or progressive CKD. An opportunity exists to reassess nephrotoxin appropriateness following an AKI episode to improve patient outcomes.

Inflammatory Cells in Nephrectomy Tissue from Patients without and with a History of Urinary Stone Disease

BACKGROUND AND OBJECTIVES

Urinary stone disease has been associated with inflammation, but the specific cell interactions that mediate events remain poorly defined. This study compared calcification and inflammatory cell patterns in kidney tissue from radical nephrectomy specimens of patients without and with a history of urinary stone disease.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Nontumor parenchyma of biobanked radical nephrectomy specimens from age- and sex-matched stone formers (n=44) and nonstone formers (n=82) were compared. Calcification was detected by Yasue staining and inflammatory cell populations by immunohistochemistry for CD68 (proinflammatory M1 macrophages), CD163 and CD206 (anti-inflammatory M2 macrophages), CD3 (T lymphocytes), and tryptase (mast cells). Calcifications and inflammatory cells were quantified in cortex and medulla using Image-Pro analysis software.

RESULTS

Calcification in the medulla of stone formers was higher than in nonstone formers (P<0.001). M1 macrophages in the cortex and medulla of stone formers were greater than in nonstone formers (P<0.001), and greater in stone former medulla than stone former cortex (P=0.02). There were no differences in age, sex, body mass index, tumor characteristics (size, stage, or thrombus), vascular disease status, or eGFR between the groups. M2 macrophages, T lymphocytes, and mast cells did not differ by stone former status. There was a correlation between M1 macrophages and calcification in the medulla of stone formers (rho=0.48; P=0.001) and between M2 macrophages and calcification in the medulla of nonstone formers (rho=0.35; P=0.001). T lymphocytes were correlated with calcification in the cortex of both nonstone formers (rho=0.27; P=0.01) and stone formers (rho=0.42; P=0.004), whereas mast cells and calcification were correlated only in the cortex of stone formers (rho=0.35; P=0.02).

CONCLUSIONS

Higher medullary calcification stimulated accumulation of proinflammatory rather than anti-inflammatory macrophages in stone formers.

Posttransplant recurrence of calcium oxalate crystals in patients with primary hyperoxaluria: Incidence, risk factors, and effect on renal allograft function

Primary hyperoxaluria (PH) is a metabolic defect that results in oxalate overproduction by the liver and leads to kidney failure due to oxalate nephropathy. As oxalate tissue stores are mobilized after transplantation, the transplanted kidney is at risk of recurrent disease. We evaluated surveillance kidney transplant biopsies for recurrent calcium oxalate (CaOx) deposits in 37 kidney transplants (29 simultaneous kidney and liver [K/L] transplants and eight kidney alone [K]) in 36 PH patients and 62 comparison transplants. Median follow-up posttransplant was 9.2 years (IQR: [5.3, 15.1]). The recurrence of CaOx crystals in surveillance biopsies in PH at any time posttransplant was 46% overall (41% in K/L, 62% in K). Higher CaOx crystal index (which accounted for biopsy sample size) was associated with higher plasma and urine oxalate following transplant (p < .01 and p < .02, respectively). There was a trend toward higher graft failure among PH patients with CaOx crystals on surveillance biopsies compared with those without (HR 4.43 [0.88, 22.35], p = .07). CaOx crystal deposition is frequent in kidney transplants in PH patients. The avoidance of high plasma oxalate and reduction of CaOx crystallization may decrease the risk of recurrent oxalate nephropathy following kidney transplantation in patients with PH. This study was approved by the IRB at Mayo Clinic.

