Chemotherapy-induced tubulopathy: a case report series

Acquired tubulopathies are frequently underdiagnosed. They can be characterized by the renal loss of specific electrolytes or organic solutes, suggesting the location of dysfunction. These tubulopathies phenotypically can resemble Bartter or Gitelman syndrome). These syndromes are infrequent, they may present salt loss resembling the effect of thiazides (Gitelman) or loop diuretics (Bartter). They are characterized by potentially severe hypokalemia, associated with metabolic alkalosis, secondary hyperaldosteronism, and often hypomagnesemia. Tubular dysfunction has been described as nephrotoxic effects of platinum-based chemotherapy. We present 4 cases with biochemical signs of tubular dysfunction (Bartter-like/Gitelman-like phenotype) related to chemotherapy.

Tips for Testing Adults With Suspected Genetic Kidney Disease

Genetic kidney disease is common but often unrecognized. It accounts for most cystic kidney diseases and tubulopathies, many forms of congenital abnormalities of the kidney and urinary tract (CAKUT), and some glomerulopathies. Genetic kidney disease is typically suspected where the disease usually has a genetic basis or there is another affected family member, a young age at onset, or extrarenal involvement, but there are also many exceptions to these "rules". Genetic testing requires the patient's written informed consent. When a patient declines testing, another later conversation may be worthwhile. Genetic testing not only indicates the diagnosis but also the inheritance pattern, likely at-risk family members, disease in other organs, clinical course, and possibly effective treatments. Sometimes genetic testing does not identify a pathogenic variant even where other evidence is strong. A variant of uncertain significance (VUS) may be reported but should not be used for clinical decision making. It may be reclassified after more information becomes available without necessarily retesting the patient. Patients should be provided with a copy of their genetic test report, the results explained, and at-risk family members offered "cascade" testing. A referral to a clinical geneticist or genetic counselor helps identify affected family members and in providing advice to assist with reproductive decisions.

Long-term kidney outcomes after leptospirosis: a prospective multicentre cohort study in Thailand

BACKGROUND

Leptospirosis is one of the most important public-health zoonotic diseases in the tropics that can cause severe organ dysfunction and death. Currently there are insufficient data on long-term renal dysfunction in patients after leptospirosis infection.

METHODS

A prospective multicentre cohort study was conducted at 15 hospitals in the Sisaket province of Thailand. Confirmed leptospirosis patients admitted from 1 December 2015 to 30 November 2018 were followed between 1 February 2020 and 31 October 2020 (median 4.1 years after hospital discharge). The primary outcome was a composite of major kidney adverse events (MAKEs) including all-cause mortality, dialysis and new-onset chronic kidney disease (CKD).

RESULTS

Of the 217 confirmed leptospirosis cases enrolled, 32.7% were classified as having severe leptospirosis. Fifteen cases (6.9%) were deceased at the time of hospital admission. After a median follow-up time of 4.18 years, 30 patients had died and 33 patients developed CKD. Patients with severe leptospirosis had a significantly higher risk of MAKEs {adjusted hazard ratio 2.45 [95% confidence interval (CI) 1.44-4.18]}. Patients with intensive care unit admission, pulmonary haemorrhage and acute kidney injury also had a higher risk of MAKEs and all-cause mortality. Participants with severe leptospirosis in the follow-up cohort showed a higher risk of developing CKD compared with non-severe leptospirosis [adjusted odds ratio 3.22 (95% CI 1.04-9.96)], especially renal magnesium and phosphate wasting.

CONCLUSION

Leptospirosis patients, especially severe leptospirosis, are associated with long-term kidney sequelae. Our finding reflects the importance of long-term follow-up and the urgent need for specific interventions.

[A rare tubulopathy: Dent's disease in the background of focal segmental glomerular sclerosis]

Dent's disease is a proximal tubulopathy with heterogeneous genetical background. The typical clinical finding is characterized by low molecular weight proteinuria, hypercalciuria, nephrocalcinosis/nephrolithiasis and progressive chronic kidney failure. The underlying cause of the disease is the genetic defect (most commonly CLCN5 mutation) of the receptor-mediated endocytosis in the structure of proximal tubules. The typical fenotype may be composed of extrarenal symptoms. In the event of clinical suspicion, Dent's disease is only verifiable by genetic testing without the necessity of any kidney biopsy. The clinical case can be associated with nephrotic-range proteinuria or kidney failure as an indication of kidney biopsy. The number of articles available at scientific literatures on Dent's disease with the inclusion of renal histology is very slight. According to the pathophysiology of the highlighted Dent's disease and additionally to the expected tubular pathology, global or focal segmental glomerular sclerosis may apply for the majority of cases. Orv Hetil. 2023; 164(20): 788-791.

Machine Learning to Identify Genetic Salt-Losing Tubulopathies in Hypokalemic Patients

Introduction

Clinically distinguishing patients with the inherited salt-losing tubulopathies (SLTs), Gitelman or Bartter syndrome (GS or BS) from other causes of hypokalemia (LK) patients is difficult, and genotyping is costly. We decided to identify clinical characteristics that differentiate SLTs from LK.

Methods

A total of 66 hypokalemic patients with possible SLTs were recruited to a prospective observational cohort study at the University College London Renal Tubular Clinic, London. All patients were genotyped for pathogenic variants in genes which cause SLTs; 39 patients had pathogenic variants in genes causing SLTs. We obtained similar data sets from cohorts in Taipei and Kobe, as follows: the combined data set comprised 419 patients; 291 had genetically confirmed SLT. London and Taipei data sets were combined to train machine learning (ML) algorithms, which were then tested on the Kobe data set.

Results

Single biochemical variables (e.g., plasma renin) were significantly, but inconsistently, different between SLTs and LK in all cohorts. A decision table algorithm using serum bicarbonate and urinary sodium excretion (FE_Na) achieved a classification accuracy of 74%. This was superior to all the single biochemical variables identified previously.

Conclusion

ML algorithms can differentiate true SLT in the context of a specialist clinic with some accuracy. However, based on routine biochemistry, the accuracy is insufficient to make genotyping redundant.

Long-Read Sequencing Identifies Novel Pathogenic Intronic Variants in Gitelman Syndrome

BACKGROUND

Gitelman syndrome is a salt-losing tubulopathy characterized by hypokalemic alkalosis and hypomagnesemia. It is caused by homozygous recessive or compound heterozygous pathogenic variants in SLC12A3 , which encodes the Na + -Cl - cotransporter (NCC). In up to 10% of patients with Gitelman syndrome, current genetic techniques detect only one specific pathogenic variant. This study aimed to identify a second pathogenic variant in introns, splice sites, or promoters to increase the diagnostic yield.

METHODS

Long-read sequencing of SLC12A3 was performed in 67 DNA samples from individuals with suspected Gitelman syndrome in whom a single likely pathogenic or pathogenic variant was previously detected. In addition, we sequenced DNA samples from 28 individuals with one variant of uncertain significance or no candidate variant. Midigene splice assays assessed the pathogenicity of novel intronic variants.

RESULTS

A second likely pathogenic/pathogenic variant was identified in 45 (67%) patients. Those with two likely pathogenic/pathogenic variants had a more severe electrolyte phenotype than other patients. Of the 45 patients, 16 had intronic variants outside of canonic splice sites (nine variants, mostly deep intronic, six novel), whereas 29 patients had an exonic variant or canonic splice site variant. Midigene splice assays of the previously known c.1670-191C>T variant and intronic candidate variants demonstrated aberrant splicing patterns.