Kidney Cysts in Hypophosphatemic Rickets With Hypercalciuria: A Case Series

Rationale & Objective

Study Design

Setting & Participants

Results

Limitations

Conclusions

Microsporidium Infection–Associated Acute Kidney Injury in a Patient With HIV

Patients infected with HIV (human immunodeficiency virus) are at an increased risk of developing acute kidney injury (AKI) compared with patients without HIV infection. We report a rare case of disseminated Microsporidium infection–associated AKI affecting the native kidneys in a 30-year-old Asian woman with HIV infection. She initially presented to an outside institution with AKI after completing treatment with trimethoprim-sulfamethoxazole (Bactrim [Hoffmann-La Roche]) and prednisone for Pneumocystis pneumonia. She was empirically treated with prednisone for presumed acute interstitial nephritis due to Bactrim, and her serum creatinine concentration improved from 3.0 mg/dL to 1.8 mg/dL. She was subsequently initiated on antiretroviral therapy and was also treated with ganciclovir for cytomegalovirus viremia. Because of persistent fever, she was transferred to our institution and was diagnosed with a disseminated Mycobacterium avium complex infection and a disseminated Microsporidium infection. Her serum creatinine concentration increased to 4.2 mg/dL. A kidney biopsy was performed because of her worsening kidney function, which revealed plasma cell–rich acute interstitial nephritis associated with disseminated Microsporidium infection. She was maintained on antiretroviral therapy and was treated with albendazole. This case highlights the fact that there are various etiologies and kidney manifestations of AKI in patients infected with HIV with equally various implications for management; thus, performing a kidney biopsy is often crucial to help elucidate the underlying pathology and guide management.

Primary Hyperoxaluria Type 3 Can Also Result in Kidney Failure: A Case Report

Primary hyperoxaluria (PH) is a group of genetic disorders that result in an increased hepatic production of oxalate. PH type 3 (PH3) is the most recently identified subtype and results from mutations in the mitochondrial 4-hydroxy-2-oxoglutarate aldolase gene (HOGA1). To date, there have been 2 cases of kidney failure reported in PH3 patients. We present a case of a young man with a history of recurrent urinary tract infections and voiding dysfunction who developed kidney failure at 33 years of age. He developed a bladder stone and bilateral staghorn calculi at 12 years of age. Initial metabolic evaluation revealed hyperoxaluria with very low urinary citrate excretion on multiple measurements for which he was placed on oral citrate supplements. Further investigation of the hyperoxaluria was not completed as the patient was lost to follow-up observation until he presented at 29 years of age with chronic kidney disease stage 4 (estimated glomerular filtration rate 24mL/min/1.73m²). Hemodialysis 3 times a week was started at 33 years of age, and subsequent genetic testing revealed a homozygous HOGA1 mutation (C.973G>A p.Gly325Ser) diagnostic of PH3. The patient is currently being evaluated for all treatment options including possible liver/kidney transplantation. All cases of a childhood history of recurrent urinary stone disease with marked hyperoxaluria should prompt genetic testing for the 3 known PH types. Hyperhydration and crystallization inhibitors (citrate) are standard of care, but the role of RNA interference agents for all 3 forms of PH is also under active study.

Estimating Glomerular Filtration Rate from Serum Myo-Inositol, Valine, Creatinine and Cystatin C

Assessment of renal function relies on the estimation of the glomerular filtration rate (eGFR). Existing eGFR equations, usually based on serum levels of creatinine and/or cystatin C, are not uniformly accurate across patient populations. In the present study, we expanded a recent proof-of-concept approach to optimize an eGFR equation targeting the adult population with and without chronic kidney disease (CKD), based on a nuclear magnetic resonance spectroscopy (NMR) derived 'metabolite constellation' (GFRNMR). A total of 1855 serum samples were partitioned into development, internal validation and external validation datasets. The new GFRNMR equation used serum myo-inositol, valine, creatinine and cystatin C plus age and sex. GFRNMR had a lower bias to tracer measured GFR (mGFR) than existing eGFR equations, with a median bias (95% confidence interval [CI]) of 0.0 (-1.0; 1.0) mL/min/1.73 m2 for GFRNMR vs. -6.0 (-7.0; -5.0) mL/min/1.73 m2 for the Chronic Kidney Disease Epidemiology Collaboration equation that combines creatinine and cystatin C (CKD-EPI2012) (p < 0.0001). Accuracy (95% CI) within 15% of mGFR (1-P15) was 38.8% (34.3; 42.5) for GFRNMR vs. 47.3% (43.2; 51.5) for CKD-EPI2012 (p < 0.010). Thus, GFRNMR holds promise as an alternative way to assess eGFR with superior accuracy in adult patients with and without CKD.