CONCLUSION

Intronic pathogenic variants explain an important part of the missing heritability in Gitelman syndrome. Long-read sequencing should be considered in diagnostic workflows for Gitelman syndrome.

Differentiated mouse kidney tubuloids as a novel in vitro model to study collecting duct physiology

Kidney tubuloids are cell models that are derived from human or mouse renal epithelial cells and show high similarities with their in vivo counterparts. Tubuloids grow polarized in 3D, allow for long-term expansion, and represent multiple segments of the nephron, as shown by their gene expression pattern. In addition, human tubuloids form tight, functional barriers and have been succesfully used for drug testing. Our knowledge of mouse tubuloids, on the other hand, is only minimal. In this study, we further characterized mouse tubuloids and differentiated them towards the collecting duct, which led to a significant upregulation of collecting duct-specific mRNAs of genes and protein expression, including the water channel AQP2 and the sodium channel ENaC. Differentiation resulted in polarized expression of collecting duct water channels AQP2 and AQP3. Also, a physiological response to desmopressin and forskolin stimulation by translocation of AQP2 to the apical membrane was demonstrated. Furthermore, amiloride-sensitive ENaC-mediated sodium uptake was shown in differentiated tubuloids using radioactive tracer sodium. This study demonstrates that mouse tubuloids can be differentiated towards the collecting duct and exhibit collecting duct-specific function. This illustrates the potential use of mouse kidney tubuloids as novel in vitro models to study (patho)physiology of kidney diseases.

Cadmium-Induced Proteinuria: Mechanistic Insights from Dose-Effect Analyses

Cadmium (Cd) is a toxic metal that accumulates in kidneys, especially in the proximal tubular epithelial cells, where virtually all proteins in the glomerular ultrafiltrate are reabsorbed. Here, we analyzed archived data on the estimated glomerular filtration rate (eGFR) and excretion rates of Cd (E_Cd), total protein (E_Prot), albumin (E_alb), β₂-microglobulin (E_β2M), and α1-microglobulin (E_α1M), which were recorded for residents of a Cd contamination area and a low-exposure control area of Thailand. Excretion of Cd and all proteins were normalized to creatinine clearance (C_cr) as E_Cd/C_cr and E_Prot/C_cr to correct for differences among subjects in the number of surviving nephrons. Low eGFR was defined as eGFR ≤ 60 mL/min/1.73 m², while proteinuria was indicted by E_Pro/C_cr ≥ 20 mg/L of filtrate. E_Prot/C_cr varied directly with E_Cd/C_cr (β = 0.263, p < 0.001) and age (β = 0.252, p < 0.001). In contrast, eGFR values were inversely associated with E_Cd/C_cr (β = -0.266, p < 0.001) and age (β = -0.558, p < 0.001). At E_Cd/C_cr > 8.28 ng/L of filtrate, the prevalence odds ratios for proteinuria and low eGFR were increased 4.6- and 5.1-fold, respectively (p < 0.001 for both parameters). Thus, the eGFR and tubular protein retrieval were both simultaneously diminished by Cd exposure. Of interest, E_Cd/C_cr was more closely correlated with E_Prot/C_cr (r = 0.507), E_β2M (r = 0.430), and E_α1M/C_cr (r = 0.364) than with E_Alb/C_cr (r = 0.152). These data suggest that Cd may differentially reduce the ability of tubular epithelial cells to reclaim proteins, resulting in preferential reabsorption of albumin.

The Assessment of Renal Functional Reserve in β-Thalassemia Major Patients by an Innovative Ultrasound and Doppler Technique: A Pilot Study

Beta-thalassemia syndromes are the most common inherited monogenic disorders worldwide. The most common pathophysiologic and clinical renal disease manifestations of in β-TM patients is the tubular dysfunctions related to iron overload, chronic anemia, and the need for chronic iron chelation therapy. The aim of this pilot study is to apply an innovative ultrasound and Doppler technique to assess the Renal Functional Reserve (RFR) in β-TM patients, and to evaluate its reliability in iron overload tubulopathy. Ultrasound assessment of intra-parenchymal renal resistive index variation (IRRIV) has recently been proposed as a safe and reproducible technique to identify RFR presence. We define the preserved RFR when the Delta Renal Resistive Index (RRI) is >0.05 (baseline RRI—minimum RRI value during stress) in the Renal Stress Test (RST). Nineteen β-TM patients were enrolled for this study. In our series, we found a strong negative correlation between mean ferritin values and Delta RRI (R = −0.51, p = 0.03). This pilot study suggested the RST as reliable tool for assessing the RFR by ultrasound. Specifically, RST could help in clinical practice suggesting the patient’s management and iron chelation therapy.

The genetic spectrum of Gitelman(-like) syndromes

PURPOSE OF REVIEW

Gitelman syndrome is a recessive salt-wasting disorder characterized by hypomagnesemia, hypokalemia, metabolic alkalosis and hypocalciuria. The majority of patients are explained by mutations and deletions in the SLC12A3 gene, encoding the Na+-Cl--co-transporter (NCC). Recently, additional genetic causes of Gitelman-like syndromes have been identified that should be considered in genetic screening. This review aims to provide a comprehensive overview of the clinical, genetic and mechanistic aspects of Gitelman(-like) syndromes.

RECENT FINDINGS

Disturbed Na+ reabsorption in the distal convoluted tubule (DCT) is associated with hypomagnesemia and hypokalemic alkalosis. In Gitelman syndrome, loss-of-function mutations in SLC12A3 cause impaired NCC-mediated Na+ reabsorption. In addition, patients with mutations in CLCKNB, KCNJ10, FXYD2 or HNF1B may present with a similar phenotype, as these mutations indirectly reduce NCC activity. Furthermore, genetic investigations of patients with Na+-wasting tubulopathy have resulted in the identification of pathogenic variants in MT-TI, MT-TF, KCNJ16 and ATP1A1. These novel findings highlight the importance of cell metabolism and basolateral membrane potential for Na+ reabsorption in the DCT.

SUMMARY

Altogether, these findings extend the genetic spectrum of Gitelman-like electrolyte alterations. Genetic testing of patients with hypomagnesemia and hypokalemia should cover a panel of genes involved in Gitelman-like syndromes, including the mitochondrial genome.

Acute kidney injury manifesting as renal tubular acidosis with proximal and distal renal tubular dysfunction in a dog with acute pancreatitis

Objective

To describe the clinical presentation and management of a critically ill dog with profound renal tubular acidosis (RTA) with proximal and distal renal tubular dysfunction.

Case Summary

A 3‐year‐old neutered female Border Terrier was presented with frequent regurgitation resulting from acute pancreatitis with severe ileus. Venous acid–base analysis and complete urinalysis confirmed the presence of normal anion gap metabolic acidosis with inappropriately alkaline urine (pH 8), consistent with distal RTA. Urinalysis, urine amino acids, and urinary fractional excretion of electrolytes revealed glycosuria (with normoglycemia), aminoaciduria, and increased fractional excretion of sodium, calcium, and phosphate consistent with generalized proximal renal tubulopathy or Fanconi syndrome. The dog responded well to supportive care and alkaline therapy and made a complete recovery.