Randomized Clinical Trial on the Long-Term Efficacy and Safety of Lumasiran in Patients With Primary Hyperoxaluria Type 1

Introduction

Primary hyperoxaluria type 1 (PH1) is a rare genetic disease caused by hepatic overproduction of oxalate, leading to kidney stones, nephrocalcinosis, kidney failure, and systemic oxalosis. In the 6-month double-blind period (DBP) of ILLUMINATE-A, a phase 3, randomized, placebo-controlled trial in patients with PH1 ≥6 years old, treatment with lumasiran, an RNA interference therapeutic, led to substantial reductions in urinary oxalate (UOx) levels.

Methods

We report data to month 12 in the extension period (EP) of ILLUMINATE-A, including patients who continued lumasiran (lumasiran/lumasiran) or crossed over from placebo to lumasiran (placebo/lumasiran).

Results

In the lumasiran/lumasiran group (n = 24), the reduction in 24-hour UOx level was sustained to month 12 (mean reduction from baseline, 66.9% at month 6; 64.1% at month 12). The placebo/lumasiran group (n = 13) had a similar time course and magnitude of 24-hour UOx reduction (mean reduction, 57.3%) after 6 months of lumasiran. Kidney stone event rates seemed to be lower after 6 months of lumasiran in both groups compared with the 12 months before consent, and this reduction was maintained at month 12 in the lumasiran/lumasiran group. At study start, 71% of patients in the lumasiran/lumasiran group and 92% in the placebo/lumasiran group had nephrocalcinosis. Nephrocalcinosis grade improved after 6 months of lumasiran in the lumasiran/lumasiran and placebo/lumasiran groups (13% and 8% of patients, respectively). After an additional 6 months of lumasiran, 46% of patients had improvement in nephrocalcinosis grade within the lumasiran/lumasiran group. Estimated glomerular filtration rate (eGFR) remained stable during the course of lumasiran treatment. The most common adverse events (AEs) related to lumasiran were mild, transient injection-site reactions (ISRs).

Conclusion

Long-term lumasiran treatment enabled sustained lowering of UOx levels with acceptable safety and encouraging results on clinical outcomes.

Clinical Outcomes and Histological Patterns in Oxalate Nephropathy due to Enteric and Nonenteric Risk Factors

INTRODUCTION

Current knowledge of risk factors and renal histologic patterns of oxalate nephropathy (ON) not due to primary hyperoxaluria (PH) has been limited to small case series and case reports. Thus, we analyzed and compared clinical risk factors, histologic characteristics, and renal outcomes of patients with biopsy-confirmed ON among a cohort of patients with enteric and nonenteric risk factors.

METHODS

A clinical data repository of native kidney pathology reports from 2009 to 2020 at all Mayo Clinic sites was used to identify 421 ON cases.

RESULTS

After excluding cases in transplanted kidneys or due to PH, 64 cases remained. Enteric risk factors were present in 30 and nonenteric in 34. Roux-en-Y gastric bypass (17) and pancreatic insufficiency (6) were most common in the enteric hyperoxaluria group. In the nonenteric group, vitamin C (7) and dietary oxalate (7) were common, while no apparent risk was noted in 16. Acute kidney injury (AKI) stage III at the time of diagnosis was present in 60%, and 40.6% required dialysis. Patients in the nonenteric group had more interstitial inflammation (p = 0.01), and a greater number of tubules contained intratubular calcium oxalate (CaOx) crystals (p = 0.001) than the nonenteric group. Patients in the enteric group were more likely to have baseline chronic kidney disease (CKD) (p = 0.02) and moderate-to-severe tubulointerstitial fibrosis and atrophy (IFTA) (OR 3.49, p = 0.02). After a median follow-up of 10 months, 39% were dialysis dependent, 11% received a kidney transplant, and 32% died. On univariate analysis, >10 tubules with CaOx crystals, baseline CKD, and AKI requiring dialysis correlated with the risk of dialysis, transplant, or death. On multivariate analysis, only AKI requiring dialysis correlated with adverse renal outcomes.