New or Unique Information Provided

To the authors’ knowledge, this is the first description of RTA with proximal and distal renal tubular dysfunction in the veterinary literature. Furthermore, the authors hypothesize that the transient RTA was a manifestation of acute kidney injury secondary to acute pancreatitis, the first report of this in the literature.

Arthrogryposis–renal dysfunction–cholestasis syndrome

Összefoglaló. Az arthrogryposis-renalis diszfunkció-cholestasis (ARC) szindróma igen rossz prognózisú autoszomális recesszív kórkép. A három vezető tünethez társulhat központi idegrendszeri érintettség, siketség, cardiovascularis anomália (pitvari és kamrai sövényhiány), thrombocytafunkció-zavar, rekurrens szepszisek, ichthyosis, valamint súlyfejlődésben való elmaradás. A háromnapos újszülöttet neuromuscularis betegség gyanúja miatt vettük át a szülészeti intézményből. Fizikális vizsgálat során pes equinovarust és hypotrophiás küllemet tapasztaltunk. Kéthetes korában súlyos tubulopathia, valamint cholestasis igazolódott normális gamma-glutamil-transzferáz-szint mellett. A perifériás vérkenet vizsgálata során abnormális morfológiájú thrombocyták ábrázolódtak. Súlygyarapodást komplex felépített enteralis és parenteralis táplálás segítségével sem sikerült elérni. Három hónapos korára a gyermek súlya 15%-kal a születési súlya alatt volt. A kórkép szövődményeként ismétlődő bakteriális véráramfertőzés súlyosbította az állapotát. Az újszülött klinikai képe az ARC-szindrómának felelt meg. A kóroki gének szekvenálása során a VPS33B-génben homozigóta c.498+1G>T variáns igazolódott, mely igazolja a betegség fennállását. Orv Hetil. 2022; 163(2): 74-78. Summary. Arthrogryposis-renal dysfunction-cholestasis (ARC) syndrome is an autosomal recessive multisystem disorder that typically presents with arthrogryposis, renal tubular leak and neonatal cholestatic jaundice. It can be accompanied by nervous system abnormalities, deafness, structural cardiac defects, abnormal platelet morphology, recurrent sepsis, ichthyosis and failure to thrive. The three-day-old neonate was admitted for a suspected neuromuscular disorder. On examination, clubfoot, jaundice and hypotonia were found. Laboratory evaluation revealed tubulopathy and cholestasis with normal gamma-glutamyl transferase level. Peripheral blood smear evaluation revealed abnormally giant platelets. Despite the combined enteral and parenteral nutrition, the infant experienced severe failure to thrive. The phenotype of the presented neonate is consistent with ARC syndrome. Sequencing of the causal genes revealed a homozygous consensus splice site VPS33B mutation (c.498+1G>T), confirming the clinical diagnosis. Orv Hetil. 2022; 163(2): 74-78.

Screening for an Underlying Tubulopathy in Children With Growth Failure, Simply Maths?

BACKGROUND

Involving pediatric nephrological input in the clinical diagnostic work-up of children with short stature, gave rise to the hypothesis that the presence of an underlying renal tubular disorder in children with short stature is possibly underestimated. This study focussed on the added value of calculated urinary fractional excretion (FE) in the early detection of tubular disorders in children with growth failure.

METHODS

This trial was designed as an observational study analyzing the medical files of children between 5 and 16 years who had been referred for short stature to the pediatric endocrinology outpatient clinic at the University Hospital Antwerp between 25/01/2015 and 01/03/2019. Based on the laboratory results of the simultaneously taken blood and urine sample, the fractional excretions of Sodium, Chloride, Potassium, Calcium, Phosphate, and Magnesium were calculated.

RESULTS

Of the 299 patients, 54 patients had at least one deviating fractional excretion value, requiring further investigation (control sample of blood and urine, kidney ultrasound or 24 h urine collection). Genetic screening for tubulopathies was performed in 19 patients. In 5 patients (1.7% of the total population) a tubulopathy was confirmed based on genetic analysis.

CONCLUSION

This study explored the possibility of using fractional excretions as a screening test to obtain an earlier diagnosis of tubular disorders in children with short stature. Of the 299 patients, 5 patients were diagnosed with a genetically confirmed tubulopathy. Based on these results, we propose a flowchart for an additional work-up in all children with a deviating fractional excretion.

Persistent dyselectrolytemia in a neonate induced by liposomal amphotericin B. A case report

BACKGROUND

Nephrotoxicity is the most frequent serious adverse effect associated with amphotericin B deoxycholate treatment, for this reason, in recent years it has been relegated from routine clinical practice and replaced by the new liposomal formulations that have less nephrotoxicity. Nevertheless, dyselectrolytemia are a frequent adverse effect of the use of liposomal amphotericin B that usually are resolved with the withdrawal of the drug.

CASE PRESENTATION

We present a preterm neonate of 25 weeks gestation, with preserved renal function and most electrolytes within normal limits for gestational age except for mild hyponatremia in the first month of life. Due to an infection of the central nervous system and growth of Candida albicans, he required treatment with endovenous liposomal amphotericin B as well as intrathecal amphotericin B deoxycholate showing severe hydroelectrolyte disturbances and clinical worsening compatible with possible tubulopathy showing hypokalemia and severe hyponatremia a few days after starting treatment that persisted over time even after withdrawal of both drugs. Subsequently to the main alterations described, hypomagnesemia, hypophosphatemia, glycosuria and tubular proteinuria were also observed. Calcium levels remained stable after amphotericin B administration and did not require supplementation. In preterm or low birth weight newborns who present unjustified, severe and difficult to correct hydroelectrolyte disturbances despite the usual treatment, a possible tubulopathy should be considered, whether hereditary, primary or secondary to toxins or drugs.

WHAT IS NEW AND CONCLUSION

We present the first case reported in a neonate in whom dyselectrolithemia has been maintained over time after withdrawal of liposomal amphotericin B.

Bartter and Gitelman syndromes

Bartter and Gitelman syndromes belong to salt-losing tubulopathies. These rare diseases may be associated with severe electrolyte disorders. Early identification of tubulopathies is essential for appropriate management. Progress in molecular genetics enabled the identification of genes and pathophysiologic mechanisms associated with these diseases. Here, we review etiology and diagnostics of these disorders from the light of current knowledge. Additionally, we discuss contemporary therapeutic approaches.

Defects in KCNJ16 Cause a Novel Tubulopathy with Hypokalemia, Salt Wasting, Disturbed Acid-Base Homeostasis, and Sensorineural Deafness

BACKGROUND

The transepithelial transport of electrolytes, solutes, and water in the kidney is a well-orchestrated process involving numerous membrane transport systems. Basolateral potassium channels in tubular cells not only mediate potassium recycling for proper Na⁺,K⁺-ATPase function but are also involved in potassium and pH sensing. Genetic defects in KCNJ10 cause EAST/SeSAME syndrome, characterized by renal salt wasting with hypokalemic alkalosis associated with epilepsy, ataxia, and sensorineural deafness.

METHODS

A candidate gene approach and whole-exome sequencing determined the underlying genetic defect in eight patients with a novel disease phenotype comprising a hypokalemic tubulopathy with renal salt wasting, disturbed acid-base homeostasis, and sensorineural deafness. Electrophysiologic studies and surface expression experiments investigated the functional consequences of newly identified gene variants.

RESULTS

We identified mutations in the KCNJ16 gene encoding KCNJ16, which along with KCNJ15 and KCNJ10, constitutes the major basolateral potassium channel of the proximal and distal tubules, respectively. Coexpression of mutant KCNJ16 together with KCNJ15 or KCNJ10 in Xenopus oocytes significantly reduced currents.

CONCLUSIONS

Biallelic variants in KCNJ16 were identified in patients with a novel disease phenotype comprising a variable proximal and distal tubulopathy associated with deafness. Variants affect the function of heteromeric potassium channels, disturbing proximal tubular bicarbonate handling as well as distal tubular salt reabsorption.

A case series of adult patients affected by EAST/SeSAME syndrome suggests more severe disease in subjects bearing KCNJ10 truncating mutations

EAST/SeSAME syndrome is a rare disease affecting the Central Nervous System (CNS), inner ear, and kidney. The syndrome is due to loss-of-function mutations in the KCNJ10 gene encoding the inward-rectifying potassium channel Kir4.1. EAST/SeSAME syndrome is mainly diagnosed during childhood with a tonic-clonic seizure being the usual first symptom. Due to a limited number of patients and recent identification of the disease, few data are available on the clinical progress of this disease in adulthood. In particular, neurologic and nephrological outcomes have not been reported. We present a case series of 4 adult patients harbouring homozygous missense mutation p.Ala167Val and homozygous frameshift mutations p.Asn232Glnfs*14 and p.Gly275Valfs*7. Effects of these mutations were predicted by in silico modelling and bioinformatic tools. Patients with truncating mutations were associated with more severe outcomes, both in tubulopathy severity and neurological symptomatology. Conversely, either missense or truncating mutations were correlated with similar severity of epilepsy, with a long free-of-event period up to 20 years old. No eGFR decline was documented. Modelling predicted that truncating mutations lead to complete Kir4.1 dysfunction. Finally, all patients had a mild increase in urinary protein excretion. Our study indicates that the prognosis of patients suffering from EAST/SeSAME syndrome is related to the severity of the mutation causing the disease. As predicted by in silico modelling, truncating mutations of KCNJ10 are associated with more severe disease, with recurrence of symptomatic hypokalemia and more severe neurological phenotype. The type of mutation should be considered for the therapy tailored to patients' phenotype.

Novel Fanconi renotubular syndromes provide insights in proximal tubule pathophysiology

The various forms of Fanconi renotubular syndromes (FRTS) offer significant challenges for clinicians and present unique opportunities for scientists who study proximal tubule physiology. This review will describe the clinical characteristics, genetic underpinnings, and underlying pathophysiology of the major forms of FRST. Although the classic forms of FRTS will be presented (e.g., Dent disease or Lowe syndrome), particular attention will be paid to five of the most recently discovered FRTS subtypes caused by mutations in the genes encoding for L-arginine:glycine amidinotransferase (GATM), solute carrier family 34 (type Ii sodium/phosphate cotransporter), member 1 (SLC34A1), enoyl-CoAhydratase/3-hydroxyacyl CoA dehydrogenase (EHHADH), hepatocyte nuclear factor 4A (HNF4A), or NADH dehydrogenase complex I, assembly factor 6 (NDUFAF6). We will explore how mutations in these genes revealed unexpected mechanisms that led to compromised proximal tubule functions. We will also describe the inherent challenges associated with gene discovery studies based on findings derived from small, single-family studies by focusing the story of FRTS type 2 (SLC34A1). Finally, we will explain how extensive alternative splicing of HNF4A has resulted in confusion with mutation nomenclature for FRTS type 4.

Estimated glomerular filtration rate slopes on tenofovir alafenamide

OBJECTIVES

The aim of the study was to analyse and compare estimated glomerular filtration rate (eGFR) slopes during exposure to tenofovir disoproxil fumarate (TDF) and tenofovir alafenamide (TAF) in individuals who initiated TAF, regardless of prior regimen, before October 2016.

METHODS

An observational cohort study was conducted at 11 clinics in the UK and Ireland. Mixed effects models with random intercept and time terms fitted were used to generate and compare eGFR slopes while participants were exposed to TDF and TAF, with adjustment for age, eGFR at TDF/TAF initiation, gender, ethnicity, and time-updated CD4 cell count and HIV RNA measurements.

RESULTS

Data were available for 357 subjects (median age 50 years; 80% male; 82% white/other ethnicity; 51% men who have sex with men; median nadir CD4 count 216 cells/µL). The median duration of exposure to TAF was 2.0 (interquartile range 1.6, 2.3) years. At TAF initiation, the median CD4 count was 557 cells/µL, the median eGFR was 80 mL/min/1.73 m², and 86% had suppressed HIV infection. The mean adjusted eGFR slope during TDF and TAF exposure was -2.08 [95% confidence interval (CI) -2.24, -1.92] and 1.18 (95% CI 0.20, 1.52) mL/min/1.73 m²/year, respectively (P < 0.001). Individuals who experienced rapid eGFR decline (> 3 or 5 mL/min/1.73 m²/year) while receiving TDF experienced significant eGFR recovery while on TAF (P < 0.001).

CONCLUSIONS

Significant improvement in eGFR slope was observed in patients who switched from TDF- to TAF-containing antiretroviral regimens. These data provide further support for the renal safety of TAF, and for switching those who experience progressive worsening of renal function from TDF to TAF.

Case Report: Renal potassium wasting in SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is associated with many potentially fatal complications. Renal involvement in various forms is common in addition to serum electrolyte disturbances. Early reports suggest that hypokalaemia may frequent those with SARS-CoV-2 infection and various aetiological factors may cause this electrolyte disturbance. A Chinese retrospective study has demonstrated renal potassium wasting in patients infected with SARS-CoV-2, however, it is not known if these patients were receiving diuretic therapy which may be a contributing factor. This case report illustrates an example of renal potassium wasting in SARS-CoV-2 infection in the absence of diuretics and extra-renal mechanisms with important lessons learned.

Case Report: Renal potassium wasting in SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is associated with many potentially fatal complications. Renal involvement in various forms is common in addition to serum electrolyte disturbances. Early reports suggest that hypokalaemia may frequent those with SARS-CoV-2 infection and various aetiological factors may cause this electrolyte disturbance. A Chinese retrospective study has demonstrated renal potassium wasting in patients infected with SARS-CoV-2, however, it is not known if these patients were receiving diuretic therapy which may be a contributing factor. This case report illustrates an example of renal potassium wasting in SARS-CoV-2 infection in the absence of diuretics and extra-renal mechanisms with important lessons learned.

The Molecular Genetics of Gordon Syndrome

Gordon syndrome is a rare inherited monogenic form of hypertension, which is associated with hyperkalaemia and metabolic acidosis. Since the recognition of this predominantly autosomal dominant condition in the 1960s, the study of families with Gordon syndrome has revealed four genes WNK1, WNK4, KLHL3, and CUL3 to be implicated in its pathogenesis after a phenotype–genotype correlation was realised. The encoded proteins Kelch-like 3 and Cullin 3 interact to form a ring-like complex to ubiquitinate WNK-kinase 4, which, in normal circumstances, interacts with the sodium chloride co-symporter (NCC), the epithelial sodium channel (ENaC), and the renal outer medullary potassium channel (ROMK) in an inhibitory manner to maintain normokalaemia and normotension. WNK-kinase 1 has an inhibitory action on WNK-kinase 4. Mutations in WNK1, WNK4, KLHL3, and CUL3 all result in the accumulation of WNK-kinase 4 and subsequent hypertension, hyperkalaemia, and metabolic acidosis. This review explains the clinical aspects, disease mechanisms, and molecular genetics of Gordon syndrome.