CONCLUSION

This is the largest cohort study of ON not due to PH. Histologic features differ in patients with enteric versus nonenteric risks. Patients in the enteric group are more likely to have baseline CKD and significant IFTA, while patients in the nonenteric group were more likely to have a greater number of tubules with CaOx crystals and corresponding interstitial inflammation. AKI requiring dialysis at the time of diagnosis was the single most significant predictor of adverse renal outcome.

Comprehensive Genetic Analysis Reveals Complexity of Monogenic Urinary Stone Disease

Introduction

Because of phenotypic overlap between monogenic urinary stone diseases (USD), gene-specific analyses can result in missed diagnoses. We used targeted next generation sequencing (tNGS), including known and candidate monogenic USD genes, to analyze suspected primary hyperoxaluria (PH) or Dent disease (DD) patients genetically unresolved (negative; N) after Sanger analysis of the known genes. Cohorts consisted of 285 PH (PHN) and 59 DD (DDN) families.

Methods

Variants were assessed using disease-specific and population databases plus variant assessment tools and categorized using the American College of Medical Genetics (ACMG) guidelines. Prior Sanger analysis identified 47 novel PH or DD gene pathogenic variants.

Results

Screening by tNGS revealed pathogenic variants in 14 known monogenic USD genes, accounting for 45 families (13.1%), 27 biallelic and 18 monoallelic, including 1 family with a copy number variant (CNV). Recurrent genes included the following: SLC34A3 (n = 13), CLDN16 (n = 8), CYP24A1 (n = 4), SLC34A1 (n = 3), SLC4A1 (n = 3), APRT (n = 2), CLDN19 (n = 2), HNF4A1 (n = 2), and KCNJ1 (n = 2), whereas ATP6V1B1, CASR, and SLC12A1 and missed CNVs in the PH genes AGXT and GRHPR accounted for 1 pedigree each. Of the 48 defined pathogenic variants, 27.1% were truncating and 39.6% were novel. Most patients were diagnosed before 18 years of age (76.1%), and 70.3% of biallelic patients were homozygous, mainly from consanguineous families.

Conclusion

Overall, in patients suspected of DD or PH, 23.9% and 7.3% of cases, respectively, were caused by pathogenic variants in other genes. This study shows the value of a tNGS screening approach to increase the diagnosis of monogenic USD, which can optimize therapies and facilitate enrollment in clinical trials.

Genotype Phenotype Correlation in Dent Disease 2 and Review of the Literature: OCRL Gene Pleiotropism or Extreme Phenotypic Variability of Lowe Syndrome?

Dent disease is a rare X-linked renal tubulopathy due to CLCN5 and OCRL (DD2) mutations. OCRL mutations also cause Lowe syndrome (LS) involving the eyes, brain and kidney. DD2 is frequently described as a mild form of LS because some patients may present with extra-renal symptoms (ESs). Since DD2 is a rare disease and there are a low number of reported cases, it is still unclear whether it has a clinical picture distinct from LS. We retrospectively analyzed the phenotype and genotype of our cohort of 35 DD2 males and reviewed all published DD2 cases. We analyzed the distribution of mutations along the OCRL gene and evaluated the type and frequency of ES according to the type of mutation and localization in OCRL protein domains. The frequency of patients with at least one ES was 39%. Muscle findings are the most common ES (52%), while ocular findings are less common (11%). Analysis of the distribution of mutations revealed (1) truncating mutations map in the PH and linker domain, while missense mutations map in the 5-phosphatase domain, and only occasionally in the ASH-RhoGAP module; (2) five OCRL mutations cause both DD2 and LS phenotypes; (3) codon 318 is a DD2 mutational hot spot; (4) a correlation was found between the presence of ES and the position of the mutations along OCRL domains. DD2 is distinct from LS. The mutation site and the mutation type largely determine the DD2 phenotype.