Early safety of tenofovir alafenamide in patients with a history of tubulopathy on tenofovir disoproxil fumarate: a randomized controlled clinical trial

OBJECTIVES

The aim of the study was to assess the effect of tenofovir alafenamide (TAF) on kidney and bone biomarkers in patients who developed proximal renal tubulopathy (PRT) while receiving tenofovir disoproxil fumarate (TDF).

METHODS

Individuals with a history of TDF-associated PRT and currently suppressed HIV infection on a tenofovir-sparing regimen were randomized 1:1 to continue current antiretroviral therapy or initiate emtricitabine (F)/TAF with discontinuation of nucleoside reverse transcriptase inhibitors (NRTIs) as appropriate. Renal and bone biomarkers were analysed at baseline, week 4 and week 12. The primary outcome was the mean difference between study arms in urine retinol-binding protein:creatinine ratio (RBPCR) change from baseline to week 12. Data were analysed using linear regression, with robust standard errors (primary outcome), and repeated measures mixed effects models (secondary outcomes). The trial was registered under European Union Drug Regulating Authorities Clinical Trials Database 2016-003345-29.

RESULTS

We randomized 31 individuals [mean age 52.4 (standard deviation 0.3) years; 97% male; 90% white); all completed the study. At 12 weeks, there was no difference in change in RBPCR (β 19.6; 95% confidence interval -35.3, 74.5; P = 0.47), and no difference in change in estimated glomerular filtration rate (eGFR) (based on creatinine or cystatin C), albuminuria, proteinuria, renal phosphate or urea handling, (fasting) urine osmolality, parathyroid hormone and bone turnover markers in the control versus the F/TAF exposed groups. No cases of PRT were observed.

CONCLUSIONS

In people with a history of proximal renal tubulopathy while on TDF, 12-week exposure to TAF did not adversely affect renal tubular function. These data support continued evaluation of the long-term safety of TAF in this group of patients.

High-throughput sequencing contributes to the diagnosis of tubulopathies and familial hypercalcemia hypocalciuria in adults

Hereditary tubulopathies are rare diseases with unknown prevalence in adults. Often diagnosed in childhood, hereditary tubulopathies can nevertheless be evoked in adults. Precise diagnosis can be difficult or delayed due to insidious development of symptoms, comorbidities and polypharmacy. Here we evaluated the diagnostic value of a specific panel of known genes implicated in tubulopathies in adult patients and compared to our data obtained in children. To do this we analyzed 1033 non-related adult patients of which 744 had a clinical diagnosis of tubulopathy and 289 had a diagnosis of familial hypercalcemia with hypocalciuria recruited by three European reference centers. Three-quarters of our tubulopathies cohort included individuals with clinical suspicion of Gitelman syndrome, kidney hypophosphatemia and kidney tubular acidosis. We detected pathogenic variants in 26 different genes confirming a genetic diagnosis of tubulopathy in 29% of cases. In 16 cases (2.1%) the genetic testing changed the clinical diagnosis. The diagnosis of familial hypercalcemia with hypocalciuria was confirmed in 12% of cases. Thus, our work demonstrates the genetic origin of tubulopathies in one out of three adult patients, half of the rate observed in children. Hence, establishing a precise diagnosis is crucial for patients, in order to guide care, to survey and prevent chronic complications, and for genetic counselling. At the same time, this work enhances our understanding of complex phenotypes and enriches the database with the causal variants described.

Evolution of tyrosinemia type 1 disease in patients treated with nitisinone in Spain

Treatment with nitisinone (NTBC) has brought about a drastic improvement in the treatment and prognosis of hereditary tyrosinemia type I (HT1). We conducted a retrospective observational multicentric study in Spanish HT1 patients treated with NTBC to assess clinical and biochemical long-term evolution.We evaluated 52 patients, 7 adults and 45 children, treated with NTBC considering: age at diagnosis, diagnosis by clinical symptoms, or by newborn screening (NBS); phenotype (acute/subacute/chronic), mutational analysis; symptoms at diagnosis and clinical course; biochemical markers; doses of NTBC; treatment adherence; anthropometric evolution; and neurocognitive outcome.The average follow-up period was 6.1 ± 4.9 and 10.6 ± 5.4 years in patients with early and late diagnosis respectively. All patients received NTBC from diagnosis with an average dose of 0.82 mg/kg/d. All NBS-patients (n = 8) were asymptomatic at diagnosis except 1 case with acute liver failure, and all remain free of liver and renal disease in follow-up. Liver and renal affectation was markedly more frequent at diagnosis in patients with late diagnosis (P < .001 and .03, respectively), with ulterior positive hepatic and renal course in 86.4% and 93.2% of no-NBS patients, although 1 patient with good metabolic control developed hepatocarcinoma.Despite a satisfactory global nutritional evolution, 46.1% of patients showed overweight/obesity. Interestingly lower body mass index was observed in patients with good dietary adherence (20.40 ± 4.43 vs 24.30 ± 6.10; P = .08) and those with good pharmacological adherence (21.19 ± 4.68 vs 28.58 ± 213.79).intellectual quotient was ≥85 in all NBS- and 68.75% of late diagnosis cases evaluated, 15% of which need pedagogical support, and 6.8% (3/44) showed school failure.Among the 12 variants identified in fumarylacetoacetate hydrolase gene, 1 of them novel (H63D), the most prevalent in Spanish population is c.554-1 G>T.After NTBC treatment a reduction in tyrosine and alpha-fetoprotein levels was observed in all the study groups, significant for alpha-fetoprotein in no NBS-group (P = .03), especially in subacute/chronic forms (P = .018).This series confirms that NTBC treatment had clearly improved the prognosis and quality of life of HT1 patients, but it also shows frequent cognitive dysfunctions and learning difficulties in medium-term follow-up, and, in a novel way, a high percentage of overweight/obesity.

Chromogranin A Tubulopathy: Differing Histopathologic Patterns of Acute Tubular Injury in the Setting of Neuroendocrine Neoplasms

Introduction

Neoplasms of neuroendocrine derivation or differentiation may express specific peptides, some of which are capable of producing clinical symptomatology and others used as biomarkers: one such peptide being chromogranin A (CGA). Herein, we describe histopathologic changes present in kidney specimens from patients with such neoplasms, and illustrate 2 patterns of acute tubular injury (ATI) attributable to CGA.

Methods

Eleven patients with a history of a neoplasm of neuroendocrine derivation or differentiation and having histopathologic sampling of the kidney were retrospectively identified, 3 of whom had ATI with either engorgement of the proximal tubular epithelium by resorbed material or tubular cast formation.

Results

Two patterns of ATI were observed. One characterized by acutely injured proximal tubular cells engorged with resorption granules that expressed CGA via immunoperoxidase staining. Another pattern was characterized by intraluminal tubular cast material associated with ATI that did not exhibit restriction of immunoglobulin light chains (LCs), but immunoperoxidase staining for CGA revealed that the cast material was composed of the neuroendocrine-associated peptide. The level of serum CGA does not appear to necessarily equate to developing either of these 2 patterns of ATI.

Conclusions

Patients with a neoplasm of neuroendocrine derivation or differentiation may develop ATI, and in certain cases may be secondary to CGA renal tubular deposition.

Missed Monoclonal Disease Manifesting in Early Post-renal Transplant Period

A 63-year-old diabetic gentleman with microvascular complications presented with advanced azotemia and anemia. He was stabilized with blood transfusion and hemodialysis. With the probable diagnosis of diabetic nephropathy-related end-stage renal disease, he underwent kidney transplantation. He had delayed graft function. Graft biopsy done on the 2^nd postoperative day showed acute tubular necrosis. Graft biopsy repeated after 2 weeks for persistent graft dysfunction showed myeloma cast nephropathy (MCN) and light chain proximal tubulopathy. Work-up for multiple myeloma was positive. He was started on plasmapheresis and chemotherapy. However, he suffered sudden cardiac death during dialysis after 1 week. The presence of MCN in the early graft biopsy implies that it must have been the cause for his native kidney failure. Thus, renal failure in a diabetic should not always be presumed to be due to diabetic nephropathy, and kidney biopsy should be done in diabetics with atypical features.

A 57 kB Genomic Deletion Causing CTNS Loss of Function Contributes to the CTNS Mutational Spectrum in the Middle East

Background: Nephropathic Cystinosis, the most common cause of renal Fanconi syndrome, is a lysosomal transport disorder with an autosomal recessive inheritance pattern. A large number of mutations in CTNS have been identified as causative to date. A 57 kb deletion encompassing parts of CTNS is most commonly identified in Caucasians but this allele has not been identified in individuals of Eastern Mediterranean, Middle Eastern, Persian, or Arab origin to date. Methods and Results: Implementing whole exome sequencing (WES) in a consanguineous Iranian family, we identified this large deletion affecting CTNS in a patient initially presenting with hypokalemic metabolic alkalosis symptoms and considerable proteinuria. Conclusion: We show WES is a cost and time efficient genetic diagnostics modality to identify the underlying molecular pathology in Cystinosis individuals and provide a summary of all previously reported CTNS alleles in the Middle east population. Our work also highlights the importance to consider the 57-kb deletion as underlying genetic cause in non-European populations, including the Middle East. Limited diagnostic modalities for Cystinosis in developing countries could account for the lack of previously reported cases in these populations carrying this allele. Further, our findings emphasize the utility of WES to define genetic causes in clinically poorly defined phenotypes and demonstrate the requirement of Copy number variation (CNV) analysis of WES data.

Bartter syndrome: causes, diagnosis, and treatment

Bartter syndrome is an inherited renal tubular disorder caused by a defective salt reabsorption in the thick ascending limb of loop of Henle, resulting in salt wasting, hypokalemia, and metabolic alkalosis. Mutations of several genes encoding the transporters and channels involved in salt reabsorption in the thick ascending limb cause different types of Bartter syndrome. A poor phenotype-genotype relationship due to the interaction with other cotransporters and different degrees of compensation through alternative pathways is currently reported. However, phenotypic identification still remains the first step to guide the suspicion of Bartter syndrome. Given the rarity of the syndrome, and the lack of genetic characterization in most cases, limited clinical evidence for treatment is available and the therapy is based mainly on the comprehension of renal physiology and relies on the physician's personal experiences. A better understanding of the mutated channels and transporters could possibly generate targets for specific treatment in the future, also encompassing drugs aiming to correct deficiencies in folding or plasma membrane expression of the mutated proteins.

Polymorphisms of tenofovir disoproxil fumarate transporters and risk of kidney tubular dysfunction in HIV-positive patients: genetics of tenofovir transporters

The association between single nucleotide polymorphisms of genes encoding transport proteins involved in the bio-disposition of tenofovir disoproxil fumarate (TDF) and kidney tubular dysfunction (KTD) in HIV-positive patients was examined in this study. Fifty-eight patients who received TDF were screened for KTD using retinol-binding protein (RBP) concentration in urine. We defined KTD as the top quartile of urinary RBP/creatinine ratio (>17 μg/mmol), regardless of estimated glomerular filtration rate (eGFR) or proteinuria. Genotyping of genes encoding transport proteins involved in the disposition of TDF was undertaken using validated Taqman 5' nuclease assays. Patients with KTD (N = 15) had higher current CD4 cell counts, lower eGFR and were less likely to possess the genotype CC at position 24 of the ABBC2 (MRP2, rs717620) gene. In multivariate analysis, genotype CC at position 24 of the ABBC2 gene was significantly associated with KTD (odds ratio =0.05, 95% confidence interval = 0.003-0.7, P = 0.027). Genotype CC at position 24 of the ABBC2 (MRP2 rs717620) gene was significantly associated with a reduced risk of elevated urinary RBP in HIV-positive patients exposed to TDF.

EAST/SeSAME syndrome: Review of the literature and introduction of four new Latvian patients

EAST (Epilepsy, Ataxia, Sensorineural deafness, Tubulopathy) or SeSAME (Seizures, Sensorineural deafness, Ataxia, Mental retardation, and Electrolyte imbalance) syndrome is a rare autosomal recessive syndrome first described in 2009 independently by Bockenhauer and Scholl. It is caused by mutations in KCNJ10, which encodes Kir4.1, an inwardly rectifying K⁺ channel found in the brain, inner ear, kidney and eye. To date, 16 mutations and at least 28 patients have been reported. In this paper, we review mutations causing EAST/SeSAME syndrome, clinical manifestations in detail, and efficacy of treatment in previously reported patients. We also report a new Latvian kindred with 4 patients. In contrast to the majority of previous reports, we found a progressive course of the disorder in terms of hearing impairment and neurologic deficit. The treatment is based on antiepileptic drugs, electrolyte replacement, hearing aids and mobility devices. Future research should concentrate on recognizing the lesions in the central nervous system to evaluate new potential diagnostic criteria and on formally evaluating intellectual disability.

Glycine Amidinotransferase (GATM), Renal Fanconi Syndrome, and Kidney Failure

Background For many patients with kidney failure, the cause and underlying defect remain unknown. Here, we describe a novel mechanism of a genetic order characterized by renal Fanconi syndrome and kidney failure.Methods We clinically and genetically characterized members of five families with autosomal dominant renal Fanconi syndrome and kidney failure. We performed genome-wide linkage analysis, sequencing, and expression studies in kidney biopsy specimens and renal cells along with knockout mouse studies and evaluations of mitochondrial morphology and function. Structural studies examined the effects of recognized mutations.Results The renal disease in these patients resulted from monoallelic mutations in the gene encoding glycine amidinotransferase (GATM), a renal proximal tubular enzyme in the creatine biosynthetic pathway that is otherwise associated with a recessive disorder of creatine deficiency. In silico analysis showed that the particular GATM mutations, identified in 28 members of the five families, create an additional interaction interface within the GATM protein and likely cause the linear aggregation of GATM observed in patient biopsy specimens and cultured proximal tubule cells. GATM aggregates-containing mitochondria were elongated and associated with increased ROS production, activation of the NLRP3 inflammasome, enhanced expression of the profibrotic cytokine IL-18, and increased cell death.Conclusions In this novel genetic disorder, fully penetrant heterozygous missense mutations in GATM trigger intramitochondrial fibrillary deposition of GATM and lead to elongated and abnormal mitochondria. We speculate that this renal proximal tubular mitochondrial pathology initiates a response from the inflammasome, with subsequent development of kidney fibrosis.

Cooperation of Antiporter LAT2/CD98hc with Uniporter TAT1 for Renal Reabsorption of Neutral Amino Acids

Background Reabsorption of amino acids (AAs) across the renal proximal tubule is crucial for intracellular and whole organism AA homeostasis. Although the luminal transport step is well understood, with several diseases caused by dysregulation of this process, the basolateral transport step is not understood. In humans, only cationic aminoaciduria due to malfunction of the basolateral transporter y⁺LAT1/CD98hc (SLC7A7/SLC3A2), which mediates the export of cationic AAs, has been described. Thus, the physiologic roles of basolateral transporters of neutral AAs, such as the antiporter LAT2/CD98hc (SLC7A8/SLC3A2), a heterodimer that exports most neutral AAs, and the uniporter TAT1 (SLC16A10), which exports only aromatic AAs, remain unclear. Functional cooperation between TAT1 and LAT2/CD98hc has been suggested by in vitro studies but has not been evaluated in vivoMethods To study the functional relationship of TAT1 and LAT2/CD98hc in vivo, we generated a double-knockout mouse model lacking TAT1 and LAT2, the catalytic subunit of LAT2/CD98hc (dKO LAT2-TAT1 mice).Results Compared with mice lacking only TAT1 or LAT2, dKO LAT2-TAT1 mice lost larger amounts of aromatic and other neutral AAs in their urine due to a tubular reabsorption defect. Notably, dKO mice also displayed decreased tubular reabsorption of cationic AAs and increased expression of y⁺LAT1/CD98hc.Conclusions The LAT2/CD98hc and TAT1 transporters functionally cooperate in vivo, and y⁺LAT1/CD98hc may compensate for the loss of LAT2/CD98hc and TAT1, functioning as a neutral AA exporter at the expense of some urinary loss of cationic AAs. Cooperative and compensatory mechanisms of AA transporters may explain the lack of basolateral neutral aminoacidurias in humans.

Fludrocortisone-a treatment for tubulopathy post-paediatric renal transplantation: A national paediatric nephrology unit experience

Calcineurin inhibitors post-renal transplantation are recognized to cause tubulopathies in the form of hyponatremia, hyperkalemia, and acidosis. Sodium supplementation may be required, increasing medication burden and potentially resulting in poor compliance. Fludrocortisone has been beneficial in addressing tubulopathies in adult studies, with limited paediatric data available. A retrospective review of data from an electronic renal database from December 2014 to January 2016 was carried out. Forty-seven post-transplant patients were reviewed with 23 (49%) patients on sodium chloride or bicarbonate. Nine patients, aged 8.3 years (range 4.9-16.4), commenced fludrocortisone 22 months (range 1-80) after transplant and were followed up for 9 months (range 2-20). All patients stopped sodium bicarbonate; all had a reduction or no increase in total daily doses of sodium chloride. Potassium levels were significantly lower on fludrocortisone, 5.2 vs 4.5 mmol/L, P = .04. No difference was noted in renal function (eGFR 77.8 vs 81.7 mL/min/1.73 m² , P = .45) and no significant increase in systolic blood pressure (z-scores 0.99 vs 0.85, P = .92). No side effects secondary to treatment with fludrocortisone were reported. A significant proportion of renal transplant patients were on sodium supplementation and fludrocortisone reduced sodium supplementation without significant effects on renal function or blood pressure. Fludrocortisone appears to be safe and effective for tubulopathies in children post-transplantation.

Simultaneous sequencing of 37 genes identified causative mutations in the majority of children with renal tubulopathies

The clinical diagnosis of inherited renal tubulopathies can be challenging as they are rare and characterized by significant phenotypic variability. Advances in sequencing technologies facilitate the establishment of a molecular diagnosis. Therefore, we determined the diagnostic yield of a next generation sequencing panel assessing relevant disease genes in children followed through three national networks with a clinical diagnosis of a renal tubulopathy. DNA was amplified with a kit provided by the European Consortium for High-Throughput Research in Rare Kidney Diseases with nine multiplex PCR reactions. This kit produced 571 amplicons covering 37 genes associated with tubulopathies followed by massive parallel sequencing and bioinformatic interpretation. Identified mutations were confirmed by Sanger sequencing. Overall, 384 index patients and 16 siblings were assessed. Most common clinical diagnoses were 174 patients with Bartter/Gitelman syndrome and 76 with distal renal tubular acidosis. A total of 269 different variants were identified in 27 genes, of which 95 variants were considered likely, 136 definitely pathogenic and 100 had not been described at annotation. These mutations established a genetic diagnosis in 245 of the index patients. Genetic testing changed the clinical diagnosis in 16 cases and provided insights into the phenotypic spectrum of the respective disorders. Our results demonstrate a high diagnostic yield of genetic testing in children with a clinical diagnosis of a renal tubulopathy, consistent with a predominantly genetic etiology in known disease genes. Thus, genetic testing helped establish a definitive diagnosis in almost two-thirds of patients thereby informing prognosis, management and genetic counseling.

Magnesium lactate in the treatment of Gitelman syndrome: patient-reported outcomes

Background: Gitelman syndrome (GS) is a rare recessively inherited renal tubulopathy associated with renal potassium (K) and magnesium (Mg) loss. It requires lifelong K and Mg supplementation at high doses that are at best unpalatable and at worst, intolerable. In particular, gastrointestinal side effects often limit full therapeutic usage.

Methods: We report here the analysis of a cohort of 28 adult patients with genetically proven GS who attend our specialist tubular disorders clinic, in whom we initiated the use of a modified-release Mg preparation (slow-release Mg lactate) and who were surveyed by questionnaire.

Results: Twenty-five patients (89%) preferred the new treatment regimen. Of these 25, 17 (68%) regarded their symptom burden as improved and seven reported no worsening. Of the 25 who were not Mg-treatment naïve, 13 (59%) patients reported fewer side effects, 7 (32%) described them as the same and only 2 (9%) considered side effects to be worse. Five were able to increase their dose without ill-effect. Overall, biochemistry improved in 91% of the 23 patients switched from therapy with other preparations who chose to continue the modified-release Mg preparation. Eleven (48%) improved both their Mg and K mean levels, 3 (13%) improved Mg levels only and in 7 cases (30%), K levels alone rose.

Conclusions: Patient-reported and biochemical outcomes using modified-release Mg supplements were very favourable, and patient choice should play a large part in choosing Mg supplements with GS patients.

Peptide Receptor Radionuclide Therapy-Induced Gitelman-like Syndrome

Peptide receptor radionuclide therapy (PRRT) is a molecular-targeted therapy in which a somatostatin analogue (a small peptide) is coupled with a radioligand so that the radiation dose is selectively administered to somatostatin receptor-expressing metastasized neuroendocrine tumors, particularly gastroenteropancreatic. Reported toxicities include myelotoxicity and nephrotoxicity, the latter manifesting as decreased kidney function, often developing months to years after treatment completion. We present a case of PRRT-induced kidney toxicity manifesting as a severe Gitelman-like tubulopathy with preserved kidney function. Because profound hypokalemia and hypocalcemia can lead to life-threatening arrhythmias, we highlight the necessity for careful monitoring of serum and urine electrolytes in patients receiving PRRT.

Interest of the combined measurement of selected urinary proteins in the diagnosis approach in nephrology

Determination of the protein composition of urine is a non-invasive method helping to diagnose renal lesions and evaluate therapeutic interventions. We present here five observations that highlight the performance and relevance of urine protein analysis combining selected glomerular and tubular protein measurements. Total urine protein level and measurements of urinary IgG, albumin, transferrin alpha-1 microglobulin and retinol binding protein were performed on a urine sample by immunonephelometry. The results were normalized for urine creatinine concentration and integrated in the MDI interpretation software that provides a "urine protein profile" (UPP). Sequential UPP were performed in two patients with drug-induced tubular toxicity. One resolved after drug withdrawal. The second concomitantly developped glomerular lesions and repeated UPP was warranted to follow evaluation of the distinct renal lesions. Two cases illustrate two distinct clinical situations in patients with multiple myeloma, respectively myeloma cast nephropathy and toxic acute tubular necrosis. Those differential diagnoses were early anticipated by UPP. In one case, UPP was in favour of the presence of large amount of urinary monoclonal light chain excretion before performing urine electrophoresis analysis and renal biopsy while this was not in the other case. In the last case, we compared sequential UPP, renal function and kidney biopsies in a patient with a diagnosis of membranous nephropathy, and demonstrated a good correlation between urine glomerular and tubular protein excretion and progression of the renal lesions. The use of the UPP in clinical practice, particularly through the accurate quantification of tubular markers, is a more efficient tool for the diagnosis and follow-up of renal diseases than the less sensitive semi-quantitative urine electrophoresis or combined assays of both total proteinuria and albuminuria.

Fetal urine biochemistry in antenatal Bartter syndrome: a case report

Bartter syndrome is a severe inherited tubulopathy responsible for renal salt wasting, and hence electrolyte disorders and dehydration. Prenatally, it is characterized by severe polyhydramnios caused by fetal polyuria. We studied for the first time fetal urine in a Bartter syndrome case and demonstrated that the tubulopathy is already present at 24 weeks of gestation.

Founder mutation in KCNJ10 in Pakistani patients with EAST syndrome

Background

EAST syndrome is an autosomal recessive disorder caused by loss‐of‐function mutations in the gene KCNJ10. Among the 14 pathogenic mutations described so far, the p.R65P mutation stands out as the most frequent one and is particularly associated with patients of Pakistani origin. As a result we aimed to establish the existence of a potential founder effect in the Pakistani population.

Methods

To this end, we genotyped 12 patients from seven families and we compared disease haplotypes with ethnically matched control chromosomes. This haplotype was used together with demographic data for Pakistan to estimate the age of this founder mutation.

Results

We identified a small homozygous 0.694 Mb region around the KCNJ10 p.R65P mutation that had identical haplotypes in all of the patients which were completely absent in the control sample. Based on current demographic data and knowledge about disease frequency, we estimate that this particular p.R65P mutation arose 20 generations (about 500 years) ago.

Conclusion

By knowing the prevalent mutation in a given population more efficient diagnostics can be performed and the families can benefit from specific counseling.

EAST syndrome: Clinical, pathophysiological, and genetic aspects of mutations in KCNJ10

EAST syndrome is a recently described autosomal recessive disorder secondary to mutations in KCNJ10 (Kir4.1), a gene encoding a potassium channel expressed in the brain, eye, ear and kidney. This condition is characterized by 4 cardinal features; Epilepsy, Ataxia, Sensorineural deafness, and (a renal salt-wasting) Tubulopathy, hence the acronym EAST syndrome. Here we review reported clinical manifestations, in particular the neurological signs and symptoms which typically have the most impact on the quality of life of patients. In addition we review the pathophysiology and genetic aspects of the disease. So far 14 different KCNJ10 mutations have been published which either directly affect channel function or may lead to mislocalisation. Investigations of the pathophysiology may provide clues to potential treatments.

Does nephrotoxicity exist in pediatric epileptic patients on valproate or carbamazepine therapy?

The aim of this study was to investigate the effects of valproate and carbamazepine, on renal glomerular and tubular functions. The patient group comprised 54 children with new-onset epilepsy treated with valproate (n = 30) and carbamazepine (n = 24). Twenty-six healthy children were in the control group. The serum creatinine and cystatin C levels and urinary excretion of N-acetyl-β-d-glucosaminidase (NAG) levels were measured and the glomerular filtration rate (GFR) was estimated. Serum creatinine and cystatin C concentrations were not different between patients and controls. The glomerular filtration rate of the patient groups were higher than those of the control group. Thus, both drugs probably lead to glomerular hyperfiltration and toxicity for glomerular functions. However, urinary N-acetyl-β-d-glucosaminidase/creatinine levels were significantly higher in patients receiving only valproate (6.1 ± 5). The difference between carbamazepine and control groups was not significant for urinary N-acetyl-β-d-glucosaminidase/creatinine levels. Our data suggest that valproate has adverse effects on renal tubular functions.

Albuminuria and sodiuria in IUGR children

OBJECTIVE

Intrauterine growth restriction (IUGR) is associated with hyperfiltration, glomerulosclerosis and albuminuria. Albuminuria may further lead to tubulointerstitial inflammation, fibrosis and tubular atrophy. The time at which this may occur is unknown. This study was designed to assess the relationship between glomerular and tubular damage in IUGR children.

METHODS

We enrolled 50 children, 25 IUGR, categorized by estimated fetal weight <10th percentile and umbilical artery pulsatility index >2 SD, and 25 appropriate for gestational age (AGA) controls at 18 months of age. We compared albuminuria among IUGR and AGA children, to assess the relationship between albuminuria and contemporary sodium and lysozyme excretion, as a measure of tubular damage.

RESULTS

The albumin-creatinine (mg/g) and sodium-creatinine (μM/L) ratios (3.12 and 441.3, versus 1.39 and 226.1 in AGA; p = 0.002 and p = 0.012, respectively) were significantly higher in the IUGR subjects compared with AGA children, and significantly correlated (rho = 0.593, p = 0.002). Conversely, urinary lysozyme was undetectable or in normal excretion range.

CONCLUSIONS

Our results show glomerulosclerosis and albuminuria in IUGR children aged 18 months. Elevated sodium excretion in the absence of abnormal lysozymuria may represent a epiphenomenon of glomerulosclerosis and of albuminuria.

Bile cast nephropathy: an often forgotten diagnosis

High bilirubin levels are nephrotoxic. Bilirubin can cause a functional proximal tubulopathy or may precipitate into casts associated with acute tubular injury. This condition is known as bile cast nephropathy. The kidney injury is generally reversible if bilirubin levels are decreased early. We present a case wherein an alcoholic patient presented with high bilirubin levels and anuric acute kidney injury. The initial urine analysis suggested intrinsic renal disease. A kidney biopsy, performed a few days after the initiation of dialysis, demonstrated the presence of bile casts along with acute tubular injury. The patient however continued to be dialysis dependent inspite of initiating prednisolone to treat acute alcoholic hepatitis